balanced connection to a 4 channel amp...will this work

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davidismynaim
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balanced connection to a 4 channel amp...will this work

Post by davidismynaim » Fri Sep 21, 2012 12:35 am

Hi everyone, looking for someone with more experience than me as to an idea I have with some recently acquired HiFi.

I have an M-DAC which has the option of balanced output via XLR. I have just bought a beast of a SS amp off ebay - it is a DBX DX3 4 channel power amp.

It has 2x stereo phono inputs, with 3 modes, 4 way, 3 way and bridged 2 way. Someone suggested I could make up special XLR to 2 phono cables. Hot to one phono cold to the other, both sharing the earth. These 2 cables could then be used as the input with the amp in 4 way mode. connecting the speakers to only the red terminals.

I have never used balanced connections and this is pushing my knowledge to the limit. But as i understand this arrangement, the speaker would see the differential between the +ve and -ve polarity on the two speaker posts and this would cancel out any common noise. Have I got this right and does this sound like a sensible plan?

The alternative is to switch the amp into bridge mode and connect up using a single set of unbalanced phono cables.

thanks for any help here...

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Nick
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Post by Nick » Fri Sep 21, 2012 11:57 am

In theory it would work as you describe, but can't say without trying it.
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davidismynaim
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Post by davidismynaim » Fri Sep 21, 2012 3:25 pm

and do you think it is a good theory ie better topology than simple phono connections (if it works) if you know what I mean. I would try it with some cheap speakers first before blowing up my Yamaha's that Colin took delivery this week... don't want to hurt those!

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Mike H
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Post by Mike H » Sat Sep 22, 2012 12:01 am

Took me a while but I think I now get what you mean ~ work it as 4-way, but can get opposite phase outputs from each pair of the amps by giving them opposite phase ('balanced') inputs?

I can see how it might work, do you need that much power
 
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Post by brig001 » Sat Sep 22, 2012 1:27 am

It should work, but I'd be a bit wary. If you scroll down this page http://sound.westhost.com/project87.htm to where it says "Hey! That's Cheating" you'll see why it might not work. There's also a good article here http://sound.westhost.com/articles/balanced-2.htm which might be useful too.

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Mike H
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Post by Mike H » Sat Sep 22, 2012 1:10 pm

No that isn't a true balanced, BUT, he HAS got balanced o/p from CD player, via 3-pin XLR, so will have + & – signals & a ground.

So I'm thinking, as he did, custom XLR to 2 x phono lead, XLR ground to each phono ground, signals to each phono pin, why shouldn't it work :D

Rather than risk the speakers you could use dummy load resistors instead. Initially :?:
 
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Post by davidismynaim » Sat Sep 22, 2012 10:59 pm

Mike that is exactly what I'm thinking. I have a cheap set of speakers to test out. It will be a lot of power each amp is 150w. So will need to be careful really gain. I have 20db attenuators so this should help.

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Mike H
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Post by Mike H » Sun Sep 23, 2012 11:18 am

Cripes do you need 150W ?

Blowing up resistors is still less than blowing up speakers, however 'cheap' :lol:
 
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Post by davidismynaim » Sun Sep 23, 2012 5:32 pm

More like 300w if this differential concept works. No don't need that amount of power. Using Yamaha ns1000m. They are quite efficient. But am interested in merit of balanced connection with its noise cancelling benefits. Hence the 20db attenuates. The amp has gain controls too. So should be able to control the power.

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Post by brig001 » Mon Sep 24, 2012 1:51 am

Mike H wrote:No that isn't a true balanced, BUT, he HAS got balanced o/p from CD player, via 3-pin XLR, so will have + & – signals & a ground.
My mixing desk has a "balanced" output on a 3 pin XLR, but is wired as the example I gave, so it is worth checking. The resistor idea is good too.

Brian.

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Nick
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Post by Nick » Mon Sep 24, 2012 8:43 am

I doubt it a issue with the solid state output on the m-dac, but balanced output doesn't need to be +- about ground, its entirely possible for the ground on the output to not be connected and the output fully floating.
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Post by Mike H » Mon Sep 24, 2012 1:08 pm

Just to confuse the issue further :lol:
 
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