Audio Button Issue...

Hello everyone!

I've built a "talkback" box for use in a broadcast situation. The gist of the box is that there is a mic preamp that's connected to several push-button switches then to each channels output.

One thing I've noticed is that on one channel, there is a popping sound when I push the button. What's odd is that I don't hear it when I plug the output into my test speaker, but only when I connect to the piece of equipment that it's supposed to be plugged into. There is a definite pop and the meters spike.

One of my smart engineer friends recommended putting a capacitor on the switch. I'm all for it, but I want to make sure that I know I'm putting it in the right spot! Can anyone tell me which of these two designs would be the best way?

The input is the hot side of the unbalanced mic pre-amp, and then goes out directly to an XLR to be connected to my actual equipment. (It's not labeled well...)

Thanks for everyone's help!

The click comes from the fact that there is different DC level at the audio source than there is at the common input to which you are switching. This manifests as a DC voltage that you could measure across the open switch with a DC voltmeter.

Here is a sim of three cases. The third one fixes the problem.

Mike,

Thanks for the sim!!

So two 100 ohm resistors to ground and then a 1uF cap. Would there be any problems if I used a 4.7uF cap instead? I think that's all I have on hand. Otherwise, I'll go out and get what I need!

Kyle

The resistors are 100,000 Ohms. 4.7uF will be fine. Put the + end of the capacitor toward the more positive dc offset, probably the source.

The 10K (10,000) resistors are likely already inside your amplifier. Check that with your Ohmmeter. Add a 10K across the amp input if there is not one there already...

Mike...

Thanks a bunch! I don't know how I missed the K when I replied... that's my bad!

Where would the DC be coming from? By source, I'm assuming you mean the output of the preamp. I guess I could find out with my MM, but I'm surprised there would be any DC on that line.

Sorry for so many questions, but I a total noob!

There was 100k of resistance between the positive input of the mic preamp and both the positive output and the ground. I'm going to assume then that I don't need that first resistor in your diagram.

I'll wire in the cap and the second resistor, the 10k to ground, and that will hopefully solve the problem!