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

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. 

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?

.