Pumped up tonebender v4 voltages (solved)

[Anonymous]

I have done a quick search for the voltages for the PUTB, but cannot find any. Does anyone know the expected voltages for this circuit?

I think I have a noisy charge pump, but I want to make sure that my issue is not related to the transistors.

Thanks!
Æ

[Anonymous]

I did further testing today, but I think I may have blown two transistors.  I could use some confirmation.  The sound is also not ideal.  The fuzz is sputtering and slightly lower volume.  Below are the voltages that I have.  The germanium transistors were hand picked by guitarpcb.

IC  1: 8.66     2:  4.59     3:  0     4:  -3.97    5: -8.51    6: 2.53     7:  1.43     8:  8.66

Q1  B:  -0.01     C: -8.43     E:  0

Q2  B:  -0.16     C: -8.43     E: 0

Q3  B:  -5.04     C: -0.44     E: -0.32

 

[Barry]

If it is a high pitched whine it is your charge pump.

Make sure it is a 7660S and make sure it is genuine.

Anything less is a guaranteed whine.

[Billy]

Your transistors need to be biased

You can either do it by ear or using your meter

Set the trimmer so you get around -7v on Q3 collector as a starting point then adjust by ear to where it sounds best to you

Biasing voltage will vary depending on transistor type and hFE / leakage anything from – 4.5 to over – 8v on Q3 collector

If you’ve got one of Barry’s matched sets you’re good to go obviously make sure you put the correct hFE transistor in the correct Q spot

When turning the trimmer you will hear a slight increase in volume that’s normally around the sweet spot I set mine round about there but as I say set it to whatever sounds best to you

I think you may have Q3 collector and base mixed up

Post some pictures of your pcb so we can clearly see all components  some of your transistor voltages look a bit off

Spluttery fuzz usually but not always means mis biased transistors

[Anonymous]

Great help. Thanks. I did notice a typo from my voltages. Below is the correct values for Q 2

Q2  B:  -0.16     C: -0.44    E: 0

I will double check Q3 leads. Based on the pin out that I found, it was E B C. It was a 2N1309. If I am wrong, let me know. Thanks again

[Billy]

Your 2N1309 should have a metal tag at the emitter pin what is it’s hFE

Did you measure each resistor before installing

Is your trimmer 203 code 20K

Was it a kit or did you source parts yourself

 

[Anonymous]

I think I have got it fixed! Thanks for all with the help. The issues were as follows- Attack potentiometer was faulty and Q 3 was poorly seated in the socket. I also rebiased it with the trimmer and found the best sound with Q3 C near -7V.

Thanks for all the help!

[Author]

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