Treble dump switch clarification

[brak]

I tried searching here but couldn't find the exact answer I'm looking for, so sorry if this has been discussed and definitively answered.

If I were to wire a switch with a cap to ground to dump some treble from the signal - either as an alternative to a standard tone or in addition to - would I need to use a resistor in series in addition to the cap or not? 
The diagrams and/or discussions around adding the resistor seem to imply that you must do this to simulate the relationship between the resistance of the pot and cap of a standard tone control (like this cap/resistor relationship is what makes it actually trim treble and it won't do that without the resistor??). But I've seen plenty of diagrams that show a simple cap to ground without the series resistor.

Example: spdt with one side doing nothing and the other side connecting a .01µf cap to ground vs same setup except adding a 300k resistor in series between the cap and the ground.

[newey]

No resistor would be needed to do this. Ever play a Fender Esquire? It uses just a cap in one position of the 3-way switch, no resistor. I have a guitar wired this way, using a .033µf cap for what Fender used to describe as a "fixed Bassy sound". It's basically like turning the tone control to "0". Using a smaller cap value, as you suggest, will cut less of the high end. .01µf is what folks often use for the Clapton "woman tone".

A cap only shunts a portion of the signal (in your example, the highs) to ground. A resistor will reduce the output across all frequencies uniformly. Usually, a cap and resistor combo like you desrcibe is used when one wants to equalize the output of 2 disparate coils, whether with a cap or not.

[reTrEaD]

May 9, 2024 7:52:19 GMT -5 brak said:

If I were to wire a switch with a cap to ground to dump some treble from the signal - either as an alternative to a standard tone or in addition to - would I need to use a resistor in series in addition to the cap or not?

The result of having a small resistor in series will be apparent. Whether or not you 'need' that resistor, depends on what you want to accomplish.

With a fairly small cap like the 10nF you mentioned, this will shift the resonant peak to a lower frequency but that peak will still be prominent. The treble will roll off quickly after the peak. A 300k resistor in series with that, will not affect the tone very much. A slight softening of the peak and slight roll off after the peak, compared to not having the cap and resistor present at all.

You might want to use a rather small resistor (maybe 1k ~ 3.3k) in series with the cap. That will flatten the peak and provide a substantial roll off at higher frequencies.