True bypass with momentary reverse

[RickL]

Something Mark Hammer wrote about the usefulness of a momentary bypass switch got me thinking and I came up with this. I hope I haven't reinvented the wheel with this and apologize for not providing a proper diagram. If someone wants to use my description and crude ASCII diagram to draw up a more readable picture it might be easier to understand.

The idea is to have two switches - one latching and one momentary. In one position of the latching switch the effect is bypassed and the momentary engages the effect. In the other position of the latching switch the effect is engaged and the momentary bypasses the effect.

Momentary dpdt switch, latching 3pdt switch.

1 2 3  a b c
4 5 6  d e f
* * *  g h i          ( *'s are place holders to make the ASCII come out right, not part of the switch). b,e and h are the commons on the 3pdt.

Connections: 1 to f, 2 to output(amp) and b, 3 to d, 4 to a and i, 5 to input(guitar), 6 to c and g, e to return(effect output), h to send(effect input).

To clarify (I hope), if this is built as a stand-alone bypass box 2 goes to output, 5 to input, e to return, h to send. If it is built into an enclosure with the effect 2 goes to the output jack, 5 to the input jack, e to the output of the effect and h to the input of the effect.

I've built it and confirm that it works. If you ignore the momentary switch it works as a straight true bypass box. In the bypass position it's easy to bring effects like a Slow Gear or and envelope filter in only on the notes you want. I'm less sure of uses for the other position. Punching a clean note into a distorted solo?

[Mark Hammer]

Sweet!

I gather this is entirely passive, using a "normal" stompswitch, and one of the momentary stompswitches that Smallbear sells?

My initial implementation that you referred to worked only inn the one direction.  That is, the effect could be engaged in a latched manner or momentarily.  Since it used an electronic switching arrangement (one of the CMOS switches from Anderton's EPFM-II), the state of the switch was indicated by an LED.  Particularly useful as user feedback since the momentary switch lacked the positive click of the latching switch.

I'm wondering if your arrangement permits bi-directional status indication.  In other words, EITHER of:
- it's off but I've turned it on for a moment
- it's on but I've turned it off for a moment

[RickL]

Yup, entirely passive and designed specifically with the Small Bear switches in mind. I don't think there's any way to add a status LED using these switches but it might be possible with a 4p2t stomp switch. The extra pole could at least show you the 'normal' status of the system (red for bypassed, green for effect engaged).

[Mark Hammer]

Okay, now you've got me thinking.  Is there something a person can physically remove from a "normal" stompswitch that would make it unlatched?  If so, then a 3PDT could be co-opted as a momentary with status indication.

[Pushtone]

Diagramed from the description in this thread. Ignor the 3rd pole on the momentary. It's really a DPDT.
by RickL.

[Mark Hammer]

Many thanks for following up on this.  Hope the recent weather out your way wasn't too harsh on you.  It was heartbreaking to watch, I'll tell you that.

[thumposaurus]

Okay, now you've got me thinking.  Is there something a person can physically remove from a "normal" stompswitch that would make it unlatched?  If so, then a 3PDT could be co-opted as a momentary with status indication.

From the few switches I've taken apart there is usually a little plastic piece that clicks into another piece to hold it in one state or another.  The problem is taking them apart, removing that piece, being able to put it back together so that it still works, and is reliable with practice. I'm sure it could be done but you might need to go through a few switches first.

[Pushtone]

From memory, inside the switch is a white plastic rocker, for lack of a better term.

I was wondering if the rocker was flipped upside down if it would then be a momentary.

Just a hunch from what I know about Lean Manufacturing. The same part used in a different orientation.
Lessens the amount of inventory the manufacturer needs to carry.

Again, just a hunch.

[tommy.genes]

I've been working on this myself lately, although I'm taking a CD4053-based approach. My reason for doing that (as opposed to the passive arrangement here) relates to broader design goals of the project that I won't bore you with at the moment.

Anyway, I was thinking I might have to do some mildly complicated logic involving a flip-flop and an XOR gate. I finally figured out, though, that I could use the common household two-way light switch scheme - with a momentary switch in one position - to control the Geofex CD4053-based bypass.

When I finally get around to building it, it should look something like this...



-- T. G. --

[Processaurus]

I have an A/B switch with a momentary reverse, and was trying to use it today at practice for a part, but the momentary side pops like hell.  The momentary stompswitch is the kind from small bear.  What's strange is that the latching switch doesn't pop as bad, so i guess its not a DC difference between the a and b inputs?  Could it all be contact bounce/grime?  Its seriously loud.  I'll try some pull down resistors, but I'm suspecting the concept would only work noiselessly with either CMOS analog switches or the boss FET style switch, with a couple ms ramp up and down on the signal controlling the switching state.  Weird how simple stuff can get so complex.  I wonder if audio relays would be a less clicky alternative, or some LED/LDR switching like some amps use like Mesa Boogie, maybe an LED/ photoFET package in the boss style.

I really like this idea for switching effects in for quick phrases, because its impossible to mess up and leave it on or off unintentionally, its less to concentrate on, plus its less shoe gazing when your performing and more opportunity for awkward staredowns with audience members.

[yeeshkul]

Hi guys, I'm apologising for being a bit slow .... can anyone please help me with what is the point of having 2 switches? I mean what id the difference between one 3PDT and this combination?

[Mark Hammer]

One switch is for latching or "set and forget": essentially what every stompbox normally comes with.  The other is for brief "punch-in" use of the effect.  The term "punch-in" comes from recording terminology, and traditionally refers to the capability of a tape recorder to temporarily go from playback to record mode and back again while the tape is already moving.  This would let the user listen to tracks already recorded, wait for just the right moment, hit the punch-in button (often a footswitch) and then add something in sync with the already-recorded material.

I can think of no finer example of the virtues of having a "punch-in" footswitch than the classic ZZ Top song "Cheap Sunglasses" where a ring modulator is used for what amounts to 8 notes at the end of the verse.  Having to step on the pedal twice to engage and disengage it is distracting in performance.  Far better to have a separate momentary/non-latching switch where you step on it to engage the effect, play  your 8 notes, and simply lift your foot up to go right back to bypass.  It doesn't sound like such a big advantage from the way I've written it out here, but try it once and you'll be convinced at its utility for the gigging musician.

[Pushtone]

I'll try some pull down resistors,

Will pull-down resistors do anything without capacitors in the circuit?


Sorry to hear about your popping. I'm just now laying out the two switches in a box for a FS&H-A1.
Guess I better test it before drilling two holes. Thanks for your report.
I thought it was too simple to have to test but sometimes the simple things can give you the most trouble.

[Processaurus]

Will pull-down resistors do anything without capacitors in the circuit?


Sorry to hear about your popping. I'm just now laying out the two switches in a box for a FS&H-A1.
Guess I better test it before drilling two holes. Thanks for your report.
I thought it was too simple to have to test but sometimes the simple things can give you the most trouble.

Yeah, the pulldowns could help if there are leaky caps and no pulldowns on the two sources being A/B'd, they're there in some commercial AB switches.  I suspect those momentary stompswitches might not be the best for switching audio cleanly.  You're wise to try out the switching first before comitting to the idea, I'm interested to hear how it works out for you.   The S+H with the momentary switching sounds fun!

[GGBB]

This topic was referenced from another topic so I wanted to post the visual diagram of this switching circuit back to this topic. A 4PDT is used so that a status LED can be added: