View Full Version : Question about bypass capacitors

James G
06-01-2010, 03:28
Sometimes I see on DIY sites where someone will add a film cap to a big electrolytic like in a power supply (usually in parallel underneath the pcb).
Could someone explain to me the effect/benefit of this? Does it in any way reduce the overall effectivness of the electrolytic (noise filtering, etc.)?
Also, is there a way to calculate the capacity of the film cap you would need based on the capacity of the electrolytic(s)? Thanks.

Rare Bird
06-01-2010, 09:39
Bypassing reduces inductive effects of larger value capacitors (Electrolytics generally).The Original cap will keep it's value btw..By bypassing you will notice more clarity thoughout the audio range... wire in parallel to your original cap 0.01uF, large caps over 0.1uF: 0.01uF + 5.0uF (or 4.7uF)..You must use very high quality bypass cap or the effects are less marked.I always use High Voltage Kimber Kaps...



(No reason for such high voltage, just the only ones available)

James G
06-01-2010, 11:21
Hi Andre, thanks for the explanation. About the last bit, say I have a cd player power supply with one position at 14,100uF and another position at 6600uF. What would you bypass with for these?
I want to let the air back out a bit, but not go too bright.

Ali Tait
06-01-2010, 16:44
You would generally make the bypass cap 1/100th of the value of the cap you are bypassing.That's what most folk do anyway.

07-01-2010, 13:52
If the 'first' cap is very large (electrically speaking) in can also be worth bypassing the bypass cap!

Ali Tait
07-01-2010, 15:49

James G
09-01-2010, 05:30
Many thanks guys!

Just wanted to share:
I went really cheap on this since it's a cheap CD player and I'm a beginner at this. First I installed an IEC socket. Then I strapped 3 2200uFx3 in parallel on a prototype board to the power supply where there was only one installed before. Then I bypassed those with a Wima MKP .47uF and a Evox MMK 2200pF. The rest of the PS caps were replaced with Fine Gold and Oscon SP.
Going out optical to my Digital Link III, it has brought up the sound of the Denon quite nicely for very little money. But I think I could get more out of it. Still some more experimenting to do. Maybe the voltage regulators too? But I have a lot more research to do before taking those on.

Edit: Ok, lesson learned. Later I tried a bunch of different small caps for bypass trying to get the sound right, then found some larger high voltage .1uF RELcaps that came out of my amp and tried those. Big difference, so much clearer and smoother sounding. So like Andre says in post #2, don't cheap out on those bypass caps.

Ali Tait
09-01-2010, 07:46
Maybe check out the lampizator site.Lots of good modding ideas there.

09-01-2010, 10:33
Be careful , using too low impedance on the output of standard three pin regulators can cause ringing/instability making things sound bright.
Also depending on the type of cap used too many bypass caps can actually cause problems, for say digital circuits or high speed op-amps I wouldn't recommend physically large caps as bypass, think about the huge lead length, added material, increases inductance which is what you don't want

As always in this hobby some things work better in one application than another:)

James G
09-01-2010, 11:16
Hi Leo. Noted and I'm not going to bypass anything else. If I just bulk up the main filter caps (after the transformer, before the regulators) and add a bypass to that, I'd be safe right?

09-01-2010, 12:29
Should be a good way to start yes, I'd personally want to check things on a scope etc before going a lot further

I remember a mate of mine had a bash at modding his cdp, half way through it caused him a lot of problems, I agreed to have a look at it for him, when it left here he was presented with a little bag of bits I'd removed he'd fitted previously ;) the mistake some people make when modding is they tend to do too much at once.

Anyway have fun and take your time, with a bit of patience you should be able to get worthwhile improvements

James G
09-01-2010, 14:08
Cheers Leo! (yer awesome dude!)