Questions about a "Voltage Controlled Shape Fuzz"

[gigimarga]

Hello,

Sometime ago I've found this project of a "Voltage Controlled Shape Fuzz": http://www.aronnelson.com/DIYFiles/up/Voltage_Controlled_Shape_Fuzz.pdf (as I can't remember where I've found it I can only thanks to the "unknown author(s)"!)

In the schematic the value of R10 is missing and I used a 22K for it (as I remebered from another schematic...I don't know which...) and for the OTA I used a JRC13600. For all the diodes I used 1N4148, excepting D7 for which I used a 1N4007. For the Gain pot I used a 220K instead of the 100K indicated.

When I tested it I was dissapointed: a light overdrive, with a lot of hiss. The Gain pot seems to do almost nothig and same thing for the Attack pot. The Decay pot cuts the note, as I expected.

So, my main question is "What it supposed to do this effect?".
I hoped that's a fuzz with the amount of distorsion controlled by the picking (as Boss DynaDrive)...

Thx a lot all!

[JKowalski]

It looks just like a tubescreamer, going into a attack/decay.... It seems like all it would do is distort the guitar in your standard way and then give you the ability to control the dynamics of the note... Not changing the sound of the distortion or the amount. The evelope follower is attached to the pre-dsitortion stage, SO I think the purpose of the whole thing is to add distortion to your guitar without getting rid of the original note behavior. The title of it seems kind of misleading...


I think the 13700 OTA is designed with less audio noise, maybe try that for the hiss... It's not very easy to get the noise caused by OTA's to acceptible levels, though, as I have found through experience.

[gigimarga]

Thx a lot JKowalski!
In this case i've lost my time...

[gigimarga]

Because I've finished it at 1AM i hadn't made much tests.
In this morning I've played more with it and I discover that his volume varies after the picking (with Attack at maximum and Decay at minimum)!!!
Theoretically, it can be used as a dynamic overdrive into a cranked channel of an amp...practically, it has a poor tracking and lot of noise...

Anyway, it's strange that the Gain pot do nothing...

[Mark Hammer]

Look at issue #4 of the scanned back issues of DEVICE on my site, and you'll see a project for a voltage-controlled distortion.  It uses a pair of CA3080s in much the same way that the VCSF attempts to, in their nonlinear region where additional gain produces distortion.  The preceding op-amp stage introduces soe clipping via the diode trio, but the OTA is intended to increase that even more.  Ideally, since the CA3080 has the worst distortion specs of all the OTAs (it starts to distort with an input >100mv), that is probably the one you want for this particular job.

[gigimarga]

Thx a lot Mark!
I will try to understand the article, and I hope that I will have some succes