CBG Elric Synthesiser (Circa 1984/5)

CBG ELRIC Synthesiser.

Elric is/was a dual-VCO monophonic keyboard synthesiser designed in 1984. It used the Curtis Electromusic analog synthesiser ICs under control of a microprocessor.

Elric has one, fixed patch: a four channel audio mixer feeds a VCF whose output feeds a VCA with stereo outputs. There are two VCOs and a ring modulator. The four inputs to the audio mixer are sourced from the VCOs, the noise generator and the ring modulator. The ring modulator inputs are hardwired to the VCO outputs. One VCO can be synched to the other.

Although there was one fixed patch, it was very powerful and all settings could be saved and restored to one of ten slots in internal, battery-backed RAM. Another ten slots contained ROM preset settings.

For modulation sources there is one ADSR transient generator dedicated to the output VCA for envelope control. Two additional ADSR transient generators were provided for general modulation functions, as well as one axis of joystick and two LFOs. The other axis of the joystick is hardwired to serve as a pitch bender.

The VCO and LFO outputs could be square, triangle or sawtooth or any combination.

Modulation destinations include Pan (serving as tremolo if mono output used), Vibrato, VCO PWM, VCF offset and resonance, VCO offset and the input gain for each of the four channels of the mixer.

The modulation routing matrix allowed every destination to be a programmable linear sum of a constant, an LFO, an ADSR and the joystick.

Other switchable features were LFO key triggering, portamento, AD instead of ADSR and exponential rather than linear transient release and decay.

A 440Hz tuning signal was provided.

Front Panel Legend.

The front panel had four pairs of dot matrix LED displays that could each display a two digit hexadecimal value: 0-99, AA-FF. These indicated the current values of whatever was being edited at that time, in groups of four variables.

The rear panel has the mains input and the mono audio output. Also, the sustain pedal plugs in here.

MIDI was very posh and new when Elric was designed and having created this implementation I was sought for consultancy for years to come.

Patching Schematic.

The main shortcoming of Elric was that old bane of analog synthesisers: staying in tune. I considered injection locking the VCOs from a digital source or automatically providing fine tuning based on measuring their current frequency and error. This was not implemented.

Rear Panel View.

Internal Views

General View of Internal Layout

Power Supply

8088 Controller Microprocessor

Front Panel Rear View

Main Board: Left-hand Side View

Main Board: Center View

Main Board: Right-hand Side View

The internal analog circuitry consists of two VCOs, a VCF, a white noise generator, ring modulator and five VCAs. Elric used an Intel 8088 processor to control all functions. The analog audio path is controlled by a single DAC that is time-division multiplexed across each function, using analog sample and hold circuits for each parameter.

The VCO oscillators are the Curtis Electromusic CEM3340 devices and the VCF is the CEM 3320. The VCAs use CA3080 transconductance amplifiers. The ring modulator is an MC1496 gilbert cell.

(C) DJ Greaves, 1984 (design) and 2008 (article).