Switching audio signals with relay

[niral622]

Hey all,
I'm new and am not sure which section to post this in, but does anyone know how to switch audio signals with a relay without getting noise in the speakers? I know I need some sort of "filter" circuit, but I have no idea how to make one...any help would be appreciated.

Thanks,
Niral

[gmarsh]

Make sure the signals you're switching are muted, and have no DC offset, and you'll be OK.

[Jan Dupont]

And make sure that your relay's will make a "Break before connection", so you avoid paralleling the two speakers

[peranders]

niral622, what sort of signals do you plan to switch? Is it input signals, speaker outputs?

It's rather important that the di/dt for the relays are reduced meaning that the switch off should be slow downed. If you only have a freewheeling diode across the relay coil you will get switch-off transients (0.7 volt over the supply voltage) from the diodes. This rather small but fast flank may cause capacitive or inductive coupling causing clicks. You can avoid this simply by making the switch-off slow but not too slow, just enough to avoid this click.

[niral622]

what sort of signals do you plan to switch? Is it input signals, speaker outputs?

I was planning on switching inputs between a CD player output and Computer sound card output

[apolon34]

hi,

i just use small signal relays from naïs with no particular circuitry. they are polarised so i don't need for protection diode.

no noise or 'click' at all.

[johnnyx]

Use gold plated cotact relays specified for low level switching, these relays have a minimum current of say 10uA.
If silver cotacts are used, they will become noisy and fail after time, the arcing when they switch cleans off the tarnish on the contact faces, and this will not occur with a CD player etc. output.
Telecomms. spec. relays should be used. I used "Type 47" relays in a preamp, with good results. I have also used reed relays.
Polarised relays still need a diode; they are polarised with a magnet to reduce the switching current in the coil, increasing sensitivity.

[till]

I use Takamisawa RY12W-K and just recived a bunch of Meisei M1B-12H. Both are also used in commercial audio equipment.

[peranders]

Originally posted by apolon34
hi,

i just use small signal relays from naïs with no particular circuitry. they are polarised so i don't need for protection diode.

no noise or 'click' at all.

Indeed, you need freewheeling diodes! Polarized means that the relay has a small permanent magnet inside which helps a bit to activate the relay (=less power consumption). If you use transistors as switching elements these diodes are essential but if you have a mechanical switch it's not that important but I recommend you to use these diodes because it will save the switch.

[apolon34]

I use bc547b in commutation to activate it.

it's running well six at least six months.

i'll add protection diode, just in case of...

thanks for the tip