On Tue, 19 Feb 2013 21:04:17 -0800 (PST), wrote:

"Use an ordinairy stereopot of ~100k, and use 2 resistors, 80K and 10k,
in parallel to simulate the tap. That should do it. "

It absolutely will not.

That tap is for the wiper to come in between it and the bottom and recieve a modified frequency response curve at the lower end of its range. This tap goes to a resistor to ground usually, and then when the "loudness compensation" is engaged, it provides added low frewquency response, and in better amps, also far high end frequency response based on the human hearing curve ploted in detail and called the "Fletcher - Munson" curve.

With normal human hearing, lows and highs are attentuated more at lower levels, and this curve is supposed to compensate. Many people do not use the "loudness" "feature" because it is oft miscalibrated and results in too boomy a sound.

High end (pre)amplifiers often have a separate loudness control so the user can add the compensation based on what he hears as well as his taste. Some are additive and others are subtractive. The type that uses the tap on the volume pot is almost always additive.

The tap always goes to a resistor to ground, this gives the pot a slower curve anyway, but when the loudness contour is engaged a capacitor is in series between the resistor and ground providing a bass boost, generally first order, shelving at about 60 Hz but boosting all the way up to about 350 Hz. More refined circuits also use a small capacitance to the top leg of the pot (the fed end) and provide a high treble boost as well when the switch is "on". All this frequency compensation is shorted out when the "loudness" or "conour" is switched off. The amp is then supposed to provide flat frequency response to the best of its abilities.

There may not be a loudnaes or conour switch in this unit. If not, it cannot be considered a high fidelity unit, but that is true of a hell of alot of audio equipment. High fidelity does not mean that it sounds better, it means that it sounds right. Everyone prefers a certain frequency content in their music, and only purists seek that original, uncolored sound.

If you look up Fletcher Munson on wiki, I bet it can splain more pretty well.

Actually I ifnd it surprising that osmeone has never seen this kind of tap before. I have seen amps with two taps, which meant two level of equalization going through the range of the control.

I have heard of pots with two taps before but never seen one.

?-)