Re: Artie's De-Mud mod

[GuitarDoc]

Re: Artie's De-Mud mod

Artie suggested using 500k resistor and .01uf cap for a pup like a 59. What effect would it have to change the values. Specifically, for a dark sounding 9-10k pup with only two wires (the mod is in series with the hot wire), would I increase or decrease the value of the resistor or cap to get more brightness?

From what I understand, increasing the resistor value should increase the amount of treble (like using a higher value volume pot), and increasing the value of the cap from .01uf to, say, .02uf would lower the frequency of tones allowed to pass through, similar to how it works on a tone pot. Is that correct? If not, please put me straight.

Also, how important is the cap? Would just using a resistor do it?

 

[freefrog]

If you want more brightness from a series cap in parallel with a resistor, you have to increase the value of the resistor and to decrease the value of the capacitor.

The most efficient hi-pass / bass-cut action would come from a crude cap without resistor - equivalent to a cap with a resistor of infinite value in parallel with it. ;-)

Rickenbacker mounted 4.7nF series cap (same value than the input cap of a Rangemaster and ten times less than a 0.047µ tone cap). G&L did go as low as 2.2nF...

And no, a resistor alone wouldn't cut the bass. It would just tame the resonant peak then lower the output level while its resistance would increase.

HTH.

 

[GuitarDoc]

Thank you very much for that response. It's interesting that when I wrote that question I was originally going to ask you to respond, knowing that I would get a definitive answer.

 

[freefrog]

You're welcome. Being definitive wasn't my goal but if my answer has been helpful, I'm happy.

 

[Chistopher]

Consider that a bass cut cap isn't going to make the pickup brighter. It can make the treble more prominent but don't count on it. Have you tried adjusting the pickup height?

 

[freefrog]

For the record, a low value hi-pass capacitor shifts up the resonant frequency of a pickup. For example, a humbucker whose resonant peak is @ 3200hz would have it @ 4000hz with a 2.2nF series cap. So hi-pass filters actually make pickups brighter (and lowers their output level, it's not always mentioned).

It's better to avoid a too low capacitance, though ("too low" being anything under 660pF approximatively). If the corner frequency / knee frequency is too high in the spectrum, the series cap will scoop the high mids and might make the pickup paradoxically... darker.

 

[GuitarDoc]

For the record, a low value hi-pass capacitor shifts up the resonant frequency of a pickup. For example, a humbucker whose resonant peak is @ 3200hz would have it @ 4000hz with a 2.2nF series cap. So hi-pass filters actually make pickups brighter (and lowers their output level, it's not always mentioned).

It's better to avoid a too low capacitance, though ("too low" being anything under 660pF approximatively). If the corner frequency / knee frequency is too high in the spectrum, the series cap will scoop the high mids and might make the pickup paradoxically... darker.

So when you say a 2.2nf cap will raise the res. peak by several hundred hz, is that with just the cap or with the 2.2nf cap in parallel with a 500k resistor?

 

[freefrog]

So when you say a 2.2nf cap will raise the res. peak by several hundred hz, is that with just the cap or with the 2.2nf cap in parallel with a 500k resistor?

With the cap only. The resistor is there to mitigate the action of the cap, FWIW: when your signal takes two parallel ways (one through the cap, one through the resistor), the lower is the value of the resistor, the less it will resist (how surprising) and the less it will let the signal pass through the cap. A super low value resistor (1 Ohm) would make the thing work as if the cap wasn't there...

That's the idea behind the hi-pass/bass-cut pot in the G&L PTB system:

https://tonefiend.com/wp-content/uploads/GL-Tone-Circuit.jpeg

 

[GuitarDoc]

:smack: Of course.


Thanks again. :yourock:

 

[Artie]

freefrog got my back . . . but the de-mud mod is basically bass-cut. I'm not sure how to increase treble. But I think freefrog covered that.

Thanks man.

 

[freefrog]

Artie, the de-mud as you've designed it IS certainly a bass-cut/hi-pass filter.

My statement about such circuits shifting up resonant frequencies was about series caps with a lower value than in your design.

Also: hope I've not been unpolite by replying to Doc. I've seen the question and spontaneously tried to help, saying to myself that you had other things to deal with... glad to see you back onboard, as it presupposes life goes on. Hope you and your family get well.


As a footnote, let's share a 5spice sim of how a series cap affects the response of a humbucker in the case of your design (in red) then with a way lower value capacitor (in black). The pickup model that I use is more complex than the usual voltage source + LRC filter, since it takes in account inductance, resistance and parasitic capacitance (partly due to 4-conductors cable) for each coil. Hence the "plateau" in the resonance, starting at a lower frequency than where the vertical line is placed.

 

[GuitarDoc]

Actually, thanks to both of you. Artie for first putting this idea into my head, and freefrog for elaborating on another way to do it.

You both are great.

 

[jeremy]

indeed they are!