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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!
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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
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.
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
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
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
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!
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