Panning mixer inside MBFM
Posted 02 January 2011 - 06:29
I housed my MBFM in a breadbox and there's plenty of space inside it and on the panel for this simple mixer I found at MFOS
It's a small circuit and it only takes up space on the faceplate of 8 knobs (and you could probably whittle that down to 4 if you just use the volume controls in the MBFM)
On the back of my machine I used 6 x 1/4" phono jacks and 4 of them need to be switching. 4 of them are individual outs and two of them are L and R for the stereo out. You can also run everything to a stereo TRS out for headphones as well.
I ran the MBFM outs to the tip side of the 4 jacks, then to the mixer inputs via the switch side, so If I want an individual out, all I have to do is plug a cable in and it breaks the connection for that channel (removing it from the stereo outs I have connected to the mixer circuit).
Since I didn't opt for a headphone out, I only need a TL082. If you use the headphone out too then you will need a TL084. You could probably use any Dual Supply Opamp in there. I'm sure there are better ones for audio for you audiophiles (although consider that every signal is already run through a TL074 on the MBFM anyway)
I can't get this file to upload. I'll try again later. Here's the Link : MFOS USSPAM
Posted 28 January 2013 - 03:18
I used those designs to make the feedback mixer circuits and main mixer in my build too. Just one thing bothers me about your first schematic: the main outs are inverted from the inputs, though the headphones are correct.
Posted 04 February 2013 - 08:03
I was thinking, was it the link I wrote he means? Hehe, The main outs are inverted, it looks like. Not being the circuit designer, I would still claim that it is a compromise to make the circuit simpler. The IC is quad opamp? And the guy designed it this way to get away with only one chip. Maybe it would be smarter inverting the headphones instead then? Maybe free Eagle was used to route the board, and there was simply not space for more opamps ...
When I design this stuff using eagle, I use a seperate PCB for the main outputs (4 opamps) and a seperate board for headphones amp. Then if I need more outputs I have them on seperate PCBs too (usually two outputs each board). Not a optimal solution, but when designing stuff for home-etching like I usually do, there's simply just no room for a lot of top layer routings and tiny traces :P. If mixer design is low channel count, like this, the inputs also goes on the main output pcb. ;).
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