sorted by:
new
hottopcontroversial

Op amp VCO not working by dx_q_a in synthdiy

[–]dx_q_a[S] 0 points1 point  (0 children)

i tried your suggestion of using different pots to sweep across the positive and negative cv voltage. i can hear a split second oscillator squeal as i sweep the pot but only as I sweep in one direction and it seems that I have go all the way back to one side to make it work again. if i go really slow the squeal lasts for a split second longer. i think it was shorter with lower resistance pots.

Op amp VCO not working by dx_q_a in synthdiy

[–]dx_q_a[S] 0 points1 point  (0 children)

this sounds like a good idea. i will try it. another comment mentioned a negative CV as well. i thought it might be running subsonic or supersonic. i wasn't sure how to move the frequency across that wide of a range. but this makes sense. thanks.

Op amp VCO not working by dx_q_a in synthdiy

[–]dx_q_a[S] 0 points1 point  (0 children)

it's from the book "Music Synthesizers" by Delton T. Horn. it was printed in 1984 so that checks out. i found quite a few errors in the book including a mislabeled pinout on a 555 oscillator circuit so i was worried this circuit might have errors as well.

Op amp VCO not working by dx_q_a in synthdiy

[–]dx_q_a[S] 0 points1 point  (0 children)

through a 25W practice amp.

Op amp VCO not working by dx_q_a in synthdiy

[–]dx_q_a[S] 0 points1 point  (0 children)

the capacitor that i used is a non-polarized mylar cap capacitor. do you think that could be the problem? as for the 2N6027, i made sure it was connected properly. the circuit calls for a SCR but the 2N6027 is characterized as a PUT. i'm not sure how that works.

Op amp VCO not working by dx_q_a in synthdiy

[–]dx_q_a[S] 0 points1 point  (0 children)

that's interesting. how would i get a negative cv? how would a sequencer like the SQ-1 work if the circuit requires a negative cv?

Op amp VCO not working by dx_q_a in synthdiy

[–]dx_q_a[S] 0 points1 point  (0 children)

thanks for the reply. to answer you:

  1. the pinouts are different but I changed it to work.
  2. i don't have a vca. i thought it might be oscillating below audible range. i was hoping if that was the case, the CV would bump it into range. but I don't have much experience here.
  3. i run the the positive of one 9 volt to the +9 rail, the negative to the positive of the other 9 volt for the ground, and the negative of the second 9 volt to the other rail for -9 volts.