working on Astrotone (or Sam Ash Fuzzz Boxx) clone

[yeeshkul]

I just threw it together on a breadboard and it sounds fairly good . Are there any suggestions about the gain of the first tranny? Also how does the tone control work? It doesn't seem to have much influence on tone and it is not really frequency dependant thing

[yeeshkul]

I used the KC507 tranny for Q1 (gain 180), that should be an equivalent of the original 2N3565  and when the fuzz button is turned fully on it gives very long tones. The other tranny doesn't seem to be an importatnt choice, but i used the same type. Both diodes i used are germanium KA206. All made by Czech Tesla factory. Voltage on collector of Q1 is 2.63V.

[yeeshkul]

i tried to experiment with diodes a bit so i added a switch - Ge, Si, LED
and here is what i've got:

Si: the weakest and most distorted signal (almost the same volume level as when turned off)
Ge: remarkably louder but less distorted
LED: the loudest and cleanest signal (just a bit louder than Ge)

PS: those things i call Si diodes is just something i've found in my drawer, so i suppose those are Si diodes ...

[yeeshkul]

CORRECTION:

hehehe, that's almost unbelievable: the diode i just found in my drawer was actually a Ge diode. The diode which was sold to me as a Ge diode was Si diode KC206.
so once again:

Ge: the weakest and most distorted signal (the same volume level as when bypassed)
Si: remarkably louder but less distorted
LED: the loudest and cleanest signal (just a bit louder than Ge)

I knew it was something wrong with that! Ge diodes open faster, so the output voltage must be lower(considering that the second tranny is just an emitor follower) and with more distortion than Si and LEDs

[yeeshkul]

So in the end i am not sure how important is the whole second transistor thing. I just plugged the output lug right after the diodes and got the same sound out of it.

Here are my LTspice analysis of the circuit:

[yeeshkul]

Does anyone have a clue what can be a reason for the emitter follower here (apart from giving it a small output impedance)? The signals as you see on the picture above are slightly differ but it is caused just by the C4. The signal right before C4 is completely the same as the signal right after the diode clip - just a bit weaker (emitter follower gives voltage amplification<1). 
The Ge diodes restrict the voltage to 200mV, which is almost the same voltage as the one that comes from the guitar (so there is not much reason for the volume pot once you use Ge diodes) and instead of kicking it a bit up, they inserted an emitter follower, hehehe.

[Paul Perry (Frostwave)]

What is the collector of Q1 alleged to be? Because, I can't see where the asymmetry is coming from, unless it is the 2N2222 being savagely overdriven.

[yeeshkul]

There is no resistor in the Q1 emitter => Vb(Q1) ~ 620mV bias => Q1 amplifies differently the positive and negative half of the signal (the negative half of the signal tend to turn Q1 off).

And then: Vc (Q1) bias is about 2.6V and amplified signal swings around it (0->5V), then it is being clipped down to 200mV by Ge diodes (diodes are between caps, so there is no bias voltage between those caps - otherwise there would be no clipping  ), then the clipped signal is being "put back on" the bias voltage again - Vb(Q2) ~1.6V (through the 1M resistor) and driven through the second tranny, where it become a bit weaker (BUT gives the whole stompbox a small output impedance, which is quite nice )

[Dan N]

Just wondering, RG has a 22K collector resistor on Q1 (Sam Ash Fuzz). What schematic are you using?

I agree, that last stage is kind of silly.

[yeeshkul]

yeah 22k is the right one but there is no difference. i was just fiddling with values and left that one there