Balanced XLR input - Do I use the High or Low for an unbalanced input.

[olds...@tubes.com]

The inputs on this commercial power amp has Balanced XLR inputs. They
are the 3 prong connectors like on modern microphones. But there is also
a barrier strip with 6 screws. (3 per channel). Each channel has GROUND,
HIGH and LOW.

To connect a short distance cord with RCA plugs from a receiver preamp
output, I know to use the GROUND for the outer shield, but do I use the
HIGH or the LOW for the signal IN?

I know the XLR is used for long distance cables, such as the "snake"
used by musical bands and theater systems. But I am not running that
kind of system, and the receiver output is simply an unbalanced short
run of cable (about 2 or 3 feet long).

I suppose I could just use the trial and error method without harming
anything, but I thought I'd just ask and do it right.

Thanks

[Gareth Magennis]

wrote in message news:cgtsfc1s1jiaodngn...@4ax.com...

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Short the XLR Low to the Ground, pin 1. The RCA ground goes to this
shorted pair. The RCA pin goes to High.


Gareth.

[olds...@tubes.com]

Great, thank you!!!

[Fred McKenzie]

In article <cgtsfc1s1jiaodngn...@4ax.com>,

Gareth's suggestion will probably work OK. If you experience any
problem with hum or distortion, look for an adapter to convert between
XLR's low impedance and your single-ended high impedance.

A family of such adapters is Shure's A95 series "Line Matching
Transformers". The A95A or A95F may meet your needs, depending on the
gender of your XLR connector.

Reference <http://www.coutant.org/matching/a95.pdf>

Fred

[Gareth Magennis]

"Fred McKenzie" wrote in message
news:fmmck-A2739E....@46.sub-75-242-165.myvzw.com...

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The output from the receiver is likely to be an op-amp.
The input of the power amp is also likely to be an op-amp.
Both at line levels.

There is very little likelihood of requiring anything other than wires to
connect these two items together IMHO.



Gareth.

[olds...@tubes.com]

This amp is strictly a power amp. I plan to get a mixer for it when I
find one at a decent price. I dont really need a mixer, since I am using
this for a home stereo, but a preamp appears to be needed, and even a
small 4 or 6 channel mixer can and will provide that preamp.

On the other hand, maybe my receiver output will have enough preamp
built into it (and I suspect it will). But I am aware that matching the
impedense should be done. I knew they made such things, but I was not
aware they could be purchased in the form of adaptors like these Shure
ones. That should be real helpful.

I found out that the inputs are balanced 600 ohm. I am not yet sure what
my receiver outputs in ohms. (Have to see if I can find a manual for
it). I did however read about some of the (same brand) mixers that are
often used with these amps, and they output 600 ohm balanced. Therefore
that is a perfect match. One of those mixers, is a 6 channel unit which
has 6 XLR connectors for microphones, but Two of those inputs also have
a 1/4" jack, called AUX, and there is a switch to use either type (the
XLR or the 1/4"). And there is also another switch to set either LOW or
HIGH gain. So I'm guessing that those 1/4" inputs can be used to connect
something with a high output, such as a receiver, or a DVD player or a
Tape Player, etc. And I can only assume that this input can also be used
for something like a guitar, when set to the HIGH gain position.

Until I get the XLR connectors I bought online, I cant do much, other
than just patch things together. But yesterday I did connect the
speakers and stick a direct probe into the XLR holes, connected to my
audio generator. It worked like a champ, but I did have to turn the
output up as high as it goes on that audio generator, which tells me
that it does surely need a preamp.

But even with just a direct test lead jammed in the connector, there was
no hum or unwanted noise, and I took it from 10cps all the way to
20Kcps, and it was clear as a bell. (At least from 30cps to 15Kcps). I
dont hear above 15Kcps, and at 10cps it just made the speaker cones move
and sound like a motor cycle engine.

[olds...@tubes.com]

On Tue, 25 Apr 2017 12:40:23 -0400, Fred McKenzie <fm...@aol.com> wrote:

>Reference <http://www.coutant.org/matching/a95.pdf>

This link PDF file is quite useful. But it dont specifically state what
devices can be plugged into them. I know there are unbalanced
microphones that have a 1/4" plug on their cord, and things like a
guitar. But it does not specify if the preamp output from a receiver
will match....

One question I have, is there some standardized output (in ohms) for
things like the preamp output from a receiver, or the output from
something like a DVD or Tape player, or even a small MP3 player?
I assume all these devices have some sort of "standard" output
impedence, or are they all different?

Most of the time I just hook the stuff up, and if it sounds OK, then I
just use it. But I know this commercial equipment, with balanced inputs,
is in a class of it's own.......

[pf...@aol.com]

Impedances are guidelines. Not hard absolutes. Most (not all) equipment is remarkably tolerant. Commercial equipment is, typically, more tolerant than consumer equipment, if only because it will get harder use under a wider range of operating conditions.

Put another way, if it sounds good, and nothing gets hot - there you are.

Peter Wieck
Melrose Park, PA

[Pat]

There is little need to match impedances unless you need to maximize
power transfer (for example, coax for radio equipment). Almost
everything you run into with consumer audio equipment has hi-z inputs.
The outputs are designed to drive those hi-z inputs (which is very
easy to do as long as the outputs are lower impedance than what they
are driving). The term for this type of signal is line level (as
opposed to mics and guitars which can be much lower level). As you
have discovered, professional audio equipment uses 600 ohm balanced
lines in order to minimize hum and be able to handle longer runs of
cable. Any preamp with RCA connectors for its output can drive the
hi-z unbalanced input of your amp. If you want to use the 600 ohm
balanced input, you need a preamp with that type of output of a
converter, but the hi-z inputs (ie, RCA connectors) will work just as
well in normal home use.

[Gareth Magennis]

>
>Most of the time I just hook the stuff up, and if it sounds OK, then I
>just use it.

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Amen.

Most of the time, hooking stuff up just works. Because that what it is
designed to do.

All this guff about impedance matching is pretty much irrelevant nowadays,
I'm not sure how it made it into this thread.




Gareth.

[Phil Allison]

olds...@tubes.com wrote:
>

>
> I found out that the inputs are balanced 600 ohm.
>

** You are wrong again, the specs say the input impedance is 30kohms balanced, or 15kohms unbalanced.



..... Phil