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Balanced outputs

  • Thread starter Dirk Bruere at NeoPax
  • Start date
D

Dirk Bruere at NeoPax

Jan 1, 1970
0
Looking for a buffer design to provide a balanced output from an
AK4396 DAC. The latter outputs a differential signal.
I found this page, which seems to provide a nice example
http://sound.westhost.com/balance.htm

Particularly, Fig. 5
Any comments on suitability, or anything I might have overlooked in
using something like this?

Dirk
 
E

Eeyore

Jan 1, 1970
0
Dirk said:
Looking for a buffer design to provide a balanced output from an
AK4396 DAC. The latter outputs a differential signal.
I found this page, which seems to provide a nice example
http://sound.westhost.com/balance.htm

Particularly, Fig. 5
Any comments on suitability, or anything I might have overlooked in
using something like this?

All looks way too complicated to me.

Did you know that a balanced output doesn't require 'symmetrical'
voltages on both its legs, merely matched impedance ? Honest.

You can do it with a single op-amp.

Graham
 
D

Dirk Bruere at NeoPax

Jan 1, 1970
0
All looks way too complicated to me.

Did you know that a balanced output doesn't require 'symmetrical'
voltages on both its legs, merely matched impedance ? Honest.

You can do it with a single op-amp.

Graham

Buffer each leg separately with a unity gain config?

Dirk
 
E

Eeyore

Jan 1, 1970
0
Dirk said:
Buffer each leg separately with a unity gain config?

No. In the simplest configuration, the output op-amp drives the + wire via
say 100 ohms.

The - wire is connected to the local ground next to the op-amp's feedback
network by another 100 ohms.

That's a balanced feed.

There are even cuter ways of doing it involving taking that second 100 ohms
into the feedback network too but that actually goes beyond being merely
balanced. It's 'active sensing' and will drive an UNbalanced input with the
same precision.

You only need 2 op-amps if you need say +28dBu output level.

Graham
 
D

Dirk Bruere at NeoPax

Jan 1, 1970
0
Dirk Bruere at NeoPax wrote:





No. In the simplest configuration, the output op-amp drives the + wire via
say 100 ohms.

The - wire is connected to the local ground next to the op-amp's feedback
network by another 100 ohms.

That's a balanced feed.

There are even cuter ways of doing it involving taking that second 100 ohms
into the feedback network too but that actually goes beyond being merely
balanced. It's 'active sensing' and will drive an UNbalanced input with the
same precision.

You only need 2 op-amps if you need say +28dBu output level.

Graham

I just need unity gain.

Interesting page
http://www.dself.dsl.pipex.com/ampins/balanced/balanced.htm

Dirk
 
E

Eeyore

Jan 1, 1970
0
Dirk said:

The one I suggested above was Fig 3. The very simplest. That will do you fine
although 5 can help fix other problems like driving unbalanced inputs.

The active sensing one is Fig 5.

If you REALLY want to learn from an expert find Bill Whitlock's article(s) on the
subject at jensen transformers. Of course he's promoting the use of transformers
but there's a lot of good stuff there and he blows a few myths away. I saw him
present this at an AES meeting actually. Very good too.

Graham
 
D

Dirk Bruere at NeoPax

Jan 1, 1970
0
Eeyore said:
The one I suggested above was Fig 3. The very simplest. That will do you fine
although 5 can help fix other problems like driving unbalanced inputs.

The active sensing one is Fig 5.

If you REALLY want to learn from an expert find Bill Whitlock's article(s) on the
subject at jensen transformers. Of course he's promoting the use of transformers
but there's a lot of good stuff there and he blows a few myths away. I saw him
present this at an AES meeting actually. Very good too.

Graham

I just want to drive some high quality audio direct from a DAC +/-
outputs over about 15m of shielded cable. I think I'll maybe reduce the
DAC outputs to single ended first using the recommended circuit and then
do one of the above - maybe using Fig 3
 
E

Eeyore

Jan 1, 1970
0
Dirk said:
I just want to drive some high quality audio direct from a DAC +/-
outputs over about 15m of shielded cable. I think I'll maybe reduce the
DAC outputs to single ended first using the recommended circuit and then
do one of the above - maybe using Fig 3

What DAC btw ?

Graham
 
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