Need help adding a gain control to first fuzz pedal

[Isg1315122]

I have built a fuzz circuit from a schematic and it offers a mod for a gain pot coming off the transistor going to ground. It says to put a lead from the ground post to the output/ input post and then out to ground. Using a 250 K A potentiometer.

I tried this every way possible I think and it works but only with the pot turned  all the way up, as soon as you back it off it cuts out.

Can anyone help explain why this is happening or what I'm doing wrong?

[patrick398]

Sounds like you want it in a fuzz face style configuration...one side of the pot to the transistor, one side to ground and the wiper through a cap to ground

https://sjeffects.files.wordpress.com/2013/02/ge_fuzzface1.jpg

[Isg1315122]

Pardon my ignorance but when you say wiper you mean what exactly? I'd guess the ground lug. I'm very new to this can you tell me which leg you mean.

[Isg1315122]

I didnt see the link at first. I think I understand what you're saying. Thanks

[thermionix]

Sounds like you want it in a fuzz face style configuration...one side of the pot to the transistor, one side to ground and the wiper through a cap to ground

https://sjeffects.files.wordpress.com/2013/02/ge_fuzzface1.jpg

Not with a 250KA.  Sounds more like a pre-gain to me.  OP can you share what documentation you're referencing?

[Isg1315122]

Sounds like you want it in a fuzz face style configuration...one side of the pot to the transistor, one side to ground and the wiper through a cap to ground

https://sjeffects.files.wordpress.com/2013/02/ge_fuzzface1.jpg

Not with a 250KA.  Sounds more like a pre-gain to me.  OP can you share what documentation you're referencing?

This is the diagram. Minus the mod which would go off the 2nd transistor. It's built with 2 2n5088s currently instead of the hard to find quickly mpsa13.

250k is the largest pot I have on hand atm. The video says a 1000k might be best for cleaner tones.

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[Isg1315122]

Also I have learned what little I know in about 2 weeks. I know nothing lol.

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[thermionix]

The diagram you posted only has one transistor.  The MPSA13 is a very high-gain darlington type.  Did you hook two 2N5088s together in darlington configuration as a substitute?

[Isg1315122]

The diagram you posted only has one transistor.  The MPSA13 is a very high-gain darlington type.  Did you hook two 2N5088s together in darlington configuration as a substitute?

Yes. This circuit built with the diagram works in this state but breaks down when adding in the tone control as mentioned in OP

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[thermionix]

You mentioned a gain pot in the OP.  Did you mean tone control?  Can you link to the info you're using as a guide?  A simple tone control can be added with a small cap in series with a pot wired as a variable resistor.  If you didn't include the cap it will kill your whole signal as you turn it down.

[Isg1315122]

You mentioned a gain pot in the OP.  Did you mean tone control?  Can you link to the info you're using as a guide?  A simple tone control can be added with a small cap in series with a pot wired as a variable resistor.  If you didn't include the cap it will kill your whole signal as you turn it down.

Ahhhh I knew the wrong wording would be my downfall. I suppose it is a tone control. The guide calls it gain control. It's through diyguitarpedals on YouTube.

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[Isg1315122]

Granted I only just read about adding a capacitor to the pot this morning. The guide never showed a full modified diagram, I did not watch the video linked in the picture. It was a PDF.

Edit: does it work like the diagram in the other link in the second comment?

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[thermionix]

Okay it is a gain control, it decreases gain by adding resistance between the emitter and ground.  Too much resistance will turn the transistor off and cut the sound.  250K is way too high of a resistance for this job.  You can still use the pot you have though if you put a fixed resistor in parallel with it.  I don't know what value, but maybe 1k is a good place to start.  Just solder it between the outside lugs of the pot and hook up as the diagram indicates.  Don't attach it too well as you might have to try a few resistor values to get the gain range you like.

[Isg1315122]

Okay it is a gain control, it decreases gain by adding resistance between the emitter and ground.  Too much resistance will turn the transistor off and cut the sound.  250K is way too high of a resistance for this job.  You can still use the pot you have though if you put a fixed resistor in parallel with it.  I don't know what value, but maybe 1k is a good place to start.  Just solder it between the outside lugs of the pot and hook up as the diagram indicates.  Don't attach it too well as you might have to try a few resistor values to get the gain range you like.

I'm using a breadboard so no solder needed yet. Just learning so far. Much appreciated I will give it a shot.

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[smallbearelec]

Since you are on a breadboard already and working with a variant of the Electra distortion, try this one:

http://diy.smallbearelec.com/HowTos/BreadboardUrsaMinor/BreadboardUrsaMinor.htm

You'll get Much better control of the distortion. The 2N5088 will work fine instead of the 2N5089 in the pics. Any other items you need should be available locally and cost pennies. +1 re Thermionix that you want a low-resistance pot in the Emitter circuit. Reverse audio ("C") taper there will give you best "feel", but linear ("B") will work if you don't have C.

[Isg1315122]

Sounds like you want it in a fuzz face style configuration...one side of the pot to the transistor, one side to ground and the wiper through a cap to ground

https://sjeffects.files.wordpress.com/2013/02/ge_fuzzface1.jpg

It looks like in this diagram that the 9v negative is connected to the circuit. Is this built in reverse polarity or is this an error/ typo in the diagram? Also I see that the resistor coming off the input doesn't have a connection symbol, am I to assume that both errors are not a worry and just hook it up with 9v + going in and negative to ground?

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[nocentelli]

The circuit posted is for a "positive ground/negative power" fuzz face that uses pnp rather than the more common npn transistors, so ground and power connections are reversed compared to the negative ground buzz fuss. That 100k resistor IS connected at both Q1 base and Q2 emitter, although the dot often used to show this is missing.

However, it's only the 1k gain pot and associated electrolytic cap hanging off the emitter that smallbearelec is suggesting you copy into your circuit.

[Mark Hammer]

Here's a trick that will see you in good stead well beyond this particular build.

You say you only have a 250k pot.  Fine.  Do you have resistors hanging around?  Stick a resistor of suitable value between the input jack and the input lug of the pot.

Let's say you have a 680k resistor.  When placed in series with the pot input, that combination behaves like a 930k pot (680+250) that can never be turned up more than about a quarter of the way (250k = 27% of 930k).  That will allow you to dial back the intensity in a more selective fashion, and the control won't be so twitchy.  And if you want more intense sounds, just use a toggle to bridge that added resistor such that it goes back to being a 250k pot again.

This is a simply way to create "ranges".  I won't promise you that it works in every single circumstance, but it works in enough of them to be worth knowing about and trying.

[pinkjimiphoton]

if ya wanna use an emitter resistor to vary gain, 250k is way too high. maybe with the proper darlington it would work, but you're better off with something between say, 500R (ohms) and 2k at the most. or it will just act like a switch, turning the transistor off and on.
instead, try it as a pregain control. put your input to the input of the pot, the wiper <center> to the input cap and don't even connect the ground connection. then you can vary the input gain of the fuzz.. by how hard you drive it. you can tie it to ground too, or stick say a 1 to 10k resistance between the pot and ground to set a "minimum" gain even.
may  be a bit easier than dicking around with calculations trying to get a huge pot like that to work in this circumstance.

[Isg1315122]

Lol I have lower ohm pots. The reason I said the 250k was because I thought, based on the video the guy made he used/ suggested a 1m pot. I'm thinking he had a different circuit built which he was referencing.

The lowest I have is 5k at the moment. I'm going to put a 5k resistor parallel and kick it down to 2.5k with a cap to ground and see where that gets me.

Thanks for all the input.

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