Performance Mixer Group. www.haraldswerk.de

Motivation

This is my take on a performance mixer with channels and groups. The panning and the volume for the channels is voltage controllable. You have two aux send per group, pre and post fader. The input gain is adjustable between 0..2 which can give nice distortion if wanted. You can add channels as needed.

Specs and features

As many as input channels as needed
Pre and post fader aux send
Left and right return (Normalized left to right)>/li>
Left and right out per group
Overdrive per channel
Variable scan depth and position
Voltage controlled pan and volume
Power consumption below 150mA each rail

Implementation

Schematic

Performance Mixer Group schematic main board 01/02 — Performance Mixer Group schematic: Main board 01/02

Performance Mixer Group schematic main board 01/03 — Performance Mixer Group schematic: Main board 02/01

Performance Mixer Group schematic main board 02/01 — Performance Mixer Group schematic: Main board 02/02

Description:

Nothing special about it. Just using standard configuration for mixers with OTA-s in the audio path.

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Calibration

First make a gross function test. All in and outs should work as expected and all potentiometer have some effect.

Connect a scope to the left and right output from the group. DC coupled. You'll need this to adjust the DC offset of the OTA's.

Group one OTA DC offset
- Set Ret-Vol pot to zero.
- Set all volume slider 1 to max.
- Set all volume slider 2 and 3 to min.
- Adjust TR_1 (board B) to zero Volt (left channel).
- Adjust TR_2 (board B) to zero Volt (left channel).
Group two OTA DC offset
- Set Ret-Vol pot to zero.
- Set all volume slider 2 to max.
- Set all volume slider 1 and 3 to min.
- Adjust TR_1 (board C) to zero Volt (left channel).
- Adjust TR_3 (board C) to zero Volt (left channel).
Group three OTA DC offset
- Set Ret-Vol pot to zero.
- Set all volume slider 3 to max.
- Set all volume slider 2 and 3 to min.
- Adjust TR_2 (board C) to zero Volt (left channel).
- Adjust TR_4 (board C) to zero Volt (left channel).

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Building hints

None

Special parts

Instead of the here used CA3280 (I am using up some NOS) you can use the new available AS3280.
The sliders are from Befaco (Thonk or Befaco)
The connectors are Thonkicons (Thonk)