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Old 26th September 2003, 04:40 PM   #1
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Default Balanced to SE

Im building a Dual mono DAC around the BB PCM1794, which gives out the balanced output. How do I convert the balance to single ended. I want the DAC to be able to output both SE and balanced.

So.... to make the blanaced output SE I guess I take the output from the DAC chip after the I/V into a converter such as INA134 to SE phono connectors. Then at the same time take the balanced output of the I/V to XLR's for balanced output?

Also how do you make a fully balanced active xover or is that asking for trouble. Do you just build twice what you would normally build, put the +into one half and the -into the second then use the INA at the end of it.??

Cheers Matt.
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Old 26th September 2003, 05:09 PM   #2
grataku is offline grataku  United States
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Balanced I/V should not be a problem, there discrete (passlabs D1 I/V stage) or op-amp solutions (for ex. the I/V of the AD1955 eval board uses ad797 op amps).
You take the balanced out (+ and -) or the se (+ and GND).
As far as xovers I don't know anything about it, if I had to guess it sounds like component tolerance may be a problem in building identical differential filters, maybe not. Professional equipment uses lots of balanced but they may convert back and forth as needed.
In my system I like balanced so much so I keep mine from the dac to the speakers and don't do active filtering.
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Old 26th September 2003, 05:56 PM   #3
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OK so after the output of the DAC I have it balanced so there is the + and -. For balanced I take all of it and for SE only I use the + and grnd. So I get the 129 SNR for SE and 132 for balanced. If I use the INA do I maintain the 132 or does the chip basically just short one output to ground.

If I want to take balanced from the DAC to the SE active xover I guess I will then need the INA in the xover.
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Old 26th September 2003, 06:37 PM   #4
tiroth is offline tiroth  United States
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If you actively convert balanced to SE via electronics or transformer you preserve the S/N of the balanced signal...if your converter has a S/N that high!

I suspect the usual method of doing balanced xovers is balun conversion at the ins/outs, but I did exactly what you described (double the circuit) with my recent crossover. The tradeoff is lower distortion/noise versus loss of CMRR, I believe. Higher component cost too, of course.
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Old 26th September 2003, 07:37 PM   #5
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OK cheers maybe ill try balanced with cheap ops to see what its like. Im doing a three way which will require quite a few as it is so doubling that would cost much more. I dont think that TI Nsemi and AD waill supply that many free samples

Im going to try and get 8opa627's for the 1st I/V section got the DAC as well as four surface mount 28pin things and another 8pin DIL.

Maybe if I can get loads of ops ill build it balanced but until then, its time to find a converter with a 132 SNR!
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Old 26th September 2003, 08:04 PM   #6
tiroth is offline tiroth  United States
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Sounds....very difficult. Although the TI specs are for A-weighted measurement, so the actual figures will likely be considerably worse. If you can get 115-120dB S/N I'd say that is about as good as is worth shooting for.
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Old 26th September 2003, 10:14 PM   #7
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Well, as standard cd's max is within that then i guess im not loosing out on much. Im going to add the converter thingymabob and compare the difference, as its only gonna cost £4 more to do so.
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Old 27th September 2003, 09:40 AM   #8
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Quote:
Originally posted by 5th element
OK so after the output of the DAC I have it balanced so there is the + and -. For balanced I take all of it and for SE only I use the + and grnd.
If you take signal from - and gnd you will have inverted polarity audio.
Selecting + or - at the dac will give you absolute polarity control.

Eric.
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Old 27th September 2003, 10:22 AM   #9
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I've just thought of something that could present a bit of a problem unless there are ways of getting round this.

How do you adjust the volume of two channel balanced with a single 2 track pot??? The only thing I can think of is convert the balanced to SE then put the pot in the signal path then convert the SE to balanced again, this seems a little bit over the top and im sure there are much better ways of doing this.
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Old 27th September 2003, 06:28 PM   #10
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This is what I did for a cheap balanced attenuator:
Attached Images
File Type: gif balancedattenuator.gif (1.9 KB, 400 views)
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