The ED104 comprises 2 LIN/LOG VCAs with additional VC Panning function.

In July 2002, EDN Network published an article by Mike Irwin on the application of op-amps to linearise the response of a voltage controlled attenuator built around the Analog Devices SSM2164. In September 2003 Phillip Gallo published a design for a Dual LIN/LOG VCA utilizing this design idea and the ED104 realises that design in a euro-synth module.

Although the ED104 has two separate VCA’s, the [LIN/LOG] control law is switched simultaneously for both VCAs so that they both operate with the same control response.

In stand-alone mode a control voltage is fed in to [CV x] while an audio signal is fed in to [AUDIO IN x] with the resultant output at [AUDIO OUT x].

With the CV level control at maximum, a 0V to 5V signal will raise the gain of the VCA from -100dB of attenuation to 0dB while increasing the voltage from 5V to 10V will further increase the gain from 0dB to +20dB.

For operation in Panner mode, a single audio signal is fed in to [PAN AUDIO] while the panning control voltage is fed in to [PAN CV]. The [CV A] and [CV B] level pots should initially be set to maximum.

The [AUDIO IN A] and [AUDIO IN B] are typically AC coupled but if desired you can fit jumper J101 to change [AUDIO IN A] to a DC coupled input and J102 to changed [AUDIO IN B] to a DC coupled input.

Please note that a manufacturing error has resulted in the centre knob being incorrectly labelled and scaled. It is currently labelled [PANNER] and has a centre-zero scaling. It should be marked [PAN DEPTH] and be scaled ‘1 – 9’.

Build Guide