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Old 6th February 2007, 03:14 PM   #1
impsick is offline impsick  United States
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Default balanced line question

ok so im building a 3 channel Lm3886 amp. R,L and sub.
I want to use it to monitor my mixes with a sub and just to basically
a/b my mixes between my JBL LSR 6328p near fields, some KRK-5's and the LM3886 (pushing JBL's and a Pioneer sub).

My question is (using Chipamp.com pcb's) if i run xlr to the Lm3886 is this still actually considered balanced? pin 1 goes to chassis ground, pin2 is hot , and pin 3 eventually get grounded too right?
Basically im confused, and i just confused myself even more. Mainly cause i just read on the FirstWatt website, Mr Pass said that most of his customers dont need a balanced cable, but i was always under the impression that a balanced cable is better, not just for long mic runs but for signal quality.
so i guess my question is will it make a difference if i run xlr or just 1/4 inch to the LM3886 coming from a balanced source?
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Old 6th February 2007, 03:37 PM   #2
BWRX is offline BWRX  United States
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Default Re: balanced line question

Quote:
Originally posted by impsick
My question is (using Chipamp.com pcb's) if i run xlr to the Lm3886 is this still actually considered balanced?
No, that will not be balanced because the amp can only accept an unbalanced input.

Quote:
Originally posted by impsick
i was always under the impression that a balanced cable is better, not just for long mic runs but for signal quality.
so i guess my question is will it make a difference if i run xlr or just 1/4 inch to the LM3886 coming from a balanced source?
Generally, balanced is better for noise rejection. It's used in pro audio because of all the long cable runs. If the amp has an unbalanced input you should use an unbalanced source. If you want to use a balanced source with your single ended input amp then you can make a balanced to single ended receiver.
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Old 6th February 2007, 03:40 PM   #3
sek is online now sek  Germany
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And again

Running balanced makes you more independent of the electrical safety earth wiring in your studio facility, as it connects chassis ground of mixer console and speakers independent of signal levels.

Unbalanced wiring uses the cable shield as signal ground, which imposes the signal reference to the chassis ground. If two chassi have different ground potential throughout your room, this will introduce an AC signal corresponding to that ground potential difference into your audio signal: hum.

Two solutions: a transformer-based input converter (called DI-box) that adapts balanced line connections to unbalanced amp inputs - or a balanced line receiver module inside your amplifier enclosure. The latter one is cooler and can be found even for chip amps. Look for Texas Instrument's INA134 if you're interrested.

Hope...

edit: Poster lgreen's website has moved, but his Click the image to open in full size. button works.
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Old 6th February 2007, 04:10 PM   #4
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ok why is it important to make a balanced to single ended receiver? either way i want to look more into this but what would it matter without the receiver? quality loss? obviously it wont be balanced but what would the receiver do different?
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Old 6th February 2007, 04:21 PM   #5
BWRX is offline BWRX  United States
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Signal quality and noise immunity are the main reasons.

You can use the + and ground wires of a balanced signal to feed an unbalanced input, but it is not designed for that so don't expect as much out of it. If you ground the - signal of a balanced signal then you are really just shorting the output of the balanced source to ground. Some sources might not like this.
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Old 6th February 2007, 04:22 PM   #6
sek is online now sek  Germany
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The whole connection would then work unbalanced, which is perfectly okay if sound quality isn't harmed. Pin 1 (always) is ground, pin 2 then becomes the only signal connection and pin 3 goes to ground in this case, too. In order to play it safe, use resistors in the order of a couple Ohm to connect pins 2 and 3.

But you can't go back, then. Doing it with a balanced line receiver lets you keep all the options...

edit: Brian, a day off?
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Old 6th February 2007, 04:26 PM   #7
BWRX is offline BWRX  United States
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sek, our brains appear to be synchronized today

I'm actually "working" at my desk today
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Old 6th February 2007, 05:20 PM   #8
sek is online now sek  Germany
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Very special!
I bet You're writing on something I'm writing on...
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Old 6th February 2007, 05:58 PM   #9
impsick is offline impsick  United States
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ok brian, Sek thanks for your input. appreciate it.
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