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#1 2011-10-01 06:12:16

Anodyne
GI-Joe
Registered: 2007-12-09
Posts: 15

Filter issues on SID2?

I seem to have poor filter response on SID2.  I am running 6581's, I understand they have crappy filters, but SID1 sounds fine.  When I swap them, it makes no difference (so it's not the chips - SID2's filters sound fine in the SID1 socket etc.)  SID2 is much quieter, but when I bypass R8 that seems to help... but not the filter.

Anybody know what the problem is here?  I've been poking around the forum trying to find and answer on my own but nothing seems definitive and I'm not an electronics expert :-)

THanks,
Owen

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#2 2011-10-01 19:38:40

CassandraX
Gianas Sister
From: Thuringia, Germany
Registered: 2011-06-09
Posts: 28

Re: Filter issues on SID2?

May be its usefull if you would list all the things you have checked already. So: Are you sure to have used the 470 pF capacitors for the filters? You have not confused the resistors with each other? No short cuts on SID2SID or with the main board through touching? Checked the soldering points for contact? Checked resistors, capacitors - if no other way possible: through changing?

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#3 2011-10-03 17:30:15

Anodyne
GI-Joe
Registered: 2007-12-09
Posts: 15

Re: Filter issues on SID2?

I got it.  Turns out there was a bad connection between one of the filter caps and one of the resistors.  I bridged them with wire, and now I have both SIDs rocking at the same volume and with functional filters.

Now does anyone know how to reduce the noise?  I grounded the audio input pin on SID1 (and double checked, I did this correctly) and it had no effect whatsoever.  This is a breadbin C64, maybe this strategy doesn't work on these?

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