Summary for those in a rush: I want to build a headphone/matrix mixer, how's the schematic look? Any suggestions?
I'm brand new to the boards, and what better way to kick things off than to dive right in, fully over my head. I've been practicing in a 6-person band in someone's basement for a while, and we really need to figure out a way to do individual headphone mixes. So my oh-so-ambitious project is to make a headphone mixer (aka monitor mixer, aka matrix mixer). I've looked around and found nothing in our budget (about 300-400) that satisfies my requirements, so I've started looking into building my own.
First, the requirements. We've got 6 people, 7 instruments (2x vocals, acoustic guitar, electric guitar, eletric bass, violin, drums). The drums are obviously the loudest, and right now we amp everything up to drum level and tune it back down with etymotic earplugs. Still, it's hard for everyone to hear themselves and hard to hear what each person is interested in, so we need a headphone mixer. 7 instruments mixed for 6 people, so I'm thinking a 7-input 6-output mixer (including either a drum overhead, or a room mic... haven't decided which yet).
I'm starting from this schematic and working forward.
[IMGHTTPDEAD]http://rocketmonkeys.com/perm/mixer/matrix_mixer.gif[/IMGHTTPDEAD]
Schematic taken straight from http://www.doepfer.de/DIY/a100_diy.htm
Obviously this is bare bones, and I don't expect professional mixer quality or results; just something functional, usable, not so noisy we hate it. I'm also trying to keep this cheap, under $100 if I can, which will probably balloon into $150 as I learn. My background is that I did computer engineering in college, took all the EE classes but mostly just worked with chips and FPGA's. I've done some soldering for fun, fixing computer parts and wiring things together. I don't mind soldering a bunch of opamps/pots/jacks together. That said, I've never tried anything nearly this ambitious.
So here's what I understand of the circuit. Each row in the circuit is basically an O-way (output) voltage divider. Each column is fed to a pair of unity gain inverting amplifiers, and then fed to the outputs. It looks like it can be expanded to any amount of inputs/outputs, with a pot at every junction.
I'm ready to order a huge amount of pots (7 input x 6 output = 42, plus 7 input gains and 6 output levels = 55 pots) and opamps, but I want to make sure of what I'm getting into here.
Some questions I have rolling around in my head:
We've got 2 mic inputs (typical cheap dynamic), 4 direct line-ins from amps, and one more mic (possibly condenser, preamped). Each output will be driving a pair of headphones of varying loads, probably pretty typical low-end closed/supra-aural headphones + IEM's. What should I expect as far as input levels/voltages? Should I count on adding buffers or preamps to the inputs? What kind of gain should I aim for at the output stages?
Why use two inverting opamps at each output stage? Why not just one non-inverting amp? I know it's probably a basic question, but I don't get it yet.
Is there any mods to the circuit you would suggest? I'm trying to keep the component count down since I'll be working with discrete components on perfboard or similar, and I'll be wiring everything by hand. Plus, every circuit will be multiplied by the amount of inputs/outputs, etc.
Any feedback, comments, criticisms, reality checks, etc is very much appreciated. I can't wait to start on this, especially if it works (it'll be such a godsend for our worn ears). Thanks so much!
I'm brand new to the boards, and what better way to kick things off than to dive right in, fully over my head. I've been practicing in a 6-person band in someone's basement for a while, and we really need to figure out a way to do individual headphone mixes. So my oh-so-ambitious project is to make a headphone mixer (aka monitor mixer, aka matrix mixer). I've looked around and found nothing in our budget (about 300-400) that satisfies my requirements, so I've started looking into building my own.
First, the requirements. We've got 6 people, 7 instruments (2x vocals, acoustic guitar, electric guitar, eletric bass, violin, drums). The drums are obviously the loudest, and right now we amp everything up to drum level and tune it back down with etymotic earplugs. Still, it's hard for everyone to hear themselves and hard to hear what each person is interested in, so we need a headphone mixer. 7 instruments mixed for 6 people, so I'm thinking a 7-input 6-output mixer (including either a drum overhead, or a room mic... haven't decided which yet).
I'm starting from this schematic and working forward.
[IMGHTTPDEAD]http://rocketmonkeys.com/perm/mixer/matrix_mixer.gif[/IMGHTTPDEAD]
Schematic taken straight from http://www.doepfer.de/DIY/a100_diy.htm
Obviously this is bare bones, and I don't expect professional mixer quality or results; just something functional, usable, not so noisy we hate it. I'm also trying to keep this cheap, under $100 if I can, which will probably balloon into $150 as I learn. My background is that I did computer engineering in college, took all the EE classes but mostly just worked with chips and FPGA's. I've done some soldering for fun, fixing computer parts and wiring things together. I don't mind soldering a bunch of opamps/pots/jacks together. That said, I've never tried anything nearly this ambitious.
So here's what I understand of the circuit. Each row in the circuit is basically an O-way (output) voltage divider. Each column is fed to a pair of unity gain inverting amplifiers, and then fed to the outputs. It looks like it can be expanded to any amount of inputs/outputs, with a pot at every junction.
I'm ready to order a huge amount of pots (7 input x 6 output = 42, plus 7 input gains and 6 output levels = 55 pots) and opamps, but I want to make sure of what I'm getting into here.
Some questions I have rolling around in my head:
We've got 2 mic inputs (typical cheap dynamic), 4 direct line-ins from amps, and one more mic (possibly condenser, preamped). Each output will be driving a pair of headphones of varying loads, probably pretty typical low-end closed/supra-aural headphones + IEM's. What should I expect as far as input levels/voltages? Should I count on adding buffers or preamps to the inputs? What kind of gain should I aim for at the output stages?
Why use two inverting opamps at each output stage? Why not just one non-inverting amp? I know it's probably a basic question, but I don't get it yet.
Is there any mods to the circuit you would suggest? I'm trying to keep the component count down since I'll be working with discrete components on perfboard or similar, and I'll be wiring everything by hand. Plus, every circuit will be multiplied by the amount of inputs/outputs, etc.
Any feedback, comments, criticisms, reality checks, etc is very much appreciated. I can't wait to start on this, especially if it works (it'll be such a godsend for our worn ears). Thanks so much!