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TM3030 VCO problem
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author TM3030 VCO problem
Hi all,
I've just completed my build of a TM3030 but I am having a problem with the output.

If I play one note it sounds correctly but when I play a second one, either legato or staccato, there is silence first and then eventually the note sounds.

I have checked all the components and done continuity tests.

I replaced the U6 (CA3083) IC just in case.

I have checked the key_CV on the oscilloscope and it appears to move correctly with each new note with no delay.

If I look at pin 1 of R45 or pin 1 of U6, I can see the saw waveform for the first note, then a 0V just when I play the second note, and finally the waveform for the second note appears.

Would anyone have an idea what could be causing this? I'm really puzzled,

thanks in advance,

mmm, I'm not sure either. I've not heard of anything like it before.

Does the silence occur even when the new note is the same pitch as the note before? The CV shouldn't change in this case, so if this is happening that would suggest the gate trigger is somehow sneaking into the VCO circuitry via a possible board short.

If it only happens when you change note, perhaps U7 or C12 is at fault.

One other question: Does Key_CV stay constant when pressing the same note repeatedly? It should.

thanks for the help. I replaced C12 but no change. I concentrated then on the transistors Q3, Q4 and Q5. Replacing Q3 seems to have fixed it. I won't say for certain until I check tomorrow...
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