From the videos it's not clear to me if this happens due to some external stimuli, like aftertouch - or if it is random and happens on and off if you just send MIDI note on and let it drone for a while with no other MIDI events.fitzcarraldo wrote:Sorry for the bump, but does nobody have any ideas what else I could try for my problem above?
It is also not clear to me that it happens on all voices. Looks to me like voice 2 is the main culprit, in particlular on the second video you hear the noise as soon as voice 2 is on, but there's not enough video to completely determine that.
An oscilloscope would be very useful tracking this down.
But best is to gather more evidence before even opening up the machine.
You said it happens on all voice cards - does it happen on all slots? The video seems to show it on slot 2 only.
Track this down further, and see if you can figure out if there is a particular control CV that is boosted, like VCF or Level, for example.
One thing I would try is to see if you can monitor the output of a voice card edge connector on the motherboard with an oscilloscope to see if these spikes are present from each voice, or if they are introduced after the voices are mixed - seems like before since it only affects voices B, but who knows. Check the schematics and look at pin 1 and 2 from the edge connector.
I would also monitor VCF-A vs VCF-B on the voice card connector to see if there are spikes in the incoming filter CV, and also look for other CV's that you think could be responsible for causing that sound if they spiked - if it happens to all voice card slots then it's probably either one of the incoming signals that are common to all cards - or after the voice card outputs, but before the A and B channels are mixed.
Somewhere in the signal path this noise is introduced, and tracing it to a CV path or audio path would be a great first step.
Finally, as you know, unfortunately the Black Corporation DIY build discussions seems to be happening on Facebook much more than Muff's.
With Facebook's focus on the "here and now" there is very little archive for the future and even though you may not want to sign up for Facebook I would advice you to sign up anyway.
Remember, you don't have to sign up as yourself, just create a "CompartmentalizedIdentity" or "DeckardsDreamBuilder" user with no friends and sign in with the browser set to 'private' or 'incognito' mode.
Keep us posted!