Brittle tone from JB when volume pot rolled back - need opposite of treble bleed cap

[freefrog]

Thanks, freefrog. As usual, you share a wealth of information.

Given the stray capacitance issue on 4-wire humbuckers, I guess it would make sense to cut the leads as short as possible.
I had been leaving them long, in case of future swapping or sale.

You"re welcome.

My merit is relative: without saying it (and maybe without conscientizing it), a famous US winder has actually based one of its well-known tricks on the use of assymetrical capacitive values. ;-)

And I wouldn't be able to share this kind of info if I hadn't helped a winder to correct one of his designs plagued by unrequested parasitic capacitance. So I thank him as you thank me. :-)


That said: when it comes to humbuckers coils wound with a same wire gauge, the problem is that stray capacitance is narrowly dependant on the physical reality of each pickup and wiring.

In many cases, one coil compensates the other and the overall frequency response appears as flat, with minor deviations. That's why some people won't never notice any issue with 4 conductors wiring.

Furthermore, even the presence of covers, wax potting, shielding foils and so on can change the overall capacitive load AND "capacitive balance" between coils.

Reason why, to obtain the same correction on two pickups of a same model, it can be necessary to use capacitors of different values... A bit like with the resistors used to "tune" Duncan stacks.

Shortening 4 conductors cables can certainly help by shifting up the "cross frequency" between coils but it doesn't prevent the potential issue created by stray capacitance, for two reasons and/or in two situations:

1)when wound with more turns of thinner wire, high DCR pickups have inherently more capacitive coils. It shifts down their main resonant peak AND the "crossover frequency" that most normal humbuckers keep out of perception. It's not always "correctible" by cutting shorter the 4 cond. cable;

2) what makes stray capacitance annoying or not because of secondary peaks in the audio range is the capacitive proportion between coils: a difference of 10pF only can solve the problem or make it worse (!).
BTW and FWIW, that's what I tried to share there: https://music-electronics-forum.com/...626#post964626

That's why I've recommended to try capacitors from 10pF to 220pF with the smallest increments possible between capacitive values.

That's also why I've not claimed it's a miraculous solution. Ideally, one would need to measure the resonant peak of a pickup by exciting it electrically to check if a capacitive correction is efficient or not...

[freefrog]

Thanks Freefrog, I'm going to check that out. One thing I've wondered about is why this does not happen with pups of lower total coil resistance. With 8-9k PAFs I've had to use treble bleed caps to retain treble when turning down the guitar volume. I suppose that somewhere around 12k a perfect balance might be achieved. I know a 13kish super distortion I have sounds quite balanced when rolled down. (500k Bournes)

Low resistance pickups are not prone to develop the problem that I've tried to explain because, hosting less wire, they are inherently less capacitive than hot humbuckers.

That what the post 18 shows in my topic on the music electronics forum.

A DiMarzio Super Dist exhibits actually a noticeable stray capacitance BUT each of its coils compensates the other because they are symetrical (in DCR and by hosting identical hex screw poles).

As I said in the previous answer, IF a pickup is brittle sounding because of a secondary peak due to stray capacitance, it's due to the proportion between capacitive values of coils + their wires. And this proportion is potentially different for each pickup in each guitar. Even disconnecting the bare wire or using more or less solder changes that...

Hence the random nature of the issue and my advices: a 47pF to ground at the junction between white and red wires might solve the problem while a 68pF makes it worse... or conversely. Like reversing the magnet AND wiring of a high gain pickup might tame the issue... or create it.

That said, I don't know if my hypothesis is correct in your case (and I can't check it since your pickup and my lab gear are probably far from each others: I live in Europe).

But in my mind, there's not hundreds of possible explanations for what you experiment.

BTW, what DCR do you read on YOUR SH4? Feel free to mention the resistance of each coil, it might help.

[zionstrat]

I love Freefrog!!!!
Every time I learn something.