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Issues with a distortion pedal

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tntero

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Hi there, some time ago i started a quite ambitious project:

To build a fuzz factory inside my guitar.

so first step, before cutting the guitar, build and test the clone, right?

so, i did that, and what i got was a distortion, with very little volume, all knobs seem to do nothing, the only knob that has any effect on the sound is the drive knob.

here's the schematic and the pcb layout:

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so, what i've been thinking:

i've not found some parts, and so i had to replace them with similar parts.
i have not used 5K Linear Pots, instead i had to used 4,7K pots.

I did not use the AC 128 Ge Transistors, I used Also Ge PNP AC 188K transistors, which seem to have a way higher gain (AC128: 55-175 ; AC 188K: 100-500).
I think the problem is the gain, but with higher gain shouldnt i get higher volume instead of lower volume?

I'm not an expert on electronics, but i know enough, so use all the technical terms you need to.

Thanks in advance
Antero Duarte
 
The voltage gain of a transistor is fixed to the circuit outside it. But the AC188 has a higher typical DC current gain so in the circuit designed for AC128 transistors it is probably biased wrong and is saturated. The collector DC voltage will show if it is saturated.
Did you measure the DC current gain?
Where did you find those very old and very poor quality germanium transistors?
 
a friend sold them to me, he gathers parts wherever xD i dont even ask... so you think its the transistors? i think that too, would the american equivalents of the ac 128 do it? thats the closest i can get to the real thing.
cant remember their part number, sorry.

EDIT: i posted a similar thread on a guitar forum, it is way more detailed by now, with pictures and all that, you can check it here if you want to : **broken link removed**
 
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a friend sold them to me, he gathers parts wherever xD i dont even ask... so you think its the transistors? i think that too, would the american equivalents of the ac 128 do it?
You used the wrong transistors so the circuit must be re-designed for the transistors you used. Then its sound will probably be different.
The transistors are almost 50 years old and had poor performance so there are no equivalents today.
 
Are they 4.7k pots of 47 k pots?

The most likely cause of very lwo sound levels is that you have wired something wrong, and/or probably connected the transistors the wrong way around.

Both AC128 and AC188 come in two different package configurations, called 2a and 3a;
2 = metal can, pins numbered from the tag across as 123 (looking from the bottom with the tag at the left (pin1)).
3 = square package, pins numbered 123 from left to right, looking at the bottom of the package with the 3 pins at the top.
a = 123 = EBC

So if you hold your transistors looking at the bottom of them, with the 3 pins at the TOP, the pins are EBC. Hoep that helps.
 
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