As I wrote already I have two of audio mixer project, because first time I designed very simple, with 4 or 8 input channels only, with master volume and line two outputs only. This project contains 2 very simple mainboards for 4 and 8 channel inputs, two output panels, and preamplifiers as module. The preamplifiers for mixer is same as my first designs, but can be connected with 12 pin male connectors to selected mixer mainboard.
For example, here is the microphone preamplifier with INA217:
The "original" PCB for this device is here:
But for modular mixer I have to modify the board design, the input and power connectors are removed, and changed to P4 connector on the bottom of board:
These preamplifier modules are smaller than the original versions, and contains "power filter" circuits as module (P5 and P6 connector at upper board). The preamplifier modules can be connected to the mixer mainboards, any preamplifier can be connected to the any connector of the mixer. The distance between preamplifiers is 25mm. This is the reason, why I have to design new versions of PCB for circuit called "power filter". This module must be smaller than 25mm. I have 5 versions of this module, with several sizes. All my preamplifiers (mic preamp with INA217, stereo dual jFET preamp, Dual OpAmp, 2 versions of single OpAmp) re-designed for modular mixer system.
The picasa gallery:
For the simplest version of my mixer project I have two mainboards with connectors for preamps, outputs, power supply, and balanced inputs for microphones:
4 channel mainboard for 4 inputs and 2 outputs:
For this board required 2 "power filter" modules, 4 preamplifiers, 1 volume board, and 1 line output board.
For the board can be connected two output PCBs. The one is for the master volume:
This PCB must be soldered after the 4th preamplifier via P5 male connector. This board working as 2 separated volume potentiometer for left and right channel, and possible to use only one stereo potentiometer for both channels on the pins of P1.
The another output module made for 2 line level outputs:
This board must be soldered to the last connector of mixer board via P1 header. The line level circuit designed to the mainboard, so this PCB contains the connectors only. The board useful for:
- 2 6.3mm jack
- 1 6.3mm jack and 1 stereo RCA
- 1 6.3mm jack and 1 3.2mm jack
- 1 3.2mm jack and 1 stereo RCA
I designed 8 channel mainboard:
This circuit is same as than the upper 4 channel design. But here is 8 connectors for input channels can be connected to preamplifiers. The two of output boards is same too. This board width is 25cm, I think this is something big, very hard to manufacture, this is the reason why i designed "expandable" version of my audio mixer with connectable small mainboards for more than 8 channel inputs.
PDF manuals for audio mixers: