VAC-PAK CV to Variable Resistance – A Circuit Bender’s Dream!

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The Synthrotek Vac-Pak

The Synthrotek Vac-Pak

Have you ever wanted to add control voltage to a parameter on your synth or circuit bent toy? Now you can!

 The Vac Pak is a vactrol-based control voltage to variable resistance circuit.
  • Connect your CV source to the input jack.
  • Set the Scale and Offset trim pots to dial in your optimal resistance, with a range between ~300 ohms to ~10M (all vactrols are a little different in range).
  • Connect the wires from J4 to your circuit to make a variable resistor.
  • Daisy-chain multiple Vac Paks to the same power source using the remaining connector (either J2 OR J3).
  • Power the Vac Pak with a 9V battery clip (wired to J2 or J3) or with your circuit’s on-board voltage source (wired to J2 or J3).
  • An onboard 5V regulator allows the Vac Pak to be powered with 6-18V DC.
  • Caution: Do not exceed +10V DC on the CV input, more may burn up your vactrol!




  1. Raf says:

    Hey Steeve!!

    I’m gonna go right away get 2-3 to mod some VCO’s or other synth-droen with it. Didn’t knew earlier about those!!! I think i’ll have to suscribe to the newsletter to be alerted next time. What a great idea. Also, i’m so greatfull that i can now take the bus or go by walk to MOOG Audio store, here in Montreal to get your stuff. The guys over there jsut have great word for your materials.

    Cheers and have a great day man!

  2. Steve Harmon says:

    Raf! that is so cool, show us a video of that you do. Moog Audio rules, and certainly ask them if you ever want anything up there, I am sure they can special order it for you. Best! Steve

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