"Correct" LED connection to 3PDT

[phillip]

What is the "correct" way for using a 3PDT switch to turn a LED on and off?  In the past I've used the switch to break the supply voltage going to the anode and left the ground connected, but I'm not sure if it's better to break the ground connection and leave the power connected instead.

In the past when I've used LEDs, even with the 3PDT, I've had an audible "pop" when the effect was turned on and off because of the LED.  Once I disconnected the LED's  power supply from the switch the pop was gone.

Any ideas?
Phillip

[Paul Marossy]

I've always broken the connection to ground with the 3PDT switch. I have rarely had a problem with popping noises due to LEDs. IME, the usual remedy for the pop is a pulldown resistor on the input and/or output.

[phillip]

I've always broken the connection to ground with the 3PDT switch. I have rarely had a problem with popping noises due to LEDs. IME, the usual remedy for the pop is a pulldown resistor on the input and/or output.

I was thinking that it might be better to break the ground to keep the voltage off the switch.

The circuit switched silently when the LED connection was removed from the switch, since it already had pulldown resistors in the input and output.  Never figured out why the LED made an audible pop with a 3PDT switch...must've been some voltage leaking through somehow.

Phillip

[cd]

It's the LED ground polluting the signal ground which causes the pop... I think there's an explanation of it on RG's site.  Or search for "nota bene", RG posted a fix on this a while back.

[Skreddy]

My popping problems went away after installing a 100uf electrolytic capacitor across the supply rails (negative lead to the ring of the input jack, positive lead to the wire the feeds the circuit its +9v).  This should supply a reserve of current for those switching transients as the LED suddenly demands power.  FWIW, I break the ground connection, too; but I don't think that's inherently better than supplying the switch with the current-limited positive voltage for the LED.

[The Tone God]

the usual remedy for the pop is a pulldown resistor on the input and/or output.

That solution works for leaky input/output caps. It does not solve ground noise from an LED switching which I belive it happening as well.

You could increase the curent limiting resistor for the LED but that would be a patch solution I think. Just something off the top of my head.

Andrew

[Paul Marossy]

Well, I do use some fairly large current limiting resistors on my LEDs...
Maybe that's why it works for me?

[The Tone God]

Well, I do use some fairly large current limiting resistors on my LEDs...
Maybe that's why it works for me?

That was just a suggestion off the top of my head. If you increase the resistor to lower the amount of current then when the LED switches on and off there would less pull on ground. Atleast thats my thinking. I have the same problem occassionally with switch LEDs with logic stuff. A resistor tweak usually fixes it.

There is probably a better answer in the archive somewhere.

Andrew

[Paul Marossy]

I remember reading somewhere that the cap in conjunction with the LED works well.

[D Wagner]

I remember reading somewhere that the cap in conjunction with the LED works well.

Jack Orman posted on this before saying that two resistors (each 1/2 total required value) with a polarized cap to ground between them would help greatly to reduce popping (I think it was a 22uf cap).

[AL]

I'm having the same problem with a recently installed LED/3PDT into my AMZ booster. It didn't pop when I had a DPDT and no LED  . Hmmm? Maybe I'll try the cap suggestion.

AL

[cd]

You guys are dancing all around the issue.  Try the search I suggested above, the answer is there.

[Torchy]

http://diystompboxes.com/sboxforum/viewtopic.php?t=23743

its all there .....

PS ... Thanks RG  :wink:

[Paul Marossy]

In my case, I never use stereo jacks, because I run all my effects off of an AC adaptor. But, I do use a mechanical switch...

[Fret Wire]

Those are good fixes. I'd go with cleaning first. Has anyone here  incorportated the pnp fix into their pcb layouts? Nothing in life is free, the best solution either adds more off board wiring, or eats up more pcb real estate. I'm thinking that the input-grounded style wiring layout might help the ground integrity.

[moogatroid2000]

I'd like to ask what effect grounding the effect input during bypass has on popping and in general?
Also, does it reason that if the effect input is grounded when bypassed that at least the input would not need a pulldown resistor?
Is there a way to wire up a switch to allow both the effect input and ouput to be grounded while in bypass?
If so, wouldn't this help with popping too?

hmmm  :?

[moogatroid2000]

I think this would work to ground both effect input and output when bypassed. Now if I only knew it would do anything for popping.

[Paul Marossy]

Something no one has asked: does it pop only when switching on, or only when switching off, or is it anytime you use the switch? If it's one of the first two, then that might be a clue as to why the popping noise occurs.

[Torchy]

I think this would work to ground both effect input and output when bypassed. Now if I only knew it would do anything for popping.

You just permanently shorted the fx input and output across the switch.

[Samuel]

yeah that switch scheme would be pretty oscillatory