How to remove audio balance control from this schema

Question

The part of the schema I need to understand is this:

^{simulate this circuit – Schematic created using CircuitLab}

It is part of the schematic of a stereo audio amplifier. Being the two channels perfectly the same, the schematic only represents the left channel. I need to understand how the Balance part works. The "To right channel" will be connected to the Right channel circuit exactly like the "Left" part? With 3.5k Ohm Resistor and all? I have a broken exemplar of this amplifier I would like to repair. The Balance potentiometer is completely destroyed, and I can't buy a replacement, because the amplifier is very old and some spare parts can't be found on the market anymore. So I would like to remove R3 or replace it with two 50K Ohm resistor. Which way would you suggest?

Answer 1

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. More complete circuit of stereo volume and balance control.

The balance circuit works by partially shorting the top of R1 and R3 to ground. For this to work there must be some source resistance from each of the pre-amplifiers feeding R1 and R3 - otherwise the preamplifiers would maintain the volume level despite the increased load of R2 to ground (fully left) or R4 to ground (fully right).

When the balance control is adjusted one channel's volume will decrease while the other increases. Thus the overall volume is maintained while the balance is changed.

If the balance potentiometer is removed there should be an increase in volume from both channels. This should not present a problem.

If the original balanced volume level is to be maintained then a pair of 50 kΩ resistors to replace the pot would be perfect. 47 kΩ is the nearest standard value and you won't hear the difference.

Answer 2

Removing the broken balance pot should work, however this will leave a hole in the front panel.

So, simply disconnecting it internally, by removing R2, might be a better solution.

Answer 3

Is the balance pot really so peculiar that you can't fit another one?

After all it is, apparently, connected to a low power circuit after a pre-amp, so it shouldn't be neither an high power one nor some kind of "low noise" contraption.

A search on, say, digikey for an high-quality 100k pot should give you plenty of results from which you could choose one that fits mechanically.

Anyway, if you posted some detailed images of the pot we could give you better hints for its substitution.