Expandable, modular audio mixer for any number of channels

This is my second audio mixer project. The difference between current and previous design is, that this design can be expandable to any number of channels, the previous is made for 4 or 8 input channels only. At the end of the PDF manual of this project I inserted examples how to build audio mixer for any number of input and output channels.

I made paper models of my design to check how possible to build the complex device:



This gallery is funny, but very cheap to find mechanical problems before manufacturing the PCBs. With this test, I detected the problem, that the PCBs of "power filter" circuits are too big, have to be smaller than 25mm. This is the reason why I have 5 several power filter PCBs, and here is the smallest, with 22mm height, and 25mm width for the modular mixers:



The schematic of power filter module to decrease the preamplifier's noise and the crosstalk between left and right channels:


This PCB is very small, much harder to build....

The required preamplifiers for input channels are exactly same as than my simplest mixer project. The new on this design, that the small mainboards can be expanded with female/male connectors to build bigger than 8 channel audio mixer.

The first module of expandable mainboard:


...and the PCB for the first mainboard module:


This design is simple 4 channel audio mixer. Possible to finalize with 4 several preamplifiers. The blue potentiometers on the bottom of PCB is the L/R balance adjustment, but these parts are ignorable if not important. These potentiometers have blue color, because must be soldered to the bottom layer. There are mono, metal case parts. The first mainboard contains connectors for powers, phantom powers, line outputs, and balanced microphone input for all channels if mic preamp inserted. The main difference is the P1 female connector. This is the part where possible to connect another mixer mainboard to make more input or output channels. This first 4 channel module working without another connected boards, but on this one no connectors for outputs, only one stereo line output on the PCB via H5 connector.

For more inputs, here is the required module can be connected to the right edge of the first board to the connector P1:


and the really small PCB with P21 male connector:


This is an input channel for 2 arbitrary preamplifiers. Upper left is the male connector can be connected to the first, to the same, or to the output boards too. Here is the reason why expandable this device to any input or output channels.

If output channels required, here is the new schematic:


And I have 2 PCB design for upper schematic:


The difference between two PCBs is the L/R balance potentiometer only. This mainboard-module made for output circuits. The board can be connected to anywhere and anytime within the whole system. I offer several output modules:

The line outputs with master volume adjustment:


...and the PCB:


The difference between this, and the previous version of line output board, that this board contains line driver circuits, not the mixer's mainboard. This board contains adjustable master output of mixer with volume potentiometer with following variations:

• 2 6.3mm jack
• 1 6.3mm and 1 3.2mm jack
• 1 6.3mm jack and 1 stereo RCA
• 1 3.2mm jack and 1 stereo RCA

This board contains only one stereo volume adjustment, but possible to soldering to the board with L/R balance potentiometer if this feature required.

Another output circuit:

This is headphone amplifier with TPA6120. I modified my previous design of this module.

The PCB:

This is the simplest application of this really good IC with 6.3mm jack output and volume adjustment feature.

I made another version of this output for my audio mixer. The difference, here is an unbalanced/balanced converter for less noise, higher dynamics, higher possible volume. The official 120dB dynamics range is really high quality.


The required PCB is bigger, with two power filter module on P3 and P4 connectors:

• PDF manual of expandable mixer with examples.

PCB sales of this project Module name Size (mm) Area (cm2) PDF SCH PCB image Tested Price (US$) Des. Sim.1 Full2 Sim.1 Full2 Man3 Power filter module 17x25 4 Yes Yes Yes - - No 3 11 Ask 1st mixer module 103x95 98 Yes Yes Yes - - No 15 24 Ask 2nd mixer module 51x93 47 Yes Yes Yes - - No 8 16 Ask 3rd mixer module 26x93 24 Yes Yes Yes - - No 5 13 Ask Line outout board 65x76 49 Yes Yes Yes - - No 9 16 Ask Headphone output board 56x71 40 Yes Yes Yes - - No 7 15 Ask Balanced headphone output board 58x105 61 Yes Yes Yes - - No 10 18 Ask Microphone preamp module V2 67x103 69 Yes Yes Yes Yes - No 11 19 Ask Microphone preamp module V3 67x103 69 Yes Yes Yes - - No 11 19 Ask 1 dual opamp preamp module 61x103 63 Yes Yes Yes - - No 10 18 Ask 2 single opamp preamp module 64x103 66 Yes Yes Yes Yes - No 11 19 Ask HQ 2 single opamp module 67x103 69 Yes Yes Yes - - No 11 19 Ask jFET guitar preamp module 65x102 66 Yes Yes Yes - - No 11 19 Ask Switch module 18x34 6 Yes Yes Yes Yes - No 3 11 Ask Simple Power supply 121x57 69 Yes Yes Yes Yes - No 11 20 Ask Power supply with 48V phantom 168x89 150 Yes Yes Yes - - No 22 32 Ask How to order? Please read the rules carefully!