Guest eirik_k Posted November 10, 2004 Report Share Posted November 10, 2004 I have working basic MbSID unit (i think :-/) and I need some help getting the filter section to work this time. Let me explain the symptoms, which are identical with both my working SID chips, which would make them unlikely candidates - also, all other functions work perfectly. The filter filters alright - but way too much. The sound is all muffled except at the most extreme settings for cutoff and res, which only opens it a bit and gives the sound a quite distorted character.I tried exchanging my fresh 470pF caps with two sets of original caps from C64 boards (the same value, presumably?) of the first generations (ie. for 6581 SIDs which is what I have). Slight difference in sound, but same problem. I could of course try several different values, but I'd be stumbling blindly. 8) :PIf I am right in my suspecting the capacitors, would the symptom described be caused by too high or too low a value for the caps. If the problem appears to be something else alltogether, what could it be?Really appreaciate any input! ??? Quote Link to comment Share on other sites More sharing options...
Jurbo Posted November 10, 2004 Report Share Posted November 10, 2004 The cap value basically affects the frequency range that will be able to pass through the filter: larger values mean more attenuation on the higher frequencies. Small caps will open up more high frequencies.In your case, it seems to me that your caps are too large (even if they work in the C64, they might be wrong for MBSID). The distortion might mean something's wrong, but the resonance parameter basically introduces some, so I wouldn't worry about it yet.I would first buy some smaller caps (several pairs with different values) and see what happens. You will probably need 2 or 3 pairs, the values can be found somewhere on the site. So it's not too much stumbling in the dark - to me, testing the differences was a minor revelation. For both my 8580 and my 6581, I ended up using non-default values.And I suppose you have the SID program installed right (you have it set up for 6581, not 8580)? Quote Link to comment Share on other sites More sharing options...
Guest eirik_k Posted November 10, 2004 Report Share Posted November 10, 2004 It is set up for 6581 yes.See, that's all I really needed to know. Just a pointer in the right direction. Ok, I'll get a few pairs of lower value caps then. Thanks a million. Quote Link to comment Share on other sites More sharing options...
Jurbo Posted November 10, 2004 Report Share Posted November 10, 2004 No problemo!Comparing the filter caps is the same kind of fun as changing the tubes on a guitar amp (only a bit geekier)! ;D Quote Link to comment Share on other sites More sharing options...
Hermes Posted November 13, 2004 Report Share Posted November 13, 2004 Just out of curiosity: What type of caps do you use Jurbo? ceramic ones or styroflex ones?cheershermes :) Quote Link to comment Share on other sites More sharing options...
Jurbo Posted November 13, 2004 Report Share Posted November 13, 2004 I'm not an expert on cap types, but I think they are styroflex, as they are little square edged plastic boxes (at least I know ceramics are those little discs).Ceramic caps are not recommended for SID filter, because they can't be manufactured to very exact values, and the filter caps should be as equal in value as possible. Quote Link to comment Share on other sites More sharing options...
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