[aeriyn]

Basically my question is, does this absolutely have to be a film-type cap?

I just saw a picture of one of MisterX's PIMETAs and it had small red radial capacitors (electrolytic?) in the C4 position...

 

[S_Dedalus]

C4 is meant to be a high speed reservoir cap. Film caps tend to be better for this kind of application, but an electrolytic can work, just probably not as well, unless you're using black gates.
EDIT The purpose is to provide the opamps and buffers with a constant amount of power, and if the caps can't keep up with the demands of the IC's, they can become unstable.

 

[aeriyn]

The only reason I ask is because I think that C4 are signal path capacitors, while the power supply caps aren't. I had the idea of placing paper-in-oil caps in the C4 position, but I wanted to know if it would work before I did so (the only paper in oils I've ever seen have been electrolytic).

 

[MisterX]

Those were black gates non-polar caps.

 

[drewd]

They're not signal path caps - they're part of the power supply. Take a look at the schematic on Tangent's web site (http://www.tangentsoft.net/audio) and you'll see that the only caps in the signal path are the optional coupling capacitors (C1).

-Drew

 

[S_Dedalus]

Quote:

Originally Posted by MisterX Those were black gates non-polar caps.

In your experience are they better than polypropylenes in this application?

 

[S_Dedalus]

Quote:

Originally Posted by aeriyn The only reason I ask is because I think that C4 are signal path capacitors, while the power supply caps aren't. I had the idea of placing paper-in-oil caps in the C4 position, but I wanted to know if it would work before I did so (the only paper in oils I've ever seen have been electrolytic).

As drewd said, these are power supply caps, and paper in oils would probably be overkill.

 

[MisterX]

Quote:

In your experience are they better than polypropylenes in this application?

Can't say.... I have never used polypropylene caps in that spot.

 

[aeriyn]

Thanks for the info, guys.

 

[bg4533]

Quote:

Originally Posted by S_Dedalus As drewd said, these are power supply caps, and paper in oils would probably be overkill.

Agreed.

I doubt there is much difference as long as you use a decent C4 (6.8uF Wima), but I think an ideal might be 2 caps there. A decent sized resevoir cap and a smaller faster cap for decoupling. Also, the closer to the opamp rails the better. You could always tack extra caps directly to the power rails of the opamps and buffers.

The Pimeta is a decent amp, but these little tweaks don't seem to yield big changes. Unless you really know what you are doing and how to optimally implement it I doubt you can improve much over what is popular here. I have a fairly maxed out Pimeta and I tried playing with things a bit and I saw no changes.

 

[aeriyn]

So, I could put two caps in each C4 position--what types?

This is boredom-induced by the way. =P

 

[tangent]

Quote:

what types?

I would keep a big box film type in C4, and then solder-tack a small ceramic (0.1 or 0.01uF) to the bottom of the board right on the power pins. You can either use one ceramic from rail-to-rail, or you can use one each from rail to ground. When going rail-to-ground, the cap-to-rail distance should be preferred shorter than the cap-to-ground distance.

Some have reported audible improvements from this tweak. If so, it's only because their amp was borderline unstable before the tweak. This cap will stabilize it.