2 Track Expander

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TornadoTed

Well-known member
Joined
Feb 2, 2006
Messages
239
Location
Mid Wales
I have a Crookwood monitor controller with only one balanced 2 track return. I am looking for the simplest way to make an expander with say 4-6 stereo un-balanced inputs for connecting CD player, iPod, Mac etc. into and then a balanced stereo out to the Crookwood.

I have VERY limited technical electronics knowledge so please be gentle with me!
 
HI Ted!


  Well, the very simplest way would be to use a Lorlin 2 x 6 rotary switch if all the sources were unbalanced. Maplins do them. This could be fed into the balanced input, shorting one of the legs to ground to un-balance it. Obviously, there would be a drop in level compared to the output of your desk or protools for instance, but you could make a simple gain make-up stage with two op-amps( or a dual op-amp), anything from NE5532 or 2 x NE5534 to 2520, OA10, etc etc. You could use an output transformer to balance, or a dedicated balancing chip, or even just impedance balance the signal.

    If this is just to be able to easily route the signal from cd, iPod etc, and not to "A-B" with protools and/or desk output at a comparable level, I'd just hack a Lorlin switch into a diecast box with phono and 3.5mm sockets in, and an un-balanced XLR output. If you need to trim all these different inputs to be same level, you will need much more jiggery-pokery - a pair of op-amps for each input, and a variable gain for each.


    KIndest regards,


    ANdyP


ps I've got limited technical electronics knowledge too, and keeping it simple is often the best way!
 
Hi Ted,

Dan Fitzgerald tells me great things about your studio!  He's an old friend from back home in Ireland and we stay in touch. 

A couple of thoughts - have you spoken with Crispin?  Apparently all of his products are based on modular building blocks so he may well be able to set you up with what you need easily and cost effectively.

One consideration with a simple rotary switch as described by Andy is offness and crosstalk.  Simple switching like that can have leakage between the contacts which may or may not be an issue for your use.  This can especially be an issue with multiple hot sources.  Douglas Self has a great section in his book Small Signal Audio Design about this issue and how to avoid it.  It is the best electronics book I own so well worth purchasing if you have any interest in the craft of it all.
 
Hi Ted,

  I am just waiting for a suitable project to bring to your studio . . .


    too much pop, not enough bands at the moment.


    KIndest regards,


      ANdyP
 
Thanks for the replies guys, I hadn't thought about asking Crispin, that would of course been the sensible first port of call  :p

You're always welcome Andy.
 
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