Modding my tuner with a stereo mute switch

[dampsquid]

What started as a relatively simple idea to build a stereo mute pedal quickly hit a snag when i realised i really don't have enough space on my pedal board.

I figured maybe I could build it into my tuner, it's already muting a mono signal, why not two of them with a change of the footswitch and two more 1/4 ins? Alas, I've opened up my peterson strobostomp hd and found it's quite a different setup. The footswitch you see from the outside isn't the switch at all! It prods a pcb mounted spst momentary switch, which presumably then runs off to a latching relay or something digital. My question is: is there a way for me to piggyback from that momentary switch to also mute another guitar line? Maybe using another latching relay? The second line wouldn't need to route through any of the tuner gubbins. I'm thinking as simple as a spst to break the connection. Made less simple by wanting it to be triggered by the original footswitch.

Bit of a random one but hopefully someone will be able to give me some pointers.

Thanks! 

[Matthew Sanford]

Just to confirm, you are wanting to add an input jack for another signal to come through or have the option to turn it off, and have it go out of the existing output jack? You could try the SPST switch and wire it between the jacks, but depending on how it comes out of the tuner it might change volume on both signals - I'd say open it up, use alligator clip wires to put it in and see, but you might need buffering on the signals to make sure they stay at the levels you want.

[dampsquid]

Thanks for your reply, Matthew.

There would be additional new input and new output jacks. My intention would be to mute the signal between them using the footswitch that's already present.

[Matthew Sanford]

ok, so new in & out jack but same footswitch. You had said what is there seems to press on a momentary switch, could you fit a small SPST there so it hits both? Otherwise I don't know you can get a momentary and SPST in one switch...

However, you could review RG's page on bosstech, you would want to determine voltage levels on each side of the momentary to see if it is just taking something to ground to make the switch. If so, you may be able to set up a flip-flop thing to do switching, room in box permitting, and have it controlled by the same switch. I'm spitballing a bit, people here are much more wise about it than I, and you might get some kind of unwanted interaction that way.

Essentially you want to turn off some other signal line when you click the tuner on to tune, right? And save space on a crowded pedal board... there might be other ways...

[amptramp]

This sounds like a job for the Burst Box.

[FiveseveN]

1. Welcome!
2. Can you trace the signal from the switch? One end will likely go to ground, but does the other go straight to the uC (maybe with some debounce filtering) or is there something else that does the latching?
3. Are you sure there's enough room in there to add jacks and potentially a(nother) relay? Can we have a picture?
4. What is your experience with electronics?

[dampsquid]

Essentially you want to turn off some other signal line when you click the tuner on to tune, right? And save space on a crowded pedal board... there might be other ways...

Yep, exactly that.

Thanks for your reply FiveseveN -
1. Long time lurker emerging from the shadows.
2. Possibly. I'll have a closer look when I'm off work.
3. I'm sure there's enough room for the jacks, within the battery compartment space. The rest of it, I have no idea, it depends on how complex this becomes. Pics added below.
4. I'm happy with wiring up a circuit based on wire and components such as my original idea of the stereo mute box. Anything complex I'd need to work from a schematic/picture rather than being able to design it myself. PCBs, other than simply replacing more obvious components such as jack sockets and switches, I have very little experience. On this build I was hoping to open up the enclosure and find a simple spst/dpdt footswitch, which I could replace with an extra pole for the second signal line. I would have been happy doing that.

[FiveseveN]

Two DPDT relays, interesting! They do say something about "a unique series of timed relays incorporated within its circuitry to shunt the signal".
Good news is you can take the ~3V signal driving the set & reset coils and use that to control your own relay driver for the extra signal path.
Bad news: if you're not familiar with basic logic (SR flip flops and the like) and relay drivers, you're gonna have to do a little digging first. You might get away with piggybacking an extra similar relay on the existing driver depending on what they used and how much margin for extra current it has.

[PRR]

Relays are clues:
HFD3/2.4-L2S
https://www.futureelectronics.com/p/electromechanical--relays--power-relays/hfd3-2-4-l2-257-hongfa-5060060
http://www.hongfaamerica.com/hq/PDF/HFD3_en.pdf

[dampsquid]

That's great. Thanks guys! I've been doing some reading up on relays already so will continue down that path and see how I get on.

You might get away with piggybacking an extra similar relay on the existing driver depending on what they used and how much margin for extra current it has.

Excuse my meagre knowledge if I'm way off here but if there is enough margin to run another relay, would this be as straight forward as taking some hookup wire from the set tabs of the current relay to the set tabs of the new, additional relay, and likewise for the reset tabs?

[FiveseveN]

Yes, that's the idea, put them in parallel. Looks like some of the existing coils are already in parallel maybe? You'd have to take it apart and investigate thoroughly, all the important bits are on the other side.

[dampsquid]

Here's a pic of the underside of the pcb, if that's helpful at all. I'll have to do a load more reading on this as that looks like a completely foreign language to me.

[Matthew Sanford]

The tie relays in makes sense, but considering the room under that momentary...is there more room on the part that pushes it down (can we call it the actuator?) to push another latching SPST between a new pair of in/out jacks?

[PRR]

We can see the start of the circuit. Imagine a guitar-plug in the jack. The plug tip will touch the jack contact where I put a pink line. Follow that to where it goes. Here it goes to a tiny copper doughnut. Actually a "via", a copper hole to connect to the other side of the board. Put your finger on that and flip the board, see what it connects to. Yes, this can be tedious and confusing. However I am having hope that all the pass/mute circuitry is on this one(1/2) board, the other board is only tuner.

(The 2nd 1/4" jack is on a sub-board only so it can be put in the box without cutting and welding, or slip-in/slip-out slots.

[dampsquid]

The tie relays in makes sense, but considering the room under that momentary...is there more room on the part that pushes it down (can we call it the actuator?) to push another latching SPST between a new pair of in/out jacks?

Here are some photos of the actuator. When in the enclosure the spring is lightly touching the momentary switch. Are you suggesting something mechanical, coming off the actuator at 90 degrees, to push a new button positioned next to the momentary?

[dampsquid]

...Here it goes to a tiny copper doughnut. Actually a "via", a copper hole to connect to the other side of the board. Put your finger on that and flip the board, see what it connects to...

It seems as though it goes to contact no.3 on the vertically alligned relay. Diagram of the relay is shown from beneath.

[Matthew Sanford]

The tie relays in makes sense, but considering the room under that momentary...is there more room on the part that pushes it down (can we call it the actuator?) to push another latching SPST between a new pair of in/out jacks?

Here are some photos of the actuator. When in the enclosure the spring is lightly touching the momentary switch. Are you suggesting something mechanical, coming off the actuator at 90 degrees, to push a new button positioned next to the momentary?

So pin pushes and spring for sure return. You could try to affix a plate of some sort to push another next to it, but I figure it'd need to be a looser type button switch and mounted at the right height (adafruit has a little $1 thing with mounting hardware on it) as you would not have that direct pressure down. You've got options

[FiveseveN]

Matthew, I'm not seeing how another momentary switch would help. Surely whatever use you're planning for it could just as well be accomplished by the existing switch?
And instead of making a separate unsynchronized flip-flop wouldn't the S & R signals from the relays be more handy?

[Matthew Sanford]

True. I was thinking a latching switch, not momentary, for a physical on/off, not using existing flip flop - but adding a relay to use existing S&R signals is probably the right way, less measuring for specific placement and getting a wider bit on the actuator to connect, etc. I just like exploring alternative options