Does anyone care to ask an amplifier designer a technical question? My door is open.
I closed the cable and fuse thread because the trolls were making a mess of things. I hope they dont find me here.
I design Tube and Solid State power amps and preamps for Music Reference. I have a degree in Electrical Engineering, have trained my ears keenly to hear frequency response differences, distortion and pretty good at guessing SPL. Ive spent 40 years doing that as a tech, store owner, and designer. . Perhaps someone would like to ask a question about how one designs a successfull amplifier? What determines damping factor and what damping factor does besides damping the woofer. There is an entirely different, I feel better way to look at damping and call it Regulation , which is 1/damping.
I like to tell true stories of my experience with others in this industry.
I have started a school which you can visit at http://berkeleyhifischool.com/ There you can see some of my presentations.
On YouTube go to the Music Reference channel to see how to design and build your own tube linestage. The series has over 200,000 views. You have to hit the video tab to see all.
I am not here to advertise for MR. Soon I will be making and posting more videos on YouTube. I don’t make any money off the videos, I just want to share knowledge and I hope others will share knowledge. Asking a good question is actually a display of your knowledge because you know enough to formulate a decent question.
Starting in January I plan to make these videos and post them on the HiFi school site and hosted on a new YouTube channel belonging to the school.
@gnaudio I’ve had several amps over the years plugged in the same room in the same AC receptable. A 300B stereo power amp didn’t hum. My current solid-state monoblocks don’t hum. 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.
I lifted the ground. I ran an extension cord from the other floor of the house. I turned off every breaker in the whole house save for the one receptable being used. I tried ground loop eliminators, like the Hum X. I tried DC blockers, like the HumDinger from AVA. I followed the "how to eliminate hum" instructions from the PS Audio webpage. I tried isolation transformers (Furman pro). I tried a PS Audio unit. I tried a variety of other power conditioners. The company blamed it on the sensitivity of my speakers. I tried different speakers, with same result. Eventually I gave up.
It’s not any kind of discovery that the quality of manufacture of transformers used in different amps varies a good deal (designing to a price point + variable QC), but this demonstrates clearly that what works in location A will not necessarily work in location B, and that makes/models that achieve considerable popularity will not work for everybody, always. Live and learn.
Because mild to moderate hum is not fun or glamorous or sexy or exciting, I suspect it's a problem that occurs more often than is reported or discussed.
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?
OK so here’s some SPL measures using db meter pro app on iphone 6 . Disclaimer: I have no info on how accurate this tool is but the numbers I am reading seem reasonable.
So in a samplling of various "typical quality nothing special" CD resolution recordings over several minutes from my closer listening position, I hit peak spl of 99 db and averaged about 86 db. Very clear and amps never break a sweat which I take as a good sign
I would rarely go louder but can and have. I’ve used amps rated at 60, 120, 180 360 and current 500w/ch into 8 ohms. I view the 500w/ch with the big OHM 5s as my insurance policy against clipping at minimum and the current Bel Canto ref1000m amps are the best sounding overall by far especially at higher SPLs. I also seem to hear the correlation between amps with specs that better double power into 4 ohm and better performance overall meaning better sound at least with the big OHM F5s. Not as much with my other smaller OHMs (8" main driver) and even smaller monitor speakers (Dynaudio contour 1.3mkII) and very small Triangle Titus that I also run off same amps.
Wow! What a fast moving post. Glad to see all the interest.
"There is a lot to this question so lets hear back from you and others."
First off, I suspect many of us non-technical types may not know much about clipping. I've been aware of it a few times but suspect it occurred other times when I was not certain what was happening. In my experience I've heard the sonics become thin, hard or harsh, even metallic (as opposed to musical) when pushed to loud levels but before the crack or pop of an actual clip. I considered that a related but slightly different issue.
When listening for pleasure it is generally in the 80-85 dB range. But I doubt my RS dB meter is accurate to identify actual peaks so I'm unsure of those.
Regarding amps > 100 wpc, for many years I enjoyed a large pair of Duntech speakers, rated at 90 dB. John Dunlavy recommended 200 wpc for "full musical enjoyment". I experimented with a variety of amps (tube and SS) rated from 30 to 300 watts. I finally settled on a pair of VTL 300 monos for a few years. That was until I heard Curl's Halo JC-1s, rated at 800 wpc into the speaker's designated 4 ohms. That was the best I found - musically accurate, solid bass (determined by good recordings of acoustic upright bass), and effortless, unstrained sonics. To be fair I don't believe the 90 dB efficiency was accurate with such a complex 1st order crossover.
I've since moved on from that system but continue to believe this question of headroom is very important. Interestingly I remember hearing several times some years ago the idea that within a given line up of amps, the model with 60 to 120 watts was likely the best sounding.
I did have a RM-9 for a few years, one of those few components I was later sorry I sold.
Roger, glad to see you pop up in this thread. I still own 2 RM-9s from the mid-1980s. At my request, you modded each to become pentode/triode switchable (dropping total power from 100 wpc pentode to 50 wpc triode). That amp in triode mode + Vandersteen 4s and VTL Ultimate remain the best sound I ever heard. My love of tubes dates from those RM-9s.
All that gear has been in storage for decades...now it's all desktop audio/headphone audio in home office, where I recently got an OTL tube unit for several high impedance headphones (Woo WA3). Impedance issues aside, everything I love about tubes is right there, just as before--the palpable feel of music, 3D notes, imaging, humane/slightly warm tonality.
Wish I could hear your more recent designs, because based on the RM-9s, they must be very very good.
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?
One is building a system in which all components sum for the final sound. A cable that sounds fine in one system may not in another. See http://ielogical.com/Audio/CableSnakeOil.php for more information. Be sure to read the PS Audio links. It’s a good primer on audio cable.
The great problem in HiFi is that products are touted as ’the solution’ when in reality, only ’an option’
A great deal of what is claimed is absolute nonsense.
tomic, I have a B&K 707 tester I got many years ago at an electronics swap meet. I really don’t know all that much about electronics but the B&K is easy to use and I’ve found it very helpful in identifying bad tubes -- not just strength but shorts and gas as well.
I would suggest finding a manual for your 667 if you can. Given the age the calibration described there may be beneficial.
Also I've seen positive reports on the Tubes4HiFi kits, including amps. I have an SP-12 line stage custom built by Don Sachs which is wonderful. But the basic unit has favorable reports as well.
@pryso thanks ! fortunately the 667 is coming checked out and calibrated by reputable tech and includes the manual and tube charts. I do have a decent Fluke DMM also, so really looking forward to this...I built a bunch of Hafler kits back in the day, but never a tube unit...
fun
RM probably rhetorical but how do we get back to those fun days...
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
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.
All ML esl's need amps that can handle the load "below" without becoming tone controls and stay stable doing it.
Stereophile tests: "The speaker drops to 3 ohms at 440Hz and to a hair over 2 at 24kHz, from which I infer that puny amplifiers, current-wise, should best be avoided. (Music has considerable energy at 440Hz, though only the occasional high-level cymbal crash will cause copious globs of HF current to be drawn from the amplifier.) MartinLogan claims a phase angle of 45° or less across the range; this graph confirms that to be the case, but the speaker’s ability to shut down the Krell with prolonged pink-noise drive did worry me." https://www.stereophile.com/images/archivesart/99Seqfig01.jpg
I've always hoped Roger would take the time to join the forum here. My RM-10 Mk II that I bought new from him in 2011 is my last amp. He personally burned it in a few days before shipping so it would be trouble-free and it has remained rock solid. People like Roger, Ralph and Almarg make a tremendous contribution thank you all!
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.
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.
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?
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.
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.
The whole idea of tuning a system with cables seems rather weak to me.
The missus once said "Those wires are the only ones where the clarinet sounds like a clarinet." [She had perfect pitch and played the clarinet.] We had decent amp and speakers, so the "wires" were the final tweak.
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.
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.
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....
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?
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.
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.
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.
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 ?
Also wanted to add this is a breath of fresh air on Audiogon , Real discussion of real topics , Not the silly fuse and cable type discussions . Thanks for taking the time to post here.
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.
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?
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.
Two 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.
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%
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.
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.
Hello, could u advise if I can use a pair of 16ohm speakers w 8 ohm amplifier? I have a pair of contrast audio speakers and a heed elixir amp. Thanks for the opportunity to ask a question, even if it doesnt apply to amp design.
I seem to prefer amplifiers that have Toroldal Transformers. Names like Naim, ATC, Belles etc. Is there something about the design of this type of transformer that gives a sound signature? Thanks Terry
"As I tell everyone. Light loading can be done on any tube amplifier. If you dont play above 80 dB go to the lowest tap. If you play 90 go one higher, if you play more than 90 you may have to use the high tap to get the volume you desire. This change should be far more apparent than a cable change. 7 ohms on the 8 ohm tap is no problem for the amp but lower taps always perform better technically though how it sounds to you is more important.
"4 ohms on the 4 ohm tap produces 100 watts. 8 ohms on the 4 ohm tap around 60 watts. As you go down in taps you spend more time in the class A region. The distortion and damping are much improved.
"Would be nice if you had a way to measure the peak voltage you require, then much better advice can be given. You can also get at that with a SPL meter at one meter at listening level. Then with speaker sensitivity we can compute it
"Everyone needs an SPL meter. For $50 its an execellent investment. People spend more than that on a poorly designed high end fuse. Please do not buy premium fuses, TuningFuses are the worst and the others I have not dissected but the people who sell them should be dissected."
*******
Just an anecdotal experience. I own an ARC Ref 150SE. It has 3 output taps: 4, 8 and 16. I settled on using the 4 ohm tap for many of the reasons you mentioned above. John Atkinson reviewed an earlier version of the a few years ago and made the following comments:
"As expected, the Ref150's output impedance varied according to the transformer tap selected. The 16 ohm tap measured 1.4 ohms at low and middle frequencies, rising to 1.9 ohms at the top of the audioband. The figures for the 8 ohm tap were 1 and 1.4 ohms; for the 4 ohm tap, they were 0.55 and 0.87 ohm. All three taps offer quite a low source impedance for a transformer-coupled design; as a result, the modulation of the amplifier's frequency response, due to the Ohm's Law action between that impedance and that of our standard simulated loudspeaker, was relatively mild." See Atkinson report here:
So, in my experience, the Ref 150 SE, on balance, sounds best when light loaded off the 4 ohm tap. At times, I thought the 8 ohm taps sounded better, but after a while, I found the sound bright, probably because there is a 20++ ohm peak at the midrange cross over point. And as you predicted, bass is tighter when played off the 4 ohm taps, although I think speaker impedance in the bass region bounces around quite a bit but has a 3.8 ohm saddle in the 50 to 200 Hz range.
As far as loudness is concerned, my speakers are rated at a 92db sensitivity and the amp has plenty of power to drive the music to uncomfortable loudness levels, albeit with little perceive distortion or signal scrambling.
So the bottom line is that there seems to be something to be said for light loading.
Thank you for posting this. I have a question specific to a tube tester I own and use. It is a Weston 981 Type 3; it incorporates a line check adjustment where the line voltage is adjusted to a mark on the meter. When I test 6550 or KT88 tubes with the tester is in Gm test mode and the line check is done the voltage drops. The voltage holds steady when testing less powerful output tubes. Should I compensate by readjusting the line voltage or use the reading with the lower line voltage? Or do I have a problem with the tube tester?
I'd like to come back to tube testers. I'm not sure I understand correctly about your recommendation for a simpler device, to measure emissions. Is this for the basic purpose of monitoring for tube failure? Would I need a tester with more capacity in order to check prospectively for tube matching?
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.
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.
If a system is not broken and has serious deficiencies cables will likely not correct the problem. How can they?
I'm not suggesting cables can cure a serious deficiencies. However, since cables interact with the amplifier and the loudspeaker, they can ameliorate slight deficiencies be it amplifier, loudspeaker or environment.
Some amplifiers are nearly immune to cables, but loudspeakers are not.
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