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Old 17th October 2012, 01:28 PM   #11
dacen is offline dacen  Norway
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Suggestion. Take a look at this one. Easy to implement:
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Old 17th October 2012, 01:30 PM   #12
Elvee is offline Elvee  Belgium
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You could use this nice circuit from Marcel, it is probably overkill for you, but it does all you need, and more:
Alternative topologies for balanced to unbalanced amplifier
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Old 17th October 2012, 10:52 PM   #13
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Default Thank You All

Between Dan and dacen's suggestions, I am digging into THAT corp application notes and learning something.

Elvee, Thanks. Marcel's design is pretty neat, but as you say, more than I need.

Thanks Demeterart. You are correct, I mis-stated the resistor relationship. I will take your suggestion and check the HF phase margin before adding a shunt capacitor.

Andrew T, Thanks for the clear definition of balanced. It is probably the best one I have read. I will take to heart the suggestion of matching stability component impedances and precision resistors.

I still have a lot to learn from you guys. Thanks again.

Jac
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Old 18th October 2012, 11:14 AM   #14
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Quote:
Originally Posted by sreten View Post
Hi,

Is this circuit needed at all ? Unless the cable is very long converting
to balanced has very little advantage if the single ended source has
decent cable driving capability

rgds, sreten.
sreten,

You are correct, of course. A good single ended system works just fine. Sometimes, I need to do a project just to learn.

Although my line level run at 4 meters is longer than many single ended runs, it isn't long enough to need a balanced system. But I am doing it anyway, just to see if I can and what it sounds like.

I have a friend with commercially built high end audio equipment that has both single and balanced outputs. He says, he can't tell me why, but he likes the sound better when using the balanced cables.

And, I have already learned something through the input given by others in this thread.

Jac
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Old 18th October 2012, 12:43 PM   #15
AndrewT is offline AndrewT  Scotland
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the "improved" sound of your friends balanced system could be due to attenuated interference.
Even though the interference is generally inaudible, that does not mean that reducing the low level interference will have no audible effect.
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Old 18th October 2012, 01:47 PM   #16
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by lehmanhill View Post
sreten,

You are correct, of course. A good single ended system works
just fine. Sometimes, I need to do a project just to learn.

Although my line level run at 4 meters is longer than many single
ended runs, it isn't long enough to need a balanced system.
But I am doing it anyway, just to see if I can and what it sounds like.

I have a friend with commercially built high end audio equipment that
has both single and balanced outputs. He says, he can't tell me why,
but he likes the sound better when using the balanced cables.

And, I have already learned something through the input given by
others in this thread.

Jac
Hi,

My point was, if you read the link, there is more than one way
of connecting a single ended output to a remote balanced input,
the simple single ended connection does not take advantage of
the balanced connection at the other end. You can wire the
cable such that is does usefully utilise features of the remote
balanced input without using a fully balanced driver.

Its not simply a case of single ended versus balanced.

rgds, sreten.
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Old 18th October 2012, 10:35 PM   #17
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sreten,

You caught me. I glanced at the link, but didn't read it deeply enough to see the interesting idea you are suggesting. There is more good information in that link and Mr. Self has a great reputation, so I will study it in detail.

Thanks.

Jac
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Old 25th October 2012, 12:30 AM   #18
dmills is offline dmills  United Kingdom
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A single ended driver with a resistor equal to the output impedance to audio 'ground' for the other leg of the output is a perfectly valid balanced output, it is exactly equivalent to a fully differential output except that the signal level is 6dB lower.

This is **very** common in pro audio and has the advantage that you do not see a 6dB level deficit if plugging an unbalanced load into such a source, of course the downside is effectively 6dB less noise rejection because the differential voltage is 6dB lower.

You will want to look a Whitlocks papers, also the stuff from Tony Walderon is solid on how to do interference free audio on a large scale.
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Old 25th October 2012, 08:47 AM   #19
AndrewT is offline AndrewT  Scotland
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Dmills,
I am not following your argument.
Are you saying that you can get the benefit of the noise attenuation of balanced impedance connections with a single ended (unbalanced) connection? And further that Whitlock confirms this assertion?
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Old 25th October 2012, 12:13 PM   #20
dmills is offline dmills  United Kingdom
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Not quite!

I am asserting that there is no need for a balanced line to be driven differentially to get the benefits.

Balanced is talking ONLY about the impedance to ground so something like an opamp with 50 ohm buildout resistor to pin 2, 50 ohm buildout resistor from circuit 0V to pin 3 and pin one bonded directly to chassis is a perfectly valid balanced line output (Omitting the RFI and P48 protection details), and assuming standard XLR pinning.

Making it differential gets you 6dB more voltage on the line of course, but you can get most of the way there with a single extra resistor at the sending end, the receiver does of course still need to be a differential input.

Whitlocks AES lecture explaining balanced lines in terms of a wheatstone bridge is worth looking out (The slides are available on line).

Regards, Dan.
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