Under the hood

What’s inside the beast? Take a peek:

Let’s take a closer look at the anatomy of this analog synthesizer with a digital brain…

The Oberheim Matrix-1000 is controlled by a 68B09 CPU that handles the UI, processing of MIDI commands and the the envelopes, ramps, LFOs and matrix modulations for all voices.

The 96 KB ROM comes in two chips, one for the operating system (latest version is 1.11) and the other for the 800 preset sounds. The static RAM holds the 200 user-modifiable sounds, global parameters and temporary data used by the operating system at runtime.

The TIMERS block has 4 chips to generate the frequencies for the 12 oscillators (two oscillators for each voice), another timer chip to generate periodic interrupts for the CPU, and the ACIA chip used for MIDI serial communication.

The DAC block contains the 12-bit DAC (it’s the IC at center top in the DAC block) which converts the digital control signals from the CPU to analog signals. The CPU is only 8-bit, a couple of ICs take care of assembling the 12-bit value (plus two extra control bits) for the DAC. Other ICs in this block are demultiplexers. Together with other demultiplexers located in each voice block, they are used to route the analog signal from the single DAC to one of the 60 analog control signals (10 for each voice).

There are six identical circuits for each of the six voices. They are essentially the same as the ones in the Matrix-6.

At the heart of the synth are the six CEM 3396 analog ICs produced by Curtis Electromusic, each one a monophonic synthesizer on its own. The specs include two oscillators, amplifiers and a 4-pole low pass filter with resonance control. The oscillator waveform can be a square wave with variable pulse width or a variety of shapes in between a sawtooth and a triangle. The filter can self-oscillate and has a “filter FM” option.

Around each CEM 3396 chip there are some supporting components, two analog demultiplexers (already mentioned) and a fourth IC dedicated for the most part to implementing oscillator sync. Many of the capacitors in this area are used to optionally smooth the analog control signals.