The Vox Tone Stack (Modified)

Posted: June 17, 2014 in Effects, Tube Amps
Tags: , , , , ,

 

This graph would not be possible without Duncan’s TSC  @ http://www.duncanamps.com/tsc/

The above picture is a graph for a modified version of the tone control from early Vox amplifiers.  As far as I can tell, the Vox Tone Control is a variation of the FMV tone stack used by Fender, Marshall, Mesa Boogie and countless others.  This circuit has no middle control.  Putting the bass and treble controls on 10 created a gigantic mid-scoop on the original settings.  This tone stack, like many others, has a very present low end.  I made adjustments for it to be used in a pedal.

My modifications were to make the potentiometers smaller and to adjust the capacitors for the slope of each control.  The bass frequencies are full, the middle isn’t completely scooped out, and the treble doesn’t get too harsh.

R2 represents what would be the setting on a mid control.  10k is slightly lower than the middle setting on a 25k control.  c2 22n sets the curve for the bass.  A 47n will make the bass fatter and taller, but I found it was too much for my tastes.  Frequencies below 100 Hz do not need to be as present on a guitar.  A bass guitar might find more use for it.  In any case, it leaves room for the bass control to add in the lower frequencies.

Because of the more gentle slope from 1 kHz to 10kHz, the treble control doesn’t sound harsh until it’s cranked.  It was important that I make the treble control with a wide range, but a little less rasp when a fuzz or high gain distortion is used.  This was accomplished.  The gentle curve from 1kHz to 5kHz makes it sound fairly natural, or at least not boosted to hell.

For the old school metal fans, the controls still make a mid-scoop when completely cranked and will give a Metallica friendly sound to distortion.

 

 

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