Mammoth Electronics Nuclear Winter Distortion

[JabboWookie]

I bought this kit a while back mainly because I thought the enclosure was cool. The PCB was crap and I could never get it to work right, and I ended up just scrapping it and keeping the components.

I had them send me the schematic and I was wondering if anybody can tell what this is specifically based on. I see the usual sections: input buffer, clipping stage, hard clipping Ge diodes, tone, and output buffer. Is it an "original" design, or is it close to something else?

Would anybody be willing to whip up a vero?

https://www.mammothelectronics.com/collections/mammoth-kits/products/b-nuclear-winter-b-br-distortion-kit-br-i-mammoth-electronics-i

[anders]

I did a vero of this a while ago. I can post it on contributions section. You pretty much nailed the circuit but the output stage. It looks like a gain stage, not an output buffer? That 470k resistor between Gate and Drain looks a bit wierd?

Anyway, will post the layout soonish.

[JabboWookie]

The problem I had with my build was that, even maxed, the volume was barely over unity. I had always assumed it was an issue with the output stage, but I'm not experienced enough to trouble shoot.

What's funny is that when I contacted Mammoth customer service for the schematic, the rep said he had the same volume issue with his build.

[Frank_NH]

This is basically a Distortion + (Ross distortion) with a BJT input buffer and a JFET output stage.  The JFET stage looks very wrong - I would remove R9 and replace it with a 1M resistor from gate to ground.  To correctly bias the J201, you would want to put a 50K trimmer in place of R7 but a 22K resistor would get your close assuming "average" Vp and Idss for the JFET.  The voltage gain is about 6.  If you wanted lower gain, use a 2N5457 with a 20K trimmer or 10K fixed resistor, which should get a gain of about 3.5.  Probably will sound pretty good after that.  

One more thing - why did they waste half of the dual IC?  You can use the output of the op amp buffer as a 4.5V bias voltage.  If you don't want to do that, then just use a single op amp chip.

Good luck with your build!