P-bass pickup hiss

[pdf64]

... the cause being a very high resonant peak as a result of the unusual pickup wind. If so then the problem might also have been reduced somewhat by changing the volume pot and shifting the peak to a different, and hopefully less audibly hissy frequency. Perhaps a higher value pot, which would also be brighter, could have shifted a resonant peak into a less offensive range and then a cap to shunt any remaining hiss could have preserved the most top end and still mitigated the hiss.?. Or, conversely, a lower value pot and a lower value capacitor.?. The basic idea being to shift the pickups frequency response in the hope of making the hiss less audible and then do less overall shunting.

Yes, my thought is that as filter Q increases so does hiss (similar to hearing the sea - hiss - when we put a seashell to our ear); so it may be that the particular characteristics of this hot PU have happened to create a very high Q resonant peak.
A good way to damp that Q down is to increase the resistive loading on the filter (PU), which is what turning the tone down a little does. To hardwire that in, a lower value volume or tone pot could be used.
A 100k vol pot would have the advantage of a more even frequency response across its range, when loaded with a regular degree of cable capacitence.

[Mick Bailey]

Seems like we have a consensus here that a pot change would be the answer. On the one hand I'm hoping not to see this bass again, on the other I'd be keen to carry out the ideas to see what the result would be. I'll find early next week whether It's good enough as it is right now. I think so, but it's got to stand up to a live environment.

[Leo_Gnardo]

A good way to damp that Q down is to increase the resistive loading on the filter (PU), which is what turning the tone down a little does. To hardwire that in, a lower value volume or tone pot could be used.
A 100k vol pot would have the advantage of a more even frequency response across its range, when loaded with a regular degree of cable capacitence.

There's also the matter of which way is the volume pot wired. The modern way, it's used as an ordinary pot, with signal across it and wiper to the output jack. The ol' fashioned way, hot was wired to the wiper, and the end of the track was connected to the output jack. I'm betting this bass is wired the modern way, it could be swapped the other way round to see whether it might work better that way, just have to swap 2 wires & listen.

[big_teee]

I thought in your test, you only had the pickup wired direct to the amp?
Was there also a pot wired in?
T

[Mick Bailey]

No pot on my 'foil-wrapped' test.

I didn't swap pot wires - just checked that the wiper connected to the output. Have to say, I've never come across an P-bass wired from the factory with the pickup connected to wiper. Even the early single pickup instruments I've seen (the ones with the 15K resistor) effectively connect the pickup to outer lug. I guess I don't get enough range of early basses to have spotted that configuration. It strikes me as being noisy in the other direction - when the pot is zeroed you have a 250k resistance that floats the output and picks up noise.

[Mick Bailey]

The owner sent me a follow-up message;

"The bass is whisper quiet. Not a problem anywhere at all. Sounds great again, works well with all my pedals again. Thank you."

I'd say that's a shared thanks to everyone here who's contributed ideas and suggestions.