switch popping noise correction?

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Curranproducer
Posts: 285
Joined: Sun Oct 16, 2011 4:58 pm
Location: Akron, Ohio

switch popping noise correction?

Post by Curranproducer »

Hey there everyone! it has been quite some time since I posted on here, and I wanted to stop in with a question about switching noise. this is not about the standby popping thing that everyone has issue with. I have a NFB three way switch, and a cathode switch on V2. there is popping when I use these little switches, and I am wondering if there is a way to get the popping to go away with a resistor or something like that?
Curran

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R.G.
Posts: 1223
Joined: Tue Dec 02, 2014 9:01 pm

Re: switch popping noise correction?

Post by R.G. »

The key to preventing switch pop is to make sure that when you switch the cap, the DC conditions on the circuit do not change as a result of adding/subtracting the cap. Using a resistor or something always devolves down to arranging the resistor(s) and the switch so the cap is already charged up to the DC voltage before the switch changes as after it changes.

This is done by noting that a capacitor is a low AC impedance but (ideally...) a DC open circuit. So if you have a cap you're switching into a circuit, you want a resistor pre-charging it to the same DC voltage it will be at after the switch throws. Luckily, with the cap being a huge DC resistance, a 1M (or so) resistor is sufficient to do the charging to the post-throw DC value.

On a cathode, you can put a 1M from the cathode to the cap. Then when you want to switch the cap in, use your switch to short across the resistor. Cap is pre-charged, so no pop. Gain just jumps. Opening the switch causes no current to flow in/out of the cap because it's already at the DC potential of the cathode, so the voltage on each side of the 1M is the same, no current flow.

Sometimes it can be tricky to arrange the switch, resistor, and cap to be the right voltage. But it can be done.
idnotbe
Posts: 24
Joined: Sat Mar 18, 2017 2:25 pm

Re: switch popping noise correction?

Post by idnotbe »

maybe the other subject... but....

i thought "relay" is the application in this situation.
for ex, channel switching, etc...

what's the difference between resistance method above and relay for taming the popping noise ?
R.G.
Posts: 1223
Joined: Tue Dec 02, 2014 9:01 pm

Re: switch popping noise correction?

Post by R.G. »

A relay is a magnetically operated switch. So in addition to getting the noise from a manual switch - if any - you get induced noise from the current and voltage needed to make the switching happen. Coil switching noise can cause issues all on its own.

So can semiconductor switching. Feed-through of the control signal is a problem with semiconductor switches that are not opto-isolated.

I've been messing with the TLP222G LED-to-MOSFET module for signal switching recently. It has some real promise for silent switching, but is no better than the mechanical switch for switch popping coming from the things it switches.
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