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Old 28th November 2007, 10:21 PM   #1
YureZzZ is offline YureZzZ  Cyprus
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Default VCA clicks

Yes, It's just On and Off. I mean I use microcontrollers output pins to switch audio.

Microcontroller pins used to drive VCA-chip. As I know microcontroller can bring 0 or +5V on the pin.
VCA chip is ssm2164 (datasheet is here).

The problem is whenever I switch output pin - I hear loud click in the sound coming thru VCA.

Tryed to put 50K resistor between microcontroller and VCA - click became lower, but VCA is not able to cut sound fully.

Any ideas?

P.S. I also tried this thing:
found somewhere on the net
" to avoid clicks when you feed your VCA with sharp shapes use resistor 10K and cap 0.22 uF from VCA input to ground "... No changes...
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Old 29th November 2007, 09:20 PM   #2
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The click is probably caused by rapidly shifting dc through the cell and amplified when going from unity to -100dB of gain rapidly. While these chip manufacturers claim small dc shifts in the gain cell, the only way to eliminate them is through a trim, which this chip doesn't offer.

You can try putting a dc offset trim on the inverting input of the opamp and trim for minimum dc offset during full on and full off.
A 50Kohm trimp pot, with end terminals connected to the power rails, and a 470kohm or so resistor from the wiper to the inverting input to the opamp should work. If you get too large an offset, try a larger resistor.

If you don't need to switch the audio off instantaneously, you can put an integrator between the controller and the control input to the VCA.

You might have better luck if you try a That's 2181 trimmed VCA, that allows trimming of the control port. You would probably still need to integrate the control voltage somewhat.

Hope this helps
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Old 1st December 2007, 06:07 PM   #3
YureZzZ is offline YureZzZ  Cyprus
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Thanks for info mate!
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