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Have a simple circuit : enter image description here

i want to create a gated effect that cuts signal in and out .. it works but i can hear the switching sound of square wave generated by arduino through my amp speaker .. (click ,click, click..)

Does anyone have a solution to get rid of this sound and maybe someone could inform me how this happens in 1st place .. im guessing its noise caused by the magnetic field created by the on/off cycle? or maybe not lol?

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  • \$\begingroup\$ You need a coupling capacitor to the input point, and another from the output point. \$\endgroup\$
    – user207421
    Mar 30, 2015 at 23:35

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Try this.

schematic

simulate this circuit – Schematic created using CircuitLab

This circuit assumes that the net DC voltage on both input and output is zero. If there is any offset, you will need to add coupling capacitors to block the DC.

The probable reason you are getting clicks with your circuit is that the switching action is too fast. I'm going to guess that the clicks are almost inaudible if there is no audio signal but become more noticeable as the audio level increases.

What you want is an attenuator that ramps from full to off as well as ramping from off back to full on.

You can play with the choice of MOSFET. The 2N7000 is an old part that doesn't have very good Rds-on ratings - this will limit the amount of attenuation that you get. But it has a low threshold voltage - this is important if you are controlling the MOSFET from an Arduino.

There are many suitable MOSFETs available that will work better.

Play with the values of R3 & C1 to change the ramp time.

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  • \$\begingroup\$ I will try this when I get chance thanks.. As regards to switching time, at moment Iam switching every 100ms.. Surely most transistors can handle that speed?? \$\endgroup\$ Mar 31, 2015 at 0:26
  • \$\begingroup\$ That's not the switching time that I'm talking about. Look at it this way. Assume that you turn the transistor ON when the incoming signal is at a high peak (either positive or negative). When the transistor turns ON, that signal suddenly goes to ground. The sharp edge that occurs is the "tick" that you are hearing. \$\endgroup\$ Mar 31, 2015 at 1:13
  • \$\begingroup\$ ah okay so the RC combination will smooth out that transition? \$\endgroup\$ Mar 31, 2015 at 14:22

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