True Bypass with Latching Relays

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Fael

New member
Joined
Sep 9, 2010
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1
I would like to know if there is a schematic or, preferably, a perfboard, veroboard, or PCB design for a latching relay based true bypass on a pedal.

There are some schematics for non-latching relays like R.G. Keen's: http://www.geofex.com/FX_images/relay%20true%20bypass%20with%20Boss-Ibanez.gif
More info about this particular schematic here: http://www.diystompboxes.com/smfforum/index.php?topic=86288.0

However, I also found this diagram: http://www.geofex.com/FX_images/relays2.gif
It does not specify if it's designed for latching or non-latching relays. Moreover, and given the other circuits I've seen, it seems way to simple to work. It would be awesome if it worked for individual pedals.

So far, the only latching relay design I've seen is this one: http://www.fredric.co.uk/
However, it is for a two coil relay. Unfortunately, only a one coil DPDT relay is available in my third world country (where, ironically, a lot of electronics are made, exported and then imported again).
Would you please explain to me what I have to do to apply this design to a one coil relay?


To sum up:
1.- Have you seen any latching relay based true bypass schematics/perfbord layout/verboard layout/PCB?
2.- Would you tell me how to modify the attached design to apply it to a one coiled relay?
 

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  • Latching Relay True Bypass.gif
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To my knowledge, there are three types of latching relays:
a) Dual-coil relays, where one contact switches on the keep coil. It is similar in operation to the example where the NO contact is used to maintain the voltage to the coil. The advantage of the dual coil relay is that the keep coil draws much less current than the main coil. The operation of this type of relay involves two switches, one that turns it on, another that turns it off.
b) polarized bistable relays, where the switching is done by changing the polarity of the control pulse. These relays do not need any keep current, but need two switches.
c) mechanical step relays, that rely on a ratchet to change status at each control pulse. These need only one switch.

I think most of these relays are not available in low power contacts rating that are needed for audio applications.

The link refers to a latching driver for relays; basically, it's an electronic circuit that allows a bistable operation with a standard relay.
A bistable circuit involves two active elements (transistors, valves, gates), cross-coupled as to be mutually exclusive turning one on automatically turns off the other).
 
Fael said:
Would you please explain to me what I have to do to apply this design to a one coil relay?

The relay coil has a plus and minus connection. Pulse the plus side for a few milliseconds and the relay will Set (the minus side will be at ground). Send a pulse to the minus side (with the plus side at ground) for a few milliseconds to Reset.

The relay coil will be rated for a certain voltage, so you need a pulse that is in the proper voltage range, and the pulse duration needs to be more than the minimum required to toggle the relay.  Usually 2 or 3 millisconds will be all that is necessary.

5v single coil latching relay: http://www.smallbearelec.com/Detail.bok?no=791

Regards, Jack

 
Why complicate things? As AMZ-FX indicated you need a pulse circuit and an H bridge to reverse the polarity of the relay. It is a bit like cracking a walnut with a sledge hammer for this application.

As used in effect pedals all you need is a flip flop and a driver transistor. Have a look at the right-bottom corner of this schematic

http://www.freeinfosociety.com/media.php?id=1936

Omit R 49-1M resistor and you'll have the circuitry you need.  

Omit R51-3.9K resistor.Replace the LED with a normal 8 -12V relay (and don't forget to shunt the coil with a discharge diode to protect the transistor).

 
> Why complicate things?

In a battery-powered pedal, the constant drain of an energized relay (or an LED!) may greatly exceed the power the actual circuit needs. Basic fuzz, 0.5mA, energized relay, 20mA. That's 40 times less battery life.

You may not need a timer and an explicit H-Bridge. I have a simpler idea, but I need to know WHICH "one" relay Fael can get to know if it is workable.

Fael posted on Aron's Stompboxes forum which is probably the better place to talk about this. (Except the first four responders there don't seem to know what a one-coil latching relay is; here three folk knew right away).
 
I'd say buy this and use it. 

It's a great little DIY for learning to put components on and Jack spent a lot of time to get it right.  Add true bypass to just about anything using a momentary switch.

http://www.muzique.com/schem/bypass.htm

How can you go wrong with $10 for a PCB and the microprocessor?

CC
 
i thought the whole process of a 'work around' for true bypass was to save some money on 3pdt switches?
this made even more sense say 10+ years ago because those switches were very expensive but $10?
+ $ for a momentary switch?
unless this is just for solder practise i think i'm missing the point ?

that's not to question the value or discredit the switching pcb above... i'm genuinely interested.
why would you do all that, as opposed to just omitting the led. or if its a really important project, just front the extra cash for a switch with more poles?  
 
kepeb said:
unless this is just for solder practise i think i'm missing the point ?
Yeah me too........just dont see the point of a micro in there
@Hi Kepeb .....nice to see someone just down the road from me  ;)
 
kepeb said:
i thought the whole process of a 'work around' for true bypass was to save some money on 3pdt switches?
this made even more sense say 10+ years ago because those switches were very expensive but $10?
+ $ for a momentary switch?
unless this is just for solder practise i think i'm missing the point ?

that's not to question the value or discredit the switching pcb above... i'm genuinely interested.
why would you do all that, as opposed to just omitting the led. or if its a really important project, just front the extra cash for a switch with more poles?  

The advantage of this board is the ability to use the existing momentary switches inside pedals like Boss or similar FET switching pedals.  These switches exist inside the pedal already (so you're not buying another one and leaving it open to be able to modified back in case someone doesn't like your mod) 

Of course, you could drill a hole in the top of a Boss pedal (as I have seen done before) and make it look real nasty - but be true bypass - shove a Carling DPDT in there - and try to remember if it is on or not (did I turn on this big nasty sounding fuzz or am I on my clean setting?).

Also in more racked like units - like the ones I'm doing these days, there is a "slickness" to being able to use momentary switches.  As well, with this board you can wire up more than 1 relay and control multiple relays at once for bypass or any number of functions.

With respect to bypass functions you could switch 4 relays for a true bypass, balanced, stereo output.  Try to find a 5PDT or 6DPT switch (without going rotary).

CC
 
hey conleycd, ah. actually the boss mod rings a bell, think i read that recently, i guess that's cause enough to warrant this approach then really.

Although i think the rest of what you explained goes pretty far beyond the scope of regular guitar effects requirements.(maybe i'm watching the wrong bands)
i cant imagine an actual scenario where you might need such complex switching in a live situation. that would do your brain in.
there are some amazing rigs out there with elaborate remote switching of multiple effects chains and midi controllers etc. but i think the Edge has them all, and we know what he sounds like.

ha. anyway.
i think i like to keep them on the floor. and quite separable if i need too. cos if one goes down and you cant get to it behind the rack, your fecked.
also... what kind of guitarist is it that doesn't realise when his 'big nasty sounding fuzz' is on or off?? ;D
the ones that still buy zoom 505's maybe.

still, the boss thing... agreed! now we know! and im sure it has lots of other uses.


EDIT: oh and hi S2udio, nice to meet you too :)
 
Yes it is a valuable (and affordable) little project.

My comments about rack gear was not regarding live use of rack gear - it was an example of using a board like this to control true bypass functions on studio gear or DIY studio gear (what is typically discussed here).  So you can use this to add true bypass function to our GSSL compressors or other such funky things actuating them with momentary switches (which look and feel better on studio rack gear than mechanical switches).

I have, more times than I care to remember, went to rip a guitar lead only to realize I didn't step on my overdrive - or whatever.  I can't live without LEDs - as you can see - or single step changes.  In fact that little FD II pedal I put a relay inside to switch the boost function from the Wobo combination switcher.

PedalBoard.jpg


P.S. I don't use the modded CS-3 I just need to fill a spot (actually it's a modded mild gain boost - my 'more' pedal).

CC
 
hey, cheers for the pic, nice.
i am really surprised to see so many shop bought/retail pedals on there... the prog looper alone must have set you back at least £250? and are those 'Modded by' stickers on some of your boss pedals, no expense spared huh?
to be honest i cant see much of a benefit in this area outside of a live situation. and in the studio you have the extra few seconds to ensure you aren't limiting your creative freedom with presets and organised single loops. the whole point of it is to enable you to be as modular as possible hence the continued popularity of patch bays.
and i would definitely question the affordability after your example. thats like 7 pedals the switching system undoubtedly cost more than the effects did and thats even calculating retail+mod prices.

also is that a 'magic stop' on there?
 
PRR said:
> Why complicate things?

In a battery-powered pedal, the constant drain of an energized relay (or an LED!) may greatly exceed the power the actual circuit needs. Basic fuzz, 0.5mA, energized relay, 20mA. That's 40 times less battery life.

I knew you would say that. I discounted it as I am also a guitar player and I never used battery on my pedals. I was also thinking of relays with much smaller coil power. However, your point is still valid.
 
kepeb said:
hey, cheers for the pic, nice.
i am really surprised to see so many shop bought/retail pedals on there... the prog looper alone must have set you back at least £250? and are those 'Modded by' stickers on some of your boss pedals, no expense spared huh?
to be honest i cant see much of a benefit in this area outside of a live situation. and in the studio you have the extra few seconds to ensure you aren't limiting your creative freedom with presets and organised single loops. the whole point of it is to enable you to be as modular as possible hence the continued popularity of patch bays.
and i would definitely question the affordability after your example. thats like 7 pedals the switching system undoubtedly cost more than the effects did and thats even calculating retail+mod prices.

also is that a 'magic stop' on there?

Well... we were mostly discussing the use of latching relays to bypass gear.  I'm making the point that keeps getting missed that this PCB board I referred to (that AMZ who posted up there made and programmed) is useful for RACK DIY gear.  I'm also making the point that it is nice to have LED indication for pedals - hence my pic.

I play live - and in the studio this affords me a ton of options.

In terms of "store bought gear" - don't reinvent the wheel.  Try to buy project box for the price of a DS-1.  That DS-1 is completely rejigged.  The FDII from '97 sounds great (remotely switchable with my relay addition), the Sparkle Drive is cool as is, I'm not about to DIY a delay.

You probably don't notice the expansion box that allows me to plug in my modulation pedalboard with a single 5 pin connector (when needed).  This provides both pre overdrive true bypass signal to the modulation board and another modulation loop that comes back into the main board.  Both loops can be switched on and off if I use my modulation or left as is without.

The box in the front is actually a mixer for the delay pedals to allow switching between the two delays but also allows their trails to be heard/mixed in when switching between the two.

Finally the box in the back is a buffer but also is a redundancy box in case my amp blows (as my AC30 released it's rectifier tube the last time I played a larger gig).  With a single flip of that Lorlin switch my signal is routed from the amplifier to a Line 6 modeller, dropped ~12db to close to mic level via a transformer, and sends the FOH board my signal down the same cable that was micing the amplifier - only from the modular.  Zero down time (well - a digital amp instead of my amp - but hey...).  As well, that big box provides for a direct microphone level output from the buffer to record a dry signal live or in the studio.

But enough about me... the AMZ latching relay control whether for Boss pedals or for rack gear is great, cheap, and works.  Done.

CC
 
whoa, easy fella.
I'm not questioning AMZ switcher or what you choose to spend your money on.
i was just curious, and i'm only chatting, different courses right? :)

I'm all up for changing my mind about any of this if it sounds better/is more cost effective/easier,faster for live stuff... i just dont think it is, and still dont think thats justified, i think its overkill, especially for such a small setup. if your fulltone and your voodoo labs sound great as standalones,  how are you saying that this method, over another simpler and more effective method is better? it didn't cost you less, doesn't sound any better or give you any more options.
if you dont like the tactile feel of proper footswitches thats a good point, and i understand thats your preference, i personally do, but thats just my opinion. i dont mind that vintage fuzz face's, octavias and ALL crybaby's dont have LEDs either, you know when you've stood on those kind of switches, so i realise when the effect is on ready for a 'solo' etc.

all thats here can be done with some diy switchers and the same amount of patches, the WOBO isn't even isolated is it?

however, i think your redundancy box is a really good idea and I'm pretty much certain that would of saved me at least 3 times i can think off the top of my head. i've had a couple of stopped dead shows because a pedal or amp went down.
did you say 'done' at the end because you are not talking to me anymore, or because what i have to say is invalid?
again, we're only chatting, right?
 
kepeb said:
whoa, easy fella.
I'm not questioning AMZ switcher or what you choose to spend your money on.
i was just curious, and i'm only chatting, different courses right? :)

I'm all up for changing my mind about any of this if it sounds better/is more cost effective/easier,faster for live stuff... i just dont think it is, and still dont think thats justified, i think its overkill, especially for such a small setup. if your fulltone and your voodoo labs sound great as standalones,  how are you saying that this method, over another simpler and more effective method is better? it didn't cost you less, doesn't sound any better or give you any more options.
if you dont like the tactile feel of proper footswitches thats a good point, and i understand thats your preference, i personally do, but thats just my opinion. i dont mind that vintage fuzz face's, octavias and ALL crybaby's dont have LEDs either, you know when you've stood on those kind of switches, so i realise when the effect is on ready for a 'solo' etc.

all thats here can be done with some diy switchers and the same amount of patches, the WOBO isn't even isolated is it?

however, i think your redundancy box is a really good idea and I'm pretty much certain that would of saved me at least 3 times i can think off the top of my head. i've had a couple of stopped dead shows because a pedal or amp went down.
did you say 'done' at the end because you are not talking to me anymore, or because what i have to say is invalid?
again, we're only chatting, right?

No... I think there may be a comprehension problem here - but I'm still willing to play in the sand box (though we are now wayyyy off topic).

1.  I'm saying that using this PCB board (of AMZ) is helpful in adding True Bypasses to Rack gear that most people are working on these forums.  STUDIO gear (but could be live too).  With STUDIO gear it is slick to have momentary switches do functions.  STUDIO gear.  I'm not talking about pedals.

2.  [Now I am talking about pedal].  The PCB is helpful for adding true bypass to fx like Boss pedals and other vintage pedals so you don't kill them with a big hole drilled in the chassis for a 3DPT switch (as is sometimes is required).

3.  I don't care about the feel of switches on my pedal board - I care about single tap configurations.  The WOBO is a true bypass switcher - anything connected to it becomes true bypass and I can access any combination of 5 effects with 1 tap.

4.  One problem with your setup is that your pedals are not true bypass.  Which doesn't matter for those that have decent buffers - perhaps - except you run your gear through more silicone than is needed.  So your Crybaby, for example, buffers the signal (if it is modern), and the switches between the buffered output and the effect.  Your crybaby is always on.  Same with your nice Fuzz Face.  It sucks your tone for next pedal when it is bypassed. 

So with the WOBO I can set various combinations of effects.  Most people aren't switching effects orders on the fly (you would have to unplug them and plug em back in anyway).  So I have - patch 1 (Sparkle drive -->FD II [non boost], Delay A/B switch, EQ].  I press 1 button and I have silent switching to all those effects.  For example, patch 2 is (Sparkle Drive, FD II Boost, DS-1, Delay, EQ), and patch 3 is clean.  I don't have to tap off 3 overdrive pedals for a clean straight through the wire signal - THAT is the advantage of the WOBO that even true bypassed pedals can't do - you have to tap 3 off.

CC
 
sand box? what is this? i think thats very rude.
Theres no need to try and be insulting.

if thats where you think we are, then so be it, i've never actually encountered one of you before so it should be fun :)

yes i covered 'STUDIO' as you insist on using CAPS for, in the first sentence, if you read it i said faster/easier in reference to live setups.

for STUDIO... 'sounds better' is probably the more important of the three points. regardless of what type of switch/button you press on your STUDIO gear.
and i still think a patch bay is easier/cheaper/more modular, and will probably end up sounding better if you arent careful with your wiring, or stick all your effects in a single large Faraday box.
I'll let the panel of judges decide what they prefer if its ok by you.
or would you like to correct my opinion again?

7.b. pedals:
my pedals are all true bypass (if i want them to be) thanks, and i have spent a long time making sure i understand where ground loops and DC noise comes from, and what poor/bad signal can be attributed to with regard to effects.

but if your using your half a grands worth of un-isolated looping, several times around that tiny board, next to your ac adapters - to get better results than i have worked on, then fine. this probably also means you wont need to replace the switch in your boss pedals anyway, because you can true bypass it 'easily' from 1' away? right?
or change an already foot controlled setting on your fulltone thing from the comfort of 6" closer too!!
brilliant. also the 'complex' switching you describe is obviously for when you have many more effects? i think i can still manage three.


and your right, this now has nothing to do with the fine AMZ design, it comes from a long list of amazing guitar effect related information from AMZ that i have used and appreciated, countless.
I think Jack should just be grateful neither of us do his marketing :)

and the original poster hasn't checked in for over two weeks, forgive me for going off topic, i was, again, only chatting.... this is a forum.
 
Oh boy... I don't mean to initiate a mean welcome to the board.  There's a lot everyone can learn here and people are quite helpful.

I don't know what you mean about ground or loop isolated?  Unbalanced signals cannot be isolated from one another unless you are using transformers in between everything.  My powersupplies are Toroidal transformers with multiple taps then regulated down to 9v.  I don't know if it's any quieter or really reduces ground problems and noise in between compared to one massive switching power supply daisy chained.  I've seen many respectable players use those.

I love to market anyone's great idea!!!  I think the folks on this board are the most generous and intelligent folks going... so more power to em.  Buy the PCB board (hehehe).

CC
 
> the original poster hasn't checked in for over two weeks

A day after "deciding" to use latching relays, he went off in a different direction (over on a stompbox forum).

Nice point about Jack's board being useful for "any" signal switching (not just pedal-world where it originated). The objection to using a CPU to compute one bit, I understand (I'm a 4007 CMOS guy) but is perhaps old-school, because such chips are now dirt-cheap and you don't have to see the internal complexity.
 
I did not mention the microprocessor powered relay because the original poster did not ask about alternatives, and I don't like to do self promotion on this forum when I'm not running ads (though I have had a listing in the White Market previously). The OP mentioned in another forum that he has dropped the project, so it is unlikely he will stop back by.

I use lots of 3PDT switches in stompboxes, and I find them to be excellent with a very low failure rate.  The 3PDT makes a very solid mechanical thunk as it toggles, and some people claim that it is microphonic and causes noise. I have never found the footswitch to be microphonic, but it is a known fact that some high gain effects pedals are!  Check out Bill Rupperts' Effectology tutorial where he is using a Big Muff pedal as a drum (starts around 1:10) - http://www.youtube.com/watch?v=vkDLQAvrEQQ

A soft momentary switch can get rid of the mechanical clunk that a microphonic pedal can send through to your guitar amp. The microprocessor also takes care of debouncing the footswitch and it even can detect if the player is holding down on the footswitch and ignore it. Also, it is driving the LED from its power supply which isolated it from the pedal - this is sometimes the source of pops with the 3PDT system as the LED snaps on and suddenly draws current from the pedal power.

Lastly, the switch pads on the relay board can be controlled by an external device so you can control your fx pedal with a separate footswitch, controller box, panel mounted switch or even under computer control - not possible with the ubiquitous blue 3PDT.

PRR, my first bypass relay system that I made back in the 1980s, used a 4049 cmos chip to control a non-latching relay.  I still have a pedal with one of these systems and it still works. The 80s vintage relay alone, without the cmos chip, was bigger than the new pcb with a micro and relay on it.  :D

The blue 3PDT is great. I use them, but sometimes there are advantages to other methods of bypassing...  whether it is the micro-relay-bypass or the Boss buffered bypass, or just the "cool factor" of having a soft touch switch.  ;D

Best regards, Jack
 
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