Electronics > Projects, Designs, and Technical Stuff
Preventing ringing in audio mute circuit
BrianHG:
DC offset in your circuit, if it's not from your source signal, may be from one mosfet in the opto turning on or off prior to the second, or one of each protection diode is switching with an initial delay.
You are using the wrong type of opto for audio. Use this guy: H11F3M
http://www.onsemi.com/pub/Collateral/H11F3M-D.pdf
looking at page 7 on the datasheet, you see that this photo-fet is designed for audio attenuation applications unlike opto-mosfets like which you are currently using.
Also, low pass filter the driven LEDs as this optocoupler has a smooth linear resistive output transfer VS the LED drive current unlike the optos you are using which harshly avalanche from megaohms right down to a few ohms without any linear transition. This should act like a fast moving volume control if you tune the right 2 resistors and cap at the LEDs so that a pop will never be generated, though, muting the audio will take around 1/20th of a second.
Also, with the over 300M-Ohm resistance in the H11F3M, you should only need 1 series optocoupler with an output load as your mute switch.
ciccio:
--- Quote from: BrianHG
You are using the wrong type of opto for audio. Use this guy: H11F3M
[url=http://www.onsemi.com/pub/Collateral/H11F3M-D.pdf ---http://www.onsemi.com/pub/Collateral/H11F3M-D.pdf[/url]
--- End quote ---
Thanks for this info: I did not know that device, and I'll order some samples to-day for a project I'm working on.
Best regards
duak:
I wonder if the reverse or body diode across the FET is acting as a photodiode and is injecting some voltage into the circuit. The pulse is about the right amplitude. I think the FET is diverting some of the photccurrent, but i there will be a time delay before the FET turns fully on. The remainder of the damped sinusoid could be due to the cabling ringing. This could be confirmed by observing the voltage across the FET out of the circuit.
cvanc:
--- Quote from: ciccio on March 24, 2019, 01:14:53 pm ---
--- Quote from: BrianHG
You are using the wrong type of opto for audio. Use this guy: H11F3M
[url=http://www.onsemi.com/pub/Collateral/H11F3M-D.pdf ---http://www.onsemi.com/pub/Collateral/H11F3M-D.pdf[/url]
--- End quote ---
Thanks for this info: I did not know that device, and I'll order some samples to-day for a project I'm working on.
Best regards
--- End quote ---
Yeah, I also did not know this device existed. Looks very useful. Thanks BrianHG!
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