Vintage fuzz schematic

[O'malley's Alley]

here is the schematic for the vintage fuzz box.  Refer back to this thread for soundclips and so on.... http://www.diystompboxes.com/sboxforum/viewtopic.php?t=16244&highlight=

http://www.picturetrail.com/gallery/view?p=999&gid=3221873&uid=1678203&members=1 (first picture at left)

enjoy!

[RDV]

It sounds cool like that, I dig mis-biased, gated sounds though. I'm guessing; but I think that perhaps replacing R8 & R10 with trimpots might allow you to get a more conventional sound out of that thing. See if you can adjust the collector voltages to 4.5v and see what happens. I kinda like it like it is though, sounds like a pissed-off elephant! It also says it requires a 1 volt input :?:  You might try driving it with a booster of some kind to drive a bit harder.

Regards

RDV

[Dan N]

Is that from an old RCA hobby manual?

Thanks for posting!

[Marcos - Munky]

Thanks for posting the schematic.

[O'malley's Alley]

its in a huge electronics manual, but I think it is from a RCA manual.  The electronics manual also has a theremin and some other stuff as well.  Pretty interesting stuff.

[Tim Escobedo]

Reminds me of one of those old John Markus circuit books. Looks interesting enough to try.

[Peter Snowberg]

More bias tricks:

Replace the R2-R3 combination with a 250K or 500K linear pot. Connect the wiper to the junction (also connected to the base), and connect each end of the pot to the +9 and GND connections with 22K resistors in series (to stop you from accidentally frying things). Thanks for posting the circuit. I’m going to have to build one with some different transistor selections.

Take care,
-Peter

[Nasse]

:wink:

[Doug B.]

Thanks for the schematic!

This is the same circuit as the "Sixties-style Fuzz" that appears at AMZ:

 http://www.muzique.com/schem/index.html

It also appears at Triode Electronics under "Fuzz Box Circuits (transistor) Version 2":

 http://www.triodeel.com/studio.htm

The only difference is the one at Triode uses a 15k potentiometer at the output instead of 10k (not really much diffference --- slightly less loading on the last transistor).  

It's good to have the original (?) source for the circuit and some design notes (lacking in the above two links)!  There has been some on and off discussion of this circuit over the years.  

The "SK" transistors are RCA's repair/replacement series (like NTE has).  If anyone's interested, i can get out my old RCA guide and post the transistor specs.  

Whoever fiddles with this circuit might also want to try a lower value for R1.  R1 (100k) looks into an impedance of not more than 200k at the base of the first transistor, which means it cuts the input voltage to about 2/3 before applying it to the first transistor.  Might not matter too much, but since this *is* a fuzz circuit....

- Doug B.

[Doug B.]

Oops!  It was late, i was tired....  Anyway, in my previous post, i series-ed the two resistors instead of paralleling them to calculate the impedance.  The 100k input resistor is really looking into about 50k (100k parallel 100k parallel transistor impedance, which we'll assume is high).  So the 100k input resistor will drop the signal voltage to about 1/3 at the transistor input.  

The purpose of the 100k, then, is probably to increase the load of the effect on the guitar to about 150k (it would be about 50k without the resistor).  So there's a tradeoff: a higher value would keep the signal more trebly/crisp but would lower the fuzziness/overdrive.  

My suggestion is still to play around with the resistor value and find what you like best.  Or make it variable with a pot!  

- Doug B.