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Old 29th June 2004, 12:41 PM   #1
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Default Balanced Inputs on Leach Amp

How would I add the ability to accept a balanced input (via an XLR connector) to the Leach Amp design? Anyone ever done this?
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Old 29th June 2004, 02:11 PM   #2
pooge is offline pooge  United States
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Use an input transformer, a la Jensen JT-11P-1 or the like, and change the input resistor on the Leach to 10K to properly load the transformer.
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Old 29th June 2004, 02:27 PM   #3
tool49 is offline tool49  Canada
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Or you could also make a small zener supply, regulate it and use the INA134 chip.

Sébastien
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Old 29th June 2004, 02:37 PM   #4
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Sorry, but those answers are a little over my head. I'd perfer to construct something that could intergrate into the existing design (so it still allows the unbalaced input to function) and would not require modifications to the leachamp PCB. Anyone have a diagram of a circuit that could accomplish this?
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Old 29th June 2004, 02:52 PM   #5
tool49 is offline tool49  Canada
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I believe that my solution answers to all your requirements!

Sadly I do not have time right now to go into more details.

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Old 29th June 2004, 03:42 PM   #6
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See ESP Project for balanced line driver/receiver. You would also need to tap off the rails to power the op-amp circuitry - Rod also has a project for this (simple pre-regulator I think it is).
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Old 29th June 2004, 04:39 PM   #7
pooge is offline pooge  United States
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Quote:
Originally posted by m0tion
Sorry, but those answers are a little over my head. I'd perfer to construct something that could intergrate into the existing design (so it still allows the unbalaced input to function) and would not require modifications to the leachamp PCB. Anyone have a diagram of a circuit that could accomplish this?

Well, you're going to have to alter SOMETHING. You have to connect the input to the board. If you don't want to change the input resistor on the board, you can add a 20k resistor across the connectors of the XLR so that it will be in parallel to the 20k input resistor on the Leach. You can find a circuit at the link. It ain't cheap, though. You could also wire the unbalanced input in parallel with the XLR, but don't connect to both inputs at the same time.



Jensen input transformer
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Old 30th June 2004, 10:03 AM   #8
djk is offline djk
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I second the use of a transformer.

Electronic balanced inputs are a waste of time and money.

A lower priced alternative to the Jensen is from EDCOR

http://www.edcorusa.com/sound/matchers/s2s10k_10k.htm
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Old 30th June 2004, 01:11 PM   #9
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Whilst transformers are undoubedly the ultimate, for a tenth (maybe even less than that) of the price the electronic version cannot be dismissed, and done properly results can be very good.
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Old 30th June 2004, 07:19 PM   #10
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Default Re: Balanced Inputs on Leach Amp

Quote:
Originally posted by m0tion
How would I add the ability to accept a balanced input (via an XLR connector) to the Leach Amp design? Anyone ever done this?
As I recall, the Leach is a simple enough differential input, and
is easily adapted to balanced inputs. Check out the discussion
of differential inputs on the A75 article at www.passdiy.com
and you'll see good enough examples.
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