Matrix Mixering

I’m building a 3×3 matrix mixer and have been scouring the Internet for examples and technical ideas. Even though a Google search can give you days of examples of opinions on which OpAmp to use at what stage, I’m more interested in the actual pedagogy of building the thing in the first place. So here are some of the better links I’ve uncovered that are useful for getting your head around the entire idea of designing a matrix mixer.

A lot of good guidance here, using OmAmps for buffering, though I think the best thing about this page is the nice wiring schematic at the very bottom on how to wire buses.

• http://sound.westhost.com/project129.htm

This JFET style mixer is basically a step up from a passive mixer with no buffers, sometimes used in place of an OpAmp:

• http://www.aaroncake.net/circuits/mixer1.asp

These are a selection of great starting points for learning how to build simple input/output buffers, focused mostly on JFET, but with some discussion of JFET OpAmps:

• http://www.muzique.com/lab/buffers.htm

Ken Stone’s well known mixer designs. PCB’s are no longer available, but the theory and technique is there:

• Matrix Mixer: http://www.cgs.synth.net/modules/cgs33_matrix_mixer.html
• “DC” Mixer: http://www.cgs.synth.net/modules/cgs04_mix.html

The Doepfer A-100 DIY Matrix Mixer example schematic (about halfway down the page):

• http://www.doepfer.de/DIY/a100_diy.htm

The Bucha Matrix Mixer Clone thread at Electro-Music contains vtl5c3’s posts about his 8×8 project, which follows the Buchla design. The only place I’ve been able to find the Buchla schematic online, and has great photos of the mixer’s guts:

• http://electro-music.com/forum/viewtopic.php?t=27275

UPDATE:

I’ve breadboarded the input/output stages with NTE451 JFET’s using a 50k pot and 56k ‘mixing’ resistors, I think I’ve found the perfect combination out of parts I already own… I need to swing by Orvac later today and possibly pick up more transistors and resistors so I can build the protoboard. -mrd 20110411