Hello,

I’ve a simple circuit for a musical instrument but I can’t seem to get it working correctly. Basically all I have is a magnetic coil pick-up sending a signal to a pre-amp. The signal is then pulsed by an analogue switch before being sent out to the amplifier.

The problem I can’t overcome is the ‘clicks’ that come from the analogue switch. I’ve tried several different models; even special audio ‘clickless’ switches but it seems to make little difference. I have followed all the recommendations in the various datasheets but without success. Is the click due to the control signal or due to the switch turning on? The audio switches are supposed to turn on gradually to eliminate this noise but it comes out loud and clear on my system. Even if there is no audio signal coming through the circuit the switching clicks are still strong.

I have tried using a SPDT version to switch the amplifier input from signal to ground; the output was silent between pulses but the switching clicks were not eliminated.

I tried putting the analogue switch on the power amp speaker leads, but that only resulted in melting the IC. I would only suppose that if the chip was placed immediately after the pick-up any click generated would be well amplified by the time it reached the speaker.

I’ve been using MAX4514 and SSM2412 switches recently (I have to use DIP chips, the others are too small to handle).

So where am I going wrong? Is there such a thing as a noiseless ‘clickless’ analogue switch and if so how do I wire it up?

All suggestions welcome. Thanks.


Vielle568

 

why do you need to pulse the switch? what are you trying to accomplish by pulsing the switch? how often you pulse it? what is duty cycle?

obviously pulsing introduces transients and they are heard as clicks.

 

Hello,

Can you post a detailed schematic?
I think the charges in the capacitors are giving trouble.

Bertus

 

The problem is not that the analogue switch makes a click, it is that it instantly turns the sound wave on/off and if the waveform is far from zero at that instant, you hear the result as a "click".

The standard fix is to ramp the analogue switch on/off over some milliseconds so it does not instantly turn on/off.

I'm not familiar with that exact analogue switch but you could try putting an RC on the switch control wire, to ramp the voltage there. You can test it easy enough with a 'scope and switching on/off a 1kHz sine. You need the ramp to be at least 50mS or so.

 

You want a "make before break" switch. Here is a link that may help - http://www.maxim-ic.com/app-notes/index.mvp/id/638 Investigate a little on the Maxim web site and you will find one to fit your needs.