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ES31 - Multi-Channel Stereo Mixer

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The ES31 is a studio quality output mixer that can be expanded by the addition of one or more ES30 modules. This Multi-Channel Stereo Mixer is an indispensiable aid for live music performance or can be used with appropriate computer control for automated stereo mix-downs in the studio.

The output section provides MASTER controls over the mixer stages by summing the stereo signal from the mixer section(s) and provides both unbalanced and balanced outputs suitable for connecting to a range of external equipment.

An important feature of the output section is a master gain VCA which controls the overall sound level of the two stereo output signals. Thus the entire output mix can be faded in, faded out, or adjusted with a single knob or control voltage.

The ES31 comprises 2 identical single channel stages and are exactly the same as those in the ES30. Each input feeds a VCA whose gain is set by a manual [GAIN] control and a control voltage [GAIN CV]. The manual control sets the level while the CV control shapes the sound. Nominal range of the CV is 60dBs with a taper of 12dB per volt.The module responds smoothly over the full 0-5V range of its envelope control. There are no blind spots, the sound is full-throated, not explosiive or hard to control, and when the VCA is off, it is completely silent.The VCA is then routed to an "equal power (c)" panning circuit which acts to accurately position sounds in a stereo sound field.

There are two manual controls to the panner - a [PAN] control to set the sound anywhere from fully L(eft) to fully R(ight), and also a [PAN CV] input jack and control which serve to set the amount and direction of a CV's effect on spatial location. With the control set clockwise to 'R-L', a positive going CV will move the sound from right to left, When set to 'L-R', a positive CV will move the sound from left to right. The [PAN CV] control can thus be set to effect quite subtle spatial results.

Auxillary inputs allow non gain controlled inputs to be added directly to the final mix.

The mixer was designed specifically to respond best using synth envelopes. The response rate is 13.5 dBs/volt so that a 5 volt envelope produces a perceptually solid amplitude change of around 60dbs. Past that, the taper accelerates to cutoff (better than -100 DBs). This produces sounds that are consistent rather than malformed and too sudden, as is the case for many VCAs available currently.

Total dynamic range, including headroom, is approximately 90+ dbs 

Panning is designed to provide accurate linear displacement of sounds between two speakers. A 1V VC into the panning input results in a displacement of 1/5 the distance between two loudspeakers. 2.5V locates the sound midway between loudspeakers. But whatever the spatial location, the net amplitude of the sound stays the same (unless its amplitude VC changes too). This is what "Equal Power" signifies, a characteristic resulting from an accurate square rooting of the loudness ratio of the sound travelling between speakers.


(c) "equal power panning"' is the copyright of Serge Modular, 1976.

Module Width
Module Depth
+12V @
-12V @

ES31 Build Guide

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