Balanced Line Implementation

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Balanced Line Implementation

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Graham Holloway
Guest

Posted: Mon Nov 29, 2004 6:19 pm Post subject: Balanced Line Implementation

Does anyone here have any specific thoughts on the means of implementing balanced lines, ie. transformers, discrete circuits using IC op-amps, dedicated driver and receiver IC's, etc. I need to buffer other audio circuits and I have yet to find anything that I feel I can confidently use as I have never done this before. Graham Holloway

Brian Allen
Guest

Posted: Tue Nov 30, 2004 12:20 am Post subject: Re: Balanced Line Implementation

Graham Holloway wrote:

Quote:

Does anyone here have any specific thoughts on the means of implementing
balanced lines, ie. transformers, discrete circuits using IC op-amps,
dedicated driver and receiver IC's, etc.

I need to buffer other audio circuits and I have yet to find anything that I
feel I can confidently use as I have never done this before.

Graham Holloway

Here are two resources I found useful. If you are looking for simple
implementation I have recently been toying with the burr brown DRV134
and INA 137 and have found them excellent for my purposes.

http://www.jensen-transformers.com/an/an003.pdf

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

Brian

Karl Uppiano
Guest

Posted: Tue Nov 30, 2004 6:22 am Post subject: Re: Balanced Line Implementation

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:41ABDBB4.1DDC77D1@hotmail.com...

Quote:

Brian Allen wrote:

Graham Holloway wrote:
Does anyone here have any specific thoughts on the means of
implementing
balanced lines, ie. transformers, discrete circuits using IC op-amps,
dedicated driver and receiver IC's, etc.

I need to buffer other audio circuits and I have yet to find anything
that I
feel I can confidently use as I have never done this before.

Graham Holloway

Here are two resources I found useful. If you are looking for simple
implementation I have recently been toying with the burr brown DRV134
and INA 137 and have found them excellent for my purposes.

http://www.jensen-transformers.com/an/an003.pdf

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

I see that Doug Self hasn't learnt how to design for equal inverting and
non-inverting input impedances on his differential input circuits.

Graham

Either figure 12 or figure 13 look OK to me...

Brian Allen
Guest

Posted: Tue Nov 30, 2004 6:22 am Post subject: Re: Balanced Line Implementation

Pooh Bear wrote:

Quote:

Brian Allen wrote:

Graham Holloway wrote:

Does anyone here have any specific thoughts on the means of implementing
balanced lines, ie. transformers, discrete circuits using IC op-amps,
dedicated driver and receiver IC's, etc.

I need to buffer other audio circuits and I have yet to find anything that I
feel I can confidently use as I have never done this before.

Graham Holloway

Here are two resources I found useful. If you are looking for simple
implementation I have recently been toying with the burr brown DRV134
and INA 137 and have found them excellent for my purposes.

http://www.jensen-transformers.com/an/an003.pdf

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

I see that Doug Self hasn't learnt how to design for equal inverting and
non-inverting input impedances on his differential input circuits.

Graham

Hi Graham, which topologies are you refering in D. Self's site? Are
you talking diferential or common mode input impedance? He notes that
the differential input imp. is non-equal on some of the layouts,
sacraficing it for common mode input imp. equality. Does the 'superbal'
circuit (fig 12) not provide equality on both though?

Brian

Pooh Bear
Guest

Posted: Tue Nov 30, 2004 6:22 am Post subject: Re: Balanced Line Implementation

Brian Allen wrote:

Quote:

Graham Holloway wrote:
Does anyone here have any specific thoughts on the means of implementing
balanced lines, ie. transformers, discrete circuits using IC op-amps,
dedicated driver and receiver IC's, etc.

I need to buffer other audio circuits and I have yet to find anything that I
feel I can confidently use as I have never done this before.

Graham Holloway

Here are two resources I found useful. If you are looking for simple
implementation I have recently been toying with the burr brown DRV134
and INA 137 and have found them excellent for my purposes.

http://www.jensen-transformers.com/an/an003.pdf

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

I see that Doug Self hasn't learnt how to design for equal inverting and
non-inverting input impedances on his differential input circuits.

Graham

Tomi Holger Engdahl
Guest

Posted: Tue Nov 30, 2004 12:11 pm Post subject: Re: Balanced Line Implementation

"Graham Holloway" <eng@wps-electronics.demon.co.uk> writes:

Quote:

You can find some general information on this field at
http://www.epanorama.net/links/audiopro.html#wiring
and lots of links to circuits for on this field at
http://www.epanorama.net/links/audiocircuits.html#diff

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

Kevin McMurtrie
Guest

Posted: Wed Dec 01, 2004 6:08 am Post subject: Re: Balanced Line Implementation

In article <cofkf1$mih$1$8302bc10@news.demon.co.uk>,
"Graham Holloway" <eng@wps-electronics.demon.co.uk> wrote:

Quote:

Simple op-amps will do this if you're not looking for common mode
rejection of more than a couple of volts. The output should unbalanced
if you're using coaxial cable with a single center conductor, but the
input still mostly balanced.

There are some exotic double shield cables for very long runs (much
longer than a house). Two amps drive the same signal to the center
conductor and the inner shield. The center conductor then sees a lower
load capacitance so it degrades more slowly. The end of it needs to be
terminated in some way to maintain noise rejection. Check an
electronics book.

Pooh Bear
Guest

Posted: Wed Dec 01, 2004 12:10 pm Post subject: Re: Balanced Line Implementation

Karl Uppiano wrote:

Quote:

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:41ABDBB4.1DDC77D1@hotmail.com...
Brian Allen wrote:

Graham Holloway wrote:
Does anyone here have any specific thoughts on the means of
implementing
balanced lines, ie. transformers, discrete circuits using IC op-amps,
dedicated driver and receiver IC's, etc.

I need to buffer other audio circuits and I have yet to find anything
that I
feel I can confidently use as I have never done this before.

Graham Holloway

Here are two resources I found useful. If you are looking for simple
implementation I have recently been toying with the burr brown DRV134
and INA 137 and have found them excellent for my purposes.

http://www.jensen-transformers.com/an/an003.pdf

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

I see that Doug Self hasn't learnt how to design for equal inverting and
non-inverting input impedances on his differential input circuits.

Graham

Either figure 12 or figure 13 look OK to me...

I've never seen them actually implemented in any audio gear. Fine in theory

Figs 9 and 10 are classic examples of poor design though. Widely seen in many
pieces of kit though. Fig 10 looks like it's from a Soundcraft Spirit Folio.

It iseasily fixable though. In Fig 9 change R2 and R4 to 3k3. This will give
equal loading on both legs with a balanced signal.

The scaling of values can be used to work this 'trick' for any gain. You end
up with some oddball values - easily fixed by a series or parallel arrangement
of resistors.

Neve used to - probably still do - have custom resistor packs made for this
topolgy.

I've improved the Fig 10 style arrangement to at least offer symmetrical
impedances in the '+4' setting.

Graham

Brian Allen
Guest

Posted: Fri Dec 03, 2004 12:06 pm Post subject: Re: Balanced Line Implementation

Pooh Bear wrote:

Quote:

Karl Uppiano wrote:

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:41ABDBB4.1DDC77D1@hotmail.com...

Brian Allen wrote:

Graham Holloway wrote:

Does anyone here have any specific thoughts on the means of
implementing
balanced lines, ie. transformers, discrete circuits using IC op-amps,
dedicated driver and receiver IC's, etc.

I need to buffer other audio circuits and I have yet to find anything
that I
feel I can confidently use as I have never done this before.

Graham Holloway

Here are two resources I found useful. If you are looking for simple
implementation I have recently been toying with the burr brown DRV134
and INA 137 and have found them excellent for my purposes.

http://www.jensen-transformers.com/an/an003.pdf

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

I see that Doug Self hasn't learnt how to design for equal inverting and
non-inverting input impedances on his differential input circuits.

Graham

Either figure 12 or figure 13 look OK to me...

I've never seen them actually implemented in any audio gear. Fine in theory

Figs 9 and 10 are classic examples of poor design though. Widely seen in many
pieces of kit though. Fig 10 looks like it's from a Soundcraft Spirit Folio.

It iseasily fixable though. In Fig 9 change R2 and R4 to 3k3. This will give
equal loading on both legs with a balanced signal.

Doesn'this then match the differential input impedance, but then
unbalance the common mode input impedance? This is what I measure when
I tested it, in fact it matched table 3 in D. Selfs article. Wouldn't
the common mode input impedance matching be more important because the
whole reason for balanced circuitry is to use the common mode rejection
for noise reduction. With audio signals having plenty of signal
typically we are not worried to much about exactly matching the
differential input impedance. Or am I mistaken and the differential
input impedance matching is more important?

Brian

Quote:

The scaling of values can be used to work this 'trick' for any gain. You end
up with some oddball values - easily fixed by a series or parallel arrangement
of resistors.

Neve used to - probably still do - have custom resistor packs made for this
topolgy.

I've improved the Fig 10 style arrangement to at least offer symmetrical
impedances in the '+4' setting.

Graham

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