foxx tone machine problem - voltages

Started by Barcode80, July 25, 2007, 12:53:54 AM

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Barcode80

i just put together the foxx tone machine from gauss' layout, and i have a problem. the volume and tone both work, but the fuzz kills the signal until you run it way open, then it gets some nasty, gated, misbiased and flat out ugly fuzz. the transistors match the build notes on GGG except for Q3, which shows .88, 1.44, and .84 (E, B, C). I've resoldered all the joints, checked continuity. all is good. the nly thing i can think of that may be wrong is that i ran a 100k and 47k in series in place of the 150k resistor because i am out of them. any thoughts?

here's the project fie from gauss' site for reference:
http://www.gaussmarkov.net/layouts/foxx/project.pdf

hellwood

i would look at R15's value and C8's polarity as well as the +9v to R15 for starters.

Barcode80

well, checked R15, its at 146, not enough variance from 150 to matter. remelted all solder joints around the tranny area again, no dice. maybe i overheated the tran?

hellwood

R15 should be 10k on the schematics on your link.

R.G.

QuoteR15 should be 10k on the schematics on your link.
Correct. Making this 15x too big would let Q3 saturate, which it does:

QuoteQ3, which shows .88, 1.44, and .84 (E, B, C)

That's enough to account for the gated, blocking signal passage.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

Barcode80

aha, i think i just checked the wrong one. i think i checked r13 thinking it was r15. i'll check the resistance again on the ACTUAL r15 when i get home :)