audio select circuit problem

[david90]

I'm using max4600 analog chip for a 2 sources audio select circuit. The problem i'm having is that the source do not turn off completely if I turn the other source on. If I select source 1, I could still hear a little bit of audio from source 2. Can somebody help me out?

 

[IanP]

According to MAX460 data sheet the crosstalk between any two switches should be -65dB, but here is the catch --> R(load)=50Ω ..
What you can try to do is to connect a load resistor of, say 1kΩ, and check it ..
If you still can hear the other channel, lower the value to 470Ω, and try again .. and continue till you are satisfied ..
If the overall volume drops down you may need to add sigle stage amplifier to compensate for this loss ..
Regards,
IanP

 

[david90]

Thanks for the help!

I used two 4600 chips to multiplex between my car's cd player and my portable mp3 player. Each 4600 chip has two switches NC and NO. NC switch in the two chip is connected to car's cd player while the NO switches are connected to my portable cd player. Because the signal is stereo, I needed two chip to multiplex between two devices.

The load resistor is connected to the output of the right and left channel from the 4600 ICs to ground? How does connecting a load resistor lower crosstalk?

 

[IanP]

In a chip like this both switches share common +/-V and who knows what elese, so there are planty of ways the other signal can "sneak" to the neigbouring channel ..
But, if you provide solid load, such as 50Ω, only the main signal will be able to produce proper outcome ..
The other signal, which has to pass through an "impedance" will be attenuated by this load (but not eliminated) ..
Regards,
IanP

 

[david90]

Thanks for the explaination.

I'm not clear on where RL suppose to be connected. Is in connected in series with the power amp input?

 

[IanP]

R(load) has to be connected in parallel with the PA input: between input and 0V ..
Regards,
IanP

 

[10kangstroms]

A low-resistance load tends to cause distortion, because the switch resistance varies with signal level.
A good way to get good isolation is to use T-switches, as below:

Lots of parts, but excellent isolation.

 

[david90]

R(load) has to be connected in parallel with the PA input: between input and 0V ..
Regards,
IanP

connected a 1.5 ohm RL is crosstalk was gone. Audio was small but I can amp it up with an op amp. I have another problem. There is a small low frequency thumping noise. Is that noise?