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dubdub 26th October 2008 01:39 PM

Potentiometer with bass boost pin for Simple SE?

I have purchased 50K Potentiometer for my Tubelab Simple SE with 4-legged connections (IN) (OUT) (GROUND) plus the fourth leg which can be used for 'bass boost'. Has anyone come across these before? I was wondering if it would be possible to hook up the 4th pin to a switch where I could flick for a bass boost on/off. Being an Ebay jobbie it probably wont sound too good but wanted to experiment anyway.

can be found here:

Any Advice would be appreciated!


Ty_Bower 26th October 2008 02:25 PM


One function of the fourth terminal on the volume pots was a tap for the loudness switch. The tap was tied to ground through a capacitor and resistor. The loudness switch would short across the capacitor. I would guess that the circuit also gave the pot a response similar to an audio taper pot. Probably a cheap way to do two things at once.

dubdub 26th October 2008 04:51 PM


Originally posted by Ty_Bower

Thanks Ty! do you have any idea of how to connect the cap and resistor to a flick switch and what value? any help/advice is appricated :)

Ty_Bower 26th October 2008 07:02 PM

There's an idea here:

You could probably dig up a bunch more by searching "loudness tap circuit" or "loudness tap schematic".

kevinkr 27th October 2008 03:57 AM

Usually there will be a series resistor and cap. Normally to defeat the loudness you short the capacitor - this prevents significant changes in signal levels above the corner frequency of the series rc network. (RC network with free end of resistor to tap, free end of cap to ground.)

The resistor in the series RC network will usually be some fraction of the resistance from the loudness tap to ground.. Near equal value provides about 6dB of boost, and something like half about 10dB. (Caveat math probably way off, but you get the point.) Cap value can be selected based on the desired corner frequency.. Something on the order of 50 - 80Hz probably would not be unusual depending on the application. You can experiment to find the best combination(s) for your speakers, listening preferences, music, etc.. You can also make the corner frequency switchable by having several switch selected capacitors - this could be a rotary switch that also provides the loudness defeat function. (Since this is a first order network something like an octave apart would be a starting point.) You can reasonably iterate until you find the appropriate values..

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