Maestro Fuzz Tone No Output

[misterc57]

I had the probe ground clip connected to the circuit ground lug. I will try scope again.

Noise is a crackling sound, loud and present with or without a signal inserted at the input. Pots at any setting.

When I had all 3 transistors replaced with the new NTE158 the noise was unacceptable but not as bad as it is now.

[misterc57]

Some pics of current circuit

[mozz]

That whole unit would give me nightmares looking at the solder connections. I don't see the 100k and the .01 input parts. Was the .01 you removed the same as the input one or was it different? Wondering if it was factory or someone added it. Tap on those disc capacitors, those legs on the 005uf look stretched. Make sure those lugs and the pots and input jack have good grounds, i would take them apart and clean the metal. If you are trying to find the noise, short the input and find which section it is coming from.

[misterc57]

That whole unit would give me nightmares looking at the solder connections. I don't see the 100k and the .01 input parts. Was the .01 you removed the same as the input one or was it different? Wondering if it was factory or someone added it. Tap on those disc capacitors, those legs on the 005uf look stretched. Make sure those lugs and the pots and input jack have good grounds, i would take them apart and clean the metal. If you are trying to find the noise, short the input and find which section it is coming from.

The 100K and .01 are under the board.

The .01 I removed at the input did not look original to the circuit.

I noticed the Q3C V is jumping around a lot, should it?

[misterc57]

You need to follow it from the start. Show me a nice sine wave on both sides of the 100k, then the .01, then directly on the base of Q1. I would be running a little hotter input , maybe 40-50 mv. Turn the fuzz pot to half. volume doesn't matter.

Sine looks good on both sides of 100K. At the base of Q1 I have this wave which is bouncing up/down.

[Helmholtz]

The .01 I removed at the input did not look original to the circuit.

The input needs to have one 0.01µ coupling cap to block DC

I noticed the Q3C V is jumping around a lot, should it?

Of course not. That would be your crackling.
Reflow all that messy solder joints, clean ground connections and especially make sure that 22k is well soldered to the fuzz pot wiper.
Also make sure transistor leads don't touch the transistor case or other wires.

[mozz]

Maybe there is a problem with the. 01 under the board, could be why a second one was added? If you lift the first electrolytic and your noise goes away that narrows it down to the first couple parts, including the nte158. Tap on all the disc caps, they do get noisy.

[Helmholtz]

Sure, ceramic caps can be damaged by tearing the leads apart.

[misterc57]

This has been a challenge on this end and I thank you all for your patience and hanging in there with me.

I have done the following

The legs of the original transistors were stressed (possible poor connection internally) and since the new transistors were less noisy, I now have all new NTE158 installed permanently.

I have double check all areas for connection to ground and all are solid with good continuity.

I do need to see if the effect on/off foot switch (which is working) is connected well (it is not shown on the schematic) I can see that one side is connected to the input before the (100K and .01u).

I also suspected the input 100K to .01 to Q1B. I have installed a temporary new 100K and .01.

I have a clean sine wave until the Q2C. Below is a scope shot of Q2C and Q3C, I had tried a new 1K5 to Q2C, no joy. Below images have attack pot about half way.

Issue of noise remains (less with new transistors) and also a pre-mature decay of guitar notes (less decay as you dial up the attack pot, which brings more noise).




and some new images...

[Helmholtz]

You can't expect a clean sine with a distortion/fuzz box.

[mozz]

Exactly. If you're getting a "decay" , otherwise known as gating, it's because of misbiased transistors. That's because the transistors are not suited to the resistor values. The correct transistors it would not do that. Your 2n270s could all be bad. Best value for that pedal is all original whether it works or not. Replacing the transistors and other parts drastically lowers it's value. I would not keep soldering on that board, I would have put wires attached to sockets and kept swapping transistors until it worked. If you go to diystompboxes. com you will get first hand advice on repairs and/ or what transistors are known to work. If you had sockets or alligator clips you could determine if any of the 2n270 are still good. I still think the voltage on Q1e is too high. Also, do not just take ground measurements, loosen the pot, clean the mating surfaces, do the same with the lug terminals, jacks etc.

[mozz]

Have you seen this webpage https://www.guitar-mod.com/rg_pedal_maestro_repair.html

[misterc57]

Have you seen this webpage https://www.guitar-mod.com/rg_pedal_maestro_repair.html

No but will do. What controls Q1E voltage?

[mozz]

Q1E voltage is controlled by the transistor leakage(as long as the resistors haven't drifted too far). Actually the 2n270 cross reference to a NTE102, not 158. 102 may be a lot leakier and work better. Here's the story. If you can wait and put this aside. I will use my FZ1 clone and find you a set of transistors that are known to work. These are genuine RCA TO-1 package but have factory part numbers on them that don't cross reference to anything. I think they are comparable to 2n404,406,408. As long as my clone has factory value resistors, they should work fine. Let me know if your customer can wait.

[Helmholtz]

What controls Q1E voltage?

Transistor leakage, transistor hFE, the base leak resistor (1M) and the emitter resistor.

Generally I think this is a poor design depending on sufficiently bad transistors (moreover sound is nasty).