How to reduce clicks and pops when switching signals with relais ?

Hi,

I'm trying do design some sort of simple insert switcher based on passive relays. I'm trying to reduce the amount of clicks and pops when switching line audio level signals. What would be the best way to remove the switching clicks? I already tried everything from 10K to 1M  pull down resistors on all in and outputs to ground, but nothing seems to help.

I checked some other designs like Igors bypass pcb, but nobody seems to use any kind of resistors to get rid of the clicks..

Is their DC going through the relays?

No, the relay coils are powered from +12V to a seperate ground. No connections between audio ground and relay power.

I'm not quite sure what you mean with "their dc". The relays are only switching audio from input to output or alternativly through an insert point. No DC coupling etc in the signal path, only relais.

Hmmm ok, well someone probably knows better, but I know when you have DC (no coupling capacitors) on at least one side of a switch, sometimes the "pop".

Up to a point there will always be a discontinuity when switching a relay in and out. It doesn't know or care what goes through it - audio or not.

But relays can get interactive with PSU rails. It's not enough that grounds are completely separate, the relatively large and abrupt change in current drain might be heard as a click if the regulators can't keep up. And they mostly won't. But this is only an issue if the relays use the same PSU as the active audio circuits do. The fix is a separate utility rail just for led and relay duties. Sometimes the snubber diodes help, but they won't take away the abrupt change in current draw.

But if the problem is discontinuities in the actual audio content, then relays are a wrong tool. You need transistor switching. With transistors it is trivial to make a slow turn on/off, or crossfades. And I mean slow as in 10-100 milliseconds - immediate change but no click.

I got snubber diodes on all the coils. Make before break relais would probably solve the problem, but I haven't seen any of those yet in my life...

Majestic12 said:

I got snubber diodes on all the coils. Make before break relais would probably solve the problem, but I haven't seen any of those yet in my life...

Click to expand...

I have some MBB relays on hand if you want to experiment.  They are the Panasonic TQ2-2M-12V.  I do find that they can help quite a bit.  FETs can work wonders as well for quick fade-out/in.

Cheers,

Mike

do you get clicks when there is no audio passing through the relays? ie monitor the output but mute the source.
If no, the the clicks you do have when audio is passing is unavoidable with relays ... you are slicing through the waveform, this sounds like a click.
If yes, then besides snubber diodes you can try feeding the control voltage through a series resistor, say 100R .... you might then need to up the control voltage to compensate for the drop across the R and also add a cap across the relay coil, say 100uF.

or, as previously mentioned if there are DC offsets in the source device feeding or recieving from the relays this will cause clicks. Put coupling caps in series with the audio with pulldown resistors to the audio ground.

Where are you inserting the switcher? 
If it is a mod for inside a console along the signal path you probably have a DC component on the sig that has to be removed, and getting an internal circuit to interface with the external world requires more than a routing switch.
If it is external then you have to make sure that all equipment involved is properly AC grounded and look for any DC relative to shields on all the equipment signal paths either side of the switch.
I design all sorts of small-scale monitor switching solutions and you have to be click-free when switching power amps at full volume.
A simple, properly de-bounced relay circuit should be click-free at normal listening levels.
Mike

What squib says: "you are slicing through the waveform, this sounds like a click"
MBB relays may not be the solution, because you end up with two outputs connected together that don't carry the same signal (if they did, why would you switch them?), which also sounds like a click.
The two solutions I know for silent switching:
a) switching when there's no signal on both lines
b) crossfading: it can be done with JFET's (takes some time to make it artefact-free), VCA's or optocouplers. The latter work very well and are very easy to implement. Power consumption is lower than relays, MTBF is 100 years (not like relays), cost is reasonable, but may need buffering. See the Silonex website for application schemos.

maybe it is not so aplicable to pro audio but engl and other guitar amps manufacturers use a circuit to mute the output for some miliseconds using a fet.

12afael said:

maybe it is not so aplicable to pro audio but engl and other guitar amps manufacturers use a circuit to mute the output for some miliseconds using a fet.

Click to expand...

It is definitely applicable, that's why I mentioned cross-fading using JFET's. Anyway, it involves buffering, which is not compatible with the original passive concept. I think only optocouplers can provide a workable passive solution - within constraints.

http://www.groupdiy.com/index.php?topic=51128.0
We talked about de-cricking switches, pretty recently..

JR