Isolate or not? Balanced audio line with 100 drivers

[Zedman]

Isolate or not?

I got a balanced audio line with approx. 100 drivers and one receiver
parallely.
(Driver: Mic amp LM358 with 2 OPAmps diff output, Receiver: INA134)
Only one driver can be online at a time.

Which is the better:

- should I isolate the others from the line when the one driver is enabled
- or is it enough to power down those amps that are not used (power
down is controlled by a MCU with an OptoCoupler)

If I should isolate than what should I use to isolate a balanced output from
the line? (It's very sensitive)

please help me,
thanks
Zed

 

[batdin]

Re: Isolate or not?

If the output swing is more than 0.5V,the signal from the working opamp will be shunted by the others.The capacitance of 100 outputs is one more problem.

 

[Zedman]

Isolate or not?

Than better I should isolate it, but how?

 

[goodboy_pl]

Re: Isolate or not?

The problem is that u r using OPAMP!
it is simple to use OTA, this works even if all of the driver are working! (if the recived voltage dos not clamped to the supply voltage i.e. nonlinearity problem)
It is a the basic audio mixer.


BEST!

 

[Zedman]

Isolate or not?

Please teach me,

I am lame to analog technics, what is OTA?

(remember my ~100 clients are connected up
with approx. 100-120 meters UTP cable)

thanks in advance,
Zed

 

[Zedman]

Isolate or not?

OTA -> Operational Transconductance Amplifier?
Is it possible to build balanced line with it?
Does it exist in singlesupply version?

If I do the isolation on + and - lines with a 5V Relay
is it OK?

please help me,
Zed

 

[goodboy_pl]

Re: Isolate or not?

OTA -> Operational Transconductance Amplifier.
An OPAMP is Voltage Controlled Voltage Source thus u can not connect output of them together but the output of VCCS (Voltage Controled Current Source) can be connected together, cos if the input voltage of any of them is zero, then the output is open circuit.
u can use a simple jfet, mosfet or even a bjt with emitter degeneration to make the VCCS (something like OTA!) and it works with single supply also; of course u need DC decoupling!!! not only for single supply operation but also for blocking offset current of VCCS(s) before saturating the reciever side!
for diff. u must use inverter amplifer also.
at the reciver side a resistor converts current to voltage and the voltage is buffered with an OPAMP...

BEST!

 

[Zedman]

Isolate or not?

Can you please show me a simple (cheap) OTA
with jfet or similar i can user with LM358 Mic preamp
to get balanced (open) output that can be connected
parallely?

Can I use the INA134 as the balanced receiver with
OTA drivers?

I saw CO3080, but there is only one amp in one
package and it's expensive for my 100 clients...

thanks
Zed

 

[Zedman]

Re: Isolate or not?

Damn,

I don't have time, so i'll do it with this 5V relay:

TAKAMISHAWA AL-D5-W

Please shout if it's sounds too lame... :roll:

 

[goodboy_pl]

Re: Isolate or not?

In fact u will not need real OTA and can make a VCCS with two opamp like LM358!

Check the Pic.
u can make it with single supply also, here iss the concept only!
each of your user have a ckt like thiss, the output of several uer (in current not voltage!) i added in a node wichi is connected to a resistor, use a simple buffer for reading the voltage.
for analog switch u can use 4016 or 4066 and supply voltage of up to 15 V, or use small/ low-cost reed relay; I think it iss better tree like addresing with binary coding iss a good solution for usser routing!

BEST!