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.
I'd like to echo Roger's comment regarding the use of the term "hybrid" in reference to the RM-200. I also once thought of this amp in the same manner, but given my access to Roger I have the opportunity to not only listen to a lot of his designs but understand how certain designs came to be. I also have the benefit of being the one who tests repaired amps and new designs in my system.
So I was able to borrow an RM-200 for a while and at first I can't say the amp thrilled me, but over time it did grow on me (I prefer 6550s to KT-88s). I certainly don't think of the circuit as hybrid any longer, in fact to me it's a tube amp, and a cleverly designed one at that. As previously mentioned it may be the only amp with a tube output that puts out more power into lower loads. In addition, as I think about it, those amps referred to as hybrids that I have heard of use tubes on the input and transistors on the output. I have not heard of any others with the opposite design configuration.
When it comes to MR amplifiers the RM-10 MkII is my all time favorite. My old friend Paul Rosenthal (RIP Pubul57) and I ran similar systems at one time. An RM-10 with Lightspeed Attenuator. We always commented to each other how such big sound could come from such a small package. As Roger mentioned one of the things he designs for is reliability. I have owned mine for 12 years now, and other than replacing the power tubes have had zero issues with it.
This is consistent, btw, with statements I believe Roger made earlier in the thread to the effect that many listeners require less power than they tend to believe.
Yes Al, in your specific case as indicated.
You have speakers that are significantly more efficient than most AND are also very easy to drive as well if I understand correctly, so relatively less watts needed to do things right.
FWIW I heard the 87 db or so efficient Fritz Carrera speakers to teh amazement of many including me knock it out of the park at fairly decent SPL levels (did not measure) at Capital Audiofest off a 8 watt/ch tube headphone amp. Very impressive! The explanation provided for that was though rated less efficient the Fritz use a "series" crossover approach that helps make them easy to drive allowing a smaller amp to overachieve compared to the norm perhaps.
There are many cases where speakers are not efficient and do not present a near perfect benign load to drive. Expect way more watts needed there, perhaps MORE than people might believe.
It can all happen....
My 60w/ch Bel Canto amp does very well with my more typical load OHM Walsh speakers up to a fairly reasonable SPL in a fairly large area. But my 500w/ch Bel Canto amps knock it out of the park with them at any listenable SPL.
Its like comparing a Toyota which drives perfectly fine within its limits to a Porshe.
Preamps are much easier and to me not so interesting
Roger, IME this statement is false. Many good amplifier designers think that a good preamp is no big deal and then go right ahead and design a poor preamp as a result. This is totally because they really in fact for real don't know what a preamp does! - which is to say, a lot more than just the gain and bandwidth, that sort of thing. If a preamp isn't right, it makes no difference how good the amp or speakers are, the missing information can't be recovered downstream.
I wanted the RM-200 to have good CMRR (hum rejection in simple terms). One cannot do that with a tube at the input.
We get pretty high figures and we do it with a tube.... As a hint, look into 2-stage CCS circuits. You aren't going to get good numbers without a decent CCS, a resistor or a single-stage CCS won't hack it.
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.
A good number of 300b SETs can do that. The Wolcott did as well.
Horn speakers tend to have peaks in the response.
Some but not all. CAD has done a lot to improve horn response- if there are problems in the throat where it couples to the horn, all is lost. But I've heard several horn setups where this common problem is overcome, and the result is that they sound very much like ESLs.
I have 6,000 LPs. A lot of them have a good bottom, some have an excellent bottom.
I love the Theodorakis performance, but alas it’s like listening through cotton.
Let’s see what it sounds like in my new room. I’ll let you know.
I have a similar number of titles. The bass really is there. There were only 1000 pressed, so its not likely to be a worn stamper.
I still find that OTLs at low impedance are current limited. As to 10
amps without damage. When I put a 6AS7 on the curver tracer and go just a
bit above the peak rated cathode current I see flakes of cathode
coating coming off like sparks from a sparkler at much less that one
amp. WIth the grid being so close they can easily fall into the grid
wire and POOF. Horizontal output tubes that Futterman and I use are
specified for high peak current about 1 amp.
I guess this really depends on what is meant by 'current' (since the word has become a charged term in audio)! And a lot depends on the 6AS7 in question too- the GAs don't hold up; most American tubes have problems in our circuit as well since they really aren't intended for fixed bias operation. We prefer the Russian variant; they hold up the best of any we've seen.
BTW, I like your approach to the whole 'damping' thing and I also appreciate your use the the phrase 'output regulation' (which I see as opposed to 'output impedance') which I see as a more accurate term. You are spot on that far too much attention has been placed on damping factor- have you seen this article by the former head engineer of EV? http://www.dissident-audio.com/Loudspeakers/CriticalLSDamping.pdfIn is we see that no speaker made needs a 'damping factor' of over 20:1 and some need quite a bit less! FWIW the original AR-1 was designed for a 1:1 damping factor. Also kudos for the comments about too much power. Many amplifiers make excess distortion at lower power levels and when too much power is available in the amp, 90% of the listening will be in this higher distortion region- so not really taking advantage of the amp's capabilities.
BTW I first met Bill Johnson and Robert Fulton at Bob Fredere's house in Minneapolis where the two would meet for listening sessions (at the time the D-150 was ARC's SOTA amp). I wound up running a set of Fulton J's and then Premiers for several years.
RM love your idea about a utility grade ( birch plywood ? ) base for an RM-10 w exchange IF client buys amp. I would be interested in that. I have to say 14# tube amp is attractive as all heck.....
STOP recommending stuff...got the B&K tube tester yesterday, Analog circuit book is due today - you scored yours for less € and now a scope? Remember the Mac MPI indicator ? I recall Marantz also has a scope on some gear, as you say fascinating....
so assuming my needs are kit amp building, ESL repair and this and that, which used scope to get ?????
Roger, lots of good information as well as memories here. So much in fact it is hard to keep up!
As one of the older audio hobbyists here I too remember these names from the past. I recall a visit from William Z Johnson at a local dealer to set up his Tympani/ARC system. Interestingly that same dealer later took on the Fulton line. Regarding Bob, "Fulton made good sounding stuff. I don't know how but I always assumed him to be a competent engineer with great listening skills.", did you know his involvement with instrument design? For example I'd read that he designed trumpet mouthpieces. That was confirmed by an alumni club buddy who played trumpet with a Fulton mouthpiece. He was so sensitive to colorations in musical reproduction that he assigned a characteristic color (his interpretation) to the unique tonality of each orchestral instrument.
Preamps are much easier and to me not so interesting
Roger, IME this statement is false. Many good amplifier designers think that a good preamp is no big deal and then go right ahead and design a poor preamp as a result. This is totally because they really in fact for real don't know what a preamp does! - which is to say, a lot more than just the gain and bandwidth, that sort of thing. If a preamp isn't right, it makes no difference how good the amp or speakers are, the missing information can't be recovered downstream.
I love being vindicated. I have personally never encountered a manufacturer who seems as neutral and knowledgeable as Ralph. Roger, you may not think that this is a technical question, but why don't you believe that preamps do more than regulate gain and provide ample bandwidth and select sources? What is your scientific engineering basis for making such a claim? Do you feel that volume controls are a simple design choice? Are off the shelf rotary pots good enough for you? You tried to put me down that I must be "new to audio" (I am not, been at it for 43 years since age 16) and yet I bet 99% of us who have similar time in this hobby are not familiar with your preamps. Heck, your amps are miles under the radar as well. Frankly, and here is a technical question for you too, your designs, particularly your RM100 appears awfully similar to those of Don Sachs. His amps are less money. What sets yours apart from his (other than is being far more widely known by word of mouth).I can't help but note that you keep insisting that this thread is for technical questions and yet on multiple occasions you have pitched your products. You in fact asked me why I did not consider your RM200 rather than my ARC Ref 150SE. The answer is one I think I answered previously; I believe as does Ralph evidently that it does no good to have a great preamp and a mediocre preamp. Shite flows downstream. I picked my ARC Ref 6 first and then picked the ARC Ref 150SE because I could count on it mating well with my pre. In addition to my question above, I have another one. And this is not meant to be a challenge despite your likely impression that it is. What is your scientific engineering basis for concluding that damping factor, adequate power, and low distortion are the most important performance criteria for an amp (reliability and serviceability not falling within performance criteria)? You keep beating the dead horse of a single Cary amp as if it that one amp represents all that is wrong with most every competitor's design! It is my impression that damping factor being a non-issue with the great majority of competently designed amps, your design philosophy boils down to your preference for the better dynamic range afforded by the high voltage of tubes combined with low distortion. I accept the former premise-greater dynamic range from higher voltage afforded by tubes-but I reject your fixation on low distortion. Note that I used the word "fixation". Sure low distortion is critical but low distortion can be obtained and yet the amp can sound terrible. An amp can sound great and provide accurate renditions of the recording and yet be on the higher side of accepted distortion levels. My point being that there is a hell of a lot more that goes into a great amp than low distortion. You admit that you eschew premium parts because they allegedly don't afford better sound and because the price increase magnifies 5 fold to the consumer (and I agree on the effect of higher priced parts). Where is your scientific engineering proof that premium parts and wire don't make a beneficial difference? You imply (no, you outright state) that my ARC amp is overpriced compared to your RM200 "at half the price" and yet you disregard that both my preamp and amp are chock-full of expensive parts. There were warnings that this thread could go south if it did not remain Q and A. I appreciate that. I promise not to respond in any way in this thread again. But let me leave with these words; I believe that most who read through this thread with an open and unbiased mind will see a lot of very useful and candid information combined with some highly biased viewpoints by Mr. Modjeski and a fair amount of self-promotion and shilling mixed in.
Im not going to go too far with the preamp vs power amp ease of design controversy. Everyone is parroting back the party line, which I disagree with.
I did a shootout for phono stages for our local audio society. It was a strict A/B. We had several name preamps all the way up to $20,000. I will never do this again for a club. They were sad that only one of 8 preamps sounded really different and that one is also well respected. However that one was +3 dB at 10 KHZ and it was obvious. They left shaking their heads because when they compare the same preamps one at a time they "think" they hear big differences.
I pride myself in preamp power supplies, RIAA accuracy, lowest noise. The RM-5 is the lowest noise 6922 preamp new or old. I know this because the noise is at the limit of the tube itself, not the circuit.
I think a lot of designers have problems with the power supplies, noise (tube rush) and hum. .These problems are not easy to solve. Perhaps that is the source of the comment.
Ralph, I measured your preamp's RIAA and it was +4 db in the bass. That is not accurate EQ. My RIAA accuracy is +/- 0.2 dB. . What interests me is how it came to be thought that preamps are harder. What designer is going around saying that? Im not.
I believe as does Ralph evidently that it does no good to have a great preamp and a mediocre preamp.
would you like to fix this sentence? did you mean one of those to me power amp, not preamp? Look i know ive stirred you up, but you did ask about ARC.I really dont care if you are familiar with my preamps or not. You have a lot to say about something you have neither heard or know anything about.
Frankly, and here is a technical question for you too, your designs, particularly your RM100 appears awfully similar to those of Don Sachs.
You tried to put me down that I must be "new to audio" (I am not, been at it for 43 years since age 16) and yet I bet 99% of us who have similar time in this hobby are not familiar with your preamps
.
If you were reading Stereophile and other print magazines pre internet you would have read reviews of the RM-5, 9, 10, and 200. I have not had a large internet presence by choice.
I have another one. And this is not meant to be a challenge despite your likely impression that it is. What is your scientific engineering basis for concluding that damping factor, adequate power, and low distortion are the most important performance criteria for an amp
I have already stated my basis for all those many times here. JA agrees with me, Peter Walker, Bill Jonhson and many others feel these are very important. Since you admit you only have 1% (100-99=1%) of my engineering knowlege how can I explain it to you. You seem to think I have some magic fairy dust I can sprinkle and make you understand. I really can't and this is making me tired.
If you cant understand regulation (damping) then you cannot appreciate its value. Why do people without technical knowledge want to engage in a technical debate? All they can do is parrott back something they have heard.
There were warnings that this thread could go south if it did not remain Q and A. I appreciate that. I promise not to respond in any way in this thread again.
Thank you for leavning us be. I think you are the only one carrying us south.
Yow, things are warming up around here ;-) . I like opinionated people, it requires and reveals passion. That’s true even if I see things differently; no two people agree on everything, and everyone develops their own priorities and tastes in music and it’s reproduction. I, not being an engineer, love reading about hi-fi design by those who are, and find discussions of design philosophy and styles very intellectually stimulating.
Like many Americans, on Thanksgiving day my assembled family expressed, member by member, what they are thankful for. I’m thankful for having Ralph, Roger, and all the passionate Audiogon music and hi-fi enthusiasts contributing to this forum!
@atmasphere
We get pretty high figures and we do it with a tube.... As a hint, look into 2-stage CCS circuits. You aren't going to get good numbers without a decent CCS, a resistor or a single-stage CCS won't hack it.
Of course i use good CCS, what concerns me is the variations in the gain of the two sections of the 6SN7. Since I have the M-60 on the bench I will measure that. What kind of numbers should I expect and at what frequency do you measure it?
I guess this really depends on what is meant by 'current' (since the word has become a charged term in audio)!
Current is well defined by science. I didnt know there was a special audio definition.???
And a lot depends on the 6AS7 in question too- the GAs don't hold up; most American tubes have problems in our circuit as well since they really aren't intended for fixed bias operation. We prefer the Russian variant; they hold up the best of any we've seen.
The 6AS7 is a pass tube in a DC power supply. Heres a link, one has to scroll down a bit and read the application paragraph at the beginning. I dont think brand is going to make a lot of difference as they are all made for the same application as stated clearly here. . https://frank.pocnet.net/sheets/191/6/6AR11.pdf
Speaking of bias I note the M-60 offset, which is entirely based in bias stability or lack of. The offset wanders +/- 100 mV at 0.5 to 5 second rate. Perhaps its all power line related, but nevertheless its quite easy to see on a scope. The DCR of a quad 57 is 0.5 ohms so there is considerable current if the offset gets large.
Having my hands on an M-60 for several weeks now has given me a better opinion of it than I had before. My customer does not want to be adjusting the offset all the time or at all. He has requested I design a servo. I now have the offset down to about 1/10 of the original.
Although we disagree on many things I do appreciate your Gentlemanly approach, unlike that other fellow who left us.
@iaelas
The solder joints just fall apart from vibration.Interesting. My Force is still going strong after 15 years. Pre ROHS.Two good questions for sub makers :)Another is "Why provide such useless controls?" Many subs are clearly not designed to be integrated in any meaningful way.Anyone interested in the effort expended, visit http://ielogical.com/Audio/SubTerrBlues.phpMost 'non-ap' listeners comment on bass definition rather than quantity
ROHS may be the death of reliability. However people are getting used to short life, recycleable electronics.
Yea the controls are pretty lame and hard to see the markings if any.
My sub is designed to work with ESLs as I like ESLs and they present a challenge to blend. An ESL is a resistance (air not ohms) loaded driver My woofer in its tiny box is also resistance loaded (air spring)
Yow, things are warming up around here ;-) . I like opinionated people, it requires and reveals passion. That’s true even if I see things differently; no two people agree on everything, and everyone develops their own priorities and tastes in music and it’s reproduction. I, not being an engineer, love reading about hi-fi design by those who are, and find discussions of design philosophy and styles very intellectually stimulating.
Like many Americans, on Thanksgiving day my assembled family expressed, member by member, what they are thankful for. I’m thankful for having Ralph, Roger, and all the passionate Audiogon music and hi-fi enthusiasts contributing to this forum!
Thanks for your kind words. I like strong opinions as long as they can be supported. So many audio "truths" are more rumors than truth. Who said what and when. I strive to quote members accurately, check spelling and grammar. (where is the spell check on this forum?)
Passion sometimes brings out the best and the worst in people. Somtimes an honest answer from someone skilled in the field is not appreciated. Sometimes no matter how well one can back up his point it is never taken. A lot of this would play miserably in a formal (Harvard style) debate.
Why do people who dont design preamps or even understand them want to say which is harder to design. Thats a very personal thing. I don't go around saying things like that. Each design, pre or power, is its own challenge. One picks his challenge and goes for it. I like to do things that have not been done before and I feel the few designs that I choose to produce and sell are my best work. Others are just studies. Thats the art part of it.
Thanks again ramtubes. Sorry did not get back to you in time. I was the one asking about the reliable electrolytics. The amp I am building is about 300 rms watts/channel int 8 ohms. I usually like over engineering things mostly for purposes of reliability and longevity rather than sound quality since after a certain point sound difference becomes indistinguishable.
I am therefore using 1800 VA toroidal and a 270 amp rectifier. Caps are 4 x 47,000 uF but s I mentioned, at 85 degrees C the caps are rated at 2000 hours. Therefore they are the weakest links in the amp. I saw some Nichicons with 105 degrees C at 10000 hours but they were about $250 EACH (phew). The rectifier, altho likely to be used for welding applications, has soft switch characteristics AND it is quit fast, so would be suitable for audio.
I over sized the rectifier so that it would easily handle the initial short circuit of the caps when the amp is first turned on. I am also using an inrush current limiter, composed of Airotronics
MC1004531J
(rated to 25 amps AC) and a flame proof 33 ohm 25 watt wirewound resistor as the current limiter.
I could not decide between a thermistor and a resistor so decided to go with a resistor. My concern was that if the relay did not engage due to a fault, the thermistor would run at about 150+ degrees, which in my opinion is NOT safe in a solid state enclosure. The resistor would most likely burn out open circuit and I would either smell it or notice it the next time I switch the amp on, when the lights dim :-)
It doesn’t make sense to me that some people get so angry/defensive/personal/nasty when discussing audio equipment! It’s fascinating in a way, but doesn’t do much to educate anyone, and most certainly impedes oneself from getting an education. I listen to music because it makes me feel good. I don’t want a discussion about the equipment needed to play music to piss me off! I believe we can agree to disagree on matters of opinion. This thread has much in the way of fact, but also with opinions masquerading as facts sprinkled in. Back on topic... What differentiates a passive “preamp” from a “tube buffer” with level and switching control? I really like the idea of a simple level control with switching capability, but as I stated earlier, my first try at using a passive, albeit a very inexpensive example, was less than stellar. Specifically, I’m looking at a Schiit Saga to try as a replacement for my tubed preamplifier. I’m weighing options for use with a tube amplifier, but I’d also like to understand what a tube buffer does differently than a tube preamp. Also, would the gain of a preamp “help” a lower powered amp sound more muscular, or is that more “made up” information?
I am also looking for a lab/bench symmetric power supply of up to +/- 100 volts DC at about 2 - 3 amps (so about 500 - 600 watts) and having a very difficult time finding it. The very rare ones I have seen are in excess of $1500. I need such a supply for testing purposes. I do not want to build one.
The 6AS7 is a pass tube in a DC power supply. Heres a link, one has to
scroll down a bit and read the application paragraph at the beginning. I
dont think brand is going to make a lot of difference as they are all
made for the same application as stated clearly here. .
I've certainly seen the page for the 6AS7 :) What I am telling you is the the 6H13C is a different tube (the Russian variant). Once preconditioned, they can hold up better than an American tube. Far less likely to see the cathode coating falling apart, at least until the tube gets weak.
Regarding bias stability, the amp has no need for a servo. If the DC Offset is unstable, its likely noise in the driver tube as the output tubes obtain their bias from the driver tube. Normally the DC Offset is the sort of thing that you set or at least check once every 6 months or so. IOW, its **very** stable!
Current is well defined by science. I didnt know there was a special audio definition.???
Although we disagree on many things I do appreciate your Gentlemanly approach, unlike that other fellow who left us.
Thanks - let's hope he stays away. His approach produces so much noise, its impossible to have an actual conversation, not to mention his creation of an entirely new wing of physics (or at least alternate meanings to words to which no-one was previously aware)...
Just to be clear, I have a lot of respect for you as I do Nelson Pass, John Curl, David Berning and a number of others. There's a lot of snake oil in this business so its refreshing when we don't have to deal with that. Like you, I've been at this a long time but went down a different path a long time ago:http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.phpand while I understand completely how the Voltage Paradigm works (IOW I don't make amps to be 'tone controls'), I'm not at all convinced that the Voltage Paradigm is the only way to achieve the most neutral presentation. For me, the reason was best expressed by Norman Crowhurst, who pointed out a good 60 years ago that while feedback of course suppresses distortion, it also introduces some of its own, which tends to be entirely higher ordered harmonics. Its not that I'm against feedback, but its inappropriate or inexpert application does bother me, and for that I'll use the current ARC amps as an example.
The problem is that the ear converts all forms of distortion into tonality (and the ear/brain system has tipping points where that tonality can be favored over actual frequency response), and the the most egregious problem in audio IMO/IME is brightness (and its twin brother, harshness), which in transistors is entirely caused by distortion; also in many tube amps that use feedback. This is because the ear uses higher ordered harmonics to sense sound pressure, so is really sensitive to them as a result (moreso than most test equipment due to the range that the ear has to cover)! The line I draw in the sand is I want it to sound like real music as opposed to a just a good stereo. To this end, I do my best to vet every customer's system and expectations in order to make a sale. This limits my sales for sure, but it also results in really excellent results both in sound and customer loyalty when everything is set up right.
Regarding the different gain in the M-60s, its entirely possible that the CCS is damaged. Clio9 was an early adopter of Mk3.3 and I suspect he has earlier CCS boards in his amps. IIRC that is... If you can send a photo of the CCS board to my email (found on the atma-sphere.com website) that will tell me a lot.
Although we disagree on many things I do appreciate your Gentlemanly approach, unlike that other fellow who left us.
Thanks - let's hope he stays away. His approach produces so much noise, its impossible to have an actual conversation, not to mention his creation of an entirely new wing of physics (or at least alternate meanings to words to which no-one was previously aware)...
Well, I lied. I have to respond. Ralph-I can't believe that you said that about me after I have done nothing on this Board (in multiple threads) but praise you and after you agreed that preamps are not easier to design (well) than amps. Yes, there were a couple typos in my last post due to being busy and typing in haste, but my points should have been clear. I could easily recite ten typos and misspellings in the various posts of Mr. Modjeski, were I to feel the need to resort to that. It is also shocking to me that Mr. Modjeski criticized the hell out of your M-60's biasing circuit and claimed your RIAA curve in your preamp is not up to snuff and you are doing nothing but kissing his arse.
Ralph, I measured your preamp's RIAA and it was +4 db in the bass. That is not accurate EQ. My RIAA accuracy is +/- 0.2 dB. . What interests me is how it came to be thought that preamps are harder. What designer is going around saying that? Im not.
The preamp's math conforms to Stanley Lipshitz's math and the parts are within 1% or better, FWIW. The thing about a good preamp is that there are so few! In that regard I would say there are a lot more competent amps than there are preamps.
Well, I lied. I have to respond. Ralph-I can't believe that you said
that about me after I have done nothing on this Board (in multiple
threads) but praise you and after you agreed that preamps are not easier
to design (well) than amps.
@fsonicsmith Sorry- my comment was not aimed at you- I had missed that you had left. I was in fact referring to someone else, who (thankfully) has not posted on this thread at all. I see now that in my haste to get thru all the new posts that I missed several posts somehow and yours was one of them. So I misinterpreted Roger's comment. I apologize- I've no reason to drag your name through the mud!
@ramtubes I am still a bit hazy on the power versus gain issue. If you increase the gain, are you not increasing the power output of the amp? So what then affects the power output, the speaker impedance only? In that case, how do we ensure that the amplifier is outputting power within the bandwidth where it has the least amount of distortion? As you stated, and can be seen from measurements, typically harmonic distortions start to increase at the upper and lower limits of the design bandwidths (20HZ and 20KHZ for arguments sake) along with increasing power output.
Thanks Ralph. That means all the world to me. I know this sounds cheap and tawdry, but when I replace my Ref 150SE, I will be absolutely slanted toward an Atma-Sphere. Since I am still here and jabbering, I still maintain that the OP's stated goal of designing an amp for all men and seasons is IMHO misguided. It makes for good marketing but it's not the real world. It may be inconvenient and expensive to buy a new amp when one chooses new loudspeakers but no one said that pursuit of lovely engaging sound is cheap. Though compared to boating and racing cars, it IS cheap. Safer too. In this holiday season, I too wish to express best wishes for health and happiness to all who contribute to this Board in good faith. Now with that, I am gone from this thread. Not from this Board, but from this thread.
@fsonicsmith
Well, I lied. I have to respond. Ralph-I can't believe that you said that about me after I have done nothing on this Board (in multiple threads) but praise you and after you agreed that preamps are not easier to design (well) than amps. Yes, there were a couple typos in my last post due to being busy and typing in haste, but my points should have been clear. I could easily recite ten typos and misspellings in the various posts of Mr. Modjeski, were I to feel the need to resort to that. It is also shocking to me that Mr. Modjeski criticized the hell out of your M-60's biasing circuit and claimed your RIAA curve in your preamp is not up to snuff and you are doing nothing but kissing his arse
.
hahahahahahahahahahaha.
Honestly this is my first reaction to reading whats above...
Thank you, I had a difficult day setting up a strict A/B.
@cakyol
I am also looking for a lab/bench symmetric power supply of up to +/- 100 volts DC at about 2 - 3 amps (so about 500 - 600 watts) and having a very difficult time finding it. The very rare ones I have seen are in excess of $1500. I need such a supply for testing purposes. I do not want to build one.
Does anyone know of one around a max of $500 ?
I would just buy two identical supplies, float the grounds and put them in series. Thats what I use on my bench.
Keep looking at ebay. What you want is rather unusual due to the amount of power, heatsinks to manage the drop across the transistors. At the power level you want a linear supply is unlikely. Almost has to be a switcher to manage the losses. Imagine if you are asking for just a few volts at 3 amps. The high side of the regulator has to be above 100 volts so 300 watts are dissipated in a linear regulator. Thats a lot of heat
What I would do is just make a brute force power supply and run it from a variac. Thats what I have done when I need that much power. Its nice, no losses, no heat.
I do recall that HP made some very high power regulated supplies and handled the dissipation by tracking the regulator with the variac. Again, that is to reduce the heat dissipation. That would be a great and not too difficult project.
Also on the subject of heat.... this is NOTHING compared to creating a beast like the 787 stick to principles, there are different approaches to solving problems
i like the emerging theme from Eric ( Bdp24 ), Ralph and RM about early audio experiences, and especially mentors. I find that very useful and also a good mentor / mentee relationship benefits both. for what it’s worth my mentor is Richard Vandersteen, a guy I greatly respect. but can and certainly will learn from others.
@ramtubes, I finally got around to reading the review by Herb Reichert of the Cary SLI-100 in the December Stereophile. Damn, what a piece of junk! Cary specs the amp at 100w/ch from a pair of KT150 power tubes per channel; John Atkinson, using 1% THD and noise as the definition of clipping, measured the amp’s output from the 8 ohm tap into an 8 ohm load as a mere 3.2 watts! Out of a pair of KT150’s! You have to work REALLY hard to make an amplifier that bad. Whomever designed this boat anchor should find a new line of work; amplifier design is obviously beyond his abilities. 3.2 watts/ch for $5995? Not a "very good value" ;-) .
And what does this tell us about Herb Reichert, who very much likes the sound the amp produces? That Herb apparently likes distortion, I would say. You are now justified in completely disregarding anything and everything Reichert has to say about hi-fi. If one "likes" a power amp this bad, what doesn’t one like?
RM: "He (Harry Pearson) was an idiot." At an instore talk in the 1980’s at a S. California hi-fi shop to introduce a new product, Bill Johnson told this story about Pearson: Bill had sent Harry a new pre-amp for evaluation and review, and soon received a call from HP, saying the pre was defective. Bill had Pearson return the pre to ARC, where it was tested and found to be operating perfectly. A phone call and questions revealed the source of the problem; Harry had installed shorting plugs, not into the pre’s unused input jacks, as they are intended to be used, but into it’s output jacks. Well duh! Should anyone that ignorant really be considered a "reviewer", and empowered as such?
About your variac suggestion :-) Funny you mentioned that since I also came to the exact same conclusion. I have rectifiers & capacitors already lying around with which I can build an un-regulated variac based power supply. All I have to do is add 2 voltage meters to it and an enclosure and voila, it works. I dont need extreme regulation anyway so it would be fine.
For isolation also, I have a 1000VA toroidal with 2 x 50 volts ac lying around which will use. This will easily give me 2 x 70 - 75 volts DC. It will be a bit heavy but will successfully work with gobs of spare power. I will have to add an inrush current limiter too unless I turn the variac down before I turn the power on, every time.
I also play around with DC motors too, so this supply could also easily be used to test them.
They left shaking their heads because when they compare the same preamps one at a time they "think" they hear big differences.
They do hear big differences at home. No doubt about it.
Long term listening does reveal bigger differences than short term listening of unfamiliar complex systems, rooms, etc.
Especially unstressed at home ---long term differences being notable -- with the entire home package being a familiar.
Anything else being paraded about....is well, horsepuckey of the most damaging kind.
Read up on listening tests and the human ear. It’s not a machine, it’s biological, and is individual and has learning curves, and these aspects take time. the ear is a living moving changing variable. and different in every single person. Seven billion different sets of hearing.
It even possesses intelligence and capacities levels like minds and IQ. Yet most people don’t mention these entirely obvious realities. Like your eyes, and mind, they come with a almost totally blank page, and you build it out from some very basic starter forms.. You learn your way to hearing, with your individual package that has as much variation in individuals as does IQ.
Bamboozling them with a test that no one can pass, without adequate amount of time spent in front of it, does not substitute for hearing knowledge and skill.
Any thoughts on kits like this modeled after the Dynaco ST-70? http://www.tubes4hifi.com/bob.htm#ST70 This isn't a mod or upgrade for stock ST70s, but a kit for building a brand-new amp. Some of the design changes are listed under 'ST70 amplifier features' if you scroll down the page a bit.
@tomic601
Also on the subject of heat.... this is NOTHING compared to creating a beast like the 787 stick to principles, there are different approaches to solving problems
i like the emerging theme from Eric ( Bdp24 ), Ralph and RM about early audio experiences, and especially mentors. I find that very useful and also a good mentor / mentee relationship benefits both. for what it’s worth my mentor is Richard Vandersteen, a guy I greatly respect. but can and certainly will learn from others. great thread jim
Thanks Jim, I liken this thread to conversations I had with my mentors. We talked about physics, acoustics, amplifier design all the way down to why I should put chokes in my RM-9 mkII. Bruce DePlama got me onto that one.
Everyone was nice, no headbanging or harshness. We just shared information. We shared that we knew to be true from our own experience. DePalma also turned me on to the 100watt one pair EL-34 application. This application is always challenged when I bring it out. It is in the data sheets I went over in my Burning Amp presentation. http://berkeleyhifischool.com/having-fun-at-burning-amp-2018/
Anyone who does not believe you can get 100 watts out of ONE PAIR of EL-34s had better have a look.
They left shaking their heads because when they compare the same preamps one at a time they "think" they hear big differences.
They do hear big differences at home. No doubt about it.
Long term listening does reveal bigger differences than short term listening of unfamiliar complex systems, rooms, etc.
Especially unstressed at home ---long term differences being notable -- with the entire home package being a familiar.
Anything else being paraded about....is well, horsepuckey of the most damaging kind.
Read up on listening tests and the human ear. It’s not a machine, it’s biological, and is individual and has learning curves, and these aspects take time. the ear is a living moving changing variable. and different in every single person. Seven billion different sets of hearing.
It even possesses intelligence and capacities levels like minds and IQ. Yet most people don’t mention these entirely obvious realities. Like your eyes, and mind, they come with a almost totally blank page, and you build it out from some very basic starter forms.. You learn your way to hearing, with your individual package that has as much variation in individuals as does IQ.
Bamboozling them with a test that no one can pass, without adequate amount of time spent in front of it, does not substitute for hearing knowledge and skill/
@jdjohn
Any thoughts on kits like this modeled after the Dynaco ST-70? http://www.tubes4hifi.com/bob.htm#ST70 This isn't a mod or upgrade for stock ST70s, but a kit for building a brand-new amp. Some of the design changes are listed under 'ST70 amplifier features' if you scroll down the page a bit.
Looks good. I like to see the 3 tube driver board. Do they have a schematic?
The original single 7199 tube driver was flawed by tube to tube variations. Some good 7199 would bias up in a region that actually produced a lot of distortion and reduced power. There are many 3 tube drivers. I would like to know more about theirs.
@cakyol I am therefore using 1800 VA toroidal and a 270 amp rectifier. Caps are 4 x 47,000 uF but s I mentioned, at 85 degrees C the caps are rated at 2000 hours. Therefore they are the weakest links in the amp. I saw some Nichicons with 105 degrees C at 10000 hours but they were about $250 EACH (phew). The rectifier, altho likely to be used for welding applications, has soft switch characteristics AND it is quit fast, so would be suitable for audio.
Electrolytic cap life is much longer than the ratings. Im not sure why they are being so conservative. Perhaps thats all they want to guarantee. They all do it. I was surprised by it too when I first saw the short lifetime. My experience was that the life was much longer.
I have nice nichcon caps in my RM-9s that ate 35 years old and just fine. They probably run at 150 F.. The thing that kills lytics is the loss of moisture over time. If the moisture stays in the caps go on forever.
So you dont need to spend $250 each. Those older caps on eBay will suit you fine, expecially if they are NOS. If one fails, no biggie since you know what to do. Please fuse accordingly with the lowest current slow blow that will get you past the inrush or come up with an inrush limiting device.
@ramtubes, I finally got around to reading the review by Herb Reichert of the Cary SLI-100 in the December Stereophile. Damn, what a piece of junk! Cary specs the amp at 100w/ch from a pair of KT150 power tubes per channel; John Atkinson, using 1% THD and noise as the definition of clipping, measured the amp’s output from the 8 ohm tap into an 8 ohm load as a mere 3.2 watts! Out of a pair of KT150’s! You have to work REALLY hard to make an amplifier that bad. Whomever designed this boat anchor should find a new line of work; amplifier design is obviously beyond his abilities. 3.2 watts/ch for $5995? Not a "very good value" ;-) .
And what does this tell us about Herb Reichert, who very much likes the sound the amp produces? That Herb apparently likes distortion, I would say. You are now justified in completely disregarding anything and everything Reichert has to say about hi-fi. If one "likes" a power amp this bad, what doesn’t one like?
RM: "He (Harry Pearson) was an idiot." At an instore talk in the 1980’s at a S. California hi-fi shop to introduce a new product, Bill Johnson told this story about Pearson: Bill had sent Harry a new pre-amp for evaluation and review, and soon received a call from HP, saying the pre was defective. Bill had Pearson return the pre to ARC, where it was tested and found to be operating perfectly. A phone call and questions revealed the source of the problem; Harry had installed shorting plugs, not into the pre’s unused input jacks, as they are intended to be used, but into it’s output jacks. Well duh! Should anyone that ignorant really be considered a "reviewer", and empowered as such?
Its good to have voice of reason here. I do know Herb and he listens at low levels. Remember he was in the Single Ended camp for many years so he doesn't need much power.
As I have said before, at very low power, less than a watt, that amp and many others will sound just fine. Its in its class A range as far as distortion is concerned. However if someone has Maggies and listens loud it will not be pleasant. If they truly need a 100 watt amp this is not the one to get.
Now HP is another matter. While he created a lot of the language we now use, some good some bad, he was essentially ignorant of electronics, amplifiers, anything technical. I am amused at the story about the shorting plugs.
While I would enjoy having Jon Atkinson's job I would not enjoy being a reviewer. They have to come up with all sorts of drivel on everything they test. I only read the subjective review if the measurements are way off.
We did some testing the other day with the QUAD 57. Both myself and my friend listen around 80-90 db. At those levels the 57 required only 10 volts peak. Sometimes 20 V on loud passages. Almost any amplifier can provide that.
I plan to write up our listening session sometime soon. It is a laborioius project to make a strict, level matched A/B, not blind test. The listener knows which amp he is listening to. Its not a test of the listener, its a test of the amp.
@tomic601
......so these A/B can describe some of the switch gear involved as a DIY project
In essence one takes one or more relays and switches a single speaker (or pair) from one amplifier to the other. That is simple. However the output levels, using pink noise, must be closely matched within 1/4 dB or better. It is well known that if one amp plays louder than the other the louder one will be preferred. Its a well known trick on how to sell the inferior product, just play it a little louder, but not enough to make the volume difference audible.
To match levels you need a pot that switches also, or the pot need not switch if the amps are ok playing unloaded, which most are.
What is hard to deal with is all the wires and little things like the long wire to the button, matching levels, checking and double checking everythings.
However this is how I evaluate my amp, my mods and other amps. I am starting to mod some popular amps that I feel I can improve. This is a new area of interest for me and I want to make sure I am not going backward. Therefore I leave one channel (or one mono) stock and compare it to my mod.
One has to know what one is looking for and what kind of music at what level will expose the differences. I try as wide a range of music as any listener might himself. Only 1 of 10 CDs I find to be useful. Some are horribly compressed, some already muddy, some dont have the right kind of instruments. For instance a harpsichord is not going to reveal distortion, Its already full of harmonics.
Perhaps here is a good place to modify my statement about the difficulty in designing amps vs preamps. Its not about the difficulty and I wonder who started that. Probably some self serving designer who doesnt know how to design a power amp. There are companies like that where their power amps do not exist or are just horrible. I simply find power amps more interesting to design so my work has focused there.
I think the RM-5 is one of the best full function 3 tube preamps out there. If I did it today, 37 years later, I would do it the same way. The RM-1 is lower distortion, wider bandwidth but a lot more complicated. I did not want to make 1,000 of something so complex, support it and deal with the people who buy the really expensive stuff. I wanted to make something that sounds good, works forever, is affordable and brings joy to the user.
I have had the opportunity to work on many higher end preamps and they are difficult, they go through tubes at an alarming rate, cause the owners much frustration and cost in keeping them going. Sadly they often don't sound that great either. If the phono EQ is fudged thats a no no.
Hi Ralph. Im curious if you use an inverse RIAA network to check your EQ. If so where did you get the values? I built mine from the advice of Peter Moncrieff, Mitch Cotter and Dick Sequerra who were the first to discover that many RIAA EQ curves were off. Of course I used precision parts.
Since then I have used my "box" to test dozens of preamps from as many manufacturers and found all of us to be in agreement within 1/2 dB except for the one we had at the SFAS phono pre shootout and yours.
What differentiates a passive “preamp” from a “tube buffer” with level and switching control? I really like the idea of a simple level control with switching capability, but as I stated earlier, my first try at using a passive, albeit a very inexpensive example, was less than stellar. Specifically, I’m looking at a Schiit Saga to try as a replacement for my tubed preamplifier. I’m weighing options for use with a tube amplifier, but I’d also like to understand what a tube buffer does differently than a tube preamp. Also, would the gain of a preamp “help” a lower powered amp sound more muscular, or is that more “made up” information?
Im sorry you had a disappointing adventure with the passive. Perhaps its specs would reveal why. Do you have some specs?
I looked at the Saga, Web page is hard to navigate and its all black.. Mike Moffatt has a good reputation, the product is likely ok , but the lack of any technica info is annoying. They are putting out a lot of product in a short time. That concerns me.
I did find the specs, you do know its a hybrid, thats odd for a buffer which is usually a cathode follower. The input impedance is rather low at 10K but most modern sources an handle it. If you are driving something easy then there is no need for the buffer. Im sure many will disagree.
If you have a good preamp, why change?
As to the muscle, No, that is made up, who is saying so?
When the ARC SP--3 was considered THE pre-amp to own, Frank Van Alstine took a look at it. He found the RIAA eq to be a little too off to be acceptable, the basic circuit to have a little too much non-linearity, and the power supply to be somewhat weak. He came up with solutions to all those faults (correcting the RIAA eq, reducing the distortion, and increasing the power supply's "stiffness"/lowering it's impedances), and offered a modestly-priced mod to correct the faults in the SP-3. Yet Bill Johnson continued to be considered a designer above all others by the High End community, and his ARC products therefore came attached with a certain cache' that others lacked. Some things never change ;-) .
For anyone looking for a modestly-powered tube amp, rather than pay $5995 for a poorly-designed amp that produces only 3.2 watts into 8 ohms and 1.2w into 4 (and at a very high output impedance, which will change the frequency response of almost all loudspeakers), take a look at, say ;-), the Music Reference RM-10 Mk.2. 25 watts pure Class A (a 35w Class A/B is also available, I believe), low output impedance, very long tube life, great sound, all for $5000. @twoch, if that strikes you as "B. kicking", so be it!
@tomic601, your mention of mentoring has jogged my memory (too much alliteration? ;-) . Everyone who met or even read the writings of Harvey Rosenberg knows what an interesting character he was. He was also a generous man, as I found out in the mid-80's.
Harvey was famously known for his love of three hi-fi produtcs: the original Quad ESL loudspeaker, the Futterman OTL amplifier, and the Decca cartridge. I had a Decca Blue back in '73/4, then moved on, along with everyone else, to a Supex SD-900e moving coil (into a Levinson JC-1 head amp). By the mid-80's, my interest in the Decca had been rekindled, partly because of Harvey's writings about it. He obviously understood the cartridge better than anyone else, so I wrote him (no email ;-) at NYAL, asking him every question I could think of about the Decca.
One day the phone rang, and it was Harvey. I hadn't included a phone number, but he called Glendale information and got it! He started talking about the Decca, but soon had to put me on hold to take care of something (a knock at the door, perhaps). I put down the phone, and ran for a pen and paper. When I again picked up the phone, he was yammering on, oblivious to me not being on the other end ;-) . He told me ALL about the cartridge: capacitive and resistive loading, appropriate arms, damping, etc. I wrote it all down, and still refer to my notes. Thanks Harvey, you are greatly missed.
Sigh, in the best way possible. The RM-5, one of my favorite components of all time regardless of price.
Speaking of Harry, I was tuning up two of his systems, one with the CAT and one with the Classe. I had my RM-5 with me and me and Harry listened to it for about two hours.
Man did I ever love that preamp! You could mate the RM-5 with anything and it would transform that amp and speaker combo. When Kenny started dampening his Pre-amp it was all over for me, I kept the RM-5 close by. It tuned better than all of them. I think I toured with the RM-5 for about 3 years.
@teo_audio actually made some reasoned and reasonable comments. Why attack him and his business here? Seriously, I am reading far to many words stating others are “dumb, morons, snake oil marketers, build poor gear” etc... Goodness it’s time to be more humble and professional about other people’s business, hard work and achievements in life.
Others have areas of expertise and experience we can all learn from. I learned long ago when I feel most everyone has it wrong and only I have the answers and truth, then it’s time for me step back and really look at my myself.
This has the potential of being one of the best threads I have read here on Agon in years. Great posts by the OP and others. I simply ask for us to please stop demeaning and name calling builders, business, posters and people we may disagree with. Plenty of very smart and experienced people like the products from these other companies and can appreciate the sonic differences that are found in these pieces of gear. Many appreciate the sonic differences and fine tuning that can be found in parts, wire, and even fuses.
What some call snake oil might, just might, be a blind spot for the person judging. No individual knows it all and there are products out there that just plain old do as advertised even though we might not fully understand why........yet!
I have a DIY 300B SET. Input tubes are 6sn7, driver are 6f6 in triod mode. I use coupling capacitors (Duelund Custom Cu) between input, driver and output tubes. I use 5K output transformer James Audio. My speakers Altec 604E ~100dB sensitivity.
I have a number of questions: 1. What is optimal transformer load for 300B? When I don't need extra power with my very sensitive speakers. 2. What do you prefer for inter-stage coupling, transformers or capacitors? 3. I'm thinking to upgrade to Hashimoto output transformers? Do you have experience with Hashimoto? 4. When you design your amplifiers, how do you calculate optimal idle current for input and driver tube stage? In the past, I increased idle current in both, input and driver tube. And in both cases it gave me a significant improvement in sound. For example, I increased current in 6sn7 from 4.2mA to 5mA. And I can to increase it let say to 5.5mA. How do I know what is optimal or good enough? 5. What is the best and cost effective way to separate power supply between output tube B+ and driver tube B+?
Hi Ralph. Im curious if you use an inverse RIAA network to check your EQ. If so where did you get the values? I built mine from the advice of Peter Moncrieff, Mitch Cotter and Dick Sequerra who were the first to discover that many RIAA EQ curves were off. Of course I used precision parts.
Of course! Its been a really long time and I do not remember where I got the values, but when used I got flat response. FWIW it also plays flat when I cut a lacquer on my lathe and play it back on the preamp. The Westerex has pretty tight curves in this regard; the electronics are matched to the cutter head.
5. What is the best and cost effective way to separate power supply between output tube B+ and driver tube B+?
You can of course make sure that the timing constants in the power supply are low enough that the driver and output section can’t talk to each other. Here’s the math:
F = 1/RC times Pi squared.
That formula results in some hard to work with numbers, since F is frequency, R is resistance and C is capacitance in Farads, which is really inconvenient. So I usually useF=1,000,000/RC * 6.28 (6.28 being Pi squared). This formula results in F in cycles per second (Hertz), R in ohms and C in uf (microfarads), which is more real-world.
In your power supply, C is the power supply bypass capacitor, which is probably an electrolytic device. R is the resistor between the power tube B+ power supply filter cap and the filter cap for the driver. The thing is, there will be a certain amount of current that the 6SN7 needs, so you have to make sure the resistor is large enough wattage to survive that.
For that you need Ohm’s Law which is R=V/I
R is resistance in ohms, V is volts, I is current (C was taken already so I is the convention for current).
To calculate wattage (of the resistor) W=V x I
So for example, if you use a 40uf filter cap, and the driver tube is drawing 9mA (0.009amps) between the two sections, then for the power supply to have a cutoff at 0.5Hz the resistor value will be 8,000 ohms. There will be a 72 volt drop across the resistor and it should be a 2 watt device.
Now the trick here is to make sure that the coupling capacitor has a cutoff frequency higher than the power supply cutoff! Otherwise, the circuit can become unstable, prone to ’motorboating’ (a low frequency oscillation) and IMD will be higher. Use the same formula to calculate the value of the coupling capacitor; R will the resistor in the grid circuit of the power tube that the capacitor is driving. To get 0 phase shift at 20Hz, the coupling cap should go 10 octaves lower, or to 2 Hz; our power supply cutoff is safely below that (although it would not hurt to go an octave lower by doubling the value of the filter capacitance). The problem here is that SET output transformers often don’t have good low frequency bandwidth, and the 300b is right on the cusp of where 20-20Hz is actually sort of possible with a good output transformer. Even though your speaker may not go that low, its a good idea to get as much bandwidth as you can to preserve phase relationships that the ear uses to detect soundstage width and depth. So get a good output transformer.
If the manufacturer has issues with low frequencies saturating the transformer, you can reduce the value of the coupling capacitor, but I would be hesitant to do much of that as phase shift in the bass robs the amp of perceived bass impact, even though its flat on the bench.
A less cost effective way to do the power supply for the driver is to use a separate power transformer and power supply for it. In this way no matter what signal condition exists in the output section, no amount of noise in the power supply of the output tube (such as a general voltage sag) can talk to the driver section. However in SETs, this usually isn’t a problem unless you run the power tube in class A2 or class A3. The latter classes of operation can draw more power from the power supply as output power is increased; class A1 does not do that.
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