Buffering necessary for master effects loop?

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deep_bias

Member
Joined
Jul 28, 2009
Messages
6
I have a very simple mixer (esp for this board, it's for djing) that I am trying to add a master effects loop to.  Here is the schem: http://www.flickr.com/photos/39296643@N08/3607984901/sizes/o/

Looking to put the loop after R11.  In terms of impedance, it seems like it will probably be driving something with a relatively high impedance input (there will basically be either a rackable EQ or variable filter on the loop), so I don't know that I would need to buffer the send plugs.  The return will get looped back into an unbalanced and a balanced output.  The bal is running on SSM2142's (soon to be THAT1646's), so it has an input buffer on the chip already and should be perfectly happy just getting the output from whatever effects unit direct (or should I also add some resistance going to ground just before the driver chips?).  Since the unbalanced out is just a simple connection from the loop in, and whatever effects unit that is on the loop would be probably happy to be going direct into whatever is on the unbalanced out or into the bal line drivers, it seems maybe that I don't need a buffer there either really.  The op amps are OPA2107's (www.ti.com/lit/gpn/opa2107) which have a short circuit current of +/-40ma and voltage output swing of 24V through the audio range (very nice sound as well, expensive but available as samples from TI).

However while all this seems fair enough I do see buffers on some effects send/receive designs on here sometimes, and I'm sure there are other factors I'm not aware of that affect the situation, so I wanted to ask the board.  Dunno also if cables are enough of a resistive or capacitive load to matter.. wouldn't think so?  We are talking 3-4 ft of mogami neglex 2944, make all my cables out of this.   Anyway thanks much appreciate the help!  Obviously not super experienced in ee matters but trying to learn.
 
3-foot cables? Just alligator-clip stuff on anywhere, anyhow. Or use connectors, it looks better.

When you have to send and return to/from the 7th floor of the other building, you want balanced floating low-Z. But little studios can be patched like guitar pedals.
 
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