the augmented Fuzzrite - how to?

[duck_arse]

https://youtu.be/DCGLFz-75mw

I was recently pointed at the above shown video. two things I noticed was feedback at the start, and [seemingly] more of what we all want - growl barge sustain. at around the 22 minute mark, the geezer looks inside and shows a third transistor on the board, but no other details.

so, with respect to the original germanium version as here seen, does anyone have any info or insights into the disposition of the extra transistor? any conjecture as to input or output, buffer or gain, or something else entirely? does anyone own one of these, or has one been -erm- forensically examined? nothing leapt at me during a peek at the other place.




thanks if looking. more if commenting [keep it clean].

[Fancy Lime]

Well, keeping it clean may be difficult with a Fuzzrite. I have no idea what the third transistor does in the model in the video but I always found that replacing Q1 in one of these "60's odd ball" fuzzes (Fuzzrite, Orpheum, Shinei Companion) with a Fuzz Face type circuit makes for some spectacular over the top fuzz. It may be possible to tame that using Ge transistors and a gain pot on the Fuzz Face bit but I for one like it with high gain silicon and gain nailed to max.

Andy

[antonis]

I presume Depth pot on video doesn't correspond to Tone pot on schematic, does it..??

[soggybag]

On the other forum there is a long Fuzzrite thread. At the end there is a schematic with three trans. Sounds like this is the author's idea and not taken from an original unit. But it might provide some insight.

Here the last transistor is an output buffer, sounds like this makes this play well with other effects and eliminates volume drop.

https://www.freestompboxes.org/viewtopic.php?p=297676#p297676

[Mark Hammer]

Looking at the FSB schematic you link to, the 3rd transistor is essentially a gain-recovery stage, similar to what we see on the Big Muff and other high-gain circuits with signal-sucking tonal bleeds just before the output.  The only thing it is intended to do is make Gain/Fuzz settings less than max loud enough.

[idy]

Isn't the third transistor on the "moded by Luksen" schematic an emitter follower buffer?

[soggybag]

From. Y beginner perspective, I see it as a low impedance output to prevent loading losses.

[Rob Strand]

On the other forum there is a long Fuzzrite thread. At the end there is a schematic with three trans. Sounds like this is the author's idea and not taken from an original unit. But it might provide some insight.

Yes there's no concrete link between the two.

On the same page of the fsb thread is a link to the 1968 Mosrite Pro Suzz Fuzz Pedal which has three transistors.   That pedal has another pot, Attack/Sustain.  If I had to guess I'd say that pedal has an extra transistor stage at the input, the output of the input stage passes to the Attack/Sustain pot which is then wired as a volume control with a resistor in pin 1 (like a Muff control) then that passes to the input of the Fuzzrite type circuit.

The video demos the Depth pot on minimum all the way to full.  From the amount of gain it should be possible to deduce if the extra stage is for gain or not.

There's no info about the biasing of the transistors.   That's going to affect the tone.  Given it's a germanium based unit there's plenty of "opportunities" for the bias points to be all over the map!

(If you weren't aware the Germanium version uses different part values.  eg.
http://diy.smallbearelec.com/Projects/FursRite/FursRite.htm
)

[Rob Strand]

Fairly stretched trace/guess from shots in video,


[the electro should be flipped.]
[transistors might be Russian MP40A.   The 140A could be "Russian pi symbol" 40A.]

Very hard to make out much.   

For some reason the 100k + 47n appears to be on Q1, not like the germanium ckt on the web.

Most of the resistor values are unknowns.  Pot values on the schematic are BS, volume could be 500k.


And just to be annoying there's this:

This one is silicon,


So I could have it around the wrong way and that would explain why the supply filter is flipped.
There is a reason I chose the transistor order like I did:  the wiring and direction of
rotation of the depth pot (see video).

[duck_arse]

There's no info about the biasing of the transistors.   That's going to affect the tone. 

I found R1 10M was the biasing hotspot - either 10M or 1M, see what the collector voltage sat at, and that's it. then the tone cap on the bass end of the tone/depth pot for decent spread. my cack ears don't tune any finer than that.


fi on npn, and silicon.

[Rob Strand]

Well I had another look at it.   It's a tough job extracting any info.   It's a bit like a jigsaw puzzle where all the pieces have the ends cut-off.  When I follow the locations of the base resistors I get this feeling some of the transistors might not have BC resistors but they have BE resistors to shunt off the leakage.

The transistors might be Russian MP40A.   The 140A could be "Russian pi symbol" 40A.