Tweakers' Asylum

Substituting poly caps for electrolytic's??

71.166.75.241

RickeyM

Last night I replaced the Elna Silmic 2's being used as output coupling caps in my CDP with some metallized polypropylene capacitors . The electrolytic's (Silmic's 2's) are 25v 100uF, two per channel. The poly's are Kimber Kaps, 4.7uF's. Is there a formula or ratio to follow when doing such substitutions? Should I have used something bigger or smaller. It sounds great as is, but if a simple tweak will make it better...

TIA for any help, opinions or suggestions.

Follow Ups:

RE: Substituting poly caps for electrolytic's?? - Tweekeng 20:44:13 09/01/07 (2)
Caps in parallel add.

So to get close to 100uF you would need 21 (98.7uF) or 22 (103.4uF) 4.7uF caps.

I would suggest using something bigger.
- CAPACITORS IN SERIES AND PARALLEL (Open in New Window)
- RE: Substituting poly caps for electrolytic's?? - RickeyM 05:41:55 09/02/07 (1)
  Except everything I've read from others who've done this is that you can use a smaller value poly in place of the electrolytic. My example seems to prove this out. Even with the lower value poly cap in place, the bass is just as good if not better.
  
  I used the Kimber Kaps because I had them on hand. The circuit board in the CDP is designed for two caps per channel (output coupling). Would I get better results if I added two more poly caps (paralleled) or should I just leave well enough alone. Mind you, it's sounding pretty good now.
  - RE: Substituting poly caps for electrolytic's?? - nightdoggy 09:02:50 09/02/07 (0)
    100 uF is probably way overkill. They are likely used there because the manufacturer was using them anyway so they get a better volume discount in theory.
    To calculate the -3 dB point the formula is F = 6.28xRxC/2. An example is:
    F = 6.28x47000x.000010/2
    where R=47,000 ohms and C=10uF
    F (-3dB) = 1.48 Hz
    You will need a schematic(s) of the amp(s) to know the value of R (to ground) which follows C and is sometimes a parallel combination of two R values depending upon the circuit(s) configuration.
    Usually 10 uF is enough with typical equipment. Even if R (or Z) was only 4.7 kohms, the -3 dB point would still be 14.8 Hz.
    
    Edits: 09/02/07

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