Hi - There are many schematics on the web for a fuzzface guitar fuzzbox. I've attached one example. I've attempted to model one with LTSpice (attached) but don't seem to be getting any sort of useful/expected output. My input is close to "middle C" and I expected to get an approx square wave out but it's "not happenin' dude". Could it be because I don't have a model of an AC128 transistor or am I missing something else?

Thanks

 

You have your battery (V1) polarity inverted. The circuit needs -9V.

 

You have your battery (V1) polarity inverted. The circuit needs -9V.

Carl,
Take a look at the transistors. It's a very old schematic, from when PNP transistors were in vogue, and negative was customarily shown towards the top of the schematic.

I got started using PNP's mainly. I had a hard time changing over to the newer standard of using NPNs and having positive voltages on the upper part of the schematic.

 

Here, I threw an LTSpice simulation together myself.

I found a generic germanium spice model on the web somewhere (forget where offhand) and used it in the simulation.

 

His simulation works with the models he shows if you change V1 to -9V.

 

Whoops - yes, it does; I thought his attached simulation was the same as the image.

I missed putting a ground between my V1/V2; the output from my simulation then changes to something very similar to Stirlings' output with the correct polarity supply.

 

Nice one guys. Thanks for your help. I will write 200 times - check once, check twice, then check again.

Thanks again.