Gibson Maestro Fuzz Tone FZ-1A - Needs Help

[misterc57]

I have a 1966 FZ-1A that needs help! Every note played sounds like a weak pluck into a torn speaker. Splat, splat, splat. I know this pedal can sound better. Perhaps it is dependent on the qualities of each germanium? Maybe there are some voltage issues to check?

I checked all components, connections, etc. Replaced R4 with a new 470K. R2 and R3 were replaced before I had it. The replacement input jack is grounded to the body.

As you dial up the 50K "Attack" pot (R6), the splat gets worse.

Q1 is a 2N2614. Q2 and Q3 are AC128. I would guess the Q1 is original, and perhaps Q2 and Q3 were replaced at some point.

Closest schematics I could find to my circuit are attached.

Explanation of circuit I found online;

Q1 is an emitter follower that provides a high input impedance to match a guitar. Some on-line references say that this stage is not necessary. By all means check this out on a breadboard if you want to--YMMV.

Q2 is forward-biased partly by R4 and partly by its internal Collector-To-Base leakage current. Potentiometer R6, together with resistors R5 and R7, determine how much Q2 is "On," and so the signal level at the Collector.

Q3 is forward-biased by its leakage current, and R9 determines how much it is "On." This stage distorts more as the level of the input signal from Q2 increases.

[Jon Snell]

2N6214 is a silicon pnp transistor and probably is not original.
I would look at the collector voltages on all transistors and act upon the results.

[misterc57]

Q1 is a 2N2614, not a 2N6214.

Collector voltages

Q1 -1.59
Q2 -1.49
Q3 -1.46

[vintagekiki]

https://archive.org/details/maestro_fz1-sm

https://www.coda-effects.fr/2016/11/gibson-maestro-fuzz-tone-fz1a-1966.html

https://www.freestompboxes.org/viewtopic.php?f=19&t=10601

http://files.effectsdatabase.com/docs/files/maestro_fz-1a_schematic-stores-manual.jpg

maestro fz1-b
https://www.diystompboxes.com/smfforum/index.php?topic=98520.0

http://www.luciferstrip.com/fuzz/maestro-fz1b-schematic2.jpg

[Helmholtz]

What is the emitter voltage of Q1? As its collector is tied to the battery, collector voltage equals battery voltage.

Collector voltages of gain stages are also close to 1.5V, means they are hardly conducting at all. Could be that the non-original AC128s have too little inherent leakage to sufficiently turn on.
From a technical POV less leakage means a "better" transistor, but the circuit seems to depend on leakage.

If you can't find better replacements, you will need to change transistor biasing. I'd say, go for at least 0.3V across R8 and R10.

BTW, all voltages must be negative.

[Mick Bailey]

It may be that Q2 and Q3 aren't leaky enough to bias the stages. I've had to use additional biasing resistors to get a decent sound out of this design as well as the earlier FZ1, otherwise the sound gets too gated.

EDIT; Helmholtz beat me to it!

[vintagekiki]

Q1 is a 2N2614, not a 2N6214.

Cross reference 2N2614

https://www.diystompboxes.com/smfforum/index.php?topic=70486.msg567015#msg567015

https://english.electronica-pt.com/components-cross-reference?ref=2N2614

https://nvhrbiblio.nl/biblio/boek/14-2nd-Transistor-Equivalent.pdf

[misterc57]

Yes all voltages read are negative.

Q1 emitter is -.283 V

So we would like to see about -1.0 V at the collectors of Q2 and Q3?

Here are my voltage across R4, R8, R10

R4 - 1.56 (this does not seem right to me). Voltage across R4 changes with the Attack 50K pot. The range is -1.52 to -1.583
R8 - .127
R10 - .172

[Helmholtz]

Q1 emitter is -.283 V

Should do.

So we would like to see about -1.0 V at the collectors of Q2 and Q3?

Yes that would be a good starting point.

Here are my voltage across R4, R8, R10

R4 - 1.56 (this does not seem right to me). Voltage across R4 changes with the Attack 50K pot. The range is -1.52 to -1.583
R8 - .127
R10 - .172

R4 voltage makes sense. Should be closer to 1.4V It's given by battery voltage minus Q2 base-emitter voltage (very low for Germanium). You will need to lower the value of R4.
And Q3 will need a resistor between base and supply as well. Start with something like 1M.

Or try increasing the values of R5 and R9 until you get desired collector voltages.

R8, R10 voltage drops are too low, but was already clear from collector voltages.

[Brian W.]

I've made a few of those years ago and seem to remember using a variable resistor for R 8 and R10. Your particular problem may be earlier in the circuit, however.

[Helmholtz]

I don't recommend to change the values of R8 and R10. It won't improve the low bias.

[Enzo]

I sold off a pair of those last year. My impression was you had to play aggressively into them or they did sound crappy.

[Brian W.]

I sold off a pair of those last year. My impression was you had to play aggressively into them or they did sound crappy.

It's the "Satisfaction" fuzz.

[mozz]

FZ-1 was the satisfaction fuzz, not the 1A. Go to DIYSTOMPBOXES.com. They will give you the correct voltages to shoot for.

[Brian W.]

FZ-1 was the satisfaction fuzz, not the 1A. Go to DIYSTOMPBOXES.com. They will give you the correct voltages to shoot for.

I saw the small box and 3 trannys and just figured "FZ". I can't remember which particular transistors I used to make them [or if I changed any caps around]. It's all the "Satisfaction fuzz" to me! The reason I was messing with the circuit was to modify it into a Tone Bender MK 1 [the "Yardbirds / Jeff Beck fuzz]. Quite an improvement on the original American FZ circuit.