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.
@atmasphere
Our MP-3 preamp is based on the first balanced preamp circuit ever sold to high end audio (our MP-1). It has a direct-coupled output (despite being a tube preamp) and has bandwidth to about 400KHz.
Hum, This is a bit self promoting of a current product.
I will quote two products no longer made that were years before the MP-3.
David Manley had a balanced phono input (which is always going to have 3 DB more noise than unbalanced as it uses two input devices) It is also not necessary as the cartridge is a foating source.
The RM-1 had Direct coupled output in 1978 and is lower noise than the MP-3. I have measured both. Clio was there for there and took notes.
That has been my attempt in the past. I try to do it without personal attacks- the principle being: attack the argument, not the poster.
A promotional device in what manner? Do you think Roger is using this thread to try and sell more products? Since you called out Roger on this I will say you are walking a fine line here Ralph, especially given what you once told me in a conversation we had about marketing. The thread was started so that Roger can share his knowledge and experience with the community. He has requested that other designers not respond to the questions asked of him, and from my perspective it’s not that you don’t bring value to the discussion (and I get it’s a public forum), but when you bring up the self promotion stuff, I have to agree with George that it is the pot calling the kettle black. You consistently promote balanced differential designs, not always mentioning products specifically, although correct me if I am wrong, but you have mentioned the MP-1 was one of the first balanced preamps in high end audio on more than one occasion. I have read many threads where you reference how your preamps solve the issue of cable artifacts coloring the sound, that you make them unity gain with a buffered output, and you have mentioned or alluded to your amplifier designs many a time as well. Granted you do so in a gentlemanly manner and as a means to educate. However, isn’t that what Roger is doing as well?
No. And I agree, its a fine line!
Tony, Roger is a friend of yours so this might be sensitive, but here’s the difference. I just try to present the facts and nothing else. I don’t see Roger doing that here; take a look at the attacks in his post just prior. I’ve got no problem with his answering questions; I’ve been doing that here for over 20 years. The difference is in that context he also sees fit to attack others- Cary, ARC, Atma-Sphere (and also me personally) and so on. And lots of mention of his amps and preamps that goes beyond just the facts. In my case when I mention our gear I make no claims about the sound, just statements about what it is- for example that our preamps are balanced. Take a look at the examples you cite. When I’ve made that statement you quoted (and others that Roger quoted), it was simply fact with zero comment about how the equipment sounds or performs, with the exception of the fact that if the equipment supports the balanced standard, then the cables used will be transparent. Go take a look. The reason for this is the audiogon rules- I can’t (or thought I can’t) just get up and say how great my stuff is while demeaning others. ’I was so amazed how this detergent cleaned the stains that that other detergent couldn’t.’ That’s *advertising*.
BTW I kept my mouth shut about this until specifically asked. FWIW, I’m a moderator on another site, and I know better than to attack others personally as we see in Roger’s posts below (and previous). I have a thick skin, which is why I know better than to return in kind:
I never imagined other amplifier designers would want to answer questions directed to me. If you think one of my answers is wrong you are wellcome to chime in but not with your paradigm or unsupported theories. I dont welcome any unsupported theories, poorly vetter answers from flawed articles.
....
Roger:
The problem here is simple: you cannot disprove anything that I’ve posted, while I can prove that its real, and have already done so on this thread. This might be the 4th time I’ve pointed this out. I am simply pragmatic; which to the best of my ability you seem to equate with ’pseudo science’. How much proof do you need? The problem here is not that I am wrong, nor is it that you don’t have engineering talent- yours are some of the better transformer coupled amps I’ve seen. But right now it seems that when presented with something that you don’t know about, it appears that you’d rather dismiss it than cause your hand to move and investigate (re.: cartridge loading, power rules). Good engineering practice is good science. In my case, I see if I can measure it; that’s how I found out that power cords can affect equipment performance both measurably and audibly.
You have a paradigm to promote with which I totally disagree. When I bring up that a widely varying impedance speaker will not sound as the designer intended, you bring your paradigm.. Perhaps your amp provides a tone control some like. I have 2 m-60s in my shop right now in my A/B test rack, anyone is welcome to come listen. One is stock one is my mod with feedback. It appears you have abandoned feeback on some psychological level rather than listening. We are just listening.
So please dont bring your, not vettet, paradigm to a scientific discusstion which is in general disagreement with it. That is self promoting to a high degree. Why post here when you have known for years we disagree about damping, distortion, current, tube applications and a host of other things? Ive read your paper over and over again and it makes little sense.
You are the only outside designer who has entered this thread.
When you answer questions from your point of view I have to deal with that and it makes more work for me. We already know what you are going to say you have said it 6,798 times.
If you really believe this then you missed the boat about what this is about.
Put it another way: Flat frequency response from any speaker in any room is flat out (if you will pardon the expression) **impossible**. You can’t name a single speaker measured by anyone that is really in fact actually flat. Plus, you can’t fix it with an equalizer- they don’t have the resolution.
We like to think speakers are flat, but such thinking is engaging in made up stories. Its fantasy.
And it turns out that for the last 80(!) years we’ve known that distortion is interpreted by the ear as tonality! See the Radiotron Designer’s Handbook, 3rd edition (page 67 IIRC). This fact is indisputable.
So what can we conclude? Certainly that the ear places an extreme emphasis on certain distortions (again, see the Radiotron), while not caring nearly so much about others.
Since feedback causes those distortions out of its application (see Norman Crowhurst), its a **guarantee** that any amp that employs it will have some coloration (brightness) due to the reasons stated above.
Brightness is the single biggest objection that people raise about audio reproduction. Women tend to have more intact hearing than men and its common for them to raise objections to brightness more than men. Anyone here with a GF or wife can attest to this. So maybe feedback to achieve a voltage source isn’t the way to go; women are after all part of the marketplace (WAF).
As I pointed out in my email to you a few days ago, in the old days before the voltage rules were introduced (1950s), speakers had to deal with the issue of unknown voltage response in amps because a lot of amps (SETs for example) didn’t employ feedback. This is the Power Paradigm, and if it irks you that I put a name to it, I’m sorry - you weren’t around when I did that- I also use ’power rules’ and ’power source’ as alternates. These speakers had controls on them to adapt the speaker to the voltage response of the amp. JBL, EV, Altec, Acoustic Research, KLH... you’ve seen these controls! I have to imagine that you must have thought they were to adjust the speaker to the room?
Some modern speakers have these controls too - Sound Lab ESLs, Classic Audio Loudspeakers and plenty more, if they are designed for amps with a high output impedance (power source). The Sound Labs aren’t, but because ESLs aren’t Voltage Paradigm devices; they need the controls in order to work with voltage source amps.
The idea of the modern Power Paradigm is simple: just don’t make the distortions to which the ear is keenly sensitive, and after that do your best to get flat response from the speaker. The Voltage Paradigm has it the other way ’round. This is why I advocate the ZERO autoformer, as it allows you to adjust the voltage response of the amp without using feedback, which I regard as the bigger sin for reasons stated above.
Quite simply I (and other designers like those that make SETs) am not trying in my designs to do what you are trying to do. I’m trying to do what SETs do, but without so much distortion (coloration) and with wider bandwidth. Its not woo voodoo- I don’t go in for that anymore than you do; its all just engineering once you know what the problem is, which is stated above, but ad nauseum: the ear converts distortion into tonality. Get rid of the distortion, and the presentation **can** be more neutral.
It would be far more creditable of you to advocate the use of a different amp to handle the problem properly, even if it’s not OTL. Instead of this costly band-aid autoformer "fix" all the time, that "enables" an OTL to be used under diminished sonics. Maybe your new venture into Class-D will show another side.
I have enjoyed posts by Ralph and Ramtubes on this forum. They are both highly qualified as designers and manufacturers. They both provide answers to technical questions about gear. Sometimes, they include opinions based on their understanding of the science behind gear. Nevertheless, their posts are almost always informative to the membership here. Occasionally, they are self referential....
... I suspect the line should be drawn somewhere in between the services provided by Ralph and Ramtubes and the disservice provided by [redacted by Al, only because it is not relevant to this thread]. Might I add that Ralph and Ramtubes are not close to that line IMHO.
+1. Well said, gpgr4blu. And to the extent that Roger or Ralph might ultimately derive some pecuniary (monetary) benefit from their contributions here, IMO it would amount to a win-win. A win for the members here who benefit from the knowledge they share with us, as well as for them.
Roger, I have a sincere question. What specific technical considerations lead you to be so negative about Ralph’s paradigm paper. Obviously suitability for use with a wide range of speakers is not a priority with his amplifier designs, as you’ve stated it is with your designs. But the only other relatively minor issue I’ve ever perceived in his paradigm paper is that as worded it might lead **some** readers to believe that the high output impedance and other characteristics of his amplifiers (and various other tube amplifiers) would result in precisely constant power delivery into varying load impedances. (In fact I’ve seen one or two posts by members here who do not have significant technical backgrounds in which that belief has been stated). Whereas the reality is simply that they will come considerably closer to accomplishing that than an amp which acts as a voltage source. To a greater or lesser degree depending on the amp’s output impedance and on how the speaker’s impedance varies as a function of frequency.
I also think it’s noteworthy that some of Nelson Pass’ First Watt amps have even higher output impedances, and consequently "poorer" output voltage regulation, than Ralph’s. In some cases vastly greater output impedances than Ralph’s designs. But it seems to me that in both cases that doesn’t mean their amps are flawed in either concept or execution, it just means that they are intentionally designed such that they are suitable for use with a relatively small subset of available speakers.
Best regards, -- Al
P.S: @Marqmike, thanks very much for the nice words in your post yesterday.
But the only other relatively minor issue I’ve ever perceived in his
paradigm paper is that as worded it might lead **some** readers to
believe that the high output impedance and other characteristics of his
amplifiers (and various other tube amplifiers) would result in precisely
constant power delivery into varying load impedances. (In fact I’ve
seen one or two posts by members here who do not have significant
technical backgrounds in which that belief has been stated). Whereas the
reality is simply that they will come considerably closer to
accomplishing that than an amp which acts as a voltage source. To a
greater or lesser degree depending on the amp’s output impedance and on
how the speaker’s impedance varies as a function of frequency.
Thanks Al, and spot on.
No amp is a true power source. But if the speaker load (which can be quite variable and that's OK) is high enough then the amp can be **relatively** constant power on that load.
When you graph the amp's power vs load impedance curve, it looks very much like an airfoil profile in cross-section. There is a maximum power output, and at lower impedances the output power falls off rapidly as more of the power is simply dissipated by the output section itself. Above that maximum, power falls off very slowly as load impedance is increased. For example our M-60 is only a few watts less at 30 ohms as compared to 16. While this is not constant power, its pretty close as the difference is less than 1/2 db.
With transformer coupled amps (VAC comes to mind) you have the ability to select the most ideal winding to push the amp more towards a voltage source or more towards a power source- depending on how the power tubes are thus loaded and the resulting output impedance. We use the ZEROs for that same purpose- years ago we used to use our Z-Music autoformer for that same reason, before the ZEROs existed.
Along with VAC, Music Reference amps provide multiple impedance (transformer winding) taps; in the RM-200 Mk.2: 1, 2, 4, and 8 ohms; in the RM-10 Mk.2: 4 and 8 ohms; in the discontinued RM-9: 4, 8, and 16 ohms.
I’ve got a question for the tube amp designers. How much of a difference does the power
transformer make in a tube amp design?
Is the output transformer more critical or the power transformer or
both? I’ve read that the output transformer
is absolutely critical and I know that they can be very expensive. However, how much would it degrade a good design
to just go buy an Edcor power transformer, which I’ve heard are decent transformers,
and use it with a high-quality output transformer?
@atmasphere Ralph, while I respect your opinions and body of work, another fine line can easily be drawn between marketing and advertising. You have mentioned to me in the past Audiogon is where you spend most of your marketing efforts. I have a degree in marketing and have been in product marketing most of my professional career. In this age of Internet technology and online consumerism branding is important. You may not agree with this, but your time here sharing your expertise, providing assistance, and yes, mentioning your products, has promoted your brand, which is YOU. Let’s look at these links as an example which are a couple you frequently drop into your posts, including on this thread which is where I pulled them from:
If I click on either of the links above I am taken to your site. Simple marketing 101 these days, drive eyeballs to your site. Not only can I read the material, I can then click on a number of links to stay on the site, one of which is products. One might come to the conclusion that it is veiled advertising, but I am not going to get into a pissing match on that one. Suffice it to say in my opinion, and I’m sure I’m not alone, you promote your brand here, albeit respectfully, in a gentlemanly manner, but also in ways that are not overt. Nonetheless though it is promotion and marketing.
Here is another example. You often mention how feedback causes harmonics that the ear/bran can interpret as brightness and provide references you feel back up this point. Again, you are educating people here that in your opinion and listening experience amplifiers employing feedback are colored, but you are also alluding to the fact, which can easily be looked up by anyone inclined to do the research, that your amps don’t provide this coloration because of their minimal or lack of any feedback. You don’t have to mention product names to effectively market or promote them (and yes you cause some diversion because you reference SET amps as well when discussing this).
Now about Roger. Yes he is a friend and I work with him. Yes he has strong opinions about people who based on his knowledge and body of work have not done justice to the science of amplifier design and he calls them out. I can see where his personality might ruffle some feathers or turn off some folks, but let’s also note, which you failed to mention, that he has praised folks like Peter Walker, Julius Futterman, Saul Marantz, Sid Smith, Nelson Pass, and James Bongiorno.
Lastly, as you know I encouraged you at first to continue contributing to this thread as I believe you have valuable things to say. Unfortunately, the self promotion accusation bit has changed that. I have an idea. Why don’t you start a thread of your own and every time you see something here you disagree with or wish to comment on you reference it on your thread and hold a discussion there, and for future reference this will be my last comment on the topic. We have diverted this valuable thread enough.
@utrak
I’ve got a question for the tube amp designers. How much of a difference does the power transformer make in a tube amp design? Is the output transformer more critical or the power transformer or both? I’ve read that the output transformer is absolutely critical and I know that they can be very expensive. However, how much would it degrade a good design to just go buy an Edcor power transformer, which I’ve heard are decent transformers, and use it with a high-quality output transformer?
Id better take this one since my amplifiers happen to have output transformers. I will admit in 1982 I did not know much about output transformers, I like many shied away from a traditional tube amp and decided to take Julius Futterman's work one step further and make it have DC output. The large output cap in Futterman's design is electrolytic and right in series with your speaker. Sold that design to Counterpoint and it became the SA-4, won some awards; yada yada yada.
I wanted to make a push pull EL-34 tube swappable amplifier so I decided to get into transformer design. You couldn't buy any off-the-shelf quality outputs in the 80s. It took a lot of time and thinking and trying things. Crowhurst taught me.
Now to your question, both are important in different ways. There was an old adage that in a mono amp the output and power should be the same size.. not terribly sensible but easy to say yay or nay to an amp at the swap meet.
The power and output do entirely different things. They both share the desire to be low loss. Loss in the power transformer makes heat, loss in the output robs potential power. Large power transformers have about 5-10% loss which becomes heat. They have a primary made of 100 feet of 16 ga wire in my case. Resistance is 1-2 ohms which is why I have trouble believing a 12 ga power cord can much enhance the situation.
Power transformers work at 50 or 60 HZ. I make those differently for each frequency otherwise the flux is 20% higher in Europe.
Output transformers are an entirely different animal. They have to work over a wide band of frequencies. To make a stable amplifier the output transformer has to go out to about 65 Khz. The laying down of the wire in an output transformer is most important. We also interleave the layers which means for instance, wind part of the primary, then part secondary, then part primary, then part secondary, then part primary. That is called a 5 layer or 5 interleaved transformer. While some makers claim 11 interleaves this causes too much capacitance and a measurable rise in plate current above a few KHz. If you play loud trumpet music you can bur up the tubes, especially if the speaker impedance is low there. It's all tradeoffs.
What happens next is how the transformers behave in the amplifier. The amplifier is literally build around the transformers. There is a big difference between designing a transformer and specifying one which is what most designers do.
Designing means figuring out all the wire gauges, insulation layers, interleaving, core size, stack, bobbin. Goes on and on.
Specifying a transformer means saying - 3db at 15 hz and 65 Khz. Done! Hope the transformer house has an old guy who knows how to do it. I have never been satisfied with outside vendors even when they wind my design. They have horrible problems with uniformity. Power transformers are easy, just count the turns and get the wire on there any way you can.
I've not tried an Edcor power, I have the outputs. Most of them are made for tube rectifiers I believe. I'm not fond of tube rectifiers in amps above 30 watt, ,certainly not 100 watts. Were you planning a tube rectifier? Which one?
I want to end this amplifier pissing contest. This is not the purpose of this thread.
If someone wants to make amplifiers out of the accepted normal standards why would he be coming here? We are discussing normal amplifiers not outliers.
99% of speakers are designed and voiced with low output impedance (high damping voltage source) amplifiers. If it were designed any other way the maker and owner would limit be limited to the amplifier the speaker guy used.
Modern amps starting with Fisher, Marantz, Eico, Heath, Williamson, have damping 10 or above. That was one of Williamson's specs along with low distortion and wide bandwidth. Williamson set the bar and all reasonable amplifiers have respected this bar because it works and sounds good. One can make amplifiers out of these standards but they will not play speakers in the way they were intended by the speaker maker. They will change the tone of the speaker to the extent that they interact.
Most reviewers are using high damping amplifiers (except when a low damping comes along). Most of the world is using high damping amplifiers. John Atkinson shows you what happens to the frequency response of the amplifier he is testing when connected to a typical speaker. If the damping is low it is not pretty. You will hear the modification of the frequency response which you might like or not. You definitely will hear the one note bass at speaker resonance. Two notes for a ported cabinet.
Speaker makers count on you having low output impedance as they did. Remember a damping factor of 10 is generally enough. Above that there is very little difference to be had and 100-1000 makes no sense except for marketing
If you would like to hear the change in frequency response caused by a damping of 1 amplifier, get a 10 ohm 10 watt resistor or a resistor similar to your speakers nominal impedance. This is not critical, if you play low volume get 5 watts. You will learn two things. Besides hearing the change of tambur of your speaker you may note undefined bass, rolled off treble, loss of air, loss of definition. Dont get into imaging too much. Play lots of different material, just listen to the frequency balance. If the vocals jump out at you. If the symbols loose their sheen.
Check the temperature of the resistor, start out low volume and don't burn yourself. At high levels you may be surprised how cool the resistor is. That resistor is getting half the power and the speaker half. You may find the resistor gets barely warm and thus shows you how much, or little, power you are using. The resistor goes in either lead in series with your speaker. You might experiment with other values.
Roger, I have a sincere question. What specific technical considerations lead you to be so negative about Ralph’s paradigm paper
I hesitate to answer your question for the fire that will reign down on me. But this is the last I will deal with
Because the paper does not make electrical sense and appears to be a excuse for making a certain kind of amplifier that has limited applications. Which is just fine. It is cleverly written, I will give you that. Perhaps Ralph could provide some frequency sweeps that show the power is constant? Then show how the speaker response is thus modified? Words alone do not convince me.
AL, you appear to know a good bit of electronics, do you not see how this paper parts from accepted electrical theory? This first sentence causes me pause.. " The Power Paradigm assumes that amplifiers produce power and speakers are power-driven " Speakers are not power driven, they are voltage driven. Lets look at the low end resonance. Most speaker climb to 40-60 ohms at resonance (35 hz lets say). The speaker designer does not want the voltage to rise into that peak. He already accounted for that peak with the mechanical damping of his speaker.
We do not want to feed more power into that frequency, the speaker is telling us not to by raising the impedance. The sensitivity of the speaker is rising rapidly at resonance. That is what resonance is and it occurs when the mass of the cone no longer determines the motion and the stiffness takes over. That is what is going on.
About high order harmonics I will ask you. Would you rather have an amplifier with 3% 3rd and 0.01 7th-11th or one with less than 1% 3rd and 0.02 7th -11th? My point is that the high ordered harmonics are rather small. Intermodulation will follow a similar path.
I will say this. I have two M 60s on my A/B system and I like Ralphs amplifier build, layout, cool circuit. I dont like the high output impedance or high distorton. I do like Ralph’s amplifiers better than his paper. I wish he would just drop the paper. Its embarassing.
Can’t he just say what his amps do without having to invent this story?
Loudspeakers that operate under Power Paradigm rules are speakers that expect constant power, regardless of their impedance. Examples include nearly all horns (currently the Avantgarde Trio is the only known exception), ESLs, magnetic planers, a good number of bass reflex and acoustic suspension designs. Horns, ESLs and magnetic planers do not get their impedance curve from system resonance and so benefit from a constant power characteristic and indeed, many of these speaker technologies are well-known as good matches with Power Paradigm amplifier designs.
This paragraph is particularly disturbing. Is he saying ESL speakers are constant impedance? The Quad 57 goes from 50 ohms to 1 ohm. Peter Walker specified and designed the QUAD II with a damping factor of 20. He designed the speaker and knew what was needed. The 57 also happens to have a DC resistance of 0.5 ohms. Therefore as little as 50mV of offset will put 100 ma through the transformer, upset the bias of the amplifier by 25 %. It is hard to keep a non servo DC amp consistantly below 50 mv even durring one listening session. You have to disconnect the speaker to see the offset easily on the meter. This is not fun.
Let’s look at these links as an example which are a couple you frequently drop into your posts, including on this thread which is where I pulled them from:
@Clio9 I put these papers up for the simple reason that I got tired of writing the same thing over and over (for example, the article about common amplifier myths gets linked a lot, as that is a very common myth around these parts). I recently added another article about balanced operation; its a lot easier to drop a link than write 200-800 word explanations all the time. That is the only place I know of where I can host something like that. Other than that, I *do* walk my talk. Beyond that if there is a statement of error, I offer the correction as I have done here. Normally that isn’t a problem, but in this case I’m getting personally attacked over stuff that is normally pretty easy to understand. While I didn’t intend it that way, apparently my presence here is part of why this thread hasn’t been removed.
I dont like the high output impedance or high distorton. I do like Ralph’s amplifiers better than his paper. I wish he would just drop the paper. Its embarassing.
Can’t he just say what his amps do without having to invent this story?
Loudspeakers that operate under Power Paradigm rules are speakers that expect constant power, regardless of their impedance. Examples include nearly all horns (currently the Avantgarde Trio is the only known exception), ESLs, magnetic planers, a good number of bass reflex and acoustic suspension designs. Horns, ESLs and magnetic planers do not get their impedance curve from system resonance and so benefit from a constant power characteristic and indeed, many of these speaker technologies are well-known as good matches with Power Paradigm amplifier designs.
This paragraph is particularly disturbing. Is he saying ESL speakers are constant impedance?
@ramtubes
I’m not saying the ESLs have a flat impedance curve- far from it. Many vary from bottom to top by about 10:1.
Here is the meat of it right here:
Speakers are not power driven, they are voltage driven. Lets look at the low end resonance. Most speaker climb to 40-60 ohms at resonance (35 hz lets say). The speaker designer does not want the voltage to rise into that peak. He already accounted for that peak with the mechanical damping of his speaker.
I am really curious right now how many times I’ll be explaining this! While the above quote is mostly true these days, its not actually 100% correct due to exceptions. First of all of course, voltage doesn’t exist without current and current times voltage is power, so obviously all speakers are actually driven by power. The bit about them being ’voltage driven’ is a **charged term or phrase**, similar to the idea of ’RMS power’; see:https://forum.audiogon.com/discussions/rms-power On that thread, we see that the term ’RMS power’ is really something that was created to satisfy FTC rules for testing amplifiers back in the 1970s. Outside of that the phrase is ambiguous. I pointed this out at the inception of that thread. There are other charged terms in audio as well- ’damping factor’ and ’output impedance’ are two that come to mind- they have *very* specific meanings in audio, not so much elsewhere in the electronics industry (IMO/IME, Roger, your use of the phrase ’output regulation’ is more accurate).
This is the case with the phrase ’voltage driven’ as well. In this case, what it means is that the speaker is is intended to be driven by an amplifier that acts as a voltage source.
The reason is that the speaker has a resonance caused by a driver in a cabinet, as we see in the quote from you just above. Since the resonance expresses an impedance peak, if you don’t throttle back the power into that peak (IOW, maintain constant voltage), you get a tonal coloration. In effect, the impedance curve of such a speaker is also a map of its efficiency vs frequency: the higher impedances needs less power, lower impedances needs more. A voltage source satisfies this.
Now an ESL is not a driver in a box. In a nutshell its impedance curve is essentially based on a capacitor. Thus its impedance curve does not also represent its efficiency vs frequency; its not following the same rules. Many solid state amps act as voltage sources; if you put one on a Quad, the result is a loss of bass and way too bright.
Now as I mentioned in my email to you, some speaker designers build their speakers to work with Power Paradigm amps, and so apply a different technique. The driver in the box has a peak, but if you do the math and place the peak at a point in the box such that the box is starting to roll off before the peak, what happens is you can extend the LF response of the speaker down another half octave for a given box size. The Acoustic Research AR-1, the world’s first acoustic suspension loudspeaker, was designed for an amplifier with a 7 ohm output impedance.
You claim that this flies in the face of electrical theory, but you then have to explain a lot! Where did the voltage rules come from? Who introduced them? When did that happen? What was out there before that? I’ve of course told you... multiple times at this point. Its audio history.
Regarding distortion:
About high order harmonics I will ask you. Would you rather have an amplifier with 3% 3rd and 0.01 7th-11th or one with less than 1% 3rd and 0.02 7th -11th? My point is that the high ordered harmonics are rather small. Intermodulation will follow a similar path.
The one with the lessor higher ordered harmonics will sound smoother/more like music to the human ear. Most would prefer that, given a speaker on which both amps make good FR. The ear treats the 3rd very much like the 2nd and in that regard its relatively insensitive. We really should be weighting the various harmonics according to the ear/brain’s sensitivity to them. But our current test and measurement regime pretty well ignores human hearing rules that have been discovered since the 1960s. But if we did that sort of rating, a 0.02% of the 7th would look only fair because its pretty audible.
It is a popular myth that if an amp is high in THD it will also be high in IMD.
This is the inconvenient truth about human hearing; feedback violates arguably the most fundamental rule of human hearing perceptual rules: how we sense sound pressure. This is why SETs have made such a huge comeback in the last 28 years.
But only in high end audio.
High end is fundamentally different from regular audio, the difference being in regular audio its all about the money. In high end its all about seeing how far you can push it, making it sound real instead of like a good hifi. That is where I draw the line- IMO/IME if the speaker requires that the amp employ feedback, it will never sound real, at best it will sound like a good stereo.
Hi Roger,One amplifier design that has always intrigued me is Bob carvers load invariant Sunfire Designs. Honestly I don’t know the premise behind how they work but was wondering what you think of them from a knowledgable designer standpoint.I always thought if I went back to ribbon speakers that I would get one of those.
I've not tried an Edcor power, I have the outputs. Most of them are made for tube rectifiers I believe. I'm not fond of tube rectifiers in amps above 30 watt, ,certainly not 100 watts. Were you planning a tube rectifier? Which one?
Thanks for the response Roger. When you say "made for tube rectifiers" are you referring to the center tap? If so, I'm under the impression that I don't have to use the center tap. I'm not an expert but based on what I've read, I'm not a fan of rectifier tubes. I currently have 2 sets of tube monoblocks and neither of them use tube rectifiers. One uses a quad of EL34s and the other uses 8 KT88s per monoblock.
As far as output transformers go, I don't have a specific one in mind right now but I would consider an Edcor or Lundahl. I would only use the latter if I were very confident with what I was building because of the cost. I would love to know how much difference really exist between the two.
I was considering building a lower power tube amp (25 - 50 watts) if I could find speakers that I could afford that sound good with a medium power tube amp. The problem is that I keep gravitating towards less efficient speakers. I used to have Thiel 3.6s and I still have a pair of 3.0s in storage. I had to move to a smaller room (11' x 16' x 10') a few years ago and I've spent the last 4 years learning room acoustics. I'm using a pair of LS50s right now, which sound really nice with both sets of monoblocks. BTW Roger, I still can't believe how much of a difference it made when I moved the LS50s from the 8-ohm tap to the 4-ohm tap on both sets of my monoblocks.
I hope this question is appropriate for this thread.
In comparing 'only' power supply VA ratings - can one judge the capability of an amp to drive a set of speakers when all other specifications are the same except the number of channels including the power supply?
Real world example:
I am comparing a 5ch and 7ch amp. Same brand and specs exactly the same except for one difference -- one is a 5ch and the other a 7ch. Same rating of Tor power supply ( 2 total valued at 1,230VA and 1,025VA)
All things being equal - will sound quality be relatively the same? Dynamics? ... or is one better than the other?
Also -- ideally how big of a power supply is best suited for an amp rated at 200wpc at 8ohms driving speakers that dip to low 3ohms?
ramtubes I poorly wrote that line about the EAR 912- My pre-amp has subminiature tubes rated for 100,000 hours, the EAR 912 can use 7DJ8s or 6DJ8s rated for 10,000 hours as you stated. My old EAR 864 NOS 12AX7s and 12AU7s only lasted about 3,000 hours before replacement. However the EAR Acute has 6DJ8s at over 7,000 hours and going strong. Depends on the tube and design of course. My Audio Research gear back in the 90s had power tubes last about 2,000 hours or less, not really good but better than my Dynaco IIIs which lasted about 9 months, 1,000 hours or less.
I've got another question for the tube amp designers. Does it matter whether the filament supply is AC or DC? I've heard arguments both ways. I think that it would be great if one could get away with an AC filament supply because it requires less current from the power transformer and reduces cost to build.
I asked the same question a little back here. Roger said AC is good as long as it is quiet.....😊 Perhaps he has more to add.....
I am upgrading and reassembling an amp with AC fils. Dead quiet.
I also wonder about rectification. My amp has an 5U4 that I am thinking of converting over to a full bridge SS rectifier. I seem to prefer the sound of tube amps and preamps that are SS rectified. My amp is only 13 watts channel/EL86 based and may be low enough power to like tube rectification just fine. I prefer SS rectification in more powerful tube amps, but am not totally sold on their value in lower wattage tube amps ..... say under 10-15 watts. I think I may like SS rectification more in these low power amps, but need to experiment more. I find SS rectification to be more dynamic while delivering much better bass. One can also beef up the supply with more capacitance and very robust Pi filters.
I am comparing a 5ch and 7ch amp. Same brand and specs exactly the same
except for one difference -- one is a 5ch and the other a 7ch. Same
rating of Tor power supply ( 2 total valued at 1,230VA and 1,025VA)
All things being equal - will sound quality be relatively the same? Dynamics? ... or is one better than the other?
Also
-- ideally how big of a power supply is best suited for an amp rated at
200wpc at 8ohms driving speakers that dip to low 3ohms?
It *might* be that the amp with 5 channels could sound a little better, solely based on your comments above, due to 5 channels sharing a common power supply instead of 7. IME probably not a very big difference in any event! With regards to the latter question, the power supply for one channel should be capable of sustaining 14 amps continuous to sustain the output section of the amplifier (assuming that the amp is doubling power as the load is halved); a bit dependent on the class of operation (for example, a class D amp won't need any more than that, while a class A amp will need a bit more to sustain its driver section. Generally though its a good idea to have some reserve available in the power supply so that it runs more reliably. I prefer to have the power supply to have considerably more energy than the amp is going to need to make so that it won't limit current when things get complex.
Roger, let me add my thanks. We spoke years ago when I had a Beveridge RM-1 and you were very helpful at that time. You mentioned a few posts earier that you produce some DD amps for electrostats. I have a pair of Acoustat Xs in need of amplification. Can you provider some information?
I have a pair of Acoustat Xs in need of amplification. Can you provider some information?
This would be a dangerous amp to own if not made by someone who knows their stuff. I’m sure from what I’ve seen, Roger will be an ideal choice for this if he wants to take it on, as it’s not part of his line, and would be a special build. Who knows maybe it could be part of his future line, as there are many Acoustat X’s out there in need of HV direct drive amps. Not to mention other ESL’s that could sound better if they were converted to take HV direct drive amps.
Thank you and the other SME's (Subject Matter Experts) for this wonderful thread, although much of it is over my head it is still a great read. Stereophile just reviewed online yesterday the Cary Audio SLI-100 integrated, I only read JA's measurement section. Are the measurements results a function of the circuit design, layout-topography, or part quality?
robertrs Stereophile just reviewed online yesterday the Cary Audio SLI-100 integrated, I only read JA’s measurement section. Are the measurements results a function of the circuit design, layout-topography, or part quality?
This is probably as a result of it’s 4.4ohm!! output resistance, that’s a damping factor of under 2 !!! From the 4 ohm tap, it’s 2.3 ohms!!, still to high in my books.
Not good to me, unless you purposely want to change the way a recording is meant to be listened to by the recording engineers, into today's semi demanding speaker loads, it will be fine into very easy to drive speakers, but they usually have their own set of problems
Right now I am using the Acoustat servos with my modified Acoustat Model 2’s until Roger makes another run of his. Roger has made DD amps in the past for some folks overseas using them with Acoustat panels. The amps are an all tube design where the Acoustat servos had a solid state device for the input.
Here is some basic information for now until Roger chimes in:
Hi, Im working on a JVC JA-S31 which I acquired from fleabay. Although it functions I feel that the left channel lacks a little clarity and low end as compaered to the right. Also the heatsinks stay cool to the touch at idle and during a listening session. I felt that a good place to start was to adjust bias. The problem is that there aren't bias pots on the board. Is it possible to insert one and be able to adjust it as easy as that? If so Im assuming that I would replace a resistor with the pot. If so, which ones would I replace. Would I replace one of the R637/R639 pair and one of the R638/640 pair? Also when taking my bias measurements where do I connect the leads? I am a newb to this and I know someone is going to flame me and say if I don't know then shouldn't be messing around with it etc , but I need to learn somehow and I bought the amp the specific purpose of doing so. Its just the way I learn. The schematics are at https://www.hifiengine.com/manual_library/jvc/ja-s31.shtml I would greatly appreciate any input to get me started in the right direction. Thank you
I had the Acoustat Xs back in the early 80s. They sounded very good with their built in high voltage amps (dangerous things). However, they looked like coffins (my late wife's terms) and had lost all its highs above the speaker height, about 4' high. Stand and you would hate the sound. I replaced them within a year with Acoustat 2&2s, very superior overall.
Hi @ramtubes Recently I added a power-amplifier Monoprice monolith to my audio/video gear and it is connected to Panamax M5300 power conditioner. Btw these all these equipments are in my basement.
When units are powered on I hear a very mild hum noise from the amplifier unit, if connect amplifier directly to the wall outlet I don't hear any hum noise. If I do the similar setup other side in the basement I don't hear any hum when connected to wall outlet or thru panamax power conditioner.
Isn't the presumption with most speakers that they will be driven by a
voltage source? And by assuming that, isn't it consequently presumed
that the amplifier will provide the current according to the impedance
while driving the voltage regardless?
Yes and yes. But emphasis on **most** speakers; not all speakers expect the amp to be a voltage source. Examples: Coincident Technology, Lowther, Audiokinesis, Pure Audio Project, Spatial Audio, Classic Audio Loudspeakers, pretty much any speaker that is used with an SET (so most horns); high end audio is a diverse community.
Aren't the output stages
of amplifiers typically followers? If so, that would make them voltage
sources, wouldn't it? If you operated the output devices in a mode that
provided both current and voltage gain than I suppose you could call the
amp a power source, but that's rare and any reactance in the speaker
will exacerbate nonlinearity, wouldn't it?
Not all amps have followers for output sections. Most transformer-coupled tube amps for example do not. Most OTLs however do. Yet both transformer coupled and OTL tube amps can behave as a voltage source if sufficient feedback is applied. IOW its all about the design.
@georgehifi, another weakness in the Cary integrated is its' very low power (much lower than spec'd) and high distortion. Modjeski made the point that in his evaluation of the amp for Stereophile, Herb Reichert may very well have been listening to only a couple of watts, where the amp is okay (in terms of distortion). If that is the case, in the Cary amp one is paying a lot more than necessary for the few "good" watts (distortion below 1%) it produces, its' relatively high price buying very little low-distortion output.
The Music Reference RM-10 Mk.2, on the other hand, produces far more power (25w Class A, 35w Class A/B), far less distortion, and far lower output impedance. And for far less $ !
we were Beveridge , Quad, Acoustat, Sound Lab dealers back in the day, along w Infinity, Wilson, Vandersteen, ADS..omg that was fun.... the 2+2 IF you could get them past WAF were stellar.....
anybody have a used RM-10 they want to part with ????? actually thinking of a new one in 2019.....
RM - took a hiatus from the book, restarted on page 59....junction temps....had a bad experience with ON Semiconductor thermal tracs.....I know you are a tube guy, can you comment about the diamond topology ?
@kalali. nice, seems like i looked a few days ago and zippo... trying to decide on the 25 wpc version w hand wound transformers vs this fine example :-) if i leap on this obe, will send you a referral bonus!!!!! red or white,
@clio09, there have been two different RM-10 Mk.2 listed here recently, one at a much lower price than the other. The cheaper sold, the other is still listed at an asking price of $2450, I believe.
I'm pretty sure the unit for $2450 sold as well. A recent RM-10 buyer contacted us and indicated he purchased a unit that was in Cypress, TX which matches the location of the unit in question. Either way, good for both buyers for getting their hands on a such a nice amp.
Hello, I have a budget system I like. It has a 25 watt Will Vincent Balwin tube amp with Coincident Dynamites. I do not have an audiophile power cord. How much do audiophile power cords help with the amp? I was thinking of getting to Anticable stage 3 power cord. Thanks, Cory in Reno
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