COLORSOUND: Hybrid Fuzz Box

The Colorsound Fuzz Box has to be one of my favourite fuzz circuits, due to its simplicity and reliable results.  It's very much a one trick pony, but if you just want a nice thick fuzz, this will to that trick quite nicely.  

If you want a bit more than the Fuzz Box, check out the D*A*M Meathead series, as they appear to be a very close relative to the Fuzz Box.  They're also a good reference to see the range of possible component values to play with.

The layout is the same as the traditional all silicon version, with some component values changed - most notably Q2 is now a germanium NPN transistor and the bypass cap has jumped up from 10u to 22u.  

COLORSOUND HYBRID FUZZ BOX - 0.15" VERO LAYOUT

If you don't have the CV7112, try any low leakage NPN germanium transistor that you can get your hands on, and see how it sounds.  Maybe you will need to tweak the resistor values a little (the 2k2 and 82 ohm in particular), hopefully you have a breadboard that you can experiment on, rather than unsoldering and soldering resistors on the board.

I was testing it on the breadboard with a 10k pot in place of the 2k2 and found that about 4K was the sweet spot for the AC127 I was using.  I also increased the 82 ohm resistor to 120 for higher output.

I've not found reliable photos of the low value resistor paired with the 2k2 (the one on the far left). I've left what I consider the stock value of 82 ohms on the layout.  It might be a little different to this - who knows...  increasing the 82 ohm resistor increases output, which might be a good thing in some cases.  It doesn't need a substantial increase to see higher output - even taking up to 120 is noticeable.

I'm sure you've seen other layouts with 820 ohm resistor instead of 82 - debate / clarification on FSB can be found here and on DIY Stompboxes.   I mostly use values that I can see in photos or verified circuit traces.  If you don't have an 82, I'm guessing you probably have a 100 ohm resistor - just use that, it will be fine.

LTSPICE RESULTS

Here's the difference between 10u and 22u on the bypass cap.  

And for the diagram below, this is what happens when the input cap is changed (retaining the 22uf bypass cap).  

In this circuit, the input cap, along with the 150k resistor and the bypass cap, mainly control the frequency response. If you want to tweak the response, the easiest way is to increase the input cap. The 220n cap on the output doesn't do much for the frequency response, so if you're looking for a bit more thickness, you could try swapping the input and output caps. For reference, a Fuzz Face uses a 10n cap on the output, so even dropping to a 100n cap still gives you plenty of room to play with.

No doubt there will be some colouration as a result of the germanium transistor, as it's not entirely unusual for some to sound tonally different to others.  i.e.  fatter or thinner at times, maybe more or less highs.  

LTspice is a handy guide, but it by no means replaces real world testing with a breadboard and a guitar plugged into an amplifier running at an obnoxious level.   

Changing the 82 ohm resistor has no effect on frequency response - the level increase is very obvious.