Bypass toggle

[manson]

It's possible to replace the DPDT stompswitch in this image with a DPDT Toggle switch isn't it? Let's say I hook up an overdrive pedal to the bypass loop. Would this cause popping when you bypass an (any) effect like this?

[ulysses]

yes you can use a toggle dpdt instead of a footswitch dpdt

the way i understand it is this: if the output of the pcb is still connected to your output jack going to your amp when you bypass the pcb then there will be a pop.

in the diagram above the "From FX output" is not connected to the output when bypassed so there should be no pop.

anyone who knows better should correct me

cheers
ulysses

[ulysses]

something about that diagram looks wrong..

i didnt spend much time looking at it.. maybe im misunderstanding the representation of the tip/ground.. but it looks like the tip of the outs is going to ground for some reason which doesnt make sense..

and why use patch-thru jacks in a diagram if you are not even using the patch-thru feature??

i wouldnt wire it up like that...

cheers
ulysses

[manson]

I don't know, I just took that image off the GEO site. I only want a pop-free true bypass box with a toggleswitch

[ulysses]

ill draw it for you right now

give me a couple of mins..

EDIT: here is how i would do it mounted in a box. note that all the grounds are connected via the conductive box. so if you are wiring it up out of the box you need to wire the ground of each jack together.


cheers
ulysses

[darron]

the dpdt will be the same whether it's a foot switch or toggle switch, and the pin layout would almost definitely be the same. BUT the action of a toggle switch wont be as fast as a foot switch because it is put under less pressure. even if you want to use your hands, i'd probably use a dpdt to be safe. if you are going to use a toggle switch, then use a large one that feels like it's high quality with a fast action on it. every switch like this makes a small pop which you hear at louder volumes, but the degree depends on the switch. because of this i wouldn't recommend it for something that you will change while you are playing.

one other option if you want it to be quite and done by hand, use the dpdt toggle switch and also mount a cheap/small momentary switch as well that connects the signal to ground. this will effectively mute everything. you could press and hold the switch in, use the bypass toggle, then release the switch for quite switching?

give it a shot and let me know how it worked out for you?

[Mark Hammer]

Absolutely nothing magical about a stompswitch, other than which bodily appendage is used to move it.  The same connections and disconnections can be made with anything having the same ability to use 6 points of contact in the same way.  That could be a toggle, a slide switch, a relay, a CMOS switch, and even one of those humungous "breaker" switches you saw in Frankenstein or any slasher flick where the killer goes in the basement and cancels all power to the house.

On a rackmount multi-FX I made almost 20 years ago, I had some electronic switches for remote footswitching, but every module could be bypassed with a toggle on the main unit.

As for popping, the source of that is not in the switch itself (unless it is a very poor example of that switch type), but rather in what is directly attached to the switch.  The most common source is "hanging caps".  These would be medium-value capacitors at either the input or output of the effect circuit where one end of the capacitor is left unconnected when the effect circuit is bypassed.  If the pedal is left unused for a few days, the caps have a chance to drain off via their internal leaky properties.  Once you plug in though, and step on the stompswitch a few times, those caps have an opportunity to store charge, but not enough opportunity to drain it off.  Consequently, when you engage the effect for the 2nd or 3rd time, any stored charge in those hanging caps will suddenly find itself with a golden opportunity to drain off that stored charge through whatever is plugged into the input (or output) jack.  What you hear as a "pop" is that sudden rush of current.

The most common example of this would be vintage effects that people have tried to adapt to "true" bypass.  Classic effects were generally designed around a SPDT switch that would leave the input of the circuit always connected to the input jack and only switch back and forth between the output of the circuit and the input jack...which still had the input cap connected to the guitar via the input jack.  Since the input cap would not be disconnected and reconnected, you might get a pop when you first plugged in, but not when you switched back and forth, since the guitar (back in the days when one might only have but a single pedal between guitar and amp) would provide a constant path to ground for the input cap.  When such a pedal was converted to "true" bypass by adding switching of the input as well as output, that input cap would find itself with a hanging end whenever bypassed.  Pop city.

The solution is to provide a path to ground for all such caps that strikes a balance between an easy path to provide quick drain of stored charge, and properly matched impedance that does not load down the signal.  This is why you will generally see a resistor to ground at the input of most effects circuits using mechanical bypass.  The resistor will be anywhere from 470k to somewhere just under 3meg.  Higher resistances provide less loading of the signal, but slower discharge of stored current.  Smaller resistances dump the current more efficiently but risk loading the signal down.  Since the amount of potentially stored current/charge will depend on the size/value of the cap, it is best to adjust the resistor with respect to the cap value.  So, a .01uf input cap will not store all that much charge, making a 2.7M input resistor quite a reasonable choice.  If the input cap is 10uf, then a resistor that large in value might not provide sufficient opportunity for the charge to drain off when the pedal is in bypass mode, and you'll still hear a pop when you switch it back on/in.  There, a smaller value such as 680k, might be more advisable.

A second source of switch pop has emerged with the popularity of 3PDT stompswitches.  These are used to provide "true" bypassing, while offering a 3rd set of contacts to turn an indicator LED on or off or switch between two indicator LEDs.  This creates audible pop by initiating a sudden current draw to illuminate the LED.  In a sense, what you hear is the LED momentarily yanking current away from the audio portion.  There are a number of solutions to this that have been discussed on the forum this past year.  One is to use superbright LEDs with larger value current limiting resistors.  With any luck, these will provide adequate illumination/visibility while drawing only a fraction of the current of "normal" LEDs and avoiding the current-yanking that produces pops.