Old guitar wiring question

[Lino22]

Guys, on the picture below, there is a diagram of full volume and partial volume on a 50's guitar wiring.

People say it keeps trebles better, when the volume is turned down. The reason can be the series resistance (created by a divider on the volume knob) adds to the input impedance seen by the pickup, but then again the series resistance also adds to the low pass filter ... is there an easy way to see why the trebles are kept?

[FiveseveN]

People say

People also say that audiophile USB cables make their files sound better. Make sure you're starting with a true premise first.

[antonis]

I presume you do know the output impedance of a pot (100k say) set at 50% rotation, don't you..??

[Lino22]

I presume you do know the output impedance of a pot (100k say) set at 50% rotation, don't you..??

since the pickup is basically a wire ... 25k? 50k||50k

[Fancy Lime]

I presume you do know the output impedance of a pot (100k say) set at 50% rotation, don't you..??

since the pickup is basically a wire ... 25k? 50k||50k

No, a pickup is not at all a wire but an inductor and that is the reason why the 50s wiring can sound less dull for *some* combinations of pickup inductance, Volume pot resistance, and Tone cap, as well as input impedance of what follows.

The pickup inductance, volume pot resistance, and tone cap form an LRC low pass filter, together with the input impedance of the amp or first pedal. With the Vol pot maxed, all of the resistance of the pot goes to ground, parallel with the input impedance of the amp/pedal. The only series resistance in the audio path before the amp/pedal input is the resistance of the pickup (typically a few kilo Ohms, so much lower than the pot value). When you turn the Vol down, you get much more series resistance and less resistance to ground, which affects the Q of the LRC lowpass. I suppose that if the involved values have the right ratio, this may cause a higher Q and thus brighter sound at lower volume settings, although I would normally expect the opposite and I don't have the time right now to run a bunch of test calculations.

HTH,
Andy

[Fancy Lime]

In case you don't primarily want to understand 50s wiring as a matter of theoretical interest, but want to keep your treble while rolling down the volume, there is a much more effective way to do that: Treble Bleed circuits. It's essentially a Bright cap on the guitar volume plus or minus a resistor to fine tune the brightness effect. I do this to all my passive basses and guitars, sometimes with the option to switch between different caps. I have one, where the bright cap and the tone cap are being switched by the pickup selector to always get the right cap for the changing inductance and resistance coming from the pickups. This makes quite a difference because two identical pickups in series have 4 times the induxtance and resistans as the same two in parallel. But it is a bit elaborate and there may be a reason why I have never heard anyone else do that.

Heres a nice comparison between trable bleed variants:
https://youtu.be/uAckphHWmAU?feature=shared

And I also prefer the series or series-parallel option. The latter can be used effectively to fine tune the top end of the Vol taper for use with low input impedance fuzzes like the Fuzz Face and give you more control near the maximum setting.

[Lino22]

Thanks Andy. Yes, i was clearly wrong by saying it was just a wire, just a brain fart, it is an AC analysis, so it is a coil with inductance.

[Fancy Lime]

Thanks Andy. Yes, i was clearly wrong by saying it was just a wire, just a brain fart, it is an AC analysis, so it is a coil with inductance.

No worries. Just as long as you don't have any brain farts while handling the Demon Core 

[Lino22]

Thanks Andy. Yes, i was clearly wrong by saying it was just a wire, just a brain fart, it is an AC analysis, so it is a coil with inductance.

No worries. Just as long as you don't have any brain farts while handling the Demon Core 

 

[amptramp]

I would have thought that the tone control should be from the top of the volume control rather than the slider.  That would give you less variation in source impedance and would have resulted in more consistent operation of the tone control.

[Fancy Lime]

I would have thought that the tone control should be from the top of the volume control rather than the slider.  That would give you less variation in source impedance and would have resulted in more consistent operation of the tone control.

Yes, that would be the "normal wiring" nowadays.
Look ye here:
https://www.fralinpickups.com/2020/03/01/50s-wiring-vs-modern-wiring/
I am only linking this for the wiring diagrams and nomenclature. I am not convinced that their tonal analysis is entirely correct.