foxx tone question

[axr]

i want to build a foxx tone machine from GGG.com site, can i substitute the 4 - 2N3565 or BC237B transistors for 4 2N2222, succesfully without changing the sound and the pedal itself???

[Rodgre]

You can use 3904s or 2222s or 5088s. The tone might change a little here or there, but I've gotten great sounds with all of them.

The place that seems to make the biggest difference to my ears is the diodes. I've tried germanium and silicon diodes and I find that the germanium have a splattier, wilder tone, and the silicons have a slightly tighter, more focused tone. I think I prefer the silicons. I use 1N4001s.

It's sort of analogous to alnico speakers versus ceramic. Both sound good, one has more give and breakup, the other can be a little more focused and punchy.

Roger

[Mark Hammer]

Roger is correct with respect to the feasibility of using a variety of different transistors and diodes in the Tone Machine.  

Note, however, that diodes are used in two different places and for different reasons.  One pair is used for dividing up the signal into the half cycles that will be combined to produce the octave effect.  A second pair is used as a normal back-to-back pair for producing distortion just prior to the tone control.  This means that whatever decisions you might make about diodes should factor in the purpose of the diode.

The octave generation requires that the upper and lower half-cycles be mixed in equal proportions.  Unequal proportions will put the octave more in the background.  For the strongest octave effect, you'll probably want a matched pair of Ge diodes (i.e., matched on your meter for approximately equal forward voltage, such as 247mv vs 239mv).

For the clipping diodes, you have more degrees of freedom in selecting them.  Ge's will yield less overall output but fuzzier tone.  1N4401's or even LED's will yield a hotter output and more crunch than fuzz.  1N914/1N4148's will provide more output than Ge's and a bit less fuzz.  A mix of types (or even one of Jack Orman's warp circuits) will yield other possible tones, without affecting the octave strength.

Now, will it be a "Tone Machine" after these assorted changes?  That's another story.