Hi,
I'm building a balanced audio mute circuit. Till now I tried using a latching DPDT relay that when activated shorts Pins 2 and 3 together to Pin 1. I used a latching relay because it is supposed to have less mechanical noise. However I can hear a tiny mechanical click when unmuting the audio (this is more evident when no audio is present). For reference the circuit is the top one in this link.
Thus I tried building something like this where I connected two optocouplers outputs to both pins 2 and 3. When activating the optocoupler this shorts the signal to Pin 1. This worked to a certain extent, because instead I am getting very low volume. Any idea why this is happening? Shouldn't I get a complete mute?
Thanks
I'm building a balanced audio mute circuit. Till now I tried using a latching DPDT relay that when activated shorts Pins 2 and 3 together to Pin 1. I used a latching relay because it is supposed to have less mechanical noise. However I can hear a tiny mechanical click when unmuting the audio (this is more evident when no audio is present). For reference the circuit is the top one in this link.
Thus I tried building something like this where I connected two optocouplers outputs to both pins 2 and 3. When activating the optocoupler this shorts the signal to Pin 1. This worked to a certain extent, because instead I am getting very low volume. Any idea why this is happening? Shouldn't I get a complete mute?
Thanks
You will only get a complete mute is the impedance of the mute circuit is less than the signal feed impedance.
Most designers use a jFET (J114 etc) or small signal transistor (DTC124etc) to mute the signal.
No pont in re-inventing the wheel.
Most designers use a jFET (J114 etc) or small signal transistor (DTC124etc) to mute the signal.
No pont in re-inventing the wheel.
There is no reason to short 2 and 3 to 1, in fact it may cause the click if there's some ground junk.
A balanced input is zero when 2 is connected to 3 and if it clicks that means there's some DC offset on either 2 or 3 or both.
Don't use a BJT or FET as switch; they have non-linear capacitance in the off state and can cause distortion.
Jan
A balanced input is zero when 2 is connected to 3 and if it clicks that means there's some DC offset on either 2 or 3 or both.
Don't use a BJT or FET as switch; they have non-linear capacitance in the off state and can cause distortion.
Jan
I initially started off like this but shorting them to Pin 1 then seemed to reduce the click further.
For testing I am switching between the L and R outputs of my Focusrite 8i6 to one speaker output and I am adding this mute switch for more functionality and to use while switching input (in case of a pop). I agree re the DC offset - however I tried adding series caps to remove any DC offset before switching but it did not help.
I believe that the click that I am getting is because the latching relay is mechanical. It seems to be different than the audio pop I experienced before when switching. It's more of a tick.
Hello, Maybe the optocoupler you are using is not closing completely. Try to adjust correctly so that they get enough power.
You can try to use optocouplers with lower switching resistance.
You can try to use optocouplers with lower switching resistance.
I tried running it at max LED current but still it remained the same. I'm using the Toshiba TLP240G(TP1,F
OK, yes, if it is mechanical there's not much you can do except close the box ;-) but it also means it does no harm.
There's two issues with using optocouplers.
One, in the off state, they present a (small) non-linear load. Depending on your source impedance, it may or may not matter to you.
Two, they will most probably not mute 100% but do you need that?
You can also argue that a mute that still allows you to hear that something is going on is a Good Thing.
Depends on where you need it for; if it is for picking up the phone, a non-perfect mute is OK.
You could also search for lowest on-resistance devices; the one you list is 50 ohms max, but for instance the TLP171A is 2 ohms max, 1 ohm typical.
Jan
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Does anyone have experience with signal relays opening and closing pin 2 and 3 after the output resistors on xlr out to short out opamp pops on ON and OFF. Any good circuits?
I eliminated clicks on my balanced mute by shorting pin 2 to 3 without switching the signal - this would be the bottom circuit of the link you posted first. "Balanced XLR switcher for phantom-powered mic inputs" . I just used a normal rotary switch dead quiet compared to switching pins 2 & 3 away from the line