Motivation
This is an often needed utility module. The mixer comes in handy for mixing CV sources and audio sources as well. This version is DC coupled, so you can use it for AC and DC mixing. There is an inverted output added. You can reverse the DC-CV mix with it or experiment with feedback loops in the audio domain. The added volume indicator us useful for finding the appropriate signal level. The volume indicator is optional. You can leave it out with no problems for the other functions.
Specs and features
- Five inputs
- Inverted and non- inverted output
- Volume indicator (optional)
- Runs on +/-12V and +/-15V
- Power consumption below 20mA each rail
Implementation
Schematic
Mixer schematic: Control board
Mixer schematic: Level indicator board
Description:
Control board: Straight forward design. The mixer is completely DC coupled. So you can use it for CV mixing as well as audio mixing. IC1D sums the five inputs and inverts the signal. P3 is used to adjust the overall signal level. IC1B inverts the signal again. IC1C and IC1A buffers the outputs.
Level indicator: The circuitry around IC2 build an precision full wave rectifier. The output is smoothed with C1. The parts around the BC560C build a constant current source for driving the LED's. The comparator LM393 (IC1A/B) switches the LED on and off according to the input level.
Calibration
- None
Building hints
- You can leave the level indication out with no problems for the other functions.
Special parts
- None
Download
Mixer level indicator board documentation downloadMixer level indicator board Gerber files download
Mixer control board documentation download
Mixer control board Gerber files download
Mixer: Front view
Mixer: Populated control PCB
Mixer: Side view
