[685] True Bypass with Relay

Date: June 29th, 2010 | Comments : [27] | Categories: DIY.

True bypass with relay

This is a project that I developed about 2 years ago for a rack amp system I was working on that has been put aside for now, so I decided to adapt the circuit for pedal use since the programming for the micro had already been done.

This is a 1″ x 1″ pc board which holds an AVR microprocessor that is controlling a latching DPDT relay. The LED indicator on the pedal is also driven by the micro. The soft-touch momentary switches that are shown several posts below were bought for this project.

You can use the pcb to build a new pedal, or retrofit it into a Boss or Ibanez box to give them true bypass.

More info is available here.


27 Responses to “True Bypass with Relay”

[1139] $uperpuma Says: 9:11 pm, June 4th, 2010


[1221] admin Says: 9:50 am, June 21st, 2010

Just a note here… the “Two LEDs on 1 AVR line” idea that is shown a few posts back was used with this bypass system in the rack prototype I was developing.

A simple mod to the bypass board allows the idea to be used with it in a stompbox.

[1242] RnFR Says: 9:25 am, July 4th, 2010

great stuff! and the price is totally right as well. 7 bucks w/ the chip? can’t beat that. now i can grab some really nice vandalproof switches, and never have to replace 3PDTs again!

[1245] Fender30 Says: 12:51 pm, July 7th, 2010


Have you considered licensing the programming that you have done on the AVR-microprocessor so that other pedal builders could incorporate the features into single board finished products? Then you derive a return from the development efforts for those who can otherwise source the parts for a unified board level product. I am not currently a commercial pedal builder, but it occurs to me that there is an opportunity here if you wish to pursue it.

[1247] admin Says: 4:31 am, July 8th, 2010

I would be glad to offer the pre-programmed microprocessor in quantity at OEM prices to any builders who want to incorporate the relay-bypass into their pedal.

[1279] admin Says: 7:55 am, August 2nd, 2010

In a post at DIYstompboxes, someone is intentionally trying to mislead the members into thinking that the AMZ relay bypass is a copy of some other switcher. This is ridiculous, as the AMZ bypass relay design is the only one that is using an AVR microprocessor, as opposed to the PIC micro that is used on the two other bypass pcb designs that I know about. This also means the number and type of components are not the same, i.e. different circuit design, and the pcb parts layout will necessarily be totally different.

As far as I know, my design is the only AVR-powered true bypass relay system.

Just for clarification…

[1284] Dave Says: 2:11 pm, August 11th, 2010


So how hard would it be to retrofit this into a boss pedal? Would it fit in the battery area?


– Dave

[1285] admin Says: 2:02 pm, August 12th, 2010


I have not tried it yet but it should be simple. Not sure where it would fit but I probably would not put it in the battery area in case you had to use the pedal on battery power one day.

regards, Jack

[1989] Jim Says: 11:40 pm, December 28th, 2010

Do you think that this could be adapted to work with the Rockman Octopus as a remote trigger for stomp boxes?

[2033] egasimus Says: 10:26 am, January 15th, 2011

Nice, and opens up a ton of possibilities – although couldn’t one achieve the same with CMOS logic? Also, one should be careful with that micro’s current sourcing capability…

[2052] pololevu Says: 6:00 am, January 30th, 2011

What happens if the pedal looses power? With a mechanical switch, I could stomp it for bypass, but with this circuit once power is gone there seems no way to toggle to bypass.
I have some Hardwire pedals that use a relay but when they loose power they automatically toggle to bypass mode (presumably this means more power is used when the FX box is engaged though).

[2057] admin Says: 7:18 am, February 5th, 2011

If the pedal loses power, the bypass relay remains in the position that it was in when the power loss occurred, since this is a latching relay.

Non-latching relays will switch to their default position on power loss, which would usually be the bypass condition, but the trade-off is that non-latching relays require a constant application of power to hold them in the active mode.

The AMZ relay board uses the latching relay so that much less power is needed to control the bypassing.

Consider that the jfet switching system in Boss and Ibanez pedals will pass no signal at all upon power loss, no matter what condition the bypass was at the time. If you lose power to your pedalboard, it’s time to pull the power plugs and run off batteries until the power supply can be checked out.

[2188] Hendrik C. van Ernst Says: 6:33 am, April 25th, 2011

I was wondering; Is the switching relay an dedicated ‘low signal’ switcher ?

Kind regards
and compliments,
H.C. van Ernst

[2198] Kevin Pepperman Says: 6:15 pm, May 4th, 2011

Nice. I have used this method with a Atmega168–
But I have recently been using a plain old 555 timer with an optical isolator instead of a transistor.
You can also use a dual 555 (LM556) to run 2 relays which is nice for routing signals to separate amps.
I have a schematic if you want it.

[2261] Jacob Says: 8:40 am, July 15th, 2011

can this function at 18v?? what if i want to put it into an 18v pedal?

[2388] nero Says: 7:56 am, October 25th, 2011

Hey, can you send a pulse to 2 or 3 of these guys from the same footswitch at the same time? how many could you run at once using a power supply like the dunlop dc brick? thanks!!!

[2392] admin Says: 7:09 am, October 27th, 2011

Yes, you can pulse as many of them as you need with one switch contact. Instructions are included in the support material that is provided with purchase.

The idle current is quite low, and it is only drawing 30ma or so (total) when the relay is pulsed, so a large number could be powered by the Brick.


[2623] Longhair Says: 5:10 pm, February 1st, 2012

Everything I am using is contrlled by MIDI except for a single DIY pedal which requires a 3PDT switch.

Would I be able to use a Boss FS-6 Dual Footswitch (Latch or Unlatch), the switch function from the Beringher FCB1010 or even an ENGL Z-11?

[3760] Triplanetary Says: 5:25 pm, February 9th, 2013

Anybody have a Mouser or an OEM number for a dpdt latching relay for the AMZ board.

There are so many types of components out there that a well documented BOM would help overall.

[3762] admin Says: 3:03 pm, February 10th, 2013

When you order the bypass pcb you get a link to the web page with the full parts list, schematic and mods. If you have already ordered and did not get it, the link is on the paper that is shipped with the pcb, or you can tell me the name you used on your order and I will email it again.

Best regards, Jack

[3890] Hans Peter Andersen Says: 9:06 am, June 6th, 2013

I very much enjoy this little gadget in all my diy pedals, thx.
Now, I like to build a A/B box, and in the retrofit article that came with the board, a such project is described. However, the project is laid out for 2 inputs and 1 output. Is it possible to do it the other way round, 1 input and 2 outputs, e.g. to switch between 2 amps? I see a possibility in the section of one switch driving 2 boards, but it would be much more space saving (and easier, and cheaper) if this is possible with only 1 board.

Regards, Hans 😉

[3891] admin Says: 9:39 am, June 6th, 2013


The input and outputs are interchangeable since they are just switch contacts in the relay, so it can be used as 1 in to 2 outs.

You can also use the DPDT relay pcb and wire it for any configuration you need. It is on the page at:


regards, Jack

[3892] Hans Peter Andersen Says: 11:05 am, June 6th, 2013

Great, thank you very much for the speedy answer – I’ll dive into it right away :-))

Have a great day, Hans.

[3910] Aaron Says: 2:33 am, June 23rd, 2013

Hi, I’m looking at getting a few of these for a true bypass/aby box, so probably looking at getting 14-16 or them. How would you recommend I attach them to the enclosure, would something like double sided tape work or could that cause shorting/overheating? Or is there a better method?

Thanks for your help


[3968] Hans Peter Andersen Says: 1:08 pm, August 13th, 2013

BTW, to my recent post…
Channel switch (A/B) with the relay works great and noiseless!
Just wanted to let you guys know… 😉

[5621] Joe Olman Says: 11:04 pm, January 18th, 2014

What is the power consumption and its affecting the battery life?
How durable is it, i.e. how many time can it be switched reliably?

[5625] admin Says: 1:38 pm, January 20th, 2014

It can be constructed with less than 1 ma idle current.

I tested it for over 100,000 operations as shown on this page:


regards, Jack


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