Bypassing big electrolytic de-coupling caps

Just because audio doesn't go "through" them doesn't mean they don't affect the sound. If you think of an amplifier as a modulated power supply, with the audio signal doing the modulating, then you can't help but see that the power supply is extremely important, if not the most important part of the device. Any non-linearities or irregularities in the power supply will be audible.

Ideally you should get rid of the electrolytics but 7,800 uF of film caps would be huge. You could redesign the power supply to have a higher output voltage and then add some fast regulators after that and get by with smaller amounts of capacitance.

For bypassing one camp subscribes to the idea that a power supply bypass should be 1/100 of the main cap so with 7,800 you might try 2 caps; one around 78 and another around .78

The 78 could be one of the oil/film motor caps you mention. I've had great results with these http://www.alliedelec.com/catalog/pf.asp?FN=1433.pdf but that would be too big to fit in your case.

I think for optimum performance you are going to have to pull the supply out to a separate box or leave the lid off with a bunch of stuff sticking out the top.

+++ Their [electrolytics] ability to hold a large charge is much more important than their sound quality. +++

Rwwear, firstly, thanks for the response but I have to strongly disagree with that statement. Ability to hold charge is largely irrelevant.

De-coupling (power supply) caps have to be able to charge/discharge quickly and do so in very linear/smooth fashion. Electrolytic caps cannot do that – they are slow and charge/discharge in very non linear and spiky way. Electrolytic are the very worst caps, be it for coupling or de-coupling applications.

I have replaced electrolytic power supply caps in a few applications with motor run caps that are about 1000 times faster, and each time I have had a tremendous improvement in sound. Detail, impact, dynamics, smoothness, naturalness, you name it, is improved.

The issue I am facing now is I have very little room so I cannot make use of motor run caps (or film caps for that matter). I am wondering how much impact a couple of 1.0uF film caps will have on 7800uF worth of electrolytics.

Thanks
Paul

While it may be true that power supply capacitors are continually charged and discharged there is no audio going through them. Their ability to hold a large charge is much more important than their sound quality. A crossover is very different in this regard as the audio signal runs through them. Electrolytics are the best type of capacitor for power supply applications.

All capacitors are audible to some extent. Power supply caps are indeed audible as they are constantly being discharged and charged as the music plays. All the energy used to play the music is stored in these caps so it is impossible that they would not affect the sound. You would notice huge differences if you were able to replace all the electrolytics with some type of film cap. Of course the problem is they would take up so much room.

Although this discussion is about caps used in a crossover it might prove useful. http://www.humblehomemadehifi.com/Cap.html

If it uses electrolytics as coupling caps I would try to replace those with film if space permits and go from there.

An improvement in sound would depend on the application of the capacitor. If the electrolytics are for the power supply there would not really be a need for bypassing them.