Advice on capacitors in Pass Aleph 4

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After disappointing results with an Aleph 4 build, I think the culprit may be my choice of capacitors.

Can the capacitor experts have a nose at the diagram and make their recommendations for each of the 6 capacitors.

I can't see that C1, C8 and C9 make much difference as they are in the constant current leg.

C4, C11 and C12 may be more critical.

Mark Finnis chose:-
C1 = 103 Poly
C4 = 680pF Silverd Mica
C8, C9 = 220uF 35V Low ESR Radial Electrolytic
C11 = 220uF 10V Tantalum
C12 = 10pF Silvered Mica

With this combination I have awful sibilance on both channels.
 

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I am far from being an expert but poor capacitor choices can cause major sonic problems which can be tough to chase down. I have done the same on a couple of these without a problem. The only cap that I wouldn't have used is the 220 tantalum. I would change it out for just about any decent quality 220 uf cap. A decent low cost option could be a Panasonic FM or FC, there are many options. Another choice would be a Cerifine Silmac.
 
Panasonic FM/FC. Nichicon HE/PW.

Panasonic is a bit more pricey typically, but they are usually more highly regarded. The Nichicons aren't talked about much, but they are pretty much the same specs as FM/FC, and they'll probably sound the same. Panasonics are prettier though. =D
 
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Panasonic FM/FC. Nichicon HE/PW.

Panasonic is a bit more pricey typically, but they are usually more highly regarded. The Nichicons aren't talked about much, but they are pretty much the same specs as FM/FC, and they'll probably sound the same. Panasonics are prettier though. =D

I agree about the Panasonic FC's; used them in an Aleph 5 build 6 years ago and never had any props with sibilance.
 
I've ordered some Panasonic FCs from RS.

Strangely the sibilance is much better with NO PUMPKIN and NO ATTENUATOR. ie the CD player driving the Aleph 4 directly.

I don't think that the PUMPKIN itself is the issue but there may an impedance mismatch somewhere.

Normally I'm feeding CD36 into PUMKIN. PUMPKIN into 100K ladder attenuator and then attenuator into Aleph 4. All driving B&W DM683s.

In the first photo the Aleph4 is still awaiting painting. It's been painted in photo 2 but is still waiting for a lid.

That's now in the process of being drilled for ventillation.
 

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Tantalums = Yecch! That's the only one I'd seriously question. I use silver-micas for many things and are pretty happy with them, but IMO polypropylene, polystyrene or Teflon is better for the truly fussy.

Mark Finnis did produce an Aleph 4 with Tantalums. I believe his rationalle was that tantalums are better in situations where a normal electrolytic will not normally see its polarizing voltage.

220uF is too large to be fabricated from non-electrolytic type caps. I'm just asking for advice as to which caps to try next.

Now that the amp is built it is not an easy job to change them.
 
FWIW, here's my philosophy. The feedback network components are entirely outside the feedback loop. Any non-ideal property of the passive components used for that network will be directly impressed on the amp. If the divider sucks, the amp sucks. Other "stuff" in the circuit is inside the loop, and imperfections will be corrected to one degree or another. The one place where you want "perfect" components is that feedback divider and anything related to it. IMO, there's no problem with modern electrolytics not having a bias voltage, though I never use very low voltage electrolytics (like 6V) as they're lousy in most regards and not terribly reliable. It seems like they fail first in test equipment. Tantalums are bad in audio circuits, though I admit it's of little consequence if no AC voltage ever appears across the part. I'd use at least a decent quality 25V or greater, 220 uF conventional electrolytic for C11. Brand and type can be anything you see a consensus on as being decent- I like Panasonic, Rubycon, Nichicon and Illinois Cap, but I'm pretty cheap.
 
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