The manual writes that they spent extra care on the smooth and balanced tone control. Well… They did not… First of all, it is a source of noise (~4dB) . Linearity and phase are really bad. The easiest is to separate C15 and C14 and also the C21 from the tone control and connect the C15 to C21 directly, skipping the bad sounding tone control.

I personally decided to keep the tone control with reconnecting the Mono/Stereo buttons (who uses Mono anyway? If you have a mono source connect it on both inputs…) So if I press in Stereo, then it is directly connected, while pushing mono reenables the tone control circuit. There is a penalty, that with some decibels the tone controlled sound has less volume, but you can increase this back with the volume control. And the path is the shortest possible.

Below are pictures of what to do. As visible on schematic when the stereo is pushed in, it disconnects the tone control on both ends and creates a shortcut between pre-pre amp and the pre-amp. Now the sound quality increased again a big step ahead.

You may remove the DIN connectors output cabling which is some source of the noise. It connects to the balance potentiometer.

This is the best time to fix the input selector, see below

Input selector fix

-Input selector switches the negative feedbacks R42, R142, on SK13 8-9, 11-12. You will not need these. Cut out cables, replace R16 with an fix 20K (carbon) resistor, through out R42, C33

-Not used inputs are shortened to GND… This was okay in old days (sources with high impedance), but nowdays you need to modify this if you do not wish short circuit on your sources if you do not listen them. As on the pictures, cut out SK11, SK12, SK13 GND line. Reconstruct GND from the preamplifier tube (B3, B103) to the input selector/ new tone control switch. Do not mix the 2 GND if you wish to keep humm noise low! Neither at the input (or there just use one of the GND). So left grouind, right ground is connected right before it enters tube. Hope you see this separation at the tone control to get the idea behind. You may use the SK13 unused 7-12 pins to make the tuner input GND also switched.

-Fix left and right if you are already here. See schematic for the bogus left and right color mix and also the fact the phono tubes operate mixed. Also DIN tape in is mostly mixed up.

All activity in pictures.

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