Hi again everyone,
I thought I would try to solve a more basic and puzzling problem before I move on with my SID. I had 2 6581s and after checking in Rutger’s editor (which is really great!!) I found they both had this same characteristic which is Osc 1 is perfectly fine, Osc 2 makes a shriek on keypress, and Osc 3 makes a quiet click on keypress. I had seen on the forums that the 6581s were often dicey so I thought - well maybe it’s the chips.
I very recently bought 2 more 6581s from a fellow midiboxer on ebay (really nice guy BTW) who had tested them on his workbench and said all 3 oscs were fine. So that was great. However, when I plugged them in to my setup, I got the same deal: Osc 1-OK, Osc 2-noise, Osc 3-click.
Having 4 chips with the same characteristic (especially now) makes me wonder whether I got something wrong. As an additional check, I built a completely separate 2nd Sid module with a 2nd Smash board just in case my first one was bad. I tested the chips in there. Still the same situation. I used the 7812 regulator and the 4701 caps on Smash’s boards.
I was wondering if anyone has had a similar situation and can point me in the right direction. I thought maybe it’s a soldering issue with regard to just Oscs 2 & 3 and so I tried to look up on Wikipedia which SID pin corresponds to which oscillator but I couldn’t figure it out. The only thing I can think of is maybe I goofed up the core (although it powers up fine and works well with MidiOX). ALso I have to run the Sid module on a separate 15v because my C64 power supplies weren’t good. I read this might add a bit of noise but didn’t think it would be Osc specific.
I’m attaching some audio files in case anyone wants a listen. Chip 1 Lead Patch.mp3 is a recording based on the first patch in the patches bank. I did 2 keypresses for the default patch, then 2 presses for Osc 1, 2 presses for Osc 2, and 2 final presses for Osc 3. Lead Patch sounds fine as a default because it doesn’t seem to use Osc 2+3.
Chip 1 Techno PWM.mp3 is from the 2nd patch in the bank. Again, 2 presses for default, Osc 1 only, Osc 2 only, and Osc 3 only. It uses Osc 2+3 and so sounds bad as default.
Chip 2 Lead Patch.mp3 is like the first recording but with one of the ebay chips.
There’s a little bit of hum between tones - that is ye olde Fender guitar amp.
I guess worst case scenario is that I can just take what I have and get 4 oscs out of 4 chips, but as any synth player knows it would be a shame to throw away 2/3rds of one’s polyphony. Thanks for any thoughts !!!
[Chip 1 Lead Patch.mp3](< base_url >/applications/core/interface/file/attachment.php?id=4432)
[Chip 1 Techno PWM.mp3](< base_url >/applications/core/interface/file/attachment.php?id=4433)
[Chip 2 Lead Patch.mp3](< base_url >/applications/core/interface/file/attachment.php?id=4434)