Output splitting

[Patrick Dunford]

I have a need to split the outputs of a mixing desk to drive two separate
devices. Because a distribution amp provides more features than needed
(more than 2 outputs in most cases) and costs a lot more, I also looked
at using a mic splitter transformer e.g.
http://www.jensen-transformers.com/datashts/dinms2p.pdf

The main issue from what I can see is the maximum input level the
transformer can accept, around 2dbV typical. Specs on the mixing desk say
its maximum output is +21dBm, although the output impedance is 75 ohms.
The input impedance of the transformer is around 1000 ohms, so the
voltage across the primary would be quite a bit less than the desk
output.

As the desk is designed to drive a 600 ohm balanced line, I'm assuming
that driving a transformer would provide a similar load to it.

Obviously we can just connect our devices in parallel without a
transformer; the point of using the transformer was to match the
impedances on the various pieces of equipment.

[Patrick Dunford]

In article > in
rec.audio.pro on Fri, 10 Sep 2004 13:59:05 +1200, Patrick Dunford
> says...
> I have a need to split the outputs of a mixing desk to drive two separate
> devices. Because a distribution amp provides more features than needed
> (more than 2 outputs in most cases) and costs a lot more, I also looked
> at using a mic splitter transformer e.g.
> http://www.jensen-transformers.com/datashts/dinms2p.pdf
>
> The main issue from what I can see is the maximum input level the
> transformer can accept, around 2dbV typical. Specs on the mixing desk say
> its maximum output is +21dBm,

Sorry +21dBu

although the output impedance is 75 ohms.
> The input impedance of the transformer is around 1000 ohms, so the
> voltage across the primary would be quite a bit less than the desk
> output.
>
> As the desk is designed to drive a 600 ohm balanced line, I'm assuming
> that driving a transformer would provide a similar load to it.
>
> Obviously we can just connect our devices in parallel without a
> transformer; the point of using the transformer was to match the
> impedances on the various pieces of equipment.
>

[Patrick Dunford]

In article > in
rec.audio.pro on Fri, 10 Sep 2004 13:59:05 +1200, Patrick Dunford
> says...
> I have a need to split the outputs of a mixing desk to drive two separate
> devices. Because a distribution amp provides more features than needed
> (more than 2 outputs in most cases) and costs a lot more, I also looked
> at using a mic splitter transformer e.g.
> http://www.jensen-transformers.com/datashts/dinms2p.pdf
>
> The main issue from what I can see is the maximum input level the
> transformer can accept, around 2dbV typical. Specs on the mixing desk say
> its maximum output is +21dBm,

Sorry +21dBu

although the output impedance is 75 ohms.
> The input impedance of the transformer is around 1000 ohms, so the
> voltage across the primary would be quite a bit less than the desk
> output.
>
> As the desk is designed to drive a 600 ohm balanced line, I'm assuming
> that driving a transformer would provide a similar load to it.
>
> Obviously we can just connect our devices in parallel without a
> transformer; the point of using the transformer was to match the
> impedances on the various pieces of equipment.
>

[Scott Dorsey]

Patrick Dunford > wrote:
>I have a need to split the outputs of a mixing desk to drive two separate
>devices. Because a distribution amp provides more features than needed
>(more than 2 outputs in most cases) and costs a lot more, I also looked
>at using a mic splitter transformer e.g.
>http://www.jensen-transformers.com/datashts/dinms2p.pdf

Why not use a line-level splitter transformer that is designed for the
job?

>The main issue from what I can see is the maximum input level the
>transformer can accept, around 2dbV typical. Specs on the mixing desk say
>its maximum output is +21dBm, although the output impedance is 75 ohms.
>The input impedance of the transformer is around 1000 ohms, so the
>voltage across the primary would be quite a bit less than the desk
>output.

So, buy a transformer that can handle higher levels. Jensen and Lundahl
make a couple transformers that can be set up for line splitting. Audisar
makes a thing with one 600 ohm primary and six 600 ohm secondaries, which
is great for press boxes.

>As the desk is designed to drive a 600 ohm balanced line, I'm assuming
>that driving a transformer would provide a similar load to it.

Right. Although most modern gear can drive lower impedances without
difficulty. Older transformer-coupled stuff may be touchy about loading.

>Obviously we can just connect our devices in parallel without a
>transformer; the point of using the transformer was to match the
>impedances on the various pieces of equipment.

These days that matters on very little gear. If you have outputs that
are transformer-coupled going into real 600 ohm inputs, you need it.
But with most gear today, we have high-Z inputs on everything and low-Z
outputs, and no transformers, so matching is a non-issue.

What a splitter transformer DOES buy you is isolation between outputs.
That can be a big deal if you're feeding to something you don't trust,
like in a press box situation.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Patrick Dunford > wrote:
>I have a need to split the outputs of a mixing desk to drive two separate
>devices. Because a distribution amp provides more features than needed
>(more than 2 outputs in most cases) and costs a lot more, I also looked
>at using a mic splitter transformer e.g.
>http://www.jensen-transformers.com/datashts/dinms2p.pdf

Why not use a line-level splitter transformer that is designed for the
job?

>The main issue from what I can see is the maximum input level the
>transformer can accept, around 2dbV typical. Specs on the mixing desk say
>its maximum output is +21dBm, although the output impedance is 75 ohms.
>The input impedance of the transformer is around 1000 ohms, so the
>voltage across the primary would be quite a bit less than the desk
>output.

So, buy a transformer that can handle higher levels. Jensen and Lundahl
make a couple transformers that can be set up for line splitting. Audisar
makes a thing with one 600 ohm primary and six 600 ohm secondaries, which
is great for press boxes.

>As the desk is designed to drive a 600 ohm balanced line, I'm assuming
>that driving a transformer would provide a similar load to it.

Right. Although most modern gear can drive lower impedances without
difficulty. Older transformer-coupled stuff may be touchy about loading.

>Obviously we can just connect our devices in parallel without a
>transformer; the point of using the transformer was to match the
>impedances on the various pieces of equipment.

These days that matters on very little gear. If you have outputs that
are transformer-coupled going into real 600 ohm inputs, you need it.
But with most gear today, we have high-Z inputs on everything and low-Z
outputs, and no transformers, so matching is a non-issue.

What a splitter transformer DOES buy you is isolation between outputs.
That can be a big deal if you're feeding to something you don't trust,
like in a press box situation.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Patrick Dunford]

In article > in rec.audio.pro on 9 Sep 2004
22:51:04 -0400, Scott Dorsey > says...
> Patrick Dunford > wrote:
> >I have a need to split the outputs of a mixing desk to drive two separate
> >devices. Because a distribution amp provides more features than needed
> >(more than 2 outputs in most cases) and costs a lot more, I also looked
> >at using a mic splitter transformer e.g.
> >http://www.jensen-transformers.com/datashts/dinms2p.pdf
>
> Why not use a line-level splitter transformer that is designed for the
> job?
>
> >The main issue from what I can see is the maximum input level the
> >transformer can accept, around 2dbV typical. Specs on the mixing desk say
> >its maximum output is +21dBm, although the output impedance is 75 ohms.
> >The input impedance of the transformer is around 1000 ohms, so the
> >voltage across the primary would be quite a bit less than the desk
> >output.
>
> So, buy a transformer that can handle higher levels. Jensen and Lundahl
> make a couple transformers that can be set up for line splitting. Audisar
> makes a thing with one 600 ohm primary and six 600 ohm secondaries, which
> is great for press boxes.

I don't see on the Jensen web site any specific model for line splitting,
they are all mic splitters.

[Patrick Dunford]

In article > in rec.audio.pro on 9 Sep 2004
22:51:04 -0400, Scott Dorsey > says...
> Patrick Dunford > wrote:
> >I have a need to split the outputs of a mixing desk to drive two separate
> >devices. Because a distribution amp provides more features than needed
> >(more than 2 outputs in most cases) and costs a lot more, I also looked
> >at using a mic splitter transformer e.g.
> >http://www.jensen-transformers.com/datashts/dinms2p.pdf
>
> Why not use a line-level splitter transformer that is designed for the
> job?
>
> >The main issue from what I can see is the maximum input level the
> >transformer can accept, around 2dbV typical. Specs on the mixing desk say
> >its maximum output is +21dBm, although the output impedance is 75 ohms.
> >The input impedance of the transformer is around 1000 ohms, so the
> >voltage across the primary would be quite a bit less than the desk
> >output.
>
> So, buy a transformer that can handle higher levels. Jensen and Lundahl
> make a couple transformers that can be set up for line splitting. Audisar
> makes a thing with one 600 ohm primary and six 600 ohm secondaries, which
> is great for press boxes.

I don't see on the Jensen web site any specific model for line splitting,
they are all mic splitters.

[John Hardy]

Patrick;

Simply use as many output transformers as required. The primary windings
connect in parallel to your one output, and each secondary goes to its
own destination. I did a project like this around 1990 with about 150
channels of mic preamps. There was a total of four output transformers
for each mic preamp output. Call Jensen for recommendations. The exact
transformer to use will depend on the details of your output circuit.

John Hardy
The John Hardy Co.
www.johnhardyco.com

[John Hardy]

Patrick;

Simply use as many output transformers as required. The primary windings
connect in parallel to your one output, and each secondary goes to its
own destination. I did a project like this around 1990 with about 150
channels of mic preamps. There was a total of four output transformers
for each mic preamp output. Call Jensen for recommendations. The exact
transformer to use will depend on the details of your output circuit.

John Hardy
The John Hardy Co.
www.johnhardyco.com

[Monte McGuire]

In article >,
Patrick Dunford > wrote:

> Obviously we can just connect our devices in parallel without a
> transformer; the point of using the transformer was to match the
> impedances on the various pieces of equipment.

Is that even required anymore? Bridging loads and low Z sources have
been standard for almost 30 years now. Carefully examine the real
requirements: a simple hardware 'Y' will have zero distortion and no
headroom problems, and will probably cost $100 less per output than a
transformer worth listening through.

Regards,

Monte McGuire

[Monte McGuire]

In article >,
Patrick Dunford > wrote:

> Obviously we can just connect our devices in parallel without a
> transformer; the point of using the transformer was to match the
> impedances on the various pieces of equipment.

Is that even required anymore? Bridging loads and low Z sources have
been standard for almost 30 years now. Carefully examine the real
requirements: a simple hardware 'Y' will have zero distortion and no
headroom problems, and will probably cost $100 less per output than a
transformer worth listening through.

Regards,

Monte McGuire

[Arny Krueger]

"Patrick Dunford" > wrote in message
. nz
> I have a need to split the outputs of a mixing desk to drive two
> separate devices. Because a distribution amp provides more features
> than needed (more than 2 outputs in most cases) and costs a lot more,
> I also looked at using a mic splitter transformer e.g.
> http://www.jensen-transformers.com/datashts/dinms2p.pdf
>
> The main issue from what I can see is the maximum input level the
> transformer can accept, around 2dbV typical. Specs on the mixing desk
> say its maximum output is +21dBm, although the output impedance is 75
> ohms. The input impedance of the transformer is around 1000 ohms, so
> the voltage across the primary would be quite a bit less than the desk
> output.
>
> As the desk is designed to drive a 600 ohm balanced line, I'm assuming
> that driving a transformer would provide a similar load to it.
>
> Obviously we can just connect our devices in parallel without a
> transformer; the point of using the transformer was to match the
> impedances on the various pieces of equipment.

Line inputs and line outputs aren't impedance matched.

A typical line output has an output impedance of a few 100 ohms, while a
typical line input has an input impedance of a few thousand or a few tens of
thousands of ohms.

Therefore, no transformer is required for impedance matching.

Unless there are grounding problems, you should have no problems whatsoever
driving two line inputs with one line output.

People who use DAs for applications like this (e.g. me on occasion) are
either worried about grounding problems, or the possibility that one of the
paralleled lines will inadvertently become shorted out or otherwise badly
loaded.

[Arny Krueger]

"Patrick Dunford" > wrote in message
. nz
> I have a need to split the outputs of a mixing desk to drive two
> separate devices. Because a distribution amp provides more features
> than needed (more than 2 outputs in most cases) and costs a lot more,
> I also looked at using a mic splitter transformer e.g.
> http://www.jensen-transformers.com/datashts/dinms2p.pdf
>
> The main issue from what I can see is the maximum input level the
> transformer can accept, around 2dbV typical. Specs on the mixing desk
> say its maximum output is +21dBm, although the output impedance is 75
> ohms. The input impedance of the transformer is around 1000 ohms, so
> the voltage across the primary would be quite a bit less than the desk
> output.
>
> As the desk is designed to drive a 600 ohm balanced line, I'm assuming
> that driving a transformer would provide a similar load to it.
>
> Obviously we can just connect our devices in parallel without a
> transformer; the point of using the transformer was to match the
> impedances on the various pieces of equipment.

Line inputs and line outputs aren't impedance matched.

A typical line output has an output impedance of a few 100 ohms, while a
typical line input has an input impedance of a few thousand or a few tens of
thousands of ohms.

Therefore, no transformer is required for impedance matching.

Unless there are grounding problems, you should have no problems whatsoever
driving two line inputs with one line output.

People who use DAs for applications like this (e.g. me on occasion) are
either worried about grounding problems, or the possibility that one of the
paralleled lines will inadvertently become shorted out or otherwise badly
loaded.

[Scott Dorsey]

Patrick Dunford > wrote:
>>
>> So, buy a transformer that can handle higher levels. Jensen and Lundahl
>> make a couple transformers that can be set up for line splitting. Audisar
>> makes a thing with one 600 ohm primary and six 600 ohm secondaries, which
>> is great for press boxes.
>
>I don't see on the Jensen web site any specific model for line splitting,
>they are all mic splitters.

Anything that has one 600 ohm primary and two 600 ohm secondaries can be
used for line splitting. Most of the "universal line" types that have
two primaries and two secondaries that can be strapped in parallel or series
for different ratios can be set up with the two primaries paralleled and the
two secondaries used as seperate outputs for this sort of work.

The mike splitter transformers are mostly high-Z-to-low-Z types to allow
one output to be bridged across another.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Patrick Dunford > wrote:
>>
>> So, buy a transformer that can handle higher levels. Jensen and Lundahl
>> make a couple transformers that can be set up for line splitting. Audisar
>> makes a thing with one 600 ohm primary and six 600 ohm secondaries, which
>> is great for press boxes.
>
>I don't see on the Jensen web site any specific model for line splitting,
>they are all mic splitters.

Anything that has one 600 ohm primary and two 600 ohm secondaries can be
used for line splitting. Most of the "universal line" types that have
two primaries and two secondaries that can be strapped in parallel or series
for different ratios can be set up with the two primaries paralleled and the
two secondaries used as seperate outputs for this sort of work.

The mike splitter transformers are mostly high-Z-to-low-Z types to allow
one output to be bridged across another.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Mike Rivers]

In article > writes:

> I have a need to split the outputs of a mixing desk to drive two separate
> devices.

> Obviously we can just connect our devices in parallel without a
> transformer; the point of using the transformer was to match the
> impedances on the various pieces of equipment.

There are certain circumstances where it's necessary to match
impedances between outputs and inputs of audio equipment (like when
you're driving 10 miles of telephone cable) but most of the time you
don't need to do so. In fact, it's standard practice for high
impedance loads to be connected to low impedance sources.

A transformer is helpfule to isolate grounding if you have a proble
with hum because of different ground potentials on the two destination
units, but otherwise you can just parallel them.

Try the simple solution first.

--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

[Mike Rivers]

In article > writes:

> I have a need to split the outputs of a mixing desk to drive two separate
> devices.

> Obviously we can just connect our devices in parallel without a
> transformer; the point of using the transformer was to match the
> impedances on the various pieces of equipment.

There are certain circumstances where it's necessary to match
impedances between outputs and inputs of audio equipment (like when
you're driving 10 miles of telephone cable) but most of the time you
don't need to do so. In fact, it's standard practice for high
impedance loads to be connected to low impedance sources.

A transformer is helpfule to isolate grounding if you have a proble
with hum because of different ground potentials on the two destination
units, but otherwise you can just parallel them.

Try the simple solution first.

--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

[Patrick Dunford]

In article > in rec.audio.pro on Fri,
10 Sep 2004 08:34:41 -0400, Arny Krueger > says...
> "Patrick Dunford" > wrote in message
> . nz
> > I have a need to split the outputs of a mixing desk to drive two
> > separate devices. Because a distribution amp provides more features
> > than needed (more than 2 outputs in most cases) and costs a lot more,
> > I also looked at using a mic splitter transformer e.g.
> > http://www.jensen-transformers.com/datashts/dinms2p.pdf
> >
> > The main issue from what I can see is the maximum input level the
> > transformer can accept, around 2dbV typical. Specs on the mixing desk
> > say its maximum output is +21dBm, although the output impedance is 75
> > ohms. The input impedance of the transformer is around 1000 ohms, so
> > the voltage across the primary would be quite a bit less than the desk
> > output.
> >
> > As the desk is designed to drive a 600 ohm balanced line, I'm assuming
> > that driving a transformer would provide a similar load to it.
> >
> > Obviously we can just connect our devices in parallel without a
> > transformer; the point of using the transformer was to match the
> > impedances on the various pieces of equipment.
>
> Line inputs and line outputs aren't impedance matched.
>
> A typical line output has an output impedance of a few 100 ohms, while a
> typical line input has an input impedance of a few thousand or a few tens of
> thousands of ohms.
>
> Therefore, no transformer is required for impedance matching.

Balanced lines operate at a typical impedance of around 600 ohms.

If a balanced output had an impedance of 600 ohms, and the actual load
was 300 ohms, problems could be expected.

In this case the output impedance is 75 ohms and the two devices are
likely to have input impedances of around 1k each, thus no problemo.

[Patrick Dunford]

In article > in rec.audio.pro on Fri,
10 Sep 2004 08:34:41 -0400, Arny Krueger > says...
> "Patrick Dunford" > wrote in message
> . nz
> > I have a need to split the outputs of a mixing desk to drive two
> > separate devices. Because a distribution amp provides more features
> > than needed (more than 2 outputs in most cases) and costs a lot more,
> > I also looked at using a mic splitter transformer e.g.
> > http://www.jensen-transformers.com/datashts/dinms2p.pdf
> >
> > The main issue from what I can see is the maximum input level the
> > transformer can accept, around 2dbV typical. Specs on the mixing desk
> > say its maximum output is +21dBm, although the output impedance is 75
> > ohms. The input impedance of the transformer is around 1000 ohms, so
> > the voltage across the primary would be quite a bit less than the desk
> > output.
> >
> > As the desk is designed to drive a 600 ohm balanced line, I'm assuming
> > that driving a transformer would provide a similar load to it.
> >
> > Obviously we can just connect our devices in parallel without a
> > transformer; the point of using the transformer was to match the
> > impedances on the various pieces of equipment.
>
> Line inputs and line outputs aren't impedance matched.
>
> A typical line output has an output impedance of a few 100 ohms, while a
> typical line input has an input impedance of a few thousand or a few tens of
> thousands of ohms.
>
> Therefore, no transformer is required for impedance matching.

Balanced lines operate at a typical impedance of around 600 ohms.

If a balanced output had an impedance of 600 ohms, and the actual load
was 300 ohms, problems could be expected.

In this case the output impedance is 75 ohms and the two devices are
likely to have input impedances of around 1k each, thus no problemo.

[Phil Allison]

"Patrick Dunford"

> > Balanced lines operate at a typical impedance of around 600 ohms.
>

** Only in the telephone business or where very long audio lines are used.


> If a balanced output had an impedance of 600 ohms,


** Is that actual source impedance or rated minumum load impedance ??

>
> In this case the output impedance is 75 ohms


** That would be an actual source impedance - but not the rated minimum
load for full level.

That is more like 500 ohms due to limited op-amp current ability.


>and the two devices are
> likely to have input impedances of around 1k each, thus no problemo.


** Cripes - what has a 1 kohm input Z these days ??




............ Phil

[Phil Allison]

"Patrick Dunford"

> > Balanced lines operate at a typical impedance of around 600 ohms.
>

** Only in the telephone business or where very long audio lines are used.


> If a balanced output had an impedance of 600 ohms,


** Is that actual source impedance or rated minumum load impedance ??

>
> In this case the output impedance is 75 ohms


** That would be an actual source impedance - but not the rated minimum
load for full level.

That is more like 500 ohms due to limited op-amp current ability.


>and the two devices are
> likely to have input impedances of around 1k each, thus no problemo.


** Cripes - what has a 1 kohm input Z these days ??




............ Phil

[Arny Krueger]

"Patrick Dunford" > wrote in message
. nz
> In article > in rec.audio.pro on
> Fri, 10 Sep 2004 08:34:41 -0400, Arny Krueger >
> says...

>> Line inputs and line outputs aren't impedance matched.

>> A typical line output has an output impedance of a few 100 ohms,
>> while a typical line input has an input impedance of a few thousand
>> or a few tens of thousands of ohms.

>> Therefore, no transformer is required for impedance matching.

> Balanced lines operate at a typical impedance of around 600 ohms.

Not in typical practice. These days "600 ohm lines" are more of a concept
than a fact.

> If a balanced output had an impedance of 600 ohms, and the actual load
> was 300 ohms, problems could be expected.

Not necessarily. Audio systems typically have great reserves of unused
headroom. How much equipment can run at +22 but never sees more than about
+12?

> In this case the output impedance is 75 ohms and the two devices are
> likely to have input impedances of around 1k each, thus no problemo.

1 K ohm input impedances? That is atypically very low.

[Scott Dorsey]

Patrick Dunford > wrote:
>
>Balanced lines operate at a typical impedance of around 600 ohms.

This was true in 1970. It is no longer true.

>If a balanced output had an impedance of 600 ohms, and the actual load
>was 300 ohms, problems could be expected.

This is true for a 1970-vintage transformer-balanced output. On a typical
balanced output today, you will find the actual output impedance is much
lower than 600 ohms. The Mackie consoles have something like 50 ohms out,
and the Great River preamps are closer to 10 ohms. It never hurts to be
able to drive more current than you need.

>In this case the output impedance is 75 ohms and the two devices are
>likely to have input impedances of around 1k each, thus no problemo.

Right. This is the normal state of affairs today for balanced connections.
Transformer inputs and outputs are very uncommon, and most of the transformer
outputs today are designed to drive higher impedance loads without ringing
(because they have to drive Mackies and the like), so termination resistors
and load barrels are a thing of the past.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Phil Allison]

"Scott Dorsey"
> Patrick Dunford
>
> >If a balanced output had an impedance of 600 ohms, and the actual load
> >was 300 ohms, problems could be expected.
>
> This is true for a 1970-vintage transformer-balanced output. On a typical
> balanced output today, you will find the actual output impedance is much
> lower than 600 ohms. The Mackie consoles have something like 50 ohms out,
> and the Great River preamps are closer to 10 ohms. It never hurts to be
> able to drive more current than you need.
>

** Output source impedance and current delivering capacity are not
related.

The output Z of an op-amp is very low ( typically under 1 ohm at 1kHz )
due to NFB - however the max available current is determined by on chip
circuitry to a figure of around 10 to 20 mA.

This prevents the op-amp burning out if the output is ever shorted to
ground.




............ Phil