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

This is why I advocate the ZERO autoformer,

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.

gpgr4blu 12-12-2018:

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. 

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