# Circuit Input grounding on 3PDT (Bypass)



## Many__Of__Horror (Jun 19, 2020)

Interested on your thoughts on if it is necessary to ground the circuit input when in bypass. I am looking to wire up a common anode bicolour LED & would need lug 6 to connect to the 2nd cathode leg.
I have only ever used the below wiring method, except for one time on an Angry Andy Plus build which used both sides with a bicolor LED. The boost side gives a pop the first time you use it then goes away. Wondering if it caused by not grounding the circuit input when bypassed?


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## phi1 (Jun 19, 2020)

On my first several builds on vero I did Not ground the circuit input in bypass. I haven’t had any issues with those.

my understanding is that that purpose of grounding the circuit input in bypass is to eliminate any possibility of signal bleed through, particularly for very high gain circuits. I never noticed an issue on my builds, but switched to doing it the “correct” way just because it is the standard.

if you have a pull down resistor on the input, i don’t think you’ll have a pop.


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## benny_profane (Jun 19, 2020)

This may be helpful for understanding the role of an LED with switch popping:






						AMZ - LED Popping
					

How to stop the pops in audio from LED current surges when switched.




					www.muzique.com


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## phi1 (Jun 19, 2020)

Yes that’s a nice article with good info. Curious if you’ve ever used this method and what the results were?

I’ve never had an issue with popping such that I’ve had to add a capacitor to the led circuit. I don’t know as I’ve noticed anyone do that in the build reports here either.


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## benny_profane (Jun 19, 2020)

I've never used it, and I've never run into a situation necessitating it. It makes sense electrically, though. I've seen people use it—it's usually a solution that comes near the end of a troubleshooting thread rather than during a build report. 

You can also use a similar method (albeit with the addition of a BJT) to make the LED fade in when switching.


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## Robert (Jun 19, 2020)

Occasionally you'll run into a circuit that will oscillate in bypass and in some cases that is audible in the bypassed signal....   Any self-oscillating fuzz (Fuzz Foundry) or delay can be a culprit.



Many__Of__Horror said:


> I have only ever used the below wiring method, except for one time on an Angry Andy Plus build which used both sides with a bicolor LED. The boost side gives a pop the first time you use it then goes away. Wondering if it caused by not grounding the circuit input when bypassed?



If you change R32 to 10K that popping will likely go away.


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## Many__Of__Horror (Jun 19, 2020)

Thanks for your thoughts guys, will try the resistor change up first


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## Many__Of__Horror (Jun 20, 2020)

Resistor change didn't clear up the pop. If anything it is now one louder pop then completely goes away. I'll keep looking. Didn't mean this to turn into a fault finding thread was just interested in why the input gets grounded on the switch is all. Thanks


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## ADAOCE (Apr 2, 2021)

Many__Of__Horror said:


> I am looking to wire up a common anode bicolour LED & would need lug 6 to connect to the 2nd cathode leg.


how did this turn out for you? I’m running to the same issue with a true bypass loop strip. Four of my loops have the common anode led so it’s red when bypassed. I wired the red cathode to lug 6 but I kept the jumper from lug 1 also connected to lug 6. If yours doesn’t pop and you kept the circuit ungrounded I might change mine up


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## Many__Of__Horror (Apr 2, 2021)

Never managed to resolve this particular "pop" with the bicolor LED. It's a 50/50 things when I use them. This particular one was on the AT+ Boost side, distortion side it didn't happen. Pretty sure if I swapped out the LED to a single colour it would go away.


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## ADAOCE (Apr 5, 2021)

Many__Of__Horror said:


> Never managed to resolve this particular "pop" with the bicolor LED. It's a 50/50 things when I use them. This particular one was on the AT+ Boost side, distortion side it didn't happen. Pretty sure if I swapped out the LED to a single colour it would go away.


Thanks for the info. Did you clip the ground connection from lug 1 to 6?


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## Many__Of__Horror (Apr 5, 2021)

I used this board - https://www.pedalpartsaustralia.com/index.php?main_page=product_info&products_id=1497


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## ADAOCE (Apr 6, 2021)

Many__Of__Horror said:


> I used this board - https://www.pedalpartsaustralia.com/index.php?main_page=product_info&products_id=1497


Ok great thanks that looks like the guitarpcb board which has been recommended to me.


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