Voz De Robo help

[RickL]

I can't find where, but some time ago a schematic from a (Brazilian?) magazine was posted here titled, on my copy, 49 - DISTOCEDOR DE VOZ (VOZ DE ROBO). I built it just recently and am having some problems.

With no input I am getting loud motorboating. If I input a signal, either from a loud guitar or from a signal generator the motorboating goes away and I get an extremely loud version of the signal I put in. As the input signal is increased from zero to about a loud strum from a humbucker equipped guitar the motorboating dies out inversely to the strength of the input signal.

Using a probe the biggest amount of gain appears on the collector of the first transistor (a PNP - I'm using a 3906). I hear the motorboating even there if there is no input signal.

If someone can help, given this not overly helpful discription or at least knows where the schematic is posted so others will know what I'm talking about, I would appreciate any help.

FWIW it's not the Robovox on Munky's site. The signal appears to go through a gain stage made up of a PNP, collector to the base of an NPN, to a phase splitter NPN, rectifier diodes then another gain stage or buffer using yet another NPN and it runs off 18 volts.

[Marcos - Munky]

Is this?
http://www.geocities.com/munkydiy/voicedoubler.jpg

The text says that you need a high impedance xtal mic. I didn't built it, but I know that it's a modded octave circuit.

[RickL]

That's the one. I wondered about the crystal mic input. I tried it with a high impedance dynamic mic but got the same results. There must be something special about using a crystal mic (or I just completely botched the build).

Now, of course, the problem is to figure out how to make it work with guitar. I'll maybe try a 1 meg input volume control and see what happens.

Thanks for the reply. I don't know how I missed finding the schematic the first time I looked at your site.

[Marcos - Munky]

If you want a simple "robot" effect to use with guitar, build the Robovox. This was for use with a mic, but I use in my guitar without problems. It's basically a note generator that mix with the guitar signal and sounds like a pseudo ring mod.

[RickL]

I'm pretty sure I've built the Robovox, I may not have boxed it up yet. I'm 8 or 10 pedals behind in boxing stuff.

I'd like to get this one working if I can. I'll report back if I have any luck.