by GP49 21st February 2012, 11:57 pm
To remove the loudness contour circuitry, remove its connection to the volume control.
I'd do this along with replacing the stock volume control, which does not sound all that good to begin with
and which often has balance tracking problems, with a switched type or a higher-quality dual potentiometer.
When hooking up the new control, leave out the connection to the loudness contour circuitry (it might not
HAVE such a point for connection anyway).
As to the filter, remove the 1400pf and .004µF capacitors from the PC-5 board, and replace the 18KΩ
resistor with a straight wire.
When the filter and loudness circuits are removed, you can use the switches for other purposes. For instance,
if you want to remove the mono/stereo/blend switch from the circuit and thus eliminate some more contacts from
the signal path, you can use one of the switches to blend the two channels for MONO use, such as when listening
to mono records or noisy FM broadcasts; when switched to STEREO the switch contacts are totally out-of-circuit.