# Relay Bypass Circuit Details



## phi1 (Jul 26, 2019)

@PedalPCB I'm looking at the relay bypass board and considering using it in a couple projects.  What's the purpose of the 2N3904?

I was reading up about Relay Bypass on the Coda-Effects blog.  He has a post about anti-pop where he mutes the signal for about 40ms by sending the effect output to ground for via a photoFET.  I was wondering if the 2n3904 here serves a similar purpose.  If not, do you have another way to combat switch popping, or have you noticed any issues?

Here's the article if anyone feels like reading (he has a few about his whole relay bypass process).








						Coda Effects: Relay bypass with anti pop system: noiseless and clickless true bypass
					

Learn more about electric guitar related electronics: DIY guitar pedals, from fuzz faces to delays and reverb, cables and circuits theory




					www.coda-effects.com


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## Robert (Jul 26, 2019)

The 2N3904 is used to pull the LED SW pad low coming from the main PCB.

There is no built in anti-pop circuitry, but so far there have been no reports of popping.


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## phi1 (Jul 26, 2019)

Ah right that makes perfect sense now. Good to know.


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## zgrav (Jul 26, 2019)

I have used the relay board on a couple of projects (Chaos Machine and Hydra Delay) with no popping.


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## Gordo (Jul 26, 2019)

I suspect it would depend the the effect but I've used it on 3 projects now and all are completely silent.  I use the Coda in a lot of builds but I REALLY like the easy momentary function in this board.


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