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Bypassing big electrolytic de-coupling caps

Is the practice of bypassing big electrolytic caps (de-couplers) a waste of time, or does it have a legitimate benefit? I recently read a post on another board (and I quote) that bypassing big electrolytic caps with small film caps are as useful as “tits on a bull”.

I have 30 (yes thirty) big electrolytic caps in my phono stage. I am thinking of bypassing them all with small(ish) film caps.

Also I am wondering that if bypassing big electrolytics is beneficial, would using inexpensive polypropylenes give close to the same benefit as more expensive film caps?

Lastly, can somebody recommend an inexpensive and physically small cap. I would like to place the bypass under the circuit board to retail a neat appearance. There is about a ¼ inch gap between the circuit board and the bottom plate.

Thanks
Paul
pauly

Showing 2 responses by herman

herman
2,216 posts
 
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.
herman
2,216 posts
 
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.
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