Hi,

I'm looking for a device that will automatically switch 2 line-level audio
signals to a single output.

One of the audio lines (A) will always have a signal. This is the default
audio.
The other signal (B) will switch on and off. When B comes on, I want it to
become the active source, for as long as it is on. When B switches off, A
should become active again.

I found a device that does this for amplified signals
(http://www.cbav.com/Merchant2/mercha...ry_Code =SI-2)
but the price ($120) is pretty steep.

Does anyone know of a cheaper device to do this, or a circuit/directions to
build such a switch?

Thanks,
JohanE

"JohanE" wrote in message ...
Hi,

I'm looking for a device that will automatically switch 2 line-level audio
signals to a single output.

One of the audio lines (A) will always have a signal. This is the default
audio.
The other signal (B) will switch on and off. When B comes on, I want it
to
become the active source, for as long as it is on. When B switches off, A
should become active again.

I found a device that does this for amplified signals

(http://www.cbav.com/Merchant2/mercha...ode=C&Category
_Code=SI-2)
but the price ($120) is pretty steep.

Does anyone know of a cheaper device to do this, or a circuit/directions
to
build such a switch?

Thanks,
JohanE


this device is a speaker level switch not line level. is this what you want?

Inherently it is a somewhat hard problem -- the question is how to make sure
the occasional noise pop on line B won't trigger it.

Look for circuits for a "VOX" (old radio term for voice-operated relay).
That may get you somewhere. Such things are used with 2-way radio
transmitters.

It would be an interesting design project but I've never actually built one.


"JohanE" wrote in message ...
Hi,

I'm looking for a device that will automatically switch 2 line-level audio
signals to a single output.

One of the audio lines (A) will always have a signal. This is the default
audio.
The other signal (B) will switch on and off. When B comes on, I want it
to become the active source, for as long as it is on. When B switches off,
A should become active again.

I found a device that does this for amplified signals
(http://www.cbav.com/Merchant2/mercha...ry_Code =SI-2)
but the price ($120) is pretty steep.

Does anyone know of a cheaper device to do this, or a circuit/directions
to build such a switch?

Thanks,
JohanE

JohanE wrote:

I'm looking for a device that will automatically switch 2 line-level audio
signals to a single output.

One of the audio lines (A) will always have a signal. This is the default
audio.
The other signal (B) will switch on and off. When B comes on, I want it to
become the active source, for as long as it is on. When B switches off, A
should become active again.

I found a device that does this for amplified signals
(http://www.cbav.com/Merchant2/mercha...ry_Code =SI-2)
but the price ($120) is pretty steep.

Does anyone know of a cheaper device to do this, or a circuit/directions to
build such a switch?

This should do what you're looking for - line (not speaker) level auto
switching/ducking.

http://www.rdlnet.com/st-vp2.htm

Not sure about the price, but you're unlikely to find much of anything
for less that $100. Too small a market for these devices to have much
in the way of economy of scale.

//Walt

"TimPerry" wrote in message
...

"JohanE" wrote in message
...
Hi,

I'm looking for a device that will automatically switch 2 line-level
audio
signals to a single output.

One of the audio lines (A) will always have a signal. This is the default
audio.
The other signal (B) will switch on and off. When B comes on, I want it
to
become the active source, for as long as it is on. When B switches off, A
should become active again.

I found a device that does this for amplified signals

(http://www.cbav.com/Merchant2/mercha...ode=C&Category
_Code=SI-2)
but the price ($120) is pretty steep.

Does anyone know of a cheaper device to do this, or a circuit/directions
to
build such a switch?

Thanks,
JohanE


this device is a speaker level switch not line level. is this what you
want?


No, it's not. It's functionally what I want, but at the wrong level. Sorry
if I didn't make that clear.

JohanE

"mc" wrote in message
...
Inherently it is a somewhat hard problem -- the question is how to make
sure the occasional noise pop on line B won't trigger it.


I don't worry about that too much, since the B-source itself switches on and
off and I want the line to follow if it comes on. While it's off I don't
expect there'll be pops.

Line A comes from an external source, beyond my control, and "always on".

JohanE

Look for circuits for a "VOX" (old radio term for voice-operated relay).
That may get you somewhere. Such things are used with 2-way radio
transmitters.

It would be an interesting design project but I've never actually built
one.


"JohanE" wrote in message
...
Hi,

I'm looking for a device that will automatically switch 2 line-level
audio signals to a single output.

One of the audio lines (A) will always have a signal. This is the default
audio.
The other signal (B) will switch on and off. When B comes on, I want it
to become the active source, for as long as it is on. When B switches
off, A should become active again.

I found a device that does this for amplified signals
(http://www.cbav.com/Merchant2/mercha...ry_Code =SI-2)
but the price ($120) is pretty steep.

Does anyone know of a cheaper device to do this, or a circuit/directions
to build such a switch?

Thanks,
JohanE

OK, the other technical problem would be response time. The reason why some
two-way radio operators start every sentence with "Ah...." is that the VOX
is likely to miss the first half of the first syllable; it takes time to
switch on.

"JohanE" wrote...
I'm looking for a device that will automatically switch 2 line-level
audio signals to a single output.

One of the audio lines (A) will always have a signal. This is the
default audio.
The other signal (B) will switch on and off. When B comes on, I want
it to become the active source, for as long as it is on. When B
switches off, A should become active again.

I found a device that does this for amplified signals
(http://www.cbav.com/Merchant2/mercha...ry_Code =SI-2)
but the price ($120) is pretty steep.

Does anyone know of a cheaper device to do this, or a
circuit/directions to build such a switch?

http://www.sescom.com/sips/audio_sips_list.html
SIP-13 Ducker Circuit
you can buy the SIP miniature PC board
they also show the schematic diagram, etc.