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Old 29th July 2007, 07:46 AM   #1
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Default Balanced Input Hookup

I am working on a balanced preamp based on this schematic

Click the image to open in full size.

For the input, I picked up a pair of Cinemag CMLI-15/15 transformers. I'd like to accept both single ended and balanced inputs, but this being my first endeavor into balanced circuits I am not sure of how to connect everything up.

Is it reasonable for balanced input to connect the + and - inputs to the two sides of the primary, and for single ended input to connect the input signal to where the balanced + connects and the input ground to where the balanced - connects? This leaves the balanced ground, but I gather this is often ignored anyway.
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Old 29th July 2007, 09:20 PM   #2
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I am confused about how your question is formed so Iíll tell you how I do it. Refer to figure 3 on http://www.raleighaudio.com/active_output.htm

Itís incredibly simple: For balanced input, connect the + signal to the + input and Ė signal to the Ė input. For single ended input, connect the signal to the + input and ground to the Ė input. Switch both sides through your source select switch so you switch +/- for balanced input and +/ground for single ended input.

Dave
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Old 29th July 2007, 10:05 PM   #3
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Thanks Dave. That is what I was trying to say in my own convoluted way. It seemed right, but I wanted to be sure I wasn't missing something.
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Old 30th July 2007, 01:45 AM   #4
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Okay good, I thought so but I wasn't sure.

One more thing: use the chassis ground for the single ended ground. Donít use the internal circuit ground.

Dave
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Old 30th July 2007, 08:42 AM   #5
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Hello Mr.
For balanced signal use + (hot), - (cold) and ground.
On a XLR (Cannon) connector Pin 1 is ground, Pin 2 +(hot) and Pin 3 - (cold).
For unbalanced use: (line signal) you have to solder - and ground together otherwise you lose 30 dB of the signal.
So the RCA connector would be: center tap + shield - and ground.
I have the experience the sound isvery dependant on what transformer you use.
In my opinion the best line-trafos ever made was the German Studer (fitted in their two-track reel to reel models), the German Haufe transformers (fitted in Neumann mics etc.), the Swedish Lundahl trafo model SR501 (specially designed for National Swedish Broadcast); and the German Dynacord trafos (fitted in amplifiers like the Eminent and MV-46).
Cheers Fredrik
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