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I'm trying to construct some kind of fuzz factory modular from regular fuzz factory pedal.

ZVex Fuzz Factory Modular

Circuit of the original pedal is pretty easy, but I've tried to add some VCAs based on LM13700. Honestly, I'm a little noob in electrical design, so I've just combined fuzz circuit with VCA circuit and got this:

arrows shows the signal path on the VCA's

Here I tried to make working CV inputs for stab, gate, comp and drive parameters with LM13700 VCAs.

So the qestion is: will it work, or how can I check it for performance (besides constructing it?)

JRE
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drdrvv
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  • Simulate it with e.g. the free tool LTspice – Huisman Nov 21 '19 at 21:35
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    I love audio, synth, and guitar... so I hate to see this question get closed - however, it's pretty broad. Can you narrow your question to make it more specific? – JYelton Nov 21 '19 at 22:46
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    It appears that "fuzz factory" is a brand name so you should write it in proper case ("Fuzz Factory") to indicate the fact (title and post). See https://grammar.yourdictionary.com/capitalization/rules-for-capitalizing-proper-nouns.html. It makes your post more clear when you do. – Transistor Nov 21 '19 at 22:50
  • Chase Bliss Audio and Zvex just released a joint midi controllable version of this pedal. It uses vactrols (15 of them) to replace the pots with digital control. – Andrew Hanlon Nov 17 '20 at 03:27

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I highly doubt that this circuit will actually work. In the Fuzz Factory, the pots are used as pots, e.g. variable resistors, and they modify impedances accross the circuit. Here, using OTA-based VCAs you will control the voltage accross the resistors, but not the actual resistance.

I am working (since a long time ...) on a digitally-controlled Fuzz Factory, and I decided to work with JFETs used as voltage-controlled resistors for the STAB, digital potentiometer for the GAIN, and fixed resistors or standard mechanical pots for the rest. The STAB control in particular is quite hard to managed since it's tied to the power supply voltage - except if using a higher voltage for polarisation or a charge pump.

I am honestly curious about the way the CV controls are implemented in the Eurorack version. I suspect the use of Vactrol LDRs but I have no clue (never seen a real one, didn't find any schematic).

Anyway, with such a complicated design, I highly suggest to make simulations (I use LTSpice too, very handy with sound files) or to try breadboarding the circuit piece by piece, e.g. not trying to mount the entire schematic, but first the fuzz factory alone (and check that it works as intended !), then adding one VCA on one control and check the effect, then another, and so on. But, as I said, and taking in account all the manipulations I did on the Fuzz Factory circuit, I am pretty sure it won't work, or at least it will not do what you think it should do :-/

Best regards

Philibert Tarouan
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