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I decided to rebuild the smaller 2ch mixer which was built from leftover parts and then disassembled to build the xover.
First I built a 19" enclosure.. the bottom panel is hardboard, sides are 18mm thick pine and the top panel is plywood. The depth at the back is 60mm and 40mm at the front so it's angled, the panel height is 300mm which is 6-7RU.
The transformer/power supply is from an old tape deck and has 630mA fuses, it provides 30VDC to the preamp and 9VDC to the power on LED. The AC input operating voltage is 230V/50Hz.
The channel configuration consists of a 6,3mm mono input channel and two RCA stereo channels which do not provide any amplification, ie. they're passive. They're summed into a bus that is preamplified and further fed to the master outputs.
The summing bus I built from a 12-pin screw terminal that has 4 left, 4 right and 4 ground parallel into L/R/gnd terminals so in other words the ground signals are summed.
The mono channel is split into L/R via 1kOhm resistors to provide stereo separation between channels. The channel strips use 100kOhm potentiometers for volume control (the mono channel is a single gang, the stereo channels are dual log)
It also has 2-track in/out, with the input connected to the summing bus and the output taken from the master preamplifier prior the master vol. The master outs are 6,3mm unbalanced via a 100kOhm stereo log, the preamp has trimmers and is wired to the summing bus using a PCB/bus connector (so it's easier to service)
It's missing knobs atm, I'm also looking to add a headphone monitor section with PFL/master cue (which requires trim pots, a 2-pole 4-pos rotary switch, level pot and an output jack, possibly a headphone amp too), per-channel HPF/EQ and -20dB pad switch as well as balance controls.
Here's a pic of the internals with the PSU and summing bus/master section visible :
..and a pic of the front panel in place :
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