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CMoy op-amp rail caps question...

post #1 of 6
7/1/11 at 10:01pm
Thread Starter 

Hello everyone! (first post here)

I recently completed my first CMoy headphone amp and came across this schematic...

 

Schematic.jpg

 

I noticed the circled 0.1uF caps in the op amp rails and wanted to know the reason these were added.

Since there's already 330uF caps going to virtual ground, what's the logic in adding another 0.1uF to each rail?

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post #2 of 6
7/2/11 at 5:07am

0.1uF are most probably film caps, placed close to the chip and aimed at providing clean low ESR power, bypassing larger caps.

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post #3 of 6
7/2/11 at 10:49am
Thread Starter 

 

Thanks Groundloop! I found this article that does a good job explaining the purpose of bypass capacitors. 

 

http://www.seattlerobotics.org/encoder/jun97/basics.html

 

So from what understand, the larger 330uF capacitors are more efficient at smoothing out larger/slower variances in voltage/current (lower frequency AC signals) while the .1uF caps can react much quicker to unwanted higher frequency changes (ripple) in the rail supply. 

 

I'm curious though, how much (or little) of an audible difference adding or omitting these bypass caps in a Cmoy circuit will have..

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post #4 of 6
7/2/11 at 11:18am

 

Quote:
Originally Posted by Lavalier View Post

I'm curious though, how much (or little) of an audible difference adding or omitting these bypass caps in a Cmoy circuit will have..


That depends on the op amps. 

Some show basically no change, others NEED these caps to work at all. 

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post #5 of 6
7/2/11 at 1:01pm
Thread Starter 

Interesting. So, in my case, I'm using the recommended (Tangent) OPA2132PA op-amp. I assume since he did not specify them in the circuit that this one of the "basically no change" op amps... It already sounds great as is, so my guess is that they would have negligible sound differences.

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post #6 of 6
7/2/11 at 2:02pm

Id bet it wont do anything with that op amp. The little caps are mostly there for really fast, higher current op amps. 

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