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Balanced vs. Single-ended

post #1 of 6
2/1/05 at 8:25pm
Thread Starter 
Hi couldn't find a proper answer to this. I thought this might be the best forum for this, not sure....

I'm just wondering (oh no...) :

1. Is the performance of a through-out balanced system to be considering something like the last 3% of the sound compared to a completely single-ended setup (if the system consisted of same amp, source etc.)

2. If you have two identical single-ended amps, can you use them as monoblocks (as a balanced setup) ? I'm mainly thinking about two identical SDS Labs headphone amplifiers: http://headwize.com/projects/showfil...stokes_prj.htm.

3. Would it be a big mistake and waste to get something like a Benchmark DAC 1, do a XLR-RCA unbalanced mod to connect it to a single-ended SDS labs headphone amp -> HD650 ? By this I mean, will it be a waste to pair it with a stand alone headphone amp, when it was engineered with HD650 in mind in the first place.

TIA
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post #2 of 6
2/1/05 at 9:48pm
1-different.better or worse ? Matter of choice.Where balaned is especailly useful if not essential is for long runs where the noise cancelling effect of a balanced topology eliminates any common mode signals which can only be from hum or noise.The audio signal will either be a positive or negative version of the original.

2-No.Not without adding circuit complexity (phase splitters) and changing the output transformer from a SE Tranny to a PP output tranny.and it is not as simple as just plugging in transformers.
Solid state is a bit easier to get the "balanced bridge" where the inputs are driven with a plus and minus siganl for the left and right intputs then theoutput is taken from both the left and right "hot" speaker terminals.both grounds are then left floating.
But attach a common ground speaker selector to such a circuit and you will lose your output stage when the selector switch shorts the "hot" to ground.

3-no.
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post #3 of 6
2/1/05 at 10:46pm
Thread Starter 
The SDS is a solid state amp, so it looks do-able from what you described... But as you said, the "improvement" could just as well be a "side step"... I can see how this techically can be superior now, though. Saved my wallet there (for now). Thx
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post #4 of 6
2/2/05 at 12:57am
The SDS labs Headphone Amp is a truly fine amp that does not get nearly the attention it should.I guess becasue the design has been around for a few years (even though the biasing scheme has been updated) it is no longer in fashion with the amp of the month club crew but i can tell you this baby will drive any headphones you throw at it and sound good too.
you do realise you can get the pcb directly from Sheldon Stoke's web site right ?
The link from headwize is not correct (unless it has been updated) and it is now http://www.quadesl.com/ for the main page and http://www.quadesl.com/schematics.shtml for the board ordering and info page.

The original SDS HPA pdf file-http://www.quadesl.com/pdf/hpart.pdf

Sheldon's original amp pics





also-if balanced operation is an imperitive for you there are steps you can take to make the SDS amp have a balanced input :

1-configure the opamp for balanced operation
2-build as per the instructions then add a balanced tranformer in
3-use an adapter and go straight to an InAmp (instrumentation Amp) to replace the opamp.

I know,WAY too much information but maybe helpful

rickmeister
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post #5 of 6
2/2/05 at 8:58am
Thread Starter 
I already made one SDS labs amp + Meier crossfeed... finished except for chassis. It was a modded PCB, meaning that it takes two mono op-amps instead of the dual, and some electrolytics have been moved slightly (since all electrolytics are 16 mm, not just 12.5 for the 330 uFs.). It features lone JFET class A biasing, and space had been made for the longer and larger diameter RN60 resistors. I'm highly satisfied with how it sounds, it's excellent .
Considering most stand-alone DACs have balanced outputs, it was just very tempting to investigate the posibilities for a balanced headphone amp. But I think i'll use it single-ended (for a long time to come at least)

Quote:
1-configure the opamp for balanced operation
2-build as per the instructions then add a balanced tranformer in
3-use an adapter and go straight to an InAmp (instrumentation Amp) to replace the opamp.
Hehe... a lot of work. About the third step - why replace them? not sure what an in-amp is compared to an op-amp either.
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post #6 of 6
2/2/05 at 12:13pm
An exellant primer on inamps :

http://www.analog.com/en/content/0,2...F43643,00.html

An audio specific "instrument" amp.not the "+" and "-" inputs and the final opamp output.This is your "balanced input" circuit-



from this device-

http://www.analog.com/UploadedFiles/...4SSM2019_0.pdf

on this age-

http://www.analog.com/en/prod/0,2877,SSM2019,00.html

TI/Burr-Brown has devices that perform the same function.Mostly these are used for balanced mic preampos and such but are equally suited to line level balanced interfaces
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