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Hi,
I recently finished my P.U.F.F. circuit and first it worked.
To make the bias settings as explained in the manual, i opened the case again and set it on (negative) 4,7V on the collector of Q2. It was difficult because between the max of 6,6V and 1V it was only a tiny little way to turn. The rest was from 1V to nearly 0V. But after a few attempts, it was on 4,7V.
But now, no more guitar signal gets through when i turn it on. I cannot say that i damaged something, the cables seem to be ok. When i touch the solder pad OUT, i can hear it in my amp.
Don’t know what happened. Maybe somehow i damaged the transistors. Could someone please explain or show me where i can find Informations on how to check my transistors and/or how to go through the parts to find the problem?
Thanks,
Henrik
Post some pictures Henrik an image of the component side of the board so we can trace all wiring to switches, jacks etc it sounds like a loose wire somewhere if it was working before
Hi,
i found the problem when i had again time to check the effect. It was simply somewhere a connection to the enclosure.
But there is another question now:
In the P.U.F.F. BuilDocument (https://guitarpcb.com/product/p-u-f-f-pumpd-up-fuzz-face-classic-fuzz-face-with-modern-features-free-charge-pump/) i have to bias the Q2 collector to (negative) 4.5-4.8V or half of the input voltage. Are these numbers really correct? I have problems to do so with the trimmer and in the forum of musikding, where i ordered the P.U.F.F. and asked at first, i got the answer that they doubt this could be correct.
Can someone tell me that the build document is right or wrong in this point?
Thank you,
Henrik
The correct voltages for biasing Q2 collector are -4.5 to -5.5v
I personally bias by ear to where I think it sounds good and it doesn’t always read within that range, it can vary
Its worth noting that hFE, leakage and temperature all affect germanium transistors, how are you taking your readings
I do the same as Billy, but I have the advantage of having an external bias knob on my Ge Fuzz Face. I decided after building the pedal to replace the on-board trimmer with the same value pot mounted on the outside of the enclosure. It allows me to change the characteristics of the fuzz slightly so I can dial it in to my liking. My FF is an NPN version with AC128 transistors and therefore not a GuitarPCB pumped up-version, but yours should behave similarly adjusting the trimmer.
FWIW, I place an external bias control on all my Ge transistor builds (except my most recent one because I used Small Bear’s recommended resistor values for the transistor set I purchased from them) because it allows slight tweaking of the sonic characteristics of the pedal.
Henrik – In my experience, the suggested bias values provided in most build documents are merely reference points that “SHOULD” get a circuit in the ballpark. I’ve found that bias value references in build docs are just the starting point. More often than not I find that my ears do a better job of setting up the bias value than my meter. Still, I follow the guides and start where suggested. From there I adjust to personal taste.
The voltages are correct. Read the Technology of the Fuzz Face article by R.G. Keen.
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