A somewhat different fuzz

[Gus]

A two stage fuzz sim.  Note the first stage gain control it adjusts both the first stage gain as a feedback resistor and the gain of the 2nd stage.  

The wiper goes to the Q1 collector one side goes to the Q1 base and the other side goes to the input of the following stage and is part of setting the gain of the 2nd stage.  The more astute will note the Bluesbreaker uses a similar type gain control but with opamps

R4 needs to be selected for a higher hfe transistor like a 2N5088 it sets the bias and a part of the max gain.  The circuit is a balancing act of transistor and resistor values.  You can remove the clipping diodes at the 2nd stage if you want

Circuit is R18 and to the right,  The left of R18 is the guitar and cable sim section

The gain control is a 500K the 1 meg is a mistake on the sim screenshot

[pinkjimiphoton]

looks  cool gus!! one more to add to the pile...


btw.. gave that last thing to my bro who's studio burned down... he loves it.. thanks man!!

[joegagan]

Looks elegantly wonderful. Lot of outta the box thinking there. I like the diodes, would like to try it!

[Gus]

R6 and R5 in the sim are one potentiometer of 500k. 
If the wiper is CCW R6 is a short and the circuit is at min gain
the collector to base feedback is R4 and (C1, R19) in parallel for the first stage
this also works with the series input R7 and C2 and the source
Also the series input resistance part R5 is at max (500k) setting the 2nd stage at min gain

If the wiper is CW the circuit is at max gain
The parallel collector to base feedback R4, (R6 at 500K, C1, R19) is at it max setting
AND R5 is shorted setting the 2nd stage gain to max

The gain circuits are the same type you find in a BMP or a text book

What is different is how R5,R6 change the gain with this type circuit.  As I posted before this similar to the way a Bluesbreaker gain control works

Anyone know of an effect circuit that sets gain like this with transistors?

Might sound nice with a passive bass

I selected a collector current for the transistors and then set the circuit up using stock parts and easy to find parts.  Not built add a filter cap and power supply protection.

[DougH]

Nice. I like the bluesbreaker approach on the gain control. Always thought that was a good idea.

[thelonious]

Love it. I had never noticed that about the Bluesbreaker gain knob. Brilliant way to adjust the gain of both at once without a dual pot.

[Digital Larry]

Any way you could show the waveform output with the sine source voltage stepping from say 10 mV to 1V?  I find that frequency response of seriously non-linear circuits is only part of the story.

[pinkjimiphoton]

hey gus,
if you can bear with me being behind a couple days, i'd be quite glad to build a "proof of concept" for you if you'd like.
this looks really cool!!

[deadastronaut]

hi gus....looks interesting.

i took the liberty of re-drawing it just to be easier on my eyes..

is this how the 'gain' pot should be wired then?...

i have room on my breadboard again  at last...i'll give it a go with 5088's later on if i get time..


cheers man , rob.

[nocentelli]

Yep, sounds good if a little bright with just the two stages - I think I like it a little better than the standard BMP sustain control.

[Gus]

deadastronaut

If we are looking at the "top" of the gain potentiometer it looks correct.  If we are looking at the back. flip the outer lug connections

I would use two 1n4148s to start.  I picked a1n914 for no good reason in the sim.  You might want to add a series resistor to the cap, diode clipping section.

If your collector voltages are way off from the sim and you want to adjust them, I would adjust R3 and R9 values for each section first. 

[deadastronaut]

cheers gus, i'll try that later...

[Gus]

nocentelli

You can install a capacitor from the 2nd transistors collector to base like in a BMP to reduce the higher frequencies.  Try 330pf or 470pf etc.

[Gus]

Anyone try this for the first two stages of a BMP like circuit?

[Gus]

Built the circuit and tested it with a J bass
I used a 1meg gain control
.47uf for C1
two 1n4148 diodes for clipping with a 10k in series with the diodes and C7
removed R2 and R10 and grounded the emitters
added a diode and cap at the DC supply

Sounds good at low settings and at full gain, however it is a kind of fast transition when the diodes start clipping
I might add a lowpass filter it is a little harsh at full gain maybe a cap from the output control wiper to ground and/or a higher value Q2 C to B cap than 330pf

[Gus]

I tested this again yesterday with a new battery.  I should have checked the first battery I used for the above post.

Sounds good to me, anyone else build it?

[pinkjimiphoton]

not yet, been waiting to get to it... so many builds...

i DID build up the fuzz only from the fender fuzz wah you'd helped me with, no dice tho... can't get it to fire.

[Gus]

pinkjimiphoton
this schematic?
http://www.diystompboxes.com/smfforum/index.php?topic=93064.0

R11 in the above link should be a 10meg not a 1meg.  I also left out the 1meg volume after the mix control.
I would try a 741.  Q1 collector and emitter voltages are important.

[brett]

Hi
Looks sweet as candy.
A couple of thoughts...
If Q1 were a low gain device, the emitter resistor could be smaller (10ohms) or taken out, and the clipping might be less symmetrical and more harmonic.
Also, the input impedance is mostly set by the 220k resistor, which is good for overall frequency response and low noise. But a lower value (say 47k) would tame the highs in the first stage, by 'loading' the pickups and allow it to 'clean up' using the volume control (one of the best attributes of a fuzz face). Someone might like to check that out in practice (note that it might mean changing the 47k resistor on the other side of Q1, but probably not much). Gus might be able to sim it it to find a good bias set up for 47k.
Just my 2c worth...
Cheers

[pinkjimiphoton]

pinkjimiphoton
this schematic?
http://www.diystompboxes.com/smfforum/index.php?topic=93064.0

R11 in the above link should be a 10meg not a 1meg.  I also left out the 1meg volume after the mix control.
I would try a 741.  Q1 collector and emitter voltages are important.

hi gus,
sorry i missed your call the other day, been busy as a one legged man in a butt kicking contest still.
i built this schematic, have checked it over quickly  so far, can't find any issues and voltages seem ok.
i will try and get some voltages in a little bit if i can, i gotta day off for a change which is kinda nice.
i didn't have a 10m resistor, so i used two 4.7m in series, but other than that and going with 47u caps (closest i had to 33) i went by the schematic.
haven't had any time to debug at all.