One Knob Fuzz with 3 Knobs and a Switch

[Ben Lyman]

Latest breadboard experiment is turning into a keeper. I started trying out a bunch of different popular "One Knob" fuzzes and gradually it morphed into this.
C1 treble bleed allows a nice variety ranging from crunchy OD to thick beefy fuzz.
Tone control is just a BMP but the magic happens when I throw the "Mid Shift" switch to go from scooped death metal rhythm tones to fat cranked Marshall leads.

It certainly does not need a "make up gain stage" but do you guys think it could benefit from an output buffer?

[Plexi]

Love the one knob fuzz...in any variation :-)

I would try a recovery or output buffer..
I asume the BMTS took a lot of output volumen.

I would take the traditional BM stage and tweak the emiter resistor to get an LPB (tons of output)

[Gus]

I like BMP type tone controls at the output collector as Ben has posted. The output off the collector is high enough not to need a following gain stage.
You can check how things change with spice with different output loading
or
You can test what the next effect/amp input resistance will do to the eq.
I would start with an amp that has a 1meg input. I would then add different resistors in parallel with the amp input try a 1meg then 470k then 220k etc.
Test at different setting of the tone and volume.

R7, R8, (R9, R10) are a DC path to ground from Q2 collector. Was this on purpose?
It should not matter much because you have a cap to the volume control wiper and the resistance is higher than the 5.6k output

IIRC There was a thread at the forum in the past where someone had a DC resistance to ground from a collector output and they posted it sounded better DC coupled vs AC coupled
I think it was an adjusted 360 fuzz.

[Ben Lyman]

Love the one knob fuzz...in any variation :-)

I would try a recovery or output buffer..
I asume the BMTS took a lot of output volumen.

I would take the traditional BM stage and tweak the emiter resistor to get an LPB (tons of output)

Plexi, it sounds like a Tone Bender, I did not know that the One Knob Fuzz had so much fuzz in it until I breadboarded it.
It really does not need any extra volume stages, as Gus noted, it takes off from Q2c and has so much that the BMTS is a welcome adjustment

I like BMP type tone controls at the output collector as Ben has posted. The output off the collector is high enough not to need a following gain stage.
You can check how things change with spice with different output loading
or
You can test what the next effect/amp input resistance will do to the eq.
I would start with an amp that has a 1meg input. I would then add different resistors in parallel with the amp input try a 1meg then 470k then 220k etc.
Test at different setting of the tone and volume.

R7, R8, (R9, R10) are a DC path to ground from Q2 collector. Was this on purpose?
It should not matter much because you have a cap to the volume control wiper and the resistance is higher than the 5.6k output

IIRC There was a thread at the forum in the past where someone had a DC resistance to ground from a collector output and they posted it sounded better DC coupled vs AC coupled
I think it was an adjusted 360 fuzz.

Gus, that's a great idea about paralleling the amp's input with different resistors, thanks! I can't do spice yet (or any of the other cool things out there) but my Champ appears to have a 1M input so I guess I can simply try different resistors on the breadboard from output to ground and see what happens. Also, I did finally get my o-scope up and running so I don't know if that is something I could use for testing purposes or not.

As for the path to ground through R 7,8,9,10, no that wasn't deliberate. thanks fro pointing it out. I originally had a 22n coupling cap b/t Q2c and the tone stack but I pulled it out to see if there was a change. I didn't notice anything and the pot doesn't crackle when I turn it but perhaps I should just throw the cap back in there anyway. 

[Plexi]

Sure!
Try 1uF over C1 (great bass response) and lower value over C2 (3n3?) [emoji6]

In this case, I prefer to pan between that two values at the input..like the Meathead Deluxe

[duck_arse]

nice to see a BC549 up front. did you measure the hFE?

[Ben Lyman]

Sure!
Try 1uF over C1 (great bass response) and lower value over C2 (3n3?) [emoji6]

In this case, I prefer to pan between that two values at the input..like the Meathead Deluxe

Sometimes I do that panning thing too, but this happy accident just sounds so good that I think I will leave it for now.

nice to see a BC549 up front. did you measure the hFE?

No Duck, I did not measure it but it is the magic transistor. Q2 can be anything, I have tried 2N5088, 2N3904, 2N2222, BC108, and an old Germanium NPN 2N1304 and everything sounds great as long as Q1 is that BC549

[Plexi]

I would ask to the wise people: did the caps base/collector, increase in some way the overall gain?

It's a doubt I have since the first one knob fuzz I've built.
And as OP says, the gain in this design is wonderfull

[Ben Lyman]

R7, R8, (R9, R10) are a DC path to ground from Q2 collector...

Check out what I just noticed in the original schematic. Even though I didn't notice it I guess I figured a coupling cap was not necessary. I tried a coupling cap just now and realized it would be in series with my "high pass" cap in the tone stack, I'm not sure if that would affect the tone control action. Anyway, I will probably just leave out a coupling cap for now.

For extra credit, can anyone see the mistake in this portion of the schematic:

[antonis]

did the caps base/collector, increase in some way the overall gain?

They actually DEcrease the overall gain, due to NFB action..
(they are used in such a way in high gain circuits to avoid oscillation at high frequencies...)

[antonis]

For extra credit, can anyone see the mistake in this portion of the schematic:

Probably you mean the DC "unblocked" path through R8/R25/R5...

[EBK]

Seems like all the best "one knob" pedals have more than one just-don't-count-this-one knobs these days.  Even the "one knob squeezer" on my pedal board has one! 

[Ben Lyman]

For extra credit, can anyone see the mistake in this portion of the schematic:

Probably you mean the DC "unblocked" path through R8/R25/R5...

No, something else is wrong with this... dead center, look again 

[EBK]

Two 6n8 caps in series would make C9=0.0034uF, not 0.0068uF.

[Ben Lyman]

Two 6n8 caps in series would make C9=0.0034uF, not 0.0068uF.

Bingo!

[antonis]

    

[duck_arse]

even so close to your [happy] birthday, antonis, no sausage!

DC unblocked path is a "design feature", no?

[antonis]

DC unblocked path is a "design feature", no?

It seems to me more like an "iniquity" between HP & LP filters... 

P.S.
On Friday (down-under local time) there will be free-beer party..

[Ben Lyman]

http://www.bigmuffpage.com/Big_Muff_Pi_versions_schematics_part1.html
Looking here ^ I see every EHX BMP is unblocked, until the bottom of the page I see the Ace Tone Fuzz Master BMP modded clone actually puts a 1uF between the collector and the tone stack.
I don't know if should I do the same or stick with the traditional EHX design. I don't want the series caps to interfere with the tone control but I guess 1uF is really not going to bring my 3n3 down much lower at all.

[Ben Lyman]

C11 1uF has been added and C6 changed to 4n7, everything still sounds good