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At press time, this was the only known OMEC Digital amplifier in existence. Features include, (left to right): 1) a socket for a remote-control unit (far right) with channel-select footswitches and effects in/out sockets, 2) a switching-mode button, 3) a keypad for selecting the function marked at the top of each button (Volume, Bass, Middle, Treble, three Distortion types, Compressor/Sustain, and Hammond reverb), the level of the selected function, or the channel to be programmed/played, 4) In and Out buttons for activating the effects loop, 5) a numerical channel display that shows you which of the four preprogrammed channels you are using.
Photo kindly provided by the owner, Billy Claire
Designer Peter Hamilton on the OMEC
“I designed the OMEC amp in 1974-75. Before that, I spent a few months as a student fixing amps part-time in the Orange Shop’s basement, and then worked with them full-time for about one year—my first job. The brief was to ‘design a computerized amp.’ With some computers costing upwards of a million pounds and needing their own building and air-conditioning plant, a few compromises were necessary.
“Some weird, new-fangled things called ‘microprocessors’ were beginning to appear in the early to mid 1970s, but they needed a lot of ‘support chips’ to make a useful system. Smaller single-chip microcontrollers existed for things like calculators, but they were permanently mask-programmed . . . the tooling costs were huge, and they were only affordable if manufactured in big quantities— hundreds of thousands.
“The only sane way to do this job was with SSI and MSI (small- and medium-scale integration) logic chips. The choice was between TTL (transistor-transistor logic), which was power-hungry but easy to get hold of and well-proven, or a new technology from RCA called COS-MOS [aka CMOS], which used hardly any power but also had a habit of self-destructing due to static damage.
“COS-MOS was too risky at the time, but that technology led to today’s CMOS microcontrollers, with built-in static protection, low power consumption, and millions of transistors on a chip—one of those could handle the whole job for a few dollars. So the OMEC Digital amp was really a digitally controlled analogue amp. Real DSP [digital signal processing] was a couple of decades away. The left-hand digital half of the board allowed numbers for each parameter (Volume, Bass, Mid, Treble, Reverb, Compression, and Distortion) to be stored in memory for each of four ‘channels.’
“Those numbers could be recalled by selecting a channel either from the front panel or the footswitch. The memory controlled the audio circuitry on the righthand half of the board via analogue switches.
“But there was a slight snag: TTL is so power-hungry [that] the memory took almost an [ampere] at 5V, so all the settings were forgotten if the power was switched off! A backup battery was added to protect against brief power cuts, but it only lasted for half an hour or so.
“Here was an idea before its time, I’m afraid. It was innovative, but there wasn’t a knob that went up to 11. I doubt that it was financially viable without investing a large amount of money. Months later, the Z80 and 6502 microprocessors appeared and spawned the personal computer industry. The rest, as they say, is history.”