[Whit]

I've read that having several parallel low esr capacitors of different values(or constructions) can cause unwanted resonances. I see that this has been dealt with partially in the ppa with the addition of R8 to add some dampening but what about the parallel combo of C1, C2, and C3?

 

[Syzygies]

A classic article on this subject is Picking Capacitors by Walter G. Jung and Richard Marsh.

I've always wondered why their "specific recommendations" differ from what is done in PPA, Pimeta, etc? In any case, they recommend dissimilar parallel caps.

 

[steinchen]

as far as I understand the article it's about using caps in the signal path and not about caps for power rail bypassing

 

[steinchen]

Quote:

Originally Posted by Whit I've read that having several parallel low esr capacitors of different values(or constructions) can cause unwanted resonances. I see that this has been dealt with partially in the ppa with the addition of R8 to add some dampening but what about the parallel combo of C1, C2, and C3?

quote from tangent's part selection guide:
This resistor (R8) forms an RC-low pass filter for the op-amp power rails in conjunction with C4||C5. (-> noise isolation)

Where have you read about the unwanted resonances ?

 

[Syzygies]

Quote:

Originally Posted by steinchen as far as I understand the article it's about using caps in the signal path and not about caps for power rail bypassing

One of their caps in Figure 17 is a 330 uF aluminum electrolytic. You're probably right, I'm too backed up with work tonight to reread the article, but does anyone in their right mind use such a cap in the signal path? I remembered them using this cap, I just assumed it was for the rails.

 

[Whit]

Quote:

Originally Posted by steinchen quote from tangent's part selection guide: This resistor (R8) forms an RC-low pass filter for the op-amp power rails in conjunction with C4||C5. (-> noise isolation) Where have you read about the unwanted resonances ?

Look here:
http://www6.head-fi.org/forums/showthread.php?t=75554

Specifically at ppl's comments.

 

[tangent]

Quote:

does anyone in their right mind use such a cap in the signal path?

Sure. Several amps (particularly single-ended class A designs) require output capacitors. Since the load is low-impedance, you need a high cap value.

 

[morsel]

Whit: I don't think this is anything to worry about. If anything, you have it backwards. Using different caps in parallel should help cover any deficiencies in ESR as it is unlikely that all of the caps have high ESR at the same frequencies.