[Migroo]

Hi guys.

I've read Tangent's pages on input caps. I currently don't have any installed in my PIMETA (the ones I ordered originally turned out to be complete monsters that wouldn't fit on the board - so I decided to run without to start with).

I'd like to try some - however in the UK the only ones I can find with the appropriate size and value are metallised polyester (which according to Tangent's site is still 'OK').

Question is, how do I choose between the 10 or so caps that meet the initial requirements? They're all roughly the same price, some are Vishay, others Panasonic or EPCOS and there is also a WIMA 'MKS' series cap.

Any advise here much appreciated.

 

[J.D.N]

Acoustic-Dimension, high-end audio and components for tube audio

This website sells Black-Gates and ships to UK fine. You might want to consider them if they have the right values.

 

[stixx]

migroo,

when you can't avoid an input coupling cap, I'd go with a polypropylene type...the only problem being the size. With only 12.5x8mm available there probably isn't that much of a choice.
Question is: you are running your Pimeta without input caps now (and it works...). Why use them then? I'd check DC offset of the source, and when everything is ok leave them out. Input caps won't do anything to the sound...only make it worse when all you can fit is something mediocre.

 

[Bjornboy81]

Along the same lines (not trying to hi-jack), but is it totally necessary to have the input caps between the pot and opamp or can it go betweent the input jack and pot? You can get a much larger cap off the board right from the jack, than on the board.

Thanks

 

[Migroo]

Hi guys - thanks for your views.

stixx - its just something I want to try

Granted- I haven't measured the amp or my sources for DC, but I'm a great believer of simply listening to see if it changes things...

Byornboy - as far as I'm aware the input caps can go anywhere before the amplification stage

 

[Pars]

They are typically placed between the pot and the opamp input to isolate the opamp input from varying impedance. The opamp input will see the pot in parallel with the input resistor to ground without the cap there. For typical JFET input opamps, the leakage current is so low that the output DC offset stays very low over the range of the pot. With BJT input opamps, this may not be the case (see mini3-ified PINT threads for example).

As mentioned, if you don't have offset issues with your source(s), no cap is always better than a cap in series.