Foxx Tone Machine

[I am the Walrus]

 Hello all. I'm new here. This is a great site, learning a lot. I wanted to try and build the GGG Foxx Tone Machine as one of my first projects. It's fairly simple and I've heard good things of it. Just wanted to know how others have done with it, and if the parts on the GGG schematic serve it well(pots, etc). Thanks for any and all replies. Gavin. .generalguitargadgets.com/pdf/ggg_ftm_sc.pdf

[antonis]

Welcome..!! 

<It's fairly simple>
Is it..??
(if so, you probably understand, in depth, the whole circuit operation toghether with separate building blocks so you can have an estimation about "well service" of the specific parts..) 

To be more serious:
I should suggest you to start building it in pieces (e.g. first 2 stage gain amp Q1/Q2 circuitry so you can play with all that gain/NFB resistors, maybe altering Q2 Emitter resistor to see how gain is going up, then add rectifing diodes to Q2 phase splitter for octave effect, then add Q3 distortion stage w & w/o clipping diodes, then add tonestack and gain recovery Q4 stage..)
It's a, more or less, flexible circuit so you can mismatch stages order, omiting some of them - just for educational fun..

[DFX-PCBS]

try Madbean's Wolfshirt project, its a great build

[I am the Walrus]

Thanks for the replies. I was going to socket quite a few parts, so I could tweak it. Antonis, what would you recommend for hfe on the 2n3904s? Is matching the diodes critical? Thanks.

[antonis]

Antonis, what would you recommend for hfe on the 2n3904s?

Can't recommend anything - I'm not a 2N3904 manufacturer..!!

As far as transistor's h_FE is higher than individual stage's gain, there shouldn't be any problem..

Is matching the diodes critical?

For D3/D4 clipping pair it isn't (audibly) critical at all..
For D1/D2 rectifier pair, hmmmm...
(theoretically, for a "perfect" octave they should be matched but, IMHO, as far as they are of the same type you shouldn't mind a lot..)

Of course, you are allowed (not to say "strongly encouraged") to play with different diode types both on octave and clipping stages but only AFTER you've build the circuit according to its initial items values/types and with only SINGLE item replacement at a time..)

[Mark Hammer]

1) There aren't many components that would warrant socketing, unless you are intending this to be an instructional project for yourself.

2) I will recommend the first pair of diodes to be either germanium or better yet, Schottky type.  The back-to-back pair just before the tone control are really more for clamping the level, so that the octave has a chance to "bloom" as the harmonics die away and leave a strong fundamental.  Some of us here have found that inserting a small value resistor (470R-1k is a good starting point) between those diodes and ground allows it to accomplish the level-clamping task without contributing too much additional distortion.  Too much fizz hides the octave.

[stringsthings]

I recommend buying a breadboard and a good DMM.
Then you're just one step away from designing a "better" fuzz box.