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Modulus-86: Composite amplifier achieving <0.0004 % THD+N.

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#1,581
Mark Johnson said:
In my opinion, this is no more and no less than a personal decision: which do you prefer? Which are you willing to pay for? Terrible, better, or best?

The oscillatory ringing waveform on the secondary with NO quieting circuitry at all, is simply terrible. Awful. The slow silicon diodes inside the GBU2510 bridge rectifier of the Power86, have terrible turn-off dI/dt and they produce ENORMOUS ringing in the secondary. The ringing is so big and so ugly that tomchr decided he wouldn't live with it.

So tomchr added a 100nF capacitor across each secondary. This reduced the amplitude of the ringing and also reduced the frequency of the ringing. My measurement of the Power86 ringing (taken on a red epoxy power86-workalike board), was presented in (post#1433) and is copied below. Ringing amplitude has been reduced to ~ 3V and ringing frequency has been reduced to ~ 90 kHz. (I don't think tomchr has published his scope photos of Power86 + AS-2222 transformer ringing; if he has, I haven't seen them.)

Some people say, "That's low enough for me. I can live with that."

Other people say, "That is indeed a welcome improvement. But we know how to improve it even more! Let's reduce the ringing amplitude from 3 volts to ZERO volts!"

It turns out to be very easy to reduce ringing amplitude to zero volts. Just replace tomchr's single-C ringing quieter, with a two-C, one-R quieter (called a CRC snubber). If you want extra, EXTRA (belt-and-suspenders) ringing reduction, install CRC snubber and also replace the terrible GBU2510 diodes, with Soft Recovery diodes. This combination does indeed reduce ringing amplitude to zero volts, shown in the picture below.

But at the bottom line it's still a human decision. What do YOU (the person connecting a power supply to some Modulus-86 amplifier boards) want? Terrible ringing? Better (smaller) ringing? Or best ringing (none whatsoever)?

Nobody disputes that the ringing is real. Nobody disputes that the ringing is easy to measure. Nobody disputes that more ringing is worse and less ringing is preferable. The only area of disagreement is: how much ringing are YOU willing to tolerate? Some people are willing to tolerate 3V peak to peak ringing. Others are not.

(Oh by the way, for those people who find that 3V ringing is acceptable to them, I would venture to ask: what is the largest magnitude of ringing amplitude which is also acceptable? 3.1V? 4V? 10V? 30V? Where's the dividing line between acceptable and unacceptable? Thanks for your reply.)
Click to expand...


I am much more interested whether this design consideration is transformer specific? Or have you looked into a variety of transformer designs?


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#1,583
Michael Bean said:
Not trying to beat you up but, what are your opinions based on? It's been proven over and over again the human perception is easily fooled. For me it's more important to adhere to sound engineering practices and measurements, not what we want to believe.



Mike
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Each opinion was based on finding dissatisfaction in the audio reproduction and tracing causes down, making changes and listening to the difference. Measurements are often not the types you see in published reports. But in my book, you have to go beyond in different ways to get to the bottom of things. Yes different people are going to have different ideas. A few days ago, I visited a Klippel workshop and talked with a student that just quit his day job to pursue his idea about room acoustics. Cannot say whether he is right or wrong, but I know there will be people willing to buy into the idea. But the fact he took the jump deserves respect.


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#1,588
Mark Johnson said:
So tomchr added a 100nF capacitor across each secondary. This reduced the amplitude of the ringing and also reduced the frequency of the ringing. My measurement of the Power86 ringing (taken on a red epoxy power86-workalike board), was presented in (post#1433) and is copied below. Ringing amplitude has been reduced to ~ 3V and ringing frequency has been reduced to ~ 90 kHz. (I don't think tomchr has published his scope photos of Power86 + AS-2222 transformer ringing; if he has, I haven't seen them.)

Some people say, "That's low enough for me. I can live with that."
Click to expand...
The published performance graphs for the Mod-86 were done without ANY snubbing. Just transformer, rectifier and smoothing caps. The 100nF was just added in case anyone wanted it. When Tom says PSRR is high he really means it.

For other amplifiers this may not be the case...
 
#1,589
billshurv said:
hate to tell you, but this is the 21st century and the IC industry is moving away from gold. You really do not seem to know very much.
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That is true, IC is not my specialty, but my general perception is that they do not last as long as the good old stuff. Hey, I still have an ASUS A3500 N while my children's notebooks have broken down and changed many times. You don't want these sorts of things happening in mission critical stuff.


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#1,591
Modulus-86: Composite amplifier achieving &lt;0.0004 % THD+N.

billshurv said:
The published performance graphs for the Mod-86 were done without ANY snubbing. Just transformer, rectifier and smoothing caps. The 100nF was just added in case anyone wanted it. When Tom says PSRR is high he really means it.

For other amplifiers this may not be the case...
Click to expand...


Well looking at the PSSR has nothing to do with transformer snubbering.


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Last edited:
#1,594
Well, I think when you look at how PSRR is measured and what the transformer snubbering is doing, it should be obvious to specialists like you.. You don't want the ringing in the transformer for similar reasons you don't want ringing in linear amplifiers.


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