Author Topic: Switching stereo audio inputs with an SPST? (IC?)  (Read 1314 times)

CodeMonk

Re: Switching stereo audio inputs with an SPST? (IC?)
« Reply #20 on: March 30, 2021, 03:30:27 AM »
"Pulldown resistor" is another search term you might want to try

DIY Dood

Re: Switching stereo audio inputs with an SPST? (IC?)
« Reply #21 on: March 30, 2021, 06:59:44 PM »
Sorry. 3-letter words baffle the Search. Try "pop resistor".

OK... studied a bit... from what I've learned (keep in mind I'm 'electronics light') it looks like the pop is usually from a typical circuit where DC can potentially mix with the AC signal. In my case, they should be totally isolated because the audio is switching through the relay.

Do you think I'm getting leakage through the switching circuit into the relay circuit? So should I be testing for DC voltage on the relay lines when they are disconnected from any input?

Or is the suggestion that the radio and "aux" input have their own issues and are putting DC on the lines from those devices and into the amp (common) output contacts? So perhaps I should try 1M pull down resistors on the audio inputs?

ElectricDruid

Re: Switching stereo audio inputs with an SPST? (IC?)
« Reply #22 on: April 02, 2021, 05:10:32 PM »
Unless the audio just happens to be at zero volts at the point you switch, there will be some voltage on the relay - after all, AC voltage spends very little of its time close to zero. And if the little metal springy contacts bounce at all (they probably do) then that voltage gets switched on and off rapidly with each bounce. That makes a pop.
I think expecting relays to be silent is a bit unrealistic. Some of them are quiet, but silent? Not really.

BTW, that's a completely different mechanism of making a pop than the usual thing you get in pedals, where you've got a bias voltage to avoid, although the fundamental problem of springy metal contacts remains.

DIY Dood

Re: Switching stereo audio inputs with an SPST? (IC?)
« Reply #23 on: April 03, 2021, 06:21:50 PM »
Unless the audio just happens to be at zero volts at the point you switch, there will be some voltage on the relay - after all, AC voltage spends very little of its time close to zero. And if the little metal springy contacts bounce at all (they probably do) then that voltage gets switched on and off rapidly with each bounce. That makes a pop.
I think expecting relays to be silent is a bit unrealistic. Some of them are quiet, but silent? Not really.

BTW, that's a completely different mechanism of making a pop than the usual thing you get in pedals, where you've got a bias voltage to avoid, although the fundamental problem of springy metal contacts remains.

Yeah, understood...  So is there a mechanism by which I can discharge that voltage? Will the 1M resistor do it (on one side of the contact or the other)?

PRR

Re: Switching stereo audio inputs with an SPST? (IC?)
« Reply #24 on: April 04, 2021, 01:56:27 AM »
It's not a guitar. Radios, iPods, etc can drive a 10k resistor, and that will bleed more leakage.

Discussing it won't fix it. Just GET some medium resistors and try it.
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DIY Dood

Re: Switching stereo audio inputs with an SPST? (IC?)
« Reply #25 on: April 05, 2021, 10:41:00 PM »
It's not a guitar. Radios, iPods, etc can drive a 10k resistor, and that will bleed more leakage.

Discussing it won't fix it. Just GET some medium resistors and try it.

Understood, I'm just unclear on where to start testing the values 10K? 1M?... and where I need the pull down. Do I place them on the common (output to amp) contacts or should they be sitting on the inbound side (the N/C & N/O contacts).