building an M-S matrix, GML style

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mikep

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Joined
Feb 18, 2006
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450
Location
Philadelphia
I use an 8200 eq in my stereo CD mastering rig. the studio has 2 more 8200's that I can use. I am not intrested in surround, I believe that is a dead end, waste of time. I am thinking about modding one of the other 8200's for full-time M-S operation. this is a little bold so I wanted some opinions first.

The reasoning for putting a mod in the EQ instead of making a stand-alone encode-decode box: I can tap into the EQ's power. I can insert the (unbalanced) matrix between the EQ circuitry and the existing balanced i/o circuits. I would use an OR gate off the left/right bypass switches so that if both are out, the whole box is bypassed, if either is in then the matrix is active as well as that channel's EQ.

I have several MS matrix designs but havent decided on one yet. Id love to use GML opamps, but that would be a little pricey. I could do it with only 4 opamps total so maybe it is worth it? any thoughts?

mike p
 
[quote author="gyraf"]
I would make it external...

And passive, transformers-only. That way you don't need the psu..

Jakob E.[/quote]

these thoughts crossed my mind. I could even build it as an external companion to the EQ and still tap into the power, as the 8200 has a daisy chain power connector on the back. also in the room I have a big pre-regulated supply at +/- 30V I can juice out from. the thing is, unless I get an analog de-sser, there will never be anything inside the matrix other than an EQ, so I thought, why not dedicate an 8200 for this purpose, since it would be patched there permanantly anyway? by putting it inside I avoid introducing 2 extra sets of balancing/unbalancing amps. I think. maybe this IS moronic.

I am concerned about the transparency of an all transformer design. I usually already have "too many" transformers in the path, via either a neve compressor, tubetech EQs, or a McIntosh poweramp-as-a-lineamp. Whe I was thinking external I was considering a design that uses a transformer to derive the difference signal and a discrete virtual earth amp for the sum. or a THAT line reciever for the difference amp.

mike
 
you can do passive and transformers and make it non coloured trafos. Jensen transformers has a great schemo in the application schematics for the very thing. going with what I said earlier, by doing an external box you are more flexible and also you don't have to hack up an 8200 to do it...
passive M-S box with trafos is the way to go... :thumb:

mikep said:
[quote author="gyraf"]
I would make it external...

the thing is, unless I get an analog de-sser, there will never be anything inside the matrix other than an EQ, so I thought, why not dedicate an 8200 for this purpose, since it would be patched there permanantly anyway? by putting it inside I avoid introducing 2 extra sets of balancing/unbalancing amps. I think. maybe this IS moronic.

mike
Not Moronic just a the hard way of doing things IMO.
 
[quote author="mikep"]The reasoning for putting a mod in the EQ instead of making a stand-alone encode-decode box: ............ I can insert the (unbalanced) matrix between the EQ circuitry and the existing balanced i/o circuits. [/quote]

[quote author="mikep"]... by putting it inside I avoid introducing 2 extra sets of balancing/unbalancing amps. I think. [/quote]

You will not avoid the two extra sets of balancing/unbalancing circuits because the GML has unbalanced out on XLR (not even impedance balanced) the input has a discrete balanced receiver with DC servo so you can't avoid it anyway.

chrissugar
 
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