Does anyone care to ask an amplifier designer a technical question? My door is open.

Hi Everybody,

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?

Thanks,

Utrak

@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:

http://www.atma-sphere.com/Resources/Common_Amplifier_Myths.php

http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

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?

What output transformer might you buy?

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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.

@almarg

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.