The Studiomaster mixers are excellent and far better than the prices indicate. The inputs are discrete designed with a set of high gain and low noise transistors forming the balanced input gain, later fed to an op-amp in balanced mode, from here and on the Eq section with fixed treble, mid and bass quasi parametric sweep by gyrators and to the sends with furter amplification after output faders. Early 70-models had one or two effect sends and a monitor send depending on model.
The later model Trilogy has 6 cue sends, 2 pre fader, 2 sets of 2 switchable pre/post fader and comprehensive routing for signals return for effects. Furtermore routing facilities with 4 subgroups. It will be too much to mention all the features ! This is really a fine mixer !
The mother company was RSD : Recording Studio Design, their “luxus” brand was Studiomaster with more facilities. It was originally designed and produced in England and had during some years an American department. They still manufacture everything needed for professional sound equipment : analog and digital mixers, a series of amplifiers and speakers all under the Studiomaster name under the “umbrella” of Soundking.
Should anyone have troubles about the RSD or Studiomaster mixers I might help with technical advice and schematics too.
I have used RSD and Studiomasters for many years and always maintained them myself. I also had RSD electronic crossover, but later on I designed my own 4 ch in stereo for PA use.
For exchange of hints and schematics I prefer mail correspondancy.