I am wiring a new house for sound customized for my equipment and
applications. In my office I have a receiver/amp that has only one
"aux" input. I would like to use this input for the line-out from my
computer sound card as well as the multi-source line output from a
control amp in another room. My question is, will this cause any damage
to any of the components involved? Many years ago, I learned the hard
way that you cannot hook up two audio amps directly to the same pair of
speakers without damaging one or both of the amps, but since line-level
audio is a much lower voltage, I'm thinking I can use this
configuration without any problems. Any feedback is appreciated.

bogotabro wrote:
I am wiring a new house for sound customized for my equipment and
applications. In my office I have a receiver/amp that has only one
"aux" input. I would like to use this input for the line-out from my
computer sound card as well as the multi-source line output from a
control amp in another room. My question is, will this cause any
damage to any of the components involved? Many years ago, I learned
the hard way that you cannot hook up two audio amps directly to the
same pair of speakers without damaging one or both of the amps, but
since line-level audio is a much lower voltage, I'm thinking I can
use this configuration without any problems. Any feedback is
appreciated.

They should be separated from each other by some sort of selector switch.
What you propose won't damage anything, so long as they're both at a pre-amp
(line) level, but the impedance of one may well interfere with the other,
even to the point of noticeable distortion or much lower output. This would
be particularly true if one were a significantly lower output impedance than
the other. If one is a digital-switching type and is turned off at the time,
it's almost guaranteed to cause problems.


Mark Z.

"Mark D. Zacharias" wrote in message
. com...
bogotabro wrote:
I am wiring a new house for sound customized for my equipment and
applications. In my office I have a receiver/amp that has only one
"aux" input. I would like to use this input for the line-out from
my
computer sound card as well as the multi-source line output from a
control amp in another room. My question is, will this cause any
damage to any of the components involved? Many years ago, I
learned
the hard way that you cannot hook up two audio amps directly to
the
same pair of speakers without damaging one or both of the amps,
but
since line-level audio is a much lower voltage, I'm thinking I can
use this configuration without any problems. Any feedback is
appreciated.

They should be separated from each other by some sort of selector
switch.
What you propose won't damage anything, so long as they're both at a
pre-amp
(line) level, but the impedance of one may well interfere with the
other,
even to the point of noticeable distortion or much lower output.
This would
be particularly true if one were a significantly lower output
impedance than
the other. If one is a digital-switching type and is turned off at
the time,
it's almost guaranteed to cause problems.


Mark Z.



Blx. The sound card analogue line output will typically have a source
impedence of 1K or thereabouts; the amp aux input will be typically
100K, so there will be no matching problem whatsoever. (Always low
impedence source, high impedence load.)

Line level maximum sensitivity is typically 150mV for full output from
the amp but can be fed with levels much higher than that, peak output
from a CD being 2V and that works! A sound card line level output is
usually adjustable under software control but should fall well within
that band.

Go ahead, connect, and enjoy..........


--
Woody

harrogate3 at ntlworld dot com

Blx. The sound card analogue line output will typically have a source
impedence of 1K or thereabouts; the amp aux input will be typically
100K, so there will be no matching problem whatsoever. (Always low
impedence source, high impedence load.)

But the problem is that he wants to TIE 2 OUTPUTS TOGETHER. Not good. Both
are low impedance and both are not designed to have a signal fed into them.

BTW, you might make a passive mixer out of a set of resistors. Others
probably have more experience doing this than I do.

"harrogate2" wrote in message

"Mark D. Zacharias" wrote in
message
. com...
bogotabro wrote:
I am wiring a new house for sound customized for my
equipment and applications. In my office I have a
receiver/amp that has only one "aux" input. I would
like to use this input for the line-out from my
computer sound card as well as the multi-source line
output from a control amp in another room.

Hopefully both aren't playing music at the same time.

My question
is, will this cause any damage to any of the components
involved?

Damage is usually not a problem when you do things like this with line outs.
However, its still usually not the best idea.

Many years ago, I learned the hard way that
you cannot hook up two audio amps directly to the same
pair of speakers without damaging one or both of the
amps, but since line-level audio is a much lower
voltage, I'm thinking I can use this configuration
without any problems. Any feedback is appreciated.

One problem is that you'll get noise added up from both sources.

They should be separated from each other by some sort of
selector switch. What you propose won't damage anything,
so long as they're both at a pre-amp (line) level, but
the impedance of one may well interfere with the other,
even to the point of noticeable distortion or much lower
output. This would be particularly true if one were a
significantly lower output impedance than the other. If
one is a digital-switching type and is turned off at the
time, it's almost guaranteed to cause problems.

If one of the sources is turned off, it might cause the other source to be
shorted out or distorted.

Blx. The sound card analogue line output will typically
have a source impedence of 1K or thereabouts;

Actually, most of them are designed to drive headphones - source impedance
of about 16 ohms.

the amp aux
input will be typically 100K, so there will be no
matching problem whatsoever. (Always low impedence
source, high impedence load.)

Agreed that low Z source driving high Z load is generally a working
situation.

"bogotabro" wrote in message
ups.com...
I am wiring a new house for sound customized for my equipment and
applications. In my office I have a receiver/amp that has only one
"aux" input. I would like to use this input for the line-out from my
computer sound card as well as the multi-source line output from a
control amp in another room. My question is, will this cause any damage
to any of the components involved? Many years ago, I learned the hard
way that you cannot hook up two audio amps directly to the same pair of
speakers without damaging one or both of the amps, but since line-level
audio is a much lower voltage, I'm thinking I can use this
configuration without any problems. Any feedback is appreciated.

Buy a cheap, $10 audio (or audio/video) switch box that has, at a minimum,
RCA connections for right and left line level audio.

Jeff
--
Remove icky phrase from email address to get a valid address.

"harrogate2" writes:

Blx. The sound card analogue line output will typically have a source
impedence of 1K or thereabouts;

The output impedance from the sound card line output is typically
from tens of ohms to one kilo-ohms. Many soundcards have combined
headphone/speaker outputs, that have typically very low output
impedance.

the amp aux input will be typically 100K,

20kohms to 100 kohms quite normal.


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

harrogate2 wrote:
"Mark D. Zacharias" wrote in message
. com...
bogotabro wrote:
I am wiring a new house for sound customized for my equipment and
applications. In my office I have a receiver/amp that has only one
"aux" input. I would like to use this input for the line-out from my
computer sound card as well as the multi-source line output from a
control amp in another room. My question is, will this cause any
damage to any of the components involved? Many years ago, I learned
the hard way that you cannot hook up two audio amps directly to the
same pair of speakers without damaging one or both of the amps, but
since line-level audio is a much lower voltage, I'm thinking I can
use this configuration without any problems. Any feedback is
appreciated.

They should be separated from each other by some sort of selector
switch. What you propose won't damage anything, so long as they're
both at a pre-amp (line) level, but the impedance of one may well
interfere with the other, even to the point of noticeable distortion
or much lower output. This would be particularly true if one were a
significantly lower output impedance than the other. If one is a
digital-switching type and is turned off at the time, it's almost
guaranteed to cause problems.


Mark Z.



Blx. The sound card analogue line output will typically have a source
impedence of 1K or thereabouts; the amp aux input will be typically
100K, so there will be no matching problem whatsoever. (Always low
impedence source, high impedence load.)

Line level maximum sensitivity is typically 150mV for full output from
the amp but can be fed with levels much higher than that, peak output
from a CD being 2V and that works! A sound card line level output is
usually adjustable under software control but should fall well within
that band.

Go ahead, connect, and enjoy..........


The low output impedance of the sound card will load the output of the
control amp. Further, there is no telling how linear that load will be if
the computer is turned off and the OP is just wanting to listen to the other
source.
Also, the OP said he was using the multi-source output from a "control amp".
This strongly suggests a digital type source selection. Again, if this unit
is not powered up at a given moment there is a high likelihood of a
non-linear loading of the sound card output.

I repair audio equipment for a living the past 25 years, and have seen these
effects first-hand many times.

I realize this is getting dangerously close to expounding on engineering
theory - which I try not to do for reasons well known to those real
engineering types around here - but this is pretty basic stuff.


Mark Z.

"Mark D. Zacharias" wrote in message
t...

Also, the OP said he was using the multi-source output from a "control
amp". This strongly suggests a digital type source selection. Again, if
this unit is not powered up at a given moment there is a high likelihood
of a non-linear loading of the sound card output.

It would be good if the OP chimed in here! "Control amp" was a term used to
describe something we don't see around much any mo A power amplifier, but
with all the controls you'd normally see on a receiver, minus the tuner.
Maybe that's what he's talking about.

In article . com, "bogotabro" wrote:
I am wiring a new house for sound customized for my equipment and
applications. In my office I have a receiver/amp that has only one
"aux" input. I would like to use this input for the line-out from my
computer sound card as well as the multi-source line output from a
control amp in another room. My question is, will this cause any damage
to any of the components involved? Many years ago, I learned the hard
way that you cannot hook up two audio amps directly to the same pair of
speakers without damaging one or both of the amps, but since line-level
audio is a much lower voltage, I'm thinking I can use this
configuration without any problems. Any feedback is appreciated.



http://www.dak.com/reviews/2020storyT.cfm

OP here, appreciate all the feedback. I haven't checked in a few days
and was pleasantly surprised at the responses! First, yes, I have an
old Onkyo SV640 control amp with a separate tuner. It has a
multi-source pre-out (line level) that I plan on feeding into the
Pioneer office amp. This amp indeed has two tape inputs along with the
auxiliary input, for a total of three line inputs (plus the phono, for
which I also have a Pioneer turntable.) The trouble is, I have four
things I need to run into the office amp--a cassette deck, a Yamaha
keyboard, the computer sound card, and the remote feed from the Onkyo
amp. Based on what's been said here, I think my best bet is to pick two
of them that I won't use at the same time and run them through an A-B
switch box, to feed into one of the line inputs. Thanks again for all
the insightful comments.