Speaker switching

[Mortel]

Hi folks,

I want to build a computer controlled stereo speaker selector. I do not
want to control the signal input to the amplifier but to control output
signal to speakers.

My big problem is to respect impedences, either the input impedence seen by
the amplifier and the output impedence seen by the speakers, wich sould be
kept to 8ohms to get best power transmission.

I could use simple relays that would directly connect the input to the
output, isolating the signal from the controll circuit. But I was wondering
if there was IC's designed to keep the input and output impedences to
constant values, I'm thinking of maybee opto-isolated mux or something like
that.

Any ideas ?

Thanks in advance.

J-F

 

[Kalman Rubinson]

On Sun, 22 Feb 2004 15:28:26 -0500, "Mortel" <No_Spam@spam.com> wrote:

Hi folks,

I want to build a computer controlled stereo speaker selector. I do not
want to control the signal input to the amplifier but to control output
signal to speakers.

My big problem is to respect impedences, either the input impedence seen by
the amplifier and the output impedence seen by the speakers, wich sould be
kept to 8ohms to get best power transmission.

I could use simple relays that would directly connect the input to the
output, isolating the signal from the controll circuit. But I was wondering
if there was IC's designed to keep the input and output impedences to
constant values, I'm thinking of maybee opto-isolated mux or something like
that.

Umm...
If you are controlling the output signal to the speakers, the input
impedance of the amp is not affected and it is irrelevant in this
task. I have done this with simple relays but they must be selected
to deal with the power levels involved (but unspecified by you). I
doubt if ICs can handle such levels.

Now, if you are talking about more than switching between speakers but
about switching in different combinations of speakers, then you need
to consider the effects of series and/or parallel speaker loads.
There, too, ordinary relays can do the heavy lifting but you'd need
some logic to select and balance the choices.

Kal

 

[Mortel]

"Kalman Rubinson" <kr4@nyu.edu> wrote in message
news:8vgi30t7c0iqnl3pv6jbm0nojlhbo869i2@4ax.com...

On Sun, 22 Feb 2004 15:28:26 -0500, "Mortel" <No_Spam@spam.com> wrote:

Hi folks,

I want to build a computer controlled stereo speaker selector. I do not
want to control the signal input to the amplifier but to control output
signal to speakers.

My big problem is to respect impedences, either the input impedence seen
by
the amplifier and the output impedence seen by the speakers, wich sould
be
kept to 8ohms to get best power transmission.

I could use simple relays that would directly connect the input to the
output, isolating the signal from the controll circuit. But I was
wondering
if there was IC's designed to keep the input and output impedences to
constant values, I'm thinking of maybee opto-isolated mux or something
like
that.

Umm...
If you are controlling the output signal to the speakers, the input
impedance of the amp is not affected and it is irrelevant in this
task. I have done this with simple relays but they must be selected
to deal with the power levels involved (but unspecified by you). I
doubt if ICs can handle such levels.

Well I gess that some power transistors would do the job (35 Watts RMS at
the output of the amplifier) but I don't want to design the impedance
matching circuits so I will use relays

Now, if you are talking about more than switching between speakers but
about switching in different combinations of speakers, then you need
to consider the effects of series and/or parallel speaker loads.
There, too, ordinary relays can do the heavy lifting but you'd need
some logic to select and balance the choices.

Kal

Yes, in fact I only want to multiplex one input to 3 or four output, only
one output activated at the time. I know that many IC companies, mostly
european (like telecontrolli) had designed audio IC series, I thought that
maybee some IC would do specifically the job.

Thanks for your answer.

J-F