@georgehifi
Just look at the frequecy response into a quite easy simulated speaker load!! that’s unacceptable, over 5db variation. no power at 200hz and at 4.5khz, nothing below 50hz and above 10khz, and two peaks at 60hz and 1.5khz
https://www.stereophile.com/images/archivesart/cad300fig1.jpg
Thats horrible indeed. For some reason people buy these things. Keep em coming. Lets try to drive this problem home. When everyone gets it we can stop. Does everyone here know the 100th Monkey story? |
@vdotman
Just wanted to say hello from someone who knew you back in the day when you were at Audio Art in Richmond. I really like the fact that you are sharing your craft and are encouraging dialogue with those who share your passion.
dale grigg
Hi Dale, To me those were the days that were most interesting of this hobby. We opened the store in 1975 when high end was just a whisper. We carried all the ESLs, had a separate where no cones were allowed, even had several of the classics come throught the store. I went to Vegas CES when it was in the unfinished Jockey Club. Things were way more fun then. Im sorry to say that 90% of what is being made today is barely interesting. In the late 70's really dedicated people like Beveridge, Bongo Jim, Arnie, and a few others were doing great work. Amusing people like Robert Fulton (first person to sell me wire over dinner), Bono Jim (Incredible SS designer and most amusing person one could imagine), Jim Strickland (the acoustat speaker was pretty darn good) and most amusing and still at it Mike Moffat. I had the honor of knowing all these guys. Somewhere I have a picture of a BBQ at my house in Santa Barbara with Bongo Jim, Bascolm King, and a few others. I will try to find it. |
@mapman I use the receivers only as a simple demonstration of the benefits of more clean power in a line that otherwise is mostly similar in design.
Just my gut feel but I suspect there are many who have underpowered systems that clip perhaps in often subtle ways and then blame the results on a bad recording and never know it. Been there, done that myself in the past for sure as well.
Whereas not taking chances with clipping even in its most subtle form is perhaps the single biggest key to getting the best possible results. That and keeping noise to a minimum which is much harder to do in any high power integrated amp or receiver with more circuit and components in closer proximity to each other compared to separate devices Sorry but this is not consistant with my experience. I find from conversations with customers that they are actually using only a fraction of the power they think they are using. In otherwords they have tons of headroom they did not think they have. Once again we do have tools to measure these things and guessing is just not good. Happy to hear any numbers you care to share in your system. I studied clipping in many classic amplifiers and in my own of course. When tube amplifiers clip they often take a long time to recover. The highly respected HK Citation tube amps are horrible clippers with very slow recovery, the ST-70 is not so good either but recovers faster. A few amps that handle clipping softly with virtually no recovery time are the Marantz and so few others I cannot even recall them. I have measured over 100 power amps in 400 pages of notes. Before I embarked on the RM-9 I had the opportunity to play with a Marantz 5 which is a mono 8. It blew me away comparet to the Dynaco and other amps I had measured. When I designed the RM-9 I was very interested in doing as well as Marantz (SId Smith) and I feel I did. Sid Smith set a standard that might just be unbeatable for clipping and recovery. I would say if you amp never never clips you have too much amp. So to sum it up. Good amps can clip a bit, Most people don't here clipping if it is gentle and recovers fast. Extreme headroom means nothing and may acually be a detriment due to making an amplifier far larger than it need be. I have never found a good argument for excess in anything. Thats just philosophical. I like to live lightly on this Earth. Over powered systems impress me not. |
@btp24
Roger, why is damping such an outdated term? ;-) I have heard you speak of how even a low output impedance amp doesn't, contrary to common believe, "damp" a woofer. You have quoted Paul Klipsch on the subject, as I recall.
As Paul said, What does it matter if you have some ohm or so of external resistance in series with 6 ohms of voice coil resistance? Its how output impedance affects and modifies the frequency response that we need look at. Its so obvious. That happens to be the first thing in every Stereophile test report. JA knows and he tells. Its fun to read the manufacturers response to high output impedance. They have no excuse but to make something up. Low damping amplifiers will bump up the bass at the resonant frequency of the speaker by providing extra voltage that is undesirable. One bump for sealed, two for ported. So we really aren't damping anything, are we? |
@stfoth... where do these forum name come from?
Hello, RM! You mentioned the recent measurements of the Cary SLI100. Reminds me a bit of one a few years back on the 300SEI.
https://www.stereophile.com/content/cary-audio-design-cad-300sei-integrated-amplifier-page-3
That's something of a sort of classic amp with quite a few fans.
Compound question.
Your thoughts on Dennis Had and legacy Cary gear?
Your thoughts on the disparity between the measurements and folks who say things like that in the subjective review?
I believe Dennis was a RF engineer that switched to audio. His first amp with the torroid output transformers was a quickly discontinued disaster. He should have know torroids are good for RF but no good for audio ouput. He learned though. I dont know anything about the legacy gear. Got a link? Anyone who thinks a gapless torroid is good for an audio output transformer is kidding himself. Luckily few exist. Not sure i understand the second question. Can u clarify and expand? |
@roberjerman I read a report by JA measuring a Prima Luna tube amp (some years ago). He found an output impedance of 8 ohms! This means a DF of 1 ohm or less! Combined with the typical varying impedance of most speakers this is way too high! How can supposedly competent engineers get away with something like this? Because the result is far from neutral, accurate SQ! No matter how pleasing the "golden ear" crowd claims!
You are correct, 8 ohns is a very high output impedance, way too high. Why do you assume the engineers are competent? Look at the lineage of the people who designed and have promoted this amplifier. From About us at the primaLuna web site. The driving force behind PrimaLuna is one of high-end audio’s most astute and colorful figures, Herman van den Dungen. WHO? "For U.S. distribution and sales advice, he once again turned to “tube guru” and friend, Kevin Deal". I have read several places that Kevin is the self proclaimed King Of Tubes. Ive met Kevin at CES, no crown, actually a humous guy, I wasnt expecting that. Unfortunately I understand he’s not too chatty unless you are buying. Here, see how much of this you can take. https://www.primaluna-usa.com/aboutI learned long ago that someone can make a horrible amplifier and someone will love it. This amp is not horrible, however it is not good. Given it is made in China someone is making a lot of money and its not the Chinese. We have no idea how long these amps will last. We have no idea the quality of the components. Its a big box of unknown. We do however know the mearurements which are not good at all. Kevin has done a wonderful job of salesmanship. Note that he is the importer so he likey gets 10% for every amp coming in the country and 40% more for the ones sells directly. Go Kevin. |
@mapman
I do not have spl measurements but will give that a shot with my cell phone over the weekend maybe and report back.
My concern about cell phone SPL meters is how do they know the sensitivity of your microphone. Is there one specific to your phone? You have some nice equipment, no SPL meter?:( bad bad Let me know when you get one. The RadioShack is known to be quite accurate. Hope its still available. Velleman has one too I have both the digital and analog RS meters and have tested them extensively. I just use my phone to tell when BART exceeds 100 Spl. Dont trust it for more than that even though its an Iphone. Whats more important is to get a peak reading meter of scope and get down to business. |
@roberjam Ohm’s Law rules the amp/speaker interaction! And I agree with you that DF need not be excessively high to have adequate results! Indeed ohm law rules everywhere. My objection is that damping factor is not damping the woofer and as long as we call it damping factor we imply we are doing something we are not. I am one of those persons who believes language both determines and confirms that the speaker understands what he is talking about. As long as we think damping controls a woofer we are missing the larger effect of frequency response modification. For those still not on board, Spend $15 or just read Atkinson’s amplifier reviews, expecially the tube ones, whether you are interested in tubes or not. Please note on your subscription I sent you. John will send me a toaster when I get 10.:) It is no secret I am interested in correcting language because it demonstrates understanding. When did unbalanced become single ended for an input? Single ended is a type of amplifier circuit, not a connector. Who did that first? I would like to have a go at him for messing things up. For those who do not yet know "single ended" refers to an amplifier where there is a single output tube as opposed to Push pull. How did that ever come to refer to an RCA cable? Would be more appropriate to call a single ended cable one which has just one end. I though cables had two ends. |
@gnaudio
I spent close to $20k on a pair of brand name monoblocks, plugged them into my dedicated 20 amp outlets and they had a loud line level hum, hired electricians, changed out grounding rods etc to the tune of $3k in costs. Took all my other equipment and cables to my dealer to make sure they weren’t the issue and they weren’t. Finally I paid $10k and bought a used amplifier and bingo the problem went away. My system is silent and absolutely glorious sounding again. The monoblocks worked at my dealer without issue but had an issue in my house. How can a designer build a product like this and what could the problem be. I am out 000’s of dollars and lots of my own time researching the issues. I borrowed isolation transformers etc as the manufacturer said it was my house that was the problem and not their amps... they were a joke to deal with and basically blew me off. The only thing they offered was to pass a name along to me if they heard of anyone wanting to buy a pair. FYI, this company has a 20 year warranty... your thoughts are appreciated. Thank you for listening to my rant...
Hey I like a good rant. I feel you man. Did you ever float the grounds on the amps? If the isolation transformers had 3 wire plugs in and out they likely carried the ground through. Sounds like you had a simple ground loop which is so common with mono amps. Two power cords, two grounds plus the preamp etc= lots of potential for hum. Did anyone technical ever look at your situation? Did the amps have balanced inputs available? I take it your 10K amplifier is stereo, thus no ground loop. |
@georgehifi
And the same, even more so, goes for preamps, if it's loud enough that's all you need, there is no advantage to have it "able to be louder" if it's loud enough already
Yes, lots of people assume that they will continue to get more power as they continue to advance the volume control. One can be at full undistorted volume at any position of the volume control. That is just a setting of gain not power. In Asia an amplifier must play very loud at 9 o'clock or it will not sell. I hope most of you know that volume control position has nothing to do with power or headroom. Might as well close your eyes. To those who want a little guidance. A well balanced gain struture will play your usual listening level at noon and a bit above. If you are down at the bottom of your volume control most of the time you have too much gain and little ability to adjust it easily. Also at low settings volume controls tend to have their worst tracking between channels so the image may shift side to side at various volume settings. Most systems I encounter have too much gain which often results in a lot of noise. I have made attenuators for several. I have found that most volume controls have 20 db attenuation at noon. This means you have 20 db more SPL available...if your speaker, amplifier and ears can handle it. I find 20 dB enough to bring up even the most quiet CDs. Im not interested in 100 db SPL |
@twoleftears
But a popular US-based, US-manufactured, relatively inexpensive, tube integrated did hum, not a lot, from *both* the transformers and through the speakers, enough that when combined the hum could be heard from listening chair when music fell silent .
Does the maker publish a hum level in his specs? With input shorted any more than 0.5 mV hum is not good. Needs to be even lower with sensitive speakers, close listening, quiet room. I know one US maker whose limit was 2.0 Mv. That is 12 dB more hum than my limit. I think it wouldnt matter where you put that amp, it just has inherent hum. Many people make the mistake of thinking that all products that reach the market are good products. This is not the case. Would you care to tell us what amplifier this was? |
@chubaka
What are rails and what to they do? Good question. In a Solid state amp there are generally equal positive and negative supplies centered around ground. A 100 watt/8 ohm amp will typically have 50 Volts plus and minus supplies. We call those the rails. It is where we draw the current to send, via the output transistors. to the speaker. The rail voltage will determine the power of the amplifier. 75 volt rails will give you 200 watts and 100 volt rails 400 watts. Rails were not much talked about until the advent of the SS power amps that were direct coupled to the speaker. In action the positive rail pushes the speaker cone out while the negative rail pulls it in. Again the output transistors determine how much which determines what the speaker reproduces. In a tube amp we have several power supplies of different voltages and currents. We call the main high voltage B+, a term that goes back to early 1900s radio. A tube amp may also have a negative bias supply, filament supply, driver supply, lots of supplies in tube amps. |
@devilscucumber
Hi Roger,I have some old Martin Logan Sequel II's which when repanelled no longer sounded pleasant with my Plinius Integrated 9100 (100w), they became overly bright and shouty. I ended up bi-amping with a Perreaux 6000B (300w mos-fet) running the panels, while the Plinius now drives the subs, my question is can you recommend a cost effective tube amp to drive these speakers, (which dip down to 2 ohms?) I live in NZ (240V/50Hz). I must admit most of the discussion on this thread is well over my head, but your experience in these matters is invaluable to help novices such as myself
First I wonder what happened to the speakers? Were they repanelled at the factory? Did some fool with the crossover? Thats a hard speaker to drive and a 100 watt integrated mignt not be up to the task. The Perreaux is much larger and probably more tollerant of the low impedance. An RM-200 will drive your speakers from the 2 ohm tap to some reasonable level. How loud do you listen, at what distance and what is the sensitivity of the speaker? The best amp for you would be a Direct Drive to the ESL. Thats what I use. I have a keen interest in ESL speakers and have measured many. What I have found is that the hard part of driving them is often the transformer, not the panel. Going direct to the panel makes a big difference. My DD amplifiers produce about 1200 VA into a capacitive load. |
@csontos
Hey Roger. What are your thoughts on designing a ss amp to drive ESLs directly? I'm currently listening to Acoustat Monitor 3 with direct drive servo charge OTL monos. It seems the ultimate comparison between ss and tubes would be a shootout with such. I find directly driven ESLs to be the ultimate in transparency and so the ultimate test bed between the two major topologies.
Many thoughts, mostly of replacing lots of fused silicon. 5,000 volts is a dangerous environment for SS devices. There are no devices over 1,500 volts and they are mostly switches or horizontal output transistors. I dont think that is the application to have a shootout. At high voltages tubes make more sense and are more reliable. Horizontal output tubes are plentiful, inexpensive and very reliable. They lend themselves to a much simpler circuit. I have worked on many of the original Servo amps. There are many improvements that can be made to their design. I once offered a drop in board with all tube driver. Perhaps I will again. |
@desktopguy
Wish I could hear your more recent designs, because based on the RM-9s, they must be very very good.
I like my new stuff, especially the RM-10. For those who have difficult loads, play loud and need power the RM-200 is designed precisely to do that. The 9 is a fine amp, excellent potted transformers, UL, Triode for you . Lots of work to make. They are starting to bring more money on the used market so dont let them go for under 3,000 each. With the triode switches even more. We only made a few like that. I hope to get a few more amps out this coming year now that I am getting more help around the shop. |
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@ieales
Unless one subscribes to the idea that cables do not alter the sound, surely it makes more sense to replace bad cables than a good amplifier to correct system deficiencies.
If a system is not broken and has serious deficiencies cables will likely not correct the problem. How can they? As I said in a previous post, sometimes a listener does not realize his system is broken and somethig needs to be fixed. |
@toddcowles Wondering what your thoughts are on the most significant transition/design element that has improved overall sound quality in today’s amplifiers. WOW what a question. I cant think of just one. There are so many ampifier designs out there now. Many of them are just horrible. However I can tell you what has not been significant. Heres a list: premium capacitors, nude resistors, torroid transformers, most cable claims, premium fuses, fancy metal work, purposely colored amplifiers...... I read every amplifier review I can get my hands on. I work on a lot of amplifiers. I rarely see one that hits me on all 8 cylinders. I think people are looking at the wrong reasons to buy a particular amplifier. John Atkinson has measured some really bad ones lately. Why does a manufacturer send him an amplifier they know will fail his tests? EVERYONE. Read the review of the Cary SLI-100 pg 91, Dec, 2018, Stereophile. What a disaster, what an embarassment, what foolishness. Then go read the manufacturers comment. They did a great marketing turnaround, or attempted to, making it appear they want it to be that way. They believe that "specs do not tell the whole story:. Well, when the specs are this bad who cares about the story. So I guess the most significant transition is putting lipstick on a pig. Marketing rules, appearance rules, internet chatter rules. I caution people about amps with poor specs, amps that if they fail will be difficult to repair. They dont care. The Benchmark that was widely discussed a few weeks ago is impossible for a non factory tech to repair. Sorry to be the bearer of bad news, but things are not looking good. I posted a thread about the MCIntosh 2300 that the Grateful Dead used. No one cares,they think it cant possibly be good, its too old. Well its damn good. Its clever, its relaible, its rugged. I dont think you can break it. Im not even a Mac guy, but I know a good design when I see one. When I got into highend design in the 1970s we were making some great advances. Smart engineers were solving problems. I had the opportunity to work with Harold Beveridge for 2 years. There were great leaps of progress. Nakamichi was perfecting cassette decks. Sumiko and others brought us MC cartridges, GAS was making good amps and preamps, We were making great ESL speakers with direct drive amplifiers. Those were days of progress. Sadly I see little progress now. Perhaps thats why this is so hard to answer. Its all about the looks, the review, the story these days, isn’t it? I will continue to give this some thought. |
@stfoth
RM, thank you for taking the time for this discussion. It's really, really refreshing.Turning back to my prior question about your thoughts on Dennis Had and his legacy Cary gear...sorry to bother if you are not familiar (https://www.caryaudio.com/products/). I suppose items like CAD-805, CAD-211, CAD120S, SLI80 (precursor to the one that was just reviewed), V12r, SLM100, 500MB, CAD1610, etc. Some links, if interested.https://www.stereophile.com/tubepoweramps/1200cary/index.htmlhttps://www.stereophile.com/tubepoweram... asked that I clarify a question about your thoughts on how there can be such glowing subjective professional reviews when the measurements are so objectively bad. For example, the 300SEI I mentioned measured poorly, but many folks, including professionals, love it. I suspect some folks will love the SLI100. I was just curious about your thoughts on how or why something might sound "good" but measure like crap. Not limited to Cary gear...just using that because we have two examples in the thread.
Where to begin, I have to nibble on this, its a lot to digest. Dennis is a prolific designer and had good people to get the rest done. I dont see the very first amp with the torroids. Wasn't Cary under another name initially? This is actually an easy question. An amp that measures badly will sound bad if you get it into the situation in which it measured badly. You have to realize that some of these reviewers listen at 0.1 watts no matter what the amplifier power is. Any amp that can pass a signal will likely sound good at 0.1 watt, This can be seen by reading reviews in Stereophile. Have you noticed that when an amp is really bad at full power JA will do the IM and other tests at very low levels? He is kind to do that because otherwise we would all by crying. When an amplifier has low distorion he does the IM at very high power. You have to read the fine print. I read the measurements several times before I can construct a reasonable picture in my mind of what is going on. So the reviewer may never play the amp loud enough to get into the distorted region. Lets say its a 100 watt amplifier played all below one watt. The new Cary SLI 100 is a good example. Most reviewers are not loud listeners in my experience. They are not pushing that amplifier but John is goning to take it for a run. Anyone who buys it and actually uses the power is going to be sadly disappointed. The amp is just going to collapse into mush. Look at the horrible SQ wave on the cary 1601. Ive never seen one that bad, however it wont change the sound. Note JA fig 3 measured distortion at just 1 watt. That wont show transformer saturation in the low end at full power.There is no spec and no measurement of the power bandwidth. How many watts will this amp do at 20 or 40 Hz. I bet not much. He is just being kind by not going there. Look at fig 8 & 9, up to a watt the amp is ok. BUT IT IS NOT A ONE WATT AMPLIFIER. At full power its like 10% |
@unreceivedogma
Why would triode sound better than pentode?
Why woukd my Altec Lansing 604Cs be better for my Julius Futterman OTL3s At 16 ohms rather than 8 ohms?
And, with regard to the great interconnect debate: do you know of any testing done that approaches that of scientific blind testing that shows that any given wire, if made out of a certain material, and wound in a certain way, and shielded in a certain way, will cause electrons to move in one manner as opposed to another that can be explained as doing so and that because of that movement can be explained as yielding sonic performance that is measurably and quantifiably superior, or even just different?
Good stuff, lets go. Triodes have inherently low output impedance and one can make a nice amp with little or no feedback and still get good performance in the areas that matter: distortion, output regulation being the most dear. Pentodes have high output impedance and something must be done to get this down by using feedback. Pentodes became popular because they produce more power per watt of tube. For instance a single 6L6 can produce 6-8 watts single ended but 100 watts per pair push pull, in pentode. Perhaps only 20 in PP triode. The problem with triodes is saturation voltage pure and simple. All OTL amps like high impedance because they have lots of voltage but limited current. Since current is the limit use the forumla Power = current squared x impedance. The amplifier max current is the same for both speakers but 16 ohms gives you twice the power of 8. Some cables intentionally modify the frequency response and act as filters. MIT is famous for that. Some cable makers, like those liquid metal guys, have made up a whole story of fake science to sell their wares. Some makers freeze their cables, treat them with RF from a Tesla Coil, yada, yada, yada. I think you can tell I dont think much or cable makers, especially the really expensive ones. The whole idea of tuning a system with cables seems rather weak to me. Harry Pearson was big on cables but he was an idiot. Since I brought him up, my favorite quote about HP, which he said to me in person as he leaned over his Corvette at Sea Cliff is... "Audio is a Drug and I'm the Audio Pusher".. I think that pretty well describes Harry. |
@tomic601 5:38pm RM I have a dead pair of ESL-63, pretty low serial numbers...thoughts on rebuild upgrade steps at same time?Ashamed to admit I dont really have a budget in mind....
My friend here has a dead pair too. Are your panels bad? Panels are harder to fix than the electronics. Panels go bad, its a shame they didnt use better glue. Do yours have the black grids? DD amps stereo amps are $6,000. its up to you. |
Hey, look at this. I just went to Stereophile to look for the Cary and they are running this review of the amp I did for Counterpoint 32 years ago. This was going to be the RM-6. I almost merged Music Reference with them. Glad I didn't. Im still here and they are not. What a pack of thieves. Never got my royalties. I had the misfortune of hiring Michael Elliott when I worked at Beveridge. What was I thinking. https://www.stereophile.com/category/tube-power-amp-reviewsAnd same time, same reviewer.. https://www.stereophile.com/content/new-york-audio-laboratories-futterman-otl-1-power-amplifierTwo versions of the Futterman circuit. East coast/West coast. Harvey was a hoot. I visited him and his gang around this time. Sadly or not, he folded too. Is there a Futterman curse? My latest OTL is one with a built in Autoformer. Ive built a few and have another one in process. |
@goheelz
Roger— thank you for sharing your expertise in this thread.
I would like to know your opinion of ideal amplifier type (and your rationale) for the following loudspeakers: Vandersteen 5A/5A Carbon. As you know, this product is relatively inefficient but uses active crossovers with bass amplification built in.
If you could specify examples by brand, that would be ideal, but I’m also interested in general advice re: power requirements, etc.
I dont know anything about that speaker. Im an ESL guy. I dont know why people keep trying to cure the shortcomings of the cone speaker. Sorry, I know most of you own cone speakers. |
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@rsf507
Great, great, great thread! Ramtubes can you tell us what amps would be good to drive the Sanders 10e electrostatic speakers?
I would like to know the capacitance of the panel itself, the electrode spacing and the polarizing voltage. Direct Drive is the best way to go. I have found many cases where half the power goes into the step up transformer and other EQ components. How does he EQ the speaker these days? I just started reading the speaker description. Sounds like its an entire system. |
@tomic601
i have been considering the 60 wpc kits Ralph puts out...thanks also for your participation here also.. The M60 is a nicely laid out amplifier, spacious inside, easy to build for even a first times. Chassis and parts are nice. One suggestion. Ralph uses all one color wire, blue, I would suggest you get a few colors it makes troubleshooting much easier. Red for B+, black ground, blue plates. This can be looked up as there is a standard. I would also use teflon stranded wire I find his solid wire a little hard to work with. If you nick a solid copper wire it will easily break at the nick. You will need a 50+ watt iron for all the terminal strips and there are many. Use low melting 37/63 solder. Since I dont believe wire has a sound I prefer colors. I use all 9 colors in my amplifiers. With colors you can actually start to see the circuit without a schematic. If you look carefully you will find some long wires repeated so you could simplify things there. Of course once its built who cares. Just dont bring me an amp with one color wires all bunded up. First thing I do is cut them free. Also make sure you speaker will be happy with high output impedance (damping is less than 1). Amp loves 16-32 ohms, an Autoformer is a good idea in some cases, no all. |
@maplegrovemusic
Roger - I own a pair of king sound - King v1 and a pair of King sound ks17 . This direct drive amp you spoke of , how does that work ? do I have to bypass the step up transformers , and do the speakers need to be modified to use that amp ?
The advantage of a DD amp on ESLs is to completely remove the enormous step up transformer and use it as a doorstop. As I have written here before, I have found cases where the step up is more than half the load. Try to find the previous posts where I get more into it. If one plays most large ESLs on reasonable volume trumpet music they need 1500-2500 watts per channel. Roger Sanders knows this, I have measure this, there is no doubt about this. Beveridge, Acoustat and Sanders use full panel rather than segmeted panel like QUAD. Thus a QUAD can be driven by 100 watts. So you see not all things are the same. What technical data can you provide me on your speakers, Capacitance, impedance, polarizing voltage...... |
@bdp24
Roger, I think you provided this information somewhere, but I can't remember where, and can't find it. So let me ask you: what is a good output impedance number to shoot for in a power amp? How low does it need to be to prevent frequency response peaks and dips due to the speaker impedance/amplifier output impedance interaction? I know the figure will be different for a speaker with a wild impedance curve (the original Quad ESL) than for one with a fairly even curve.
Great Question... Damping of 10 which is an output impedance of 1/10 the load is a nice number and about all one can achieve in a tube amp and maintain staility. Quad achieved 20 on the model II for the ESL57 because Walker wanted 20, he said so in the speaker spec. The II is a fairly low power ampifier, yet a great one. Futterman had a damping factor approaching 100 perhaps more. It has lots of well applied feedback which it can tollerate due to no transformer and its excellent internal bandwith (open loop bandwidth). I think it is clear that he was interested in low output impedance. The open loop response of a tube amp is almost entirely dependent on the output transformer. When you see those peaks after 20Khz in JAs measurements that is all from the transformer actually reversing phase and making the feedback positive. Great indication of an amp that will oscillate into certain loads. Ringing on the square wave shows the same thing. Since you brought up the Quad 57, Walker or Baxandall did a very smart thing in the transformer to keep the impedance from going to infinity in the bass. They put 3 shorted turns of #16 wire, very loosely coupled inside the transformer. I only know because I melted the wax of one. *(by accident)* This clever idea helps tame the bass if an amplfier had very high output impedance. Even protecting the amp from overvoltage at low F so as not to arc the amp's transformer. This may take some further explanation. I had to sit down when i saw it. Of course SS amps can have much lower output impedance, approaching that of a heavy speaker cable or even lower than that cable. JA measures with a few feet if realistic cable. As I write this, every time I write "damping factor" I have to back and change it to either output impedance or regulation. I think I left it twice in the hope of shifting the tide a little bit. The Futterman is an amazing amplifier I hope to cover in depth in the future. Waiting for questions to arise. |
@prof What a terrific thread! Thank you Roger!
I hope you can answer a couple questions that have long baffled me about the sound of some amplifiers - in this case, using my own as example.
Earlier in the thread, you mentioned how the impedance interaction with a speaker is a significant factor in how one amp might sound different than another, depending on the design.
I’ve always understood (or not understood?) this to mean that if the amps performance varies with impedance swings presented by the speaker, you will start to get contoured sound around those impedance swings - e.g. more or less bass here, more or less highs there etc. Like a tone control.
And if I have that right, and one is using an amp that is very susceptible to altering the signal based on the impedance character of a speaker, then the "tone control" variations ought to vary as you switch between speakers. So one speaker may sound fairly neutral (if it doesn’t present a tough impedance load with said amp), another may sound rolled off, another boosted in the bass, etc.
The thing is, in my subjective experience, the character of an amplifier (at least the ones I own) tends to seem more constant than that.
So take my Conrad Johnson Premier 12 tube monoblocks - for reference, measurements here:
https://www.stereophile.com/content/conrad-johnson-premier-twelve-monoblock-amplifier-measurements
I have had a ton of speakers of varying designs - Quad 63s, big Thiel speakers, transmission line bass, reflex, sealed, tough impedance curves, easy ones....
And I’ve tried numerous amps, including some solid state (Harmon Kardon, Bryston 4BST, and others), and the thing is, the "character" I hear when I implement the CJ amps seems to remain constant: a slightly more rounded sound, that classic bit of "golden glow" in the upper mids/high frequencies, rounded but taught bass, etc. I just don’t seem to hear the tonal variation I should think may happen.
An even worse example is my Eico HF81 14W integrated. I’m sure you know this infamous little "classic" amp. It sure didn’t seem to measure well:
https://www.stereophile.com/content/eico-hf-81-integrated-amplifier-measurements
And, if I understand the implications of those measurements at all, it would suggest the amp would be susceptible to sonic variation, as speaker loads vary.
And yet, the little guy just seems to "sound the same" no matter what speaker they drive: from easy to drive monitors I own, all the way to MBL radialstrahler 121 omnis (a brutal load), to even my big Thiel 3.7s. They always have that same sound - a sort of lush, thickened, sparkly not "dark" sound, with a swollen bottom end that makes any speaker sound "bigger." (My hunch had always been this was some "low damping factor" in the performance of the amp that gives it this character across speakers, but now you’ll slap me upside the head for that).
So my questions are:
1. Why might I be perceiving that the amps have the same essential character even when used across a wide array of varying speaker loads?
2. Even more confusing to me: We are often told that the distortion signature of an amp tends to give it a sound. But for the most part, this arises only when power is under high demand, clipping etc, correct? If so, why do the amps seem to retain their specific character no matter what volume I play them at?
I don’t tend to listen loud. Often topping at around 75 dB or so. As I understand it, at least when I’m not listening to music with dramatic dynamics, most amps should essentially be cruising in terms of distortions. So if they are not going in to the type of distortion that starts to distinguish amp distortion profiles, why do they still sound different even at lower volume levels? All those "tubey" characteristics seem to be there no matter the volume.
Now, of course a confounding variable here is listener bias. But, if I’m hearing what I think I hear, I’d appreciate your unraveling my confusion.
Thanks! First I noticed that the conrad and the Eico both have similar damping factors. As I have said before that is the first thing we hear. Therefore they will modify the speaker frequency response in the same way. If you can get a low impedance amp then you can hear what the speaker designer intended you to hear. Since you listen at such low levels both amps are playing no power at all and thus both have very little distortion. Are there some yes/no questions I could answer. It hard for me to see exactly what you are getting at. The Eico has the added problem of the tone controls which are hard to make flat. One has to remember, the world of hi fi when the Eico was built is nothing like what we are dealing with today with your Conrad. Pre war the frequency range for good music was 80 Hz-8Khz. Post war it became 20-20K, thanks to DNT Williamson. 78’s were replaced with vinyl, Prerecorded tapes had a fair market and were excellent. Some record companies got serious about RIAA and getting things right. The Eico is just on the cusp of all that. Heath, Fisher, Lafayette, Knight and Scott all became very hot. The progress made then far surpasses the progress in amplifiers we are making now, if we are making any at all. Now its alll about a pretty face isnt it. I am blessed that my dad built a Heathkit preamp, amp and tuner when I was 4 years old. Mom says I watched all of it,though I cannot recall the images. The W2 is an excellent amp. Very open chassis, not expensive on eBay. Rather unknown. I mean what could be better than a Williamson. :) |
@rsf07
I wish I could tell you more on the specs of the speaker but there's little info. Roger Sanders does use a dbx Venue360 DSP unit he modifies (there are no crossovers or transformers in the speakers that I'm aware of). When you say "direct drive" amps since I'm non-technical what are you referring too? Can you send links to your own direct drive amps?Much appreciated.
I will soon publish something about my amp, but as you can see without your information my specs will do you no good. I can build up to about 5,000 volts. Beyond that its like building a radio transmitter. My speakers work at that peak and 2,500 V polarizing. I contend running the polarizing high for sensitivity causes air gap saturation. Ive heard it! Once again try to get some info on your speakers. Look at the DIY and ESL forums. Call the manufacturer. Here is the essence of direct drive. A direct drive amplifier is a bridge where each electrode goes to one side of the bridge. One side goes up while the other goes down. The problem with step-up transformers has been covered widely. What is not ever discussed is how much capacitance they have compared to what they are driving. There are very few people designing or making step ups these days and my objection to the Plitron has been covered here in depth. The problem is that designing such transformers is close to a lost art. Without some numbers I cannot say if the King transformers are good or not. I found this link. The minimum is 1.8 ohms at 25 Khz, sensitivity 83 db http://kingsaudio.com.hk/D001.jpg. Not horrible, but choose your amp wisely. Its strange that none of their amplifiers will drive this speaker at all. I havent looked at the rest which are rather Martin Logan style. |
@cakyo .. I am building a symmetric plus/minus 70 volts dc (2 x 50 volt ac secondaries) power supply for an amplifier I am building. Mechanical issues are giving me more trouble than electronics such as drilling holes accurately etc. To this end, I want to build this so I do not have to change the smoothing capacitors for a LOOOONG while so I dont have to re-drill holes etc if and when they break. I am concentrating on those specific capacitors since they are large electrolytics and hence are most likely the least reliable of the components.
In your experience & opinion, which make (and series/types) of such large electrolytics are the MOST reliable in the long term ? I am considering about 40 to 80 milli farads at 100 volts per each side of the supply, depending on the price & physical dimensions. I predict that these capacitors will be in a vicinity with a temperature of about 60 - 65 C most of the time. Some sellers are asking big money, just wait for an auction like this. eBay item number:192627561898 Just an example. I had some 49,000 at 75 V, look for something like that. Do you have your power transformer yet? Hope its at least 6-10 amps. How do you intend to use this power? 10,000uF 100V Sangamo Electrolytic Capacitor Computer Grade Crown Power Amp BGW. These went for $8 each. No problem with age or use, they last forever. Get a few extra at this price and never worrry. Besides the diameters are pretty standard in only a few sizes so there is a lot of interchangeability. Mallory, Sprague and other US makers made these. Its sad how many of these I had to thrown away. Tried to sell them on eBay, no luck. Which is good for you as there are people who will let them go for nothing. I see one for sale now fot $380.. he's a newbie. :) |
@wolf_garcia On another note, neither of my current fave tube guitar amps has a "standby" switch as they’re relatively low powered (18 and 15 watts respectively), so the question is: When can I get my beer? Another question I’ve asked elsewhere is how do Premium Fuses work? What do they do and why? Thanks in advance for the answer (or answers). The standy switch on a small amp doesnt save enough to pay for it. When you have 4 x 6L6s and a 5U4 then it makes sense. Premium fuses don’t work. They don't protect wery well. They have caused a great deal of damage in DC circuits like the tube fuse in my RM-9. Hi Fi TuningFuses demonstrated their complete lack of knowledge by putting the fuse wire in a teflon sleve to "reduce microphonics"... Fuse microphonics, how cleverly stupid. The teflon containes the plasma which is the opposite of what a sand filled fuse does. The writers of the literature come from the bottom of the barrel with no knowledge of electronics. Just ask them sometime.. I have. Read my first sentence in the OP. I had to shut down a fuse thread because we were not getting anywhere. I realized there is no logical argument that will sway them an inch. The Fuse evidently makes them feel a certain way. My advice stick with Buss and LittleFuse. They know what they are doing and won’t rob you like those Premium fuse peopls. They are all theives preying on the unwashed audiophile. Fuses bring out trolls perhaps thats how they work. I am truly sorry anyone ever thought of Premium fuses. |
@unrecievedogma Hi ramtubes,thank you for that and here’s a followup. If triodes are low impedance and OTLs like high impedance, what was Jon doing then when he switched the OTLs to triode?i can tell you that the amps sound better after the conversion, and they are more stable too. The bias and the balance don’t drift anymore. Jon Specter made the conversion with some guidance from George Kaye of Moscode. Both formerly worked at NY Audiolabs.
Are we talking about NYAL Futterman? Perhaps I have missed something in this thread? Do you mean Jon Snyder? This may help. Triodes are low impedance at the plate. The Futterman circuit doesnt care about that. Ive made some triode and some pentode. One gets more power with pentode and I can image they drift more in pentode. |
@hearincolor
Hello.
I am very slowly learning how power amplifiers work and have a hybrid car amp with low voltage 12ax7 tubes for the input signal that got hot and melted the plexiglass cover and some nearby hot glue. Do they normally get warm enough to cause these symptoms? It is a USamps Ax-Tu1000. They use what is called "vacuum tube current sync drive" and cannot find any info or a more universal name regarding it. I purchased it used and the previous owner claims his speakers got ruined but find it hard to believe.
Thank You.
Cool member name, I get it. A few things. A 12AX7 is not a low voltage tube. It likes to see a 300 volt power supply. A 12AX7 is the coolest running twin triode. It should not get so hot. So they are doing something wrong. Perhaps a few holes in the plex are in order. Sync drive is a totally made up term. Marketing talk, there is no universal name. You do realize that the 12AX7 has no business being in a car amp. Its just another piece of bait. At 300 watts it can ruin lots of speakers, Im not surprised the previous owner blew his up.. Can yours take it? |
@rost
I´m using a balanced configured Pass SS XP20 pre with output impedence stated at 1K/leg, balanced and 200 ohm, single ended (according to manuel) driving tube monoblocks with rated input resistance at 47K.
Amps have both RCA & XLR (only + phase) inputs. So my question is what input is preferable and why ?
Your response will be greatly valued and appreciated.
If I understand your correctly the XLR is unbalanced + only. If that is the case there is no difference which input you use. |
@unreceivedogma
What you are doing sounds fine to me. Shows are shows and rarely a good place to judge a system. I'm lucky to fiind one system I like. |
Is there a particular Direct Drive Amp you can recommend to drive the panels? (Again I’m in a 240V 50Hz country). I dont know of anyone making DD amps but myself. It a rather special thing.
|
@russellstone Hi. I was turned off tubes when a Mac 2275 couldn’t properly drive my ML Summit X’s (yep, ‘soft’ bass’). After some searching I found an Accuphase E-600 matched beautifully. My question is: how can Accuphase make a class A amp that runs cooler than many A/B amps, and substantially cooler than other class A amps that can give you serious burns when touched? The Mac could not handle the low impedance. The Accuphase has lots of current. I looked it up, its 30 watts at 8 ohms, therefore low voltage supplies. A 30 watt class A amp can run cool, but not a 100 watt Class A. thats the difference. Here is a great example where 30 watts at 8 ohms is better than 75 watts from the Mac. Did you try the 4 ohm taps on the Mac? |
@fsonicsmith \\
Roger, I have two questions though the second is a doozy.
1) What do you think of the Tungsol KT150?
2) What are your top 5 criticisms of the ARC Ref series components (i.e. the Ref 75SE or Ref 150SE amp and the Ref 6 preamp)?
I ask because I own and am proud to own the Ref 150SE and Ref 6 and more importantly, they deliver untempered joy and because while you said some negative things about Bill Johnson, you passed over the fact that Ward Fiebiger was the mind behind the latest designs.
Hears what JA had to say in Stereophile..
The Audio Research Reference 75 measures well for a classic tube amplifier design with a single pair of output tubes for each channel and a modest degree of loop negative feedback. Its output transformers are also of good quality, the only proviso being that the amplifier should not be used with loudspeakers whose impedance drops significantly below the nominal value of the output transformer tap Read more at https://www.stereophile.com/content/audio-research-reference-75-power-amplifier-measurements#jbpCd1H...He wasnt too happy about the output impedance. I have tested the KT-150 but as yet not interested in using it as it has a single source. It is expensive, It is cool looking in some ways, the data sheet is way off and there are no curves. #2 What do I think of ARC. No tech likes to work on their equipment. I won't any longer. I did a repair on the M200 that had been back to the factory for expensive repairs that did not fix the problem. The problem was a regulator transistor installed backwards. So much for QC. Since the same mistake was made in two mono amps, how many other amps off that run had the same problem. It was intermittant, very hard to find. Bill Johnson got way over the top with complicated circuits, never learned how to make a proper power supply that was short circuit protected. The first SP-6 took the regulator transistor out of safe area every time you turned it on. So the 6A had a little zener board to bypass the turn on. I mean really, this is the solution of a child. Since the power supply problem never got fixed he finally put a tube in place of the transistor... and called it a sonic improvement, of course. They made too many versions of everthing collecting $$ everytime you passed go. Most of the mods were called "sonic improvements" but all the mods on the SP-6 (which went to E) were reliability mods not sonic. Their build quality is lovely sadly their circuits are not. I have not met Ward. I see that things are departing from Bill's complexity back to something reasonable. Yet why send an amp to JA that is not going to test well? The IM on that amp is pretty high. It doesn't meet its own spec. The new power amps have the power tubes on the PCB which is a horrible thing to do. If not for Harry Pearson they might have died on the vine. Harry, the self claimed "Audio Pusher" got in bed with them and profited from a lot of loans never returned. When I visited Harry at Sea Cliff there was a ARC preamp standing on its side in the bar sink. The meters are cool looking, the price is high, I can see why people buy it but I cannot recommend it. Im sorry, but you asked. I'm sorry to be so negative about ARC, but I was a dealer for them from 1975 to 1980. If you have not heard about the "pink papers" thats a story in itself. ARC treats dealers with a heavy hammer, large opening order and threats if you do not follow the party line. Bill called us up one day because he heard we were doing A/B comparisons for our customers. He said "stop immediately or I will pull the line" |
@prof
If my amps are being run at levels that do not bring on distortion, why do they still have that classic "tube-amp" character even at those low listening levels? If it’s not the clipping characteristics that are coming in to play...what is it that produces that classic tube sound as I described it? I don't know what "classic tube-amp sound" is. I mean I don't design for it. I just make a good amp and I like to use tubes rather than transistors. Though I see some amps intentionally colored like this Cary SLI-100 Most of us designers dont do that.Good performance is not a mystery. I am tempted to call Cary and ask them what are they thinking. I read the review and the manufacturers comment. This is a sad turn for a company that was making some good stuff. I will be sad if anyone buys that amplifier, however someone will like it. There always someone. With low damping the response modification will simply follow the impedance curve. I set up an A/B this past week and we did some listening today. We could easily hear the differences, levels matched, carefully set up for instant comparison. If I were simply swapping amps not by a relay, I doubt the difference would be as apparent. I did one other thing that astounded me when we went from the QUAD 57 to a competent Alan Jones monitor I said... Why do people listen to little monitors when they can have a nice, room filling ESL? |
@musicpod
Slew rate. Some people feel that this is a significant amp spec. Would you please give your thoughts on the importance of slew rate.
Slew rate is another way to look at the power bandwith of an amplifier. The Jadis 200 had horrible slew rate (intentionally it seems) and this 200 watt amplifier could make less than 5 watts at 20Khz. It was not broken! Like any spec, some manufacturers will focus on this and get a geat number. If the amp can make full power without turning the sine wave into a triangle at 20Khz then thats good enough. 10V/us is enough though you will see numbers much higher.
At what db level do you consider a speaker efficient? At what level inefficient?
Would it be possible to provide context to where Mr. Levinson may have been coming from regarding the 400-watt optimum power level?
I have discovered in speaking with many audiophiles that almost everyone has way too much power and too much gain. People overestimate their listening level typically by 10 dB which means they are using 1/10 the power they think they are using. I will not advise anyone on power unless they know their speaker sensitivity and have a Radio Shack or better SPL meter. Quoting listening level without and SPL meter is pure foolishess.
The range of listening levels is much wider than the range of speaker sensitivity. Therefore one must know their listening level. I would be really impressed if someone quoted their peak voltage at the speaker terminals. So far this has not happened. Mr Levinson does not design amplifiers. However his engineers have made everything from 25 watts to whatever. Where he comes up with 400 watts I have no idea but I would say thats is a crazy high number for most people. |
@unreceivedogma
The triode mods actually have more power somehow. I know Jon put a tiny little transformer in there somewhere, he explained what it is for and that it’s not in the output circuitry but I’m not technical enough to remember.
I have built both triode and pentode Futtermans with the same tubes you have and I cannot agree that triode has more power. I did triode for simplicity in a low power Futterman I offer with a built in Autotransformer. It does about 3 watts into 8 ohms direct but 30 watts into any load via the Autoformer. I plan to make more OTL/autoformer amplifiers. Including the Autoformer in the amplifier feedback loop is far better than having it outside the loop. Did you happen to see the measurements before and after? There are several builders offering fancy cabinets for the classic speakers like the 604. Who can say what a piece of fine furniture should cost? Of course for that money there is better sound to be had. I would like someone to tell me why spend big bucks on cone speakers when there are better technologies. |
HI, Roger here with a question.
I would like to hear how each of you figured out how much power you needed to buy in watts?
I would appreciate the following information in your response.
Your listening level LOUD SPL (preferably measured at 1 meter from the speaker with a REAL SPL meter. Your low listening level. If you are using a cell phone app then you have confirmed it?
Your speaker sensitivity?
Listening Distance from speakers?
How many watts at your load is the amp is rated to supply?
|
@shkong78 Many people believe that SET tube amplifier give more mid range magic than Push pull tube amplifier.Do you agree on the notion as designer of tube amplifier?If so, could tell me why it is so? There are some things about SET amplifiers that can be magic. I have always found the simplest circuit that can do the job well will do it best. Here are some things that are special about SET amps - They have very simple circuits
- THe output transformer runs on only one side of the BH curve never crossing through zero.
- They are class A by nature.
Not all SET amplifiers are good, they are often light on specs. The important specs are - Distortion vs level and frequency. His helps avoiding a really bad one.
- Damping doesnt matter so much if you are using it in a bi-amp situation where it only drives the midrange/tweeter. Use an adequate SS or tubes amp for the bottom.
- Some are noisy. Many don't spec noise. Somehow you have to find out.
Explore the idea of Bi-amping with a line level crossover. We have developed a nice mono amp where the crossover is built in. The bass part is push pull about 15 watts and the top is SET at 2.5 watts. Because IM distortion is eliminated less power is required. |
@fsonicsmith Your own decision to go hybrid with your higher powered amp and to go true balanced with your higher powered amp but not your lowered power amp is a head-scratcher. If-as you state-monos are more susceptible to hum than stereo amps, why do you implement RCA-only vs. offering true balanced in the opposite direction? And while a solid state input stage may very well offer better measurements, where is the proof that it sounds better? At the end of the day, isn’t it indisputable that it is cheaper to produce and less complicated? You on the one hand have little good to say about Rogue and yet when it comes to hybrid tube amps, I think of Rogue (and Musical Fidelity though I don’t count their "tubes" as tubes). I do not understand the first sentence at all. Where is the head-scratcher? Sound, reliability, completeness of design, ease of service are all pretty equal in my mind. Sound is subjective. The other are objective and will bite you in the butt. I think you misunderstand the RM-200 and RM-10 so lets get this straight. I dont like the term hybrid at all. In a good design we use the parts and circuits that do the job best. I wanted the RM-200 to have good CMRR (hum rejection in simple terms). One cannot do that with a tube at the input. One needs two active devices that are critically matched and stay matched. So I used a "supermatched pair". That is not a made up term but a technical term for a pair of transistors where each transistor is 100 transistors in parallel. I can trim the CMRR to 90 dB or better and it will stay that good for a very long time. The RM-200 has many other special characteristics such as, fully balanced input to output, taps down to 1 ohm, reasonable damping, good power bandwidth. It also has something few amps do not have which is the abilty to drive a dipping load with increased power rather than decreased power. Neither CJ, Rogue, ARC or anyone else I can think of has done that. The RM-10 is a sweet little EL84 amp that appears to delight QUAD owners, can be switched to mono or stereo with a unique driver circuit that does not require gain matching or summing resistors like the Stereo 70 and others do. You can look this up as to how stereo tube amps are converted to mono. BTW they are not bridged. For a small amp like the RM-10 I saw now need and have not had even one request for balanced. The RM-10 is unique in that is produces 35 watt from one pair of EL-34s where most produce 17.5 watts. I spoke about this application at Burning Amp 2018. Perhaps you might watch the video. http://berkeleyhifischool.com/having-fun-at-burning-amp-2018/Monos are generally suseptible to hum because of power cord grounds. Not much else. I dont understand your point of "going in the opposite direction" The RM-10 is a very affordable amp. It is one of a very few tube amps that has no PCB. Its hand wired start to finish. It seems to me that JA has a tendency to disagree with his own reviewer’s perceptions as to which output tap is best rather than criticizing the design of this amp and it’s output tap measurements per se. As far as JA is concerned. The reviewer writes what he writes, JA measures and comments and sometimes wonders why the reviewer didn’t hear distortion or damping or whatever. He is trying to make sense of sometimes disparate opinions as I would. The reviewer does not see JAs measurements or comments till publication. Read MIke Fremers lead in to the RM-200. To paraphrase, "I know I wont get caught with my pants down when JA measures this amp" In other words, he knows it will measure well. I am still amused at manufacturers like Cary where the marketing guy really got caught with his pants down. I am far more interested in JA’s measurements than the fluff about this record and that CD sounded. The reviewers rarely tell us anyting about how much power they are using, what the speaker and amp interaction might be. IMO most of them listen around a watt. Should JA only measure up to a watt on a 100 watt amp where someone might really need 100 watts? This may dismay you quite a bit from an engineering standpoint, but I take measurements of tube amps to be very analogous to measurements of DAC’s; the best measuring DAC’s don’t often sound the best. This dismays me not at all. How does this analogy apply? A DAC drives no load at all. A speaker drives a host of loads and will sound different into each of them, with output impedance being the most obvious factor and distortion the next. How can you make such a statement? Now if you think speakers should be matched with a particular amp then your are faced with the problem of changing both at the same time or hunting for another speaker that likes your amp or amp that likes your speaker. I am proud to say that my amps sound damn good on a wide variety of speakers and that is what good engineering is all about. Just to lay your mind at ease. Your ARC is not a bad amp at all. Im glad you like it. Its just not up to my standards.... or John’s as he warned in the end of his measurements. What is intereresting is that current ARC power amps are not up to Bill Johnson’s standards. All of Bill’s amps were very low distortion, high damping. I dont particularly like the way he went about it but it is crystal clear that he valued those two parameters in all his amplifiers. The current designer has an entirely different set of values. I appreciate that he has gone to simplicity. Now all he needs to do is get the performance up a bit. What do we know about his background? While I agree that not all things can be measured I am writing about things that can be measured and their effect can be understood. May I ask since the RM-200 had both excellent sound according to Mike Fremmer and excellent measurements at half the price 33% more power, why did you not buy and RM-200? |
@bdp24 Roger I happened to make my first visit to a new hi-fi shop just opening in Livermore, CA in 1973, Audio Arts. It was a 1-man shop, that man being Walter Davies, now the maker of the great Last Record Care products. And as luck would have it, that was the same day Bill Johnson was delivering and installing a complete ARC system in his new dealer Walt’s listening room; a Thorens TD-125 MK.2, a Decca Blue mounted on a prototype ARC arm (it never went into production), an ARC SP-3, and Tympani T-I’s (as you said, at the time distributed by ARC) bi-amped with a D75 and D51. I was just a kid, and spent a couple of hours getting an education in high end hi-fi. A couple of months later I had that exact system (with a Decca arm) in my own room. All set up and connected, I pushed in the power switch on my SP-3, and immediately heard a "poof" and smelled the aroma of something burning, which turned out to be a resistor in the power supply. Welcome to the wonderful world of using under-rated parts!
Thank your for the walk back in time. Anyone who is not old enough to have your experience I encourage to read every word above. Thats exactly how is was back then. My store in Richmond VA was called Audio Art and is still in business. Manufacturers visited us. Nakamichi flew in on their private Mitsubishi plane. We ate, we drank, Bob Fulton told the story how the monkeys behaved when they heard sounds carried by different speaker cables.He said bad cables confused them. No kidding. In his Fulton J system, one of the best things going back then, he used Ford solenoid coils for woofer chokes. He was delightful.
The J was cool because you made it in pieces as your funds allowed. First you bought the bookshelf speaker which was a fine speaker in itself. Did what a good "monitor" should. Then you could either buy the 8 Cu Ft woofer box or the RTR ESL tweeter. When you were done you could please the missus with a dark brown cloth and wood "hat" that covered the whole thing. Stood about 4-5 ft tall. Marvelous. No bullshit, even the monkey story is better than most cable claims today. He made some good wire when this current crowd of cable makers were babies. I think some of them are still babies the way they rant and bend science. As to your "POOF of smoke" thats is simply an unprotected power supply. Bill didnt seem to get the point that the down side filter capacitor looks like a short every time you turn on the preamp. Rather than take the time to discover how to make a Short Protected power supply he just added band-aids. It was always claimed to be some "sonic improvement" to make it easier to swallow. Most times it was a fixing a failure mode in an unfinished design. Power supply failures were never mentioned. As I recall the SP-6A upgrade was $150 for a little circuit board with two diodes and a resistor. He always kept the price you paid plus the upgrade cost equal to the price of the newer unit. Of course you had to send the preamp back, wait 6 months and some claim they got someone elses preamp back. ARC database has lots of information, though no stories. http://www.arcdb.ws/ It is the work of a group of dedicated ARC fans. Good place for ARC info on prices, modification dates, some schematics. Back then the joke was. If you buy an ARC preamp you have to get two because one will always be in the shop and by the time you get that one back its aready one or more behind the latest version. People like Harry Pearson turned that inconvenience into a virtue. If you dont believe me ask bdp24. He has obviously been around the block. Im sad for the horrible choices newbies have to make. The pressure to buy expensive cables and power cords and fuses and products that do nothing. Those did not exist when I got into this. We had to make real stuff. However we had coloful fellows like Bob Fulton, Jim Whiney, Matt Polk and Co, Arthur Jansen was still alive and I interviewed him as well as Saul Marantz and SId Smith. And last but not lease Harold Beveridge, my mentor. |
@prof
I still love to "visit" electrostatics (the Quad ESL 57s being my favorite), for their unique qualities. But every time I listen to an electrostatic, of any make, I come away happy to have moved on to cone speakers.That includes every hybrid I’ve ever heard: The cones seem to add some body, but only within their frequency range. As the frequencies climb up to where they are handled by the panel, the sound character changes to my ears to that ghostly quality, so I am always aware of this discontinuity.
The term "visit electrostats", the 57 in particular is apt as I "visited" mine today. I am in the process of modifying a OTL amp to improve its "specs", cure offset drift and increase reliability and life of the tubes. I am using the 57 in that test because of its widely variant impedance and revealing nature. The differences are palpable. I do not like all ESLs. Beveridge made a great one but it is very hard to place. The 57 as it was called. is truly "Walker's little wonder". I owned 63's and do not miss them. I like line sources. I like the wide dispersion and center fill that line sources produce. So perhaps its the line source I like the most. I have heard some large cone line sources and I would say they approach ESLs. But the drivers will never do what ESL drivers do. I have been around ESLs all my life and sometimes when I hear cone speakers I just want to run out of the room. As far as moving air a 12 inch cone has to go a lot farther than a 4-8 sq ft piece of 1/2 mill mylar that has virtually no mass. Be aware, a cone speaker is a "mass loaded driver" by its vary nature. This cannot be disputed. An ESL is an "air loaded driver" Id rather have air than mass to move around. In closing, and not to be a tall poppy, but it takes knowledge of both acoustics and electronics to make an ESL. One has to make his own drivers, step up transformers, polarizing supplies and at voltages that scare most people. Cone drivers are bought off the shelf, the good ones have already published curves that you can count on, no high voltage and not much knowledge to hook them up. Red wire, Black wire, cap, choke nothing dangerous, nothing EXCITING. |
@d2girls
Is it harder to design a amp or preamp?
Thanks for a lovely simple question. Preamps are much easier and to me not so interesting as power amps. In my career I have designed two major preamps, the RM-1 a very high performance preamp that was not at all easy and then the RM-5 which was quite easy. With power amps I could go on forever. They are challenging because one has to consider the wide variety of loads they will encounter, there is a lot of energy so if things go *BANG* lots of stuff can be destroyed. I have designed dozens of power amps and only produced the ones I feel will perform well in a variety of systems. |
@fsonicsmith you can’t possibly mean that preamps are easier in general and I am unaware of any accolades for your preamps (whereas you are lauded for your amps). Obviously you mean that for your tastes and purposes, preamps are easier than amps. I mean precisely that. You might want to do a little more reading on the RM-1 and RM-5. Perhaps you are new to this hobby. This has nothing to do with my tastes and purposes. The RM-1 (1976) was lauded for its RIAA EQ accuracy, was the first popular preamp to use the 6DJ8/6922, has the lowest noise possible for that tube. Has 5 fully regulated, short circuit proof power supplies. Built in two chassis and weighs 55 pounds ! It is the only tube preamp to my knowledge that id DC coupled throughout with servos, relay protection and no output coupling capacitor. That was a lot of work, But once you make a good preamp what is there left to do? Power amps, on the other hand are a world of variety. Circuit topoligies, output transformers, protection, tube life. These are really difficult things to do. Granted most people who dont design preamps will agree with you, but they dont design preamps, now do they? A great preamp does more than attenuate a signal. It breathes life into music. A great preamp is quietly powerful, while a great amp simply provides grunt. A preamp does not attenuate a signal, it amplifiers a signal, provides selection of sources and control of volume, accurate phono EQ. But these are easy to obtain. There are only about 3 ways to make a preamp gain stage. There are an unlimited distinct ways of making a power amp and a good one is a challenge. I will say that many preamps fail because of poor power supplies. My power supplies are among the finest and they dont break like ARC power supplies. You can short my power supply, go to lunch, come back, remove the short and all is well, doesn’t even get hot. One millisecond short on an ARC power supply and you wont have time for lunch or dinner. Ask any tech. A power amp is the finess in a system, certainly not the grunt. May I remind you this is a thread to ask a technical question. |
@mapman
I figured it out by listening and trial and error over time and based essentially on those parameters as a guide. However specifications alone seldom tell the whole story. The devil is always in the details much of which is never specified. Detailed measurements like those in Stereophile help a lot but I have found there may still be surprises playing real music even with very comprehensive test measurements at ones finger tips, though if done correctly, measurements certainly help with the decision making process of what to try next or not.
Today I compared two identical amplifiers, level matched, A/B switch in hand. I played Willy Nelson (raspy male voices are very telling), I played Bach Organ works, piano, lots of things. Sometimes listeners bring in music to these tests that they like, but will not expose differences. All I had done is add 12 dB of feedback to one amp and left the other stock. i didnt change any caps, didnt replace resistors with naked ones, didnt put in premium wire or fuses. Both had been measured and were in proper operating condition. 12 dB of feedback will reduce distortion by a factor of 4 and increase damping by a factor of 4. It was not hard to hear the clairty, dynamics, and defined (rather than one note) bass. This is the story that the specs told and the listening confirmed. Come on over and have a listen. Lets not worry about comprehensive measurements when even the basic ones arent even good. The stock amp has a damping factor of less than 1 and 4% distortion at full power and I played it at full power. These tests are not easy to do even for me. It can take a whole day to set it up, and ive only been doing it for 40 years. Very few people set up these tests. Why do audiophiles try so hard to ignore, object to, claim that measurements are irrelevent? Why is one reviewers impression more important? Many readers of Stereophile dislike measurements so much they say its a waste of space? I don't design by measurement but I know what minimum performance is required to make a good amplifier. Of course some designers loose sight of balance in design and drive one spec to the limit. That often results in a bad sounding amplifier. What are you going to say to the poor lad who buys the Cary SLI-100 hooks it up to a pair of Maggies, turns it up loud and smiles. If you have a good sense of clean sound you will not enjoy 10% distortion, compression, muddy bass. Without JA's measurements there would be no warning. His reviewer did not use more than a few watts of a 100 watt amplifier, what happens when someone does? |
