I'm drawing up a wiring diagram for a new patchbay. I think I have most
of the balanced/unbalanced connections worked out, but have hit a
hitch...
The outputs of the tape deck are balanced and half normaled.
A couple gates and compressors have unbalanced sidechains.

In a situation where I put a patch cable into the Channel 1 output to
feed the side chain of a compressor so that signal still flows to
Channel 1 of the board, but also to the sidechain of one of the
compressors/gates. Should the side chain plug be wired:

A) TS plug with the ring and the ground of the patchbay jack connected
to the sleeve of the plug and tip of the jack connected to the tip of
the plug. (this seems wrong, as it would unbalance and halve the level
of the line going into the board as a side effect when taking a tap off
the bay to feed the sidechain)

B) TS plug with ground of the jack connected to the sleeve of the plug
and the tip of the jack connected to the tip of the plug and the ring
on the jack unconnected. (strikes me as more right but maybe still a
bit off).

Or is there a different place one would usually draw signal for the
sidechain?

Thanks, Andy

apa wrote:
I'm drawing up a wiring diagram for a new patchbay. I think I have most
of the balanced/unbalanced connections worked out, but have hit a
hitch...

There's a very simple way to handle this. Just wire up everything as if
it was balanced, with two-conductor cable. When you have a piece of
two-conductor cable in one hand and an unbalanced device in the other
hand, simply connect the low and shield together on the unbalanced end.
Use two-conductor (balanced) patch cables and everything will work
fine. If you have a hum problem when you patch in an unbalanced device,
your first line of defense, and it's easy to do assuming you're
building your own cables, is to life the shield on the unbalanced end.

The outputs of the tape deck are balanced and half normaled.

Half-normalled to what? A console line input or tape return?

A couple gates and compressors have unbalanced sidechains.

In a situation where I put a patch cable into the Channel 1 output to
feed the side chain of a compressor so that signal still flows to
Channel 1 of the board, but also to the sidechain of one of the
compressors/gates.

Making this connectiion unbalances the output of the tape deck. No big
deal.

should the side chain plug be wired:

A) TS plug with the ring and the ground of the patchbay jack connected
to the sleeve of the plug and tip of the jack connected to the tip of
the plug.

Yes.

So the unbalancing of the tape deck outs shouldn't be a big concern.
That's was the heart of my question. Thanks again, Mike.

apa wrote:
So the unbalancing of the tape deck outs shouldn't be a big concern.
That's was the heart of my question.

It isn't the best thing in the world, but if you wanted the best with
less worry (that's a qualifier, not an endorsement), you wouldn't be
using gear with unbalanced I/O. You wn't blow anything up. There are a
few possibilities for things to be wroing:

1. Nothing - it'll work and sound just fine.

2. You might have some hum to track down, but if you wire everything
with two-conductor shielded cable, you can easily try all of the
ground-lift possibilities. And as a last resort, you can put
transformers in line where they're needed without changing any wiring
to the patchbay.

3. Some "balanced" outputs are constructed by passing the single-ended
output through an inverter and connecting the inverted output to the
"low" side of the balanced output. Depending on how they do this, you
may have an output circuit that doesn't like to have its low side
grounded, and will cause distortion in the non-inverted output (or in
the extreme case, blow up, but I"ve never seen that happen). If this is
what you have, just disconnect the "Pin 3" wire at the unbalanced end
and use the Pin 1 and 2 wires as if it was an unbalanced output. This
is the famous "You lose 6 dB when going from balanced to unbalanced"
case (and the only case where it's true).

Alternately, some balanced output configurations NEED to have their low
side tied to ground when going to an unbalanced input. The new Mackie
Onyx 1640 and 1620 (but not 1220) mixers are like this. If that's the
kind of output stage your recorder has (and I can't think of one that
does) then you'll need to tie Pin 3 to Pin 1 at the unbalanced end.
This will bring the level between Pins 1 and 2 back to what it's
supposed to be (no 6 dB loss). In the case of the Mackies that I've
tested, you can't ignore this (and the manual does indeed tell you to
connect Pins 1-3 when the main balanced outputs are going to an
unbalanced destination) because with no "Pin 3 reference" the signal
voltage between pins 1-2 isn't predictable. For the same level on tape,
one channel might put out +6 dBu between pins 1-2, and another channel
might put out -2 dBu. Doesn't do much for your tape deck calibration.
g



How do you know what you got? If the manufacturer doen't have any
recommendations, experiment. It's easy to do, you can almost always
tell by ear, and you'll learn something.

Is it common to have gear with balanced sidechains? The gates I have (
a DBX Supergate and a Valley Dynamite ) are balanced I/O but unbalanced
sidechains (as I remember - I'll check again to be sure). I had assumed
that was the way of the world.

What is an output that passes a single ended output through an inverter
called? Is this differential or a subcategory of differential?




Mike Rivers wrote:
apa wrote:
So the unbalancing of the tape deck outs shouldn't be a big concern.
That's was the heart of my question.

It isn't the best thing in the world, but if you wanted the best with
less worry (that's a qualifier, not an endorsement), you wouldn't be
using gear with unbalanced I/O. You wn't blow anything up. There are a
few possibilities for things to be wroing:

1. Nothing - it'll work and sound just fine.

2. You might have some hum to track down, but if you wire everything
with two-conductor shielded cable, you can easily try all of the
ground-lift possibilities. And as a last resort, you can put
transformers in line where they're needed without changing any wiring
to the patchbay.

3. Some "balanced" outputs are constructed by passing the single-ended
output through an inverter and connecting the inverted output to the
"low" side of the balanced output. Depending on how they do this, you
may have an output circuit that doesn't like to have its low side
grounded, and will cause distortion in the non-inverted output (or in
the extreme case, blow up, but I"ve never seen that happen). If this is
what you have, just disconnect the "Pin 3" wire at the unbalanced end
and use the Pin 1 and 2 wires as if it was an unbalanced output. This
is the famous "You lose 6 dB when going from balanced to unbalanced"
case (and the only case where it's true).

Alternately, some balanced output configurations NEED to have their low
side tied to ground when going to an unbalanced input. The new Mackie
Onyx 1640 and 1620 (but not 1220) mixers are like this. If that's the
kind of output stage your recorder has (and I can't think of one that
does) then you'll need to tie Pin 3 to Pin 1 at the unbalanced end.
This will bring the level between Pins 1 and 2 back to what it's
supposed to be (no 6 dB loss). In the case of the Mackies that I've
tested, you can't ignore this (and the manual does indeed tell you to
connect Pins 1-3 when the main balanced outputs are going to an
unbalanced destination) because with no "Pin 3 reference" the signal
voltage between pins 1-2 isn't predictable. For the same level on tape,
one channel might put out +6 dBu between pins 1-2, and another channel
might put out -2 dBu. Doesn't do much for your tape deck calibration.
g



How do you know what you got? If the manufacturer doen't have any
recommendations, experiment. It's easy to do, you can almost always
tell by ear, and you'll learn something.

apa wrote:
Is it common to have gear with balanced sidechains?

Not very common. SInce the side chain output and input needs to be
normalled with nothing patched in, if it's balanced, there must be
separate jacks for input and output. The common arrangement is to use a
single TRS jack with the output (send) typically being between the tip
and sleeve and the input (return) being between the ring and sleeve.

What is an output that passes a single ended output through an inverter
called? Is this differential or a subcategory of differential?

I don't know that it has a name. At least nobody uses it if it does.
It's usually just called a "balanced output." The only configuration
that seems to have a name that stuck (and I think I might have invented
the term but I don't claim it) is "impedance balanced." This is a
single ended output that's wired to a two-conductor connector. The
signal goes between the hot side (Tip or Pin 2) and ground (sleeve or
Pin 1). Theres a fixed resistor equal to the source impedance of the
driven output connected between the low side (ring or Pin 3) and
ground. Whe feeding a differential input, noise picked up by the cable
appears at the same amplitude to both the inverting and non-inverting
inputs of the input stage, and gets cancelled like a balanced
connection is supposed to do.

This actually meets the definition of "balanced" so a manufacturer who
calls such isn't cheating or lying. But it isn't differential. The way
you can tell if this is the kind of output you have is by looking for a
signal on the tip and ring. If ther's signal on the tip but not the
ring, it might be an "impedance balanced" output. Check the DC
resistance between the ring and sleeve. If it's zero or very close,
they cheated and connected the low side to ground for you right at the
connector. If it's between about 50 and 1000 ohms or so, it's probalby
at least an attempt at being balanced. If it's open, that's another
form of cheating.

Thanks again Mike.

Both of these use a front panel switch to select the "External
Sidechain" instead of a switching TRS jack (like an insert) - so the
jack doesn't need to normal the signal. So I guess they (the
manufacturers) could balance it but don't bother?

Which means (since most sidechains are unbalanced) that if you are
using sidechains fed from a balanced patchbay you pretty much have to
accept the unbalancing of the tape out or derive your sidechain signal
elsewhere. Or have a "sidechain patch cable" with a cheap little
transformer in it?

apa wrote:

Both of these use a front panel switch to select the "External
Sidechain" instead of a switching TRS jack (like an insert) - so the
jack doesn't need to normal the signal. So I guess they (the
manufacturers) could balance it but don't bother?

Probably so. Or maybe there wasn't space on the panel for two jacks or
a convenient way to connect them to the insides. Or more likely if the
used separate jacks, too many people would ask if they have to use both
jacks or could they use just one.

Which means (since most sidechains are unbalanced) that if you are
using sidechains fed from a balanced patchbay you pretty much have to
accept the unbalancing of the tape out or derive your sidechain signal
elsewhere. Or have a "sidechain patch cable" with a cheap little
transformer in it?

Yeah, but it's not that big of a deal unless you have some really
crummy equipment. It's kind of unusual to drive a sidechain input
directly from a tape deck anyway. I can see it if you're using one tape
track to key a gate for a different track, but sidechain jacks are
usually used to patch an equalizer into the path to the detector of a
compressor to make it frequency sensitive.

Incidentally, while it's not a side chain insert point, large consoles
with a built-in patchbay often have several insert points, all on pairs
of balanced connectors. For example, the Sony MXP-3000 has normalled
jacks for:

Mic Pre Out
Mic Pre Return

EQ Out
Fader In

Line Out
Multitrack Recorder In

Multitrack Recorder Out
Line In

There are a bunch of non-normalled jacks labeled "Tie Lines" and those
would normally go to the inputs and outputs of outboard equipment, and
side chain inserts for those devices that have them.

"apa" wrote in
oups.com:

Thanks again Mike.

Both of these use a front panel switch to select the "External
Sidechain" instead of a switching TRS jack (like an insert) -
so the jack doesn't need to normal the signal. So I guess they
(the manufacturers) could balance it but don't bother?

Which means (since most sidechains are unbalanced) that if you
are using sidechains fed from a balanced patchbay you pretty
much have to accept the unbalancing of the tape out or derive
your sidechain signal elsewhere. Or have a "sidechain patch
cable" with a cheap little transformer in it?

Consider also making a small box that contains an op-amp to convert
the balanced signal to unbalanced. noise and distortion are not
extremely critical in the side-chain so you don't need a
sophisticated IC.

--
Bob Quintal

PA is y I've altered my email address.

Mike Rivers wrote:

apa wrote:
Is it common to have gear with balanced sidechains?

Not very common. SInce the side chain output and input needs to be
normalled with nothing patched in, if it's balanced, there must be
separate jacks for input and output. The common arrangement is to use a
single TRS jack with the output (send) typically being between the tip
and sleeve and the input (return) being between the ring and sleeve.

What is an output that passes a single ended output through an inverter

Do you mean this?

|\
| \
signal -------| O ------ inverted output
| /
|/

Or this?

+------------- inverted output
| |\
| | \
signal ----+--| O ------ uninverted output
| /
|/

If the former, it is simply an inverted output. If the latter, it is
a symmetrical output. It might also be a balanced output but only if
the source impedance of the uninverted and inverted outputs are equal.

Is this differential or a subcategory of differential?

Differential is a property of an input/receiver circuit. A differential
input accepts two signals and outputs their difference.

I don't know that it has a name. At least nobody uses it if it does.
It's usually just called a "balanced output." The only configuration
that seems to have a name that stuck (and I think I might have invented
the term but I don't claim it) is "impedance balanced." This is a
single ended output that's wired to a two-conductor connector. The
signal goes between the hot side (Tip or Pin 2) and ground (sleeve or
Pin 1). Theres a fixed resistor equal to the source impedance of the
driven output connected between the low side (ring or Pin 3) and
ground. Whe feeding a differential input, noise picked up by the cable
appears at the same amplitude to both the inverting and non-inverting
inputs of the input stage, and gets cancelled like a balanced
connection is supposed to do.

A differential receiver is used in balanced audio applications to achieve
common mode rejection. Because the source impedances of the "legs" of a
balanced line are equal, noise induced along the line is a common mode
signal, that is, it is induced equally on both conductors of a balanced
line. For the noise components, the differential amplifer therefore
generates:

noise - noise = 0

Noise is cancelled or "rejected".

For the signal components of a symetrical balanced line, the differential
amplifer generates:

signal - (-signal) = signal + signal = 2 * signal

For the signal components of an "impedance balanced" line, the
differential amplifer generates:

signal - 0 = signal

This actually meets the definition of "balanced" so a manufacturer who
calls such isn't cheating or lying. But it isn't differential. The way
you can tell if this is the kind of output you have is by looking for a
signal on the tip and ring. If ther's signal on the tip but not the
ring, it might be an "impedance balanced" output. Check the DC
resistance between the ring and sleeve. If it's zero or very close,
they cheated and connected the low side to ground for you right at the
connector. If it's between about 50 and 1000 ohms or so, it's probalby
at least an attempt at being balanced. If it's open, that's another
form of cheating.

--
================================================== ======================
Michael Kesti | "And like, one and one don't make
| two, one and one make one."
mrkesti at comcast dot net | - The Who, Bargain

Michael R. Kesti wrote:

Do you mean this?

|\
| \
signal -------| O ------ inverted output
| /
|/

Or this?

+------------- inverted output
| |\
| | \
signal ----+--| O ------ uninverted output
| /
|/

How about this?:

+------------- uninverted output
| |\
| | \
signal ----+--| O ------ inverted output
| /
|/

If the former, it is simply an inverted output. If the latter, it is
a symmetrical output. It might also be a balanced output but only if
the source impedance of the uninverted and inverted outputs are equal.

Correct, but "inverted" and "uninverted" means nothing without a
reference. I assumed two outputs, one inverted with respect to the
other. If there's also an input, then we usually assume that the
"uninverted" side of the output has the same polarity as the input.

Mike Rivers wrote:

Michael R. Kesti wrote:

Do you mean this?

|\
| \
signal -------| O ------ inverted output
| /
|/

Or this?

+------------- inverted output
| |\
| | \
signal ----+--| O ------ uninverted output
| /
|/

How about this?:

+------------- uninverted output
| |\
| | \
signal ----+--| O ------ inverted output
| /
|/

How DID I manage to put the "un" on the wrong output?!

If the former, it is simply an inverted output. If the latter, it is
a symmetrical output. It might also be a balanced output but only if
the source impedance of the uninverted and inverted outputs are equal.

Correct, but "inverted" and "uninverted" means nothing without a
reference.

Yes, and the reference here is the "signal," assumed to be in true polarity.

I assumed two outputs, one inverted with respect to the
other. If there's also an input, then we usually assume that the
"uninverted" side of the output has the same polarity as the input.

Of course. My point is that "an output that passes a single ended output
through an inverter," assuming that the OP meant the now corredted latter
configuration, is called is "symmetrical" or "symmetrically driven."

--
================================================== ======================
Michael Kesti | "And like, one and one don't make
| two, one and one make one."
mrkesti at comcast dot net | - The Who, Bargain