Hello Hello--
   I tried this a couple of days ago but screwed it up..........
The "60's style Fuzz" on the AMZ site looks interesting to me but I was wondering about using different si. trannys for Q1 and Q3.  [3906, 3904, etc. ??]  Also, can you suggest any resistor value changes to  fine-tune the circuit to these different trannys??
Thanks much!
Brian.

If I were building that schematic I would put a 10k trimpot on the board for Q3's collector, with a 2k resistor tied to it...replacing the resistor value for Q3's collector.
 If I didn't have a trimpot, I would put a socket where that....NO
 I would use a long socket of like 5 pins, and use the bottom three pins for the transistor leads, and the top two for the resistor leads...then you can plug in treansistor and resistors to matche bias for Q3.
 Q's 1 and 2 [emitter followers] Collectors being tied to the top rail...should read whatever your PS voltage is.
 With a trimpot on Q3 you can mess with differnet transistor biases easily, and tune misbaises to taste...of course if you want a higher resistance than 10k or 12k on Q3 collector use a larger pot or add a larger resistor.
 Because the schem calls for 2k7...A 10k pot should give you enough resistance range for that position.

hello Pete--
    Yeah, that's what I'm getting ready to do now.  Maybe I should just worry about "fine tuning" the other trannys after I get the 3rd stage up and running.  I'll report back later with the results.
Thanks-
Brian.

hey brian~
yeah, let us know. thats about the onlt fuzz circuit i can think of that i havn't messed around with... i'm kind of curious too...
take it easy man,
~ryanS

The "Sixties-style Fuzz" that appears at AMZ originally came from an RCA hobby publication.  It has recently been posted at another site with some design notes (first picture at left):

http://www.picturetrail.com/gallery/view?p=999&gid=3221873&uid=1678203&members=1

I contributed some posts to that thread, but i'll repeat some of it here.

An almost-identical circuit from a British publication 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 also doesn't specify the transistor types.  (Darn!)

The "SK" transistors are RCA's repair/replacement series (like NTE has). If anyone's interested, i can get out my old RCA manual 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 50k at the base of the first transistor (100k parallel 100k), which means it cuts the signal to about 1/3 (!) before applying it to the first transistor (an emitter-follower stage -- no gain). The other effect of R1 is to increase the impedance of the input to about 150k; leaving it out will drop the impedance, as i said, to about 50k.  So lowering R1 will increase the fuzz/overdrive/gain but will reduce the treble frequencies driving it.  A tradeoff.  

- Doug B.

QuoteThe "60's style Fuzz" on the AMZ site looks interesting to me but I was wondering about using different si. trannys for Q1 and Q3. [3906, 3904, etc. ??] Also, can you suggest any resistor value changes to fine-tune the circuit to these different trannys??

I found the circuit in an old magazine called Experimenter's Projects or something similar....  any common silicon bipolar pair such as the 3904/3906 or 5087/5088 should work just fine.

From just looking the schematic over I'd say it will sound very "buzzy".

regards, Jack

Hello Hello---
 Alright, I perf-boarded a version using 3904's for Q1 and Q3 and tried various PNP germs for Q2.   I also used a trimpot for Q3 collect.
THE RESULTS-------------------blat......fart.............sizzle.....?
I suppose if you had never heard a good Fuzz Face or Tonebender circuit this MIGHT be a useable  circuit for  mis-biased fuzz effects.  I'm very interested in the mods that you guys brought up........it did sound like it needed a kick in the front end of the circuit.
Any more ideas??  I know that some circuits can only sound "okay" regardless of any mods and improvements.........maybe this is one of those.
Brian.

Quote from: brian wenzAny more ideas??  I know that some circuits can only sound "okay" regardless of any mods and improvements.........maybe this is one of those.

Give us the dc voltages off the connections of each of the transistors and we'll start there.

regards, Jack

Hello Hello Jack and everybody--
  Well, I went through and swapped some res. values [removed the 100K after the input for starters] and basically got the thing as tweaked as I could and it DID sound better  [more fuzz] .  I don't think I'll keep it, though, 'cuz  the Maestro FZ-1a circuit does the '60's fuzz thing' much better.  I had the same experience with the Olsen New Sound Fuzz......not much fuzz in that one either without a little re-working of the circuit.
I'd like to hear from anybody else who's built any of these circuits [just in case I've missed something!!]
 I just keep thinking that there must be some undiscovered circuit out there that's a complete FUZZ MONSTER....................the search continues!
Thanks Jack and everybody--
Brian.

Brian -

Glad the tip helped... if only a little.  I breadboarded this guy quite a while ago and don't remember much about how it sounded.  But here's a few more comments from just looking at the schematic.  

Germanium transistors generally have more variability in specs than silicon and are more temperature sensitive, so the second transistor will likely be the most finicky about biasing... and because there is no emitter resistor for temp stability!  But notice also that the third transistor is *direct* coupled to the second... so the second transistor's biasing will also affect the biasing of the third transistor!  

I might substitute an adjustable bias network for the fixed biasing network at the base of Q2.  For example, a 47k resistor in series with a 100k trimmer (wired as a variable resistor, not a voltage divider) in place of the 100k resistor (keep the 15k the same) would allow some manual adjustment of the biasing for the particular transistor you have in the second stage.  

Here's some brief specs for these transistors from the "RCA SK Series Top Of the Line 1975 Replacement Guide".  

SK3020 NPN silicon audio-frequency transistor, medium-power driver/output:

 Pt = 1 watt (max)
 Ic = 800 milliamp (max)
 hfe = 125 (Vce = 10 volt, Ic = 100 milliamp)
 GxBW = 150 MHz

SK3005 PNP germanium radio-frequency transistor, AM broadcast-band receiver stages (hah!):

 Pt = 0.08 watt (max)
 Ic = 10 milliamp (max)
 hfe = 90 (Vce = 9 volt, Ic = 1 milliamp)
 GxBW = 10 MHz

Keep us posted on your results.  (Maybe i'll have another go at the circuit this weekend -- they're predicting more snow for the northeast!)  

- Doug B.

Hello Hello Doug--
    Thanks for the help!  
Yeah, the second tranny was  "adjusted"  'til I was blue in the face....different trannys, different value res., everything that could be changed!  
Have you messed with the Maestro FZ-1a circuit??   I found this one to much more  in line with the sound I was hearing in my head  [more "useable"].  
Are their any older circuits that you know about that have the slightly cheesy fuzz but with more gain??   [Actually, more FUZZ and more gain, too!]
Brian.

..........actually,  the Kay Fuzz mentioned in another post might be a contender [Shin-ei circuit]...........