In the mid to late 70's, there was very little in the way of afforable mixing desks so I thought I would turn my two interests, electronics and recording to producing a good quality, low noise desk.
The design of each channel consists of:
Mic/Line-In - Balanced/non-balanced mic with variable 40db gain, line-in 1Vpp, both with low noise filter
Three band equaliser
Pan signal anywhere within a stereo image
Mixed Fold Back output
Mixed Echo Send output
Channel level slider
Capability to break into channel after the mic/line-in and the equaliser
Left and Right channel overall gain sliders
Monitor Left and Right channel overall gain sliders
1 Khz oscillator (sine/square/triangle), switchable to master or ES/FB outputs
PPM meters for each channel
I built each channels' electronics on a single PCB with additional boards for the mixers and PPM meters. The case was custom made from aluminium and plywood with the facing painted, lettered and varnished.
At the end of 2016 after finishing the Syntom/Symbal drum effects I needed additional mixer inputs so 35-40 years after building the mixer I built a 10 channel extension. I simplified the extension by excluding the equaliser, Mic input and no break in points.
The set of diagrams:
Sheet 1, Maplins 50W Power amplifier - not part of the mixer
Sheet 2, Mixer and Power Amplifier power supply - not built into the mixer
Sheet 3, Single mixer channel
Sheet 4, A, B, ES, FB mixers with PPM meters