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I have a Pignose 7-100, which I think is from about the mid 90's, that I bought with a broken input jack. I've replaced the jack and it's working now, but there is an odd sounding distortion which I think can't be right. I can hear clean-ish signal, but there's a layer of heavy, nasty distortion behind everything, regardless of volume settings on the amp or my guitar. This sounds like a silly question, but do they always sound like this, or is something amiss? I'm sure I remember my friends Pignose sounding semi clean at lower volumes. It's not due to tired batteries, as it sounds the same running on a 9 volt adaptor. Should I be looking at trying a different speaker, or are there other known issues that happen with these? I'm not sure if there are different revisions of the 7-100. The circuit looks much like the schematics I've seen, transistor based with interstage and output transformers.
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Update; I've just tried running the preamp out into another amp, and the unpleasant distortion is still there. This suggests to me that it is not the speaker. I'll look at the transistors next... -
Look at the circuit. Is there any bias between the push and pull sides? (Are the opposing bases just wired together?) I could be wrong, but in my mind is a picture of no bias, so the crossover distortion might be what you hear.Education is what you're left with after you have forgotten what you have learned.Comment
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The bases are connected together, so does that mean that crossover distortion is just the nature of the beast? The distortion does sound like it could be crossover distortion, as it appears as a constant layer under everything regardless of level, rather than just on louder parts.Comment
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Louder signals tend to obscure crossover distortion, since the louder the signal the smaller the portion of it is crossover notch. Like a slightly rubbing voice coil, it is most noticed when not played loud, or when notes trail off.
If the opposing bases are wired together, then there is no bias, and there will be crossover distortion.
OK, I just scoured up a few diagrams for that 7-100 series. All of them have a driver transformer, so if you just measured for continuity, you were going through a transformer winding. Unless there is an even newer version - quite possible. The transformer circuit provides some bias, but I woldn;t count on it.Education is what you're left with after you have forgotten what you have learned.Comment
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Thanks for your help.
OK, l've checked the pinout of the transistors and the bases aren't wired together - my mistake. The bases of the output transistors go to either end of the interstage transformer secondary. One base has 0.7v on it and the other one pretty much 0v. This can't be right can it? I've also checked a few youtube videos demonstrating the Pignose, and mine is definitely not sounding right!
The schematic appears to be this one:Comment
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Clearly the opposing bases must be at the same DC level. Assuming you had continuity between the bases - did you? - then the transformer is not open. Open transformer would have been my first thought at zero on the base. Recheck that. That 0.7v would be established by that diode across the 220 ohm resistor. since the emitters are common and only 3 ohms above ground, a shorted output transistor could ground off the base. Check the outputs.Education is what you're left with after you have forgotten what you have learned.Comment
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I have a Pignose 7-100 that is about 8 years old and has stopped working. Do you have a clean copy of the schematic you might be able to send me? ThanksOriginally posted by Martin Beer View PostComment
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