headphone mixer/amp with MS matrix

[James HE]

a long long time since I've visited here!

I record myself a lot, and I'm brainstorming ideas for a little mixer / headphone amp to make my life a little easier.

I think what I want is a mixer with 2 stereo inputs. Input 1 would have a switchable MS matrix. Input 2 would be switchable to mono. Then, of course a headphone amp after that.

I think I can cobble together parts of different schematics to build it (hopefully)
for the MS matrix i will likely use this http://www.groupdiy.com/index.php?topic=21795&highlight=matrix

for the headphone amp something like...
http://headwize.com/projects/showfile.php?file=cmoy2_prj.htm

and hopefully muddle through the switching and summing. I'm very much a newb. I got into a little DIY about a year ago, studied and read a lot, but never successfully built anything. So any guidance I can get will be most helpful. I wish I had more specific questions at this point, but I'm just digging back in.

I will be coming out of the balanced / unbalanced outputs of my soundcard, so unbalanced input should be fine. (will also decrease the cabling I need to send to the thing) Should I use an opamp buffer on the inputs at all in this case?

I'd love to just use stuff I have on hand for this. I have some INA134 to use for the MS matrix and some ne5532 that I'd like to use for the rest. Is there a more suitable circuit for the headphone amp since I will be using 5532's?

Should I use active summing here? Or could I passively sum the inputs and let the headphone amp provide makeup gain?

When I get a preliminary scem I'm comfortable with enough to post I will.

Thanks!

 

[James HE]

OK proof that I have no idea what I'm doing.. lol
(sorry for the big image)

I'm sure there's got to be something wrong in there. I didn't get around to labeling my inputs in a logical way, but should be apparent.

2 stereo inputs, gain controls for each. The MS matrix switchable in front of the first channel. The second channel switches to mono (left only).

THis is, obviously minus the HP amp itself. I haven't decided what to do as of yet. any suggestions there?

 

[James HE]

[quote author="mediatechnology"]
In your drawing what's SW2 and the link above it for? The link appears to tie the two op amps together. For the M-S to be accurate the source impedance feeding the INA134/THAT1240 needs to be low as it becomes part of the matrix gain equation. You might want to buffer those if you can. I need to check the pin outs in that section.[/quote]

SW2 is supposed to be a mono switch for the second input, but it's in the wrong place I think now that I look at it. Needs to be before my gain control. Will fix that and label things properly.

I am looking at a schematic for a symetrix headphone mixer amp for the "inspiration" for my input stages here. The symetrix has a stereo (mono switchable) input and a mono "cue" input.

I will buffer my inputs if that's better. Was thinking possibly powering this with batteries, but that's probably not going to be possible.


Thanks for the reply!