Filter caps for 8580 - default value 2,2 nF or 22 nF - which is correct?

MIDIbox SID
1

Hello!

After a silence of a couple of years I’m back lurking the forum, getting ready to upgrade my MBSID V1 to V2. I think I have pretty much understood what supplies I need for the upgrade and will be ordering stuff soon.

But to the topic - the default filter caps for the 8580 are often referred as 22 nF on this forum but also in many places around the net. Is this really correct, or should it actually be 2,2 nF?

I found a schematic:

http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/252312-right.gif

and it clearly states 2200 pF as the caps, doesn’t this mean 2,2 nF?

My MBSID 8580 caps say 4700 on them (value chosen by testing different caps way back then, number means pF’s I think), meaning 4,7 nF, right?

2

That schematic says 22000pF for C70,C71 (the SID filter caps) which is 22nF. C80,C81 are not the filter caps (they are for the joystick pots).

Use 22nF, these give a good filter cutoff range.

3

Whoops, it totally is so!

So I’ve been happily wailing away on my 8580 with just 4,7 nF for a couple of years… Thinking that even they were “a bit larger than usual” for the SID… I’ll definitely have to check where the 22 nF’s will take me!

Thanks a lot for the clarification, I think I have some things to try and find out…  ;D

4

Hmm, yes the 22 nF works ok, and the low end blockiness of the filter definitely went away, while introducing a slight blockiness to the higher mid area. However, I felt the upper end just a bit restricted, so I’ll test with 15 nF and 10 nF when I get some of those in my sweaty palms…

Any comments on the Wima FKP2 range of capacitors - should be high quality, but does someone have actual SID experience of them?