Mumbo-Jumbo and power supply caps

Speaking of mumbo-jumbo...

Yesterday I found unexplainable fact. I was working on a tweaking of a power amp prototype. The amp was perfectly tuned and aligned. Better selection of tubes, better regimes, better distortion profile... But the sound was less real!
I could not understand why. FFT plots, especially in dynamics, shows it is better. But it sounded worse!

Previous versions had 800V B+ shunted by 2 uF film cap. The main capacitor is 235 uF electrolytic (a couple of 470 uF/450V low ESR electrolytics), so I decided to save on mumbo-jumbo this time. All other stages, and screen grids of output tubes, are powered from voltage stabilizers...

I soldered a couple of 4 uF/400V film capacitors in parallel with each 470 uF electrolytic, and the miracle happened!
Sound become alive. Binaural imaging become more precise. I tried to find any difference by measuring, but could not find it!

Since it affected imaging, and even oscilloscope on 800V B+ shows no differences, and no differences on FFT plots on different power levels, I believe it is related to modulated phase shifts that are invisible with such tests. But can you imagine how small they should be in order to be audible?!
According to experiments, monaural perceptibility is more than 10 milliseconds, while binaural perceptibility is 10 micro(!)seconds.
I can't find better explanation, because amplitude-related measurements show nothing
 
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Wavebourn,
Although my amp is nothing compared to yours, I had a similar experience with the OPUS. In that I used those huge eletrolytics, bypassed by 100uF motor run, with a 1uF bypass at the point of consumption. Take the motor run and bypass out and the amp is dead/dull sounding. On the other hand without the electrolytics, I find it to be analytical and thin sounding.
 

kevinkr

Administrator
Paid Member
Hi Wavebourn,
I have had similar experiences and like you was unable to relate it to anything that I could measure at the time. Glad to hear that I am not the only one to hear this, still would be great if there was some plausible explanation. The effect was not subtle in my recollection - these days I usually use film caps in my supplies, and like you I regulate almost everything.
 
Details, schemos please. Was this a SE or PP design?

It is Pyramid-VII, schemos were here several times. And it does not matter, actually.

800V powers anodes of GU-50 tubes only, with 10K P-P transformers. Both channels from the same PS. The rest, including screen grids, is powered from voltage stabilizers (+400V for phase splitter, and +270V for screen grids).
 
.......i know that phenomenon. i always thought it depends on/changes the output impedance of the psu.
usually it sounds more bright with paralelled plastic caps.........(with all types of amps?).

Sure, but if it changes impedance value only it would be at least measurable!

I still believe, it is result of phase inter-modulations caused by electrolytics that can't be measured in static amplitude-related tests.
 
lets say that we can explain that with intrinsic inductance of electrolytic cap , but - we can't measure that precise enough .

explanation is simple , but proof is completely other thing - at least with measuring equipment I have :clown:

that's why I'm putting 50-70uF motor-runs even in solid state A class amps PSU

if memory serves me well - newest example of motor-run caps usage (as final bypass ? ) in commercial amp is EL34 PP , made by Audiomat ;

edit - I just found image on net ( this one not exactly EL34 , which I saw in flesh ) :

[IMGHTTPDEAD]http://www.audiodrom.cz/AudiomatFestival_files/audiomat_festival_inside.JPG[/IMGHTTPDEAD]
 
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lets say that we can explain that with intrinsic inductance of electrolytic cap , but - we can't measure that precise enough .

Why not?
We can. Also, we can add some inductance in series, after neutralizing the effect by shunting caps, to check was it it, or not. But I doubt that an inductance added would cause something similar. At least, I would spot it's results.

No, it's non-linear effects in caps that cause phase inter-modulation, I firmly believe. :trapper:
 

M Gregg

Disabled Account
2010-06-28 11:04 pm
UK
Sure, but if it changes impedance value only it would be at least measurable!

I still believe, it is result of phase inter-modulations caused by electrolytics that can't be measured in static amplitude-related tests.

Wavebourn,

I also notice this with power supplies it is as if something is being blocked untill the bypass caps are put in circuit. Could it be related to Xc of the electrolytic. I have found the sound will change with PIO, Polypropylene, wax, polystyrene. It almost seems like a filter is being created that each cap is allowing through different frequencies! It has no measurable effect that I can find. If you "tune" the system like this eventually you will find that the system can start to become biased to certain types of ambient sound. IE some recordings will become weak sounding, others will sound better! Then any weaknesses in your sources will begin to show.
Be prepared to get flamed. You have stepped out of the safe zone!:)

Regards
M. Gregg
 

M Gregg

Disabled Account
2010-06-28 11:04 pm
UK
Here comes the burning question!
That has been a pain in the a— to me for years!

How do you tune the power supply so it is transparent across all frequencies if you can't measure the effect! You can only tune by "ear".

Because "yes" all other weaknesses in the system will start to show!

Regards
M. Gregg
 
Sorry Anatoliy, I have not understood quite clearly; Are you saying that although you usually bypass the PSU output cap, in this case you are bypassing the reservoir cap?

It is the only PSU cap for 800V B+

Nothing is powered from it directly except CTs of output transformers.

The effect is well audible on stereo, but is not audible on mono. Presence/absence of shunting caps does not affect channel separation at all. It is odd to repeat, but I will repeat for you especially: presence / absence of shunting caps have no effect on non-linear distortions. It has no effect on frequency response
It has effect on stereo imaging only.

One more experiment: to add 10 uF film capacitor in parallel.
Results:
either 2 uF, ot 10 uF, have the same effect. If either 2 uF, or 10 uF already added, no more shunting changes anything.
 
Am I right in thinking that many of the most hardcore devotees of zero FB SE amps often invoke tiny unmeasurable time domain effects to explain their claims? Maybe there is something in what they say!

I believe they are right.

Actually, experiments demonstrate that when experts tell 1 or 2 sparks clapped in some the same direction, threshold of perceptibility is about 10 miliseconds.
But when sparks are engaged in different places, on equal distances to the right and left ears, the threshold of perceptibility is about 10 microseconds! It equals to one period of 100 kilohertz sine wave!

But of course, it is perceived as a single spark shifted to the right, or to the left.
 
Yes Anatoliy, you will certainly get no argument from me on the extreme capability of the human senses! I bypass all my PSU's as a matter of course but I always assumed that I was doing it for reasons of frequency response.

Alistair; you can find some inexpensive caps on ebay that will totally destroy the audiophool caps in the matter of bypassing.
 
Yes Anatoliy, you will certainly get no argument from me on the extreme capability of the human senses! I bypass all my PSU's as a matter of course but I always assumed that I was doing it for reasons of frequency response.

I did that for the same reason!
But this time decided, it is an audiophoolery; no way it is reflected on frequency response; and did not shunt... And got a lesson! :Pinoc: