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I was wanting to construct a "fuzz" distortion guitar pedal, but being indecisive, I wanted to be able to change the type of transistors in the circuit at will.

I found the idea of using a double-pole rotary switch to switch in and out a multitude of different transistor or capacitor configurations, allowing for a highly customizable tone.

Credit to randofo of Instructables.com

Credit to randofo of Instructables.com

However, I was wanting to instead use a thumbwheel as it has more positions and is more readily available, the difference being, they are only single-poled. I don't think this would have an effect on switching out the capacitors as I could easily make one leg common and have the other leg attached to the respective switch position, but because the transistors are active, multi-legged components, I'm not sure of the wiring configuration.

Would it be best to switch out the Emmiter, Collector or the Base? I think I can see a noise-problem occurring by having a bunch of transistors in my circuit where all but one have a base hanging in an open-circuit at any given moment.

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You can use the thumbwheel for the transistors as well. Keep the emmiters and collectors connected but have the base switch. The only problem with this is the leakage current for all of the unconnected transistors. I do not think this will be a big problem, but your gain will be reduced slightly.

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  • \$\begingroup\$ Awesome, thank you for the answer. Is there any chance you might be able to expand on what pitfalls the other methods would have? Also I was planning on switching between 10 transistors on both the first and second gain stage, how would I know how much current leakage to expect? (And resulting gain drop) \$\endgroup\$ – Al Longley Nov 19 '14 at 3:44
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    \$\begingroup\$ About .15nA per stage, from looking at the spice models, which is negligible. For a guitar pedal, you will not notice this. This is probably the best method, it is the easiest to use and wire up. You will probably pick up more noise from wiring each emmiter or collector to a switch, since I am assuming you are not going to make a PCB for this. \$\endgroup\$ – Sergei_Grishin Nov 19 '14 at 4:04
  • \$\begingroup\$ Perfect, couldn't ask for more. +1 and accepted \$\endgroup\$ – Al Longley Nov 19 '14 at 4:06

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