Tone caps for EMG

[Tinderwet]

I have a pair of EMG HA pickups in my Ibanez. Since I rarely if ever used the tone knob, and there's no room to install any of the active tone systems in the guitar, I was wondering if I could just change the stock .1u capacitor to something smaller for a certain effect. What I would like to achieve is a roll off at around 2 - 2.5kHz, just below the resonance of the pickup (listed at 3.75kHz), so I could have another usable tone at hand. Is there any way to calculate this? Also, I guess in the case of EMGs, the tone circuit doesn't form a resonant peak when rolled off fully, because it doesn't interact with the inductance of the pickup, so it's simply a first order low pass filter. Am I right about that?

Thanks!

[Mick Bailey]

The EMG pickup 'sees' its own internal preamp (just a single op-amp configured as a differential amplifier) and the tone/volume controls are buffered from the pickup inductance and self-capacitance. The resonant frequency isn't therefore affected in the same way as a passive pickup by tone control loading or cable capacitance, so isn't useful in calculating tone control values.

The way I would approach this is to use a couple of short clip-leads and try different caps until I got the one I liked best. You could model the tone stack and output impedance of the amp (10k ohm) in PSpice and do an AC sweep analysis to visualise what's happening, but in the end it comes down to your hearing and perception of the sound. I've found that changes to EMG caps need to be fairly drastic to make meaningful/useful differences to tone.

[Tinderwet]

Thank you Mick. I guess I can't get away without trying a couple of caps (just to return to the original value and screw the whole thing, lol).