Grounding on an amp footswitch & adding momentary switching

[iShawn]

Hey all, I've decided to instead of spending 50 dollars on a new crappy footswitch for a Fender Deluxe Reverb to build one myself.

Bought a small pre-painted housing, the necessary switches, and assume I can make it out of the 22 gauge wire I already have...
Here's the schematic for the footswitch.  I opened up the back of it and saw that there was an unshielded wire connecting things and soldered to the housing.  I was wondering if this was necessary to ground to the box, and if I needed to use the unshielded wire like what Fender did.  Does the dotted line connected to nothing (schematic) mean it's grounded to something metal?



A photo I found of the actual fooswitch itself:


As you might know, the DRRI's footswitch is for vibrato and reverb.  I was going to run another switch, this one momentary on from the vibrato switch so that I could add a vibrato effect when I'm comping, or at the end of a tune, or just for some texture on a chord, it seemed brilliant but I wanted to know if this would actually work; and how I'd need to wire it off of the regular on/off vibrato switch.  I ordered the parts from smallbearelec.com and ordered one SPST momentary switch, and two SPST traditional switches.

I'm very new to this, and this is why I'm probably asking a very simple question, but I just wanted to know, so I could get this ball rolling.  I'm also wanting to do this because the footswitch uses a connected cable that I can't unplug from the footswitch so I can't leave it on my pedalboard...

[Pushtone]

Does the dotted line connected to nothing (schematic) mean it's grounded to something metal?

The schem shows the dotted line connected to the enclosure.
Fender did it this way because the enclosure is hardwired.

Do the same or use a TRS jack to make a disconnect at the box.
Then your shield can connect to the jack ground lug.




I think the momentary idea is cool and should work ok when the latching one is open.
When the latching switch is closed the momentary won't do anything.

Wire the two in parallel and test for continuity at the plug end of the cable.
Continuity between ground and TIP.

[iShawn]

The schem shows the dotted line connected to the enclosure.
Fender did it this way because the enclosure is hardwired.

Do the same or use a TRS jack to make a disconnect at the box.
Then your shield can connect to the jack ground lug.

I'm a very beginner here, so does this mean that if I intend to use a disconnecting stereo plug as the only output (or, I guess input for the amp) I don't have to shield to the casing?  Then I take that wire and attach it to the sleeve of the TRS?  What does hardwired refer to?

I think the momentary idea is cool and should work ok when the latching one is open.
When the latching switch is closed the momentary won't do anything.

Wire the two in parallel and test for continuity at the plug end of the cable.
Continuity between ground and TIP.

When you mean it will work the latching one is open, do you mean the "off" position since it's SPST?  As drawn in the schematic as an arrow pointing to nothing?  Just making sure my interpretation of your techincal words is right... 
What can I do to wire the two in parallel?  Does it mean the two switches ins and outs are connected together, so if one circuit is open, the other will work when it's closed?

[axg20202]

'Hardwired' means the footswitch is on a flying lead i.e the lead is integrated and only detachable at the amp end. Using a TRS (stereo) socket on the pedal will solve this problem - you'll use a cable with a stereo plug at both ends to connect the switch to the amp.

You are correct re the sleeve connection. Just connect the sleeve (i.e. the braid that has no sheeth) to the sleeve/ground connection of the TRS socket. This leaves the 'tip' and 'ring' of the socket to connect the other two wires for switching. 

As for switching terminology, open means off, closed means on. To connect the two switches in parallel just means to have a Y-juntion before and after the two switches (which are side-by-side), if that makes sense.

[iShawn]

Okay, I was pretty certain that's what hardwired meant, but wanted to double-check.  Since I'll be using a jack instead of hardwired cable, can I use regular wire for everything (radio shack PVC 300V 18-gauge stranded), or do I need to use a bare braid thing like what Fender did?

[axg20202]

Doesn't matter - use your radioshack wire inside the footswitch. The bare braid is the '3rd conductor' of the connecting cable (it has 2 conductors plus the shield brade). You'll be using all three of these when you mount a new stereo plug (tip, ring and sleeve connections) on the end of this wire when you cut it away from the footswitch (assuming you're planning to reuse the existing cable that runs to the amp).

[iShawn]

Doesn't matter - use your radioshack wire inside the footswitch. The bare braid is the '3rd conductor' of the connecting cable (it has 2 conductors plus the shield brade). You'll be using all three of these when you mount a new stereo plug (tip, ring and sleeve connections) on the end of this wire when you cut it away from the footswitch (assuming you're planning to reuse the existing cable that runs to the amp).

Well there's something wrong with the footswitch, which is why I was planning on replacing it in the first place.  My reverb doesn't want to switch on and off, it may be the plugs, may be the cable, may be just the pots but I'm not sure.  I might try to reuse the cable but I could find a cheap stereo cable almost anywhere and might just go buy one for a few bucks.  Thanks for the tips, keep them coming if you have any.  I got an email from Steve at SmallBearElec saying my order shipped yesterday so whenever I get it together I'll post more.

[Pushtone]

Can you get your hands on an old XLR microphone stage cable?
That would work.
It will have two insulated conductors and a spiral or braided shield.
It's also called "shielded twisted pair".


You could also use an old Ethernet cable. It won't be shielded but that doesn't matter.
A footswitch cable doesn't need a shield, just three conductors.

[iShawn]

Well I already have stereo jacks laying around, so it'd just be cheaper to get a stereo cable somewhere...

[Pushtone]

Well I already have stereo jacks laying around, so it'd just be cheaper to get a stereo cable somewhere...

Stereo has nothing to do with it.
It's the number of conductors.
You need at least three conductors.
The cable shield can be considered a conductor in this application.

The techie way to say it is you need two conductors and a ground.
Mic cable has that. Guitar cable does not. Guitar cable has one conductor and a ground.

If you ask for stereo cable you'll most likely get a twined pair of single conductor cable, like what you would get in the box with a CD player with two RCA plugs on each end.

Don't think stereo.
Think conductors and shield.

PS some cable biz folks call the shield a "drain".
Sorry if this sounds confusing.

[iShawn]

Stereo has nothing to do with it.
It's the number of conductors.
You need at least three conductors.
The cable shield can be considered a conductor in this application.

The techie way to say it is you need two conductors and a ground.
Mic cable has that. Guitar cable does not. Guitar cable has one conductor and a ground.

If you ask for stereo cable you'll most likely get a twined pair of single conductor cable, like what you would get in the box with a CD player with two RCA plugs on each end.

Don't think stereo.
Think conductors and shield.

PS some cable biz folks call the shield a "drain".
Sorry if this sounds confusing.

Nah man, it's okay.  It is confusing, but that is why I'm here.

Here's what I gather from what's been posted the last 24 hours:
You don't need to ground to the casing, in the case of what Fender did to the footswitch if you're going to use an actual jack (stereo), in that case you run your ground to the sleeve of the stereo jack.  Now would one jack going to the amp be considered an in or an out (that way it's not too confusing to refer to)?  If you want to substitute one switch for another (in my case, momentary and regular "on/off") then you'll need to wire those two switches in parallel.  I don't need to use a special kind of wire, the standard insulated kind I have would work just fine.  To test if the modded schematic will work, I need to test between ground and tip on the jack, if all is well it'll let me know. 

I assumed I could find a stereo cable that has the jacks with a tip a ring and sleeve on them, and it work as if there was nothing wrong with the footswitch in the first place.  This provides the 3 conductors that I need, right?  Or is ground not considered a conduction, is ground the same as shield?  I'm talking about stereo instrument cable, which as far as I know (correct if wrong) has two conductors and a shield, compared to guitar's one conductor and shield.

I want to use a stereo jack and stereo instrument cable because I won't need to change anything as far as what the amp does and it's footswitch input is.  In order to be able to leave my new footswitch on the pedalboard with a cable, I assumed and wanted to add a stereo jack disconnect/input which would feed to the amp via a stereo instrument cable.  I didn't want to use another kind of cable because I have no idea how to wire a different cable to the same stereo jack connection that would be required on the amp.

[axg20202]

Nah man, it's okay.  It is confusing, but that is why I'm here.

Here's what I gather from what's been posted the last 24 hours:
You don't need to ground to the casing, in the case of what Fender did to the footswitch if you're going to use an actual jack (stereo), in that case you run your ground to the sleeve of the stereo jack.  Now would one jack going to the amp be considered an in or an out (that way it's not too confusing to refer to)?  If you want to substitute one switch for another (in my case, momentary and regular "on/off") then you'll need to wire those two switches in parallel.  I don't need to use a special kind of wire, the standard insulated kind I have would work just fine.  To test if the modded schematic will work, I need to test between ground and tip on the jack, if all is well it'll let me know. 

I assumed I could find a stereo cable that has the jacks with a tip a ring and sleeve on them, and it work as if there was nothing wrong with the footswitch in the first place.  This provides the 3 conductors that I need, right?  Or is ground not considered a conduction, is ground the same as shield?  I'm talking about stereo instrument cable, which as far as I know (correct if wrong) has two conductors and a shield, compared to guitar's one conductor and shield.

I want to use a stereo jack and stereo instrument cable because I won't need to change anything as far as what the amp does and it's footswitch input is.  In order to be able to leave my new footswitch on the pedalboard with a cable, I assumed and wanted to add a stereo jack disconnect/input which would feed to the amp via a stereo instrument cable.  I didn't want to use another kind of cable because I have no idea how to wire a different cable to the same stereo jack connection that would be required on the amp.

This is covered in the posts above. As we've said, what you need is "2 conductors plus shield" cable. (Shield = drain = sleeve = ground). A more common example of this is microphone cable, which some people incorrectly call 'balanced' cable (it's the equipment that's balanced, not the cable!). The thing is, you have some already -  your footswitch has been made using some! I don't see the value in buying more cable. Just buy a TRS (Tip, Ring, Sleeve; 'stereo') panel-mount jack socket to mount in the footswitch and buy a TRS line jack plug to solder onto the end of the cable you cut away from the footswitch (cut it as close as possible to that plastic cable entry gland on the footswitch). The other end of this cable (which plugs into the amp) should have a TRS plug on it already - so there's your TRS to TRS cable made. Take your multimeter and set it to 'continuity mode' (beeps when a circuit is 'made') - use this to check that the tip of one TRS plug is connected to the tip of the TRS plug at the other end of the cable, do the same for the sleeve and ring sections of the plugs. This will ensure that you have wired up the new TRS plug properly (tip should go to tip, ring goes to ring and sleeve goes to sleeve). Then, follow the schematic for the internal wiring for the footswitch and you're done, adding in the parallel momentary switch as already discussed.

A final word on cable choice. In this application, pretty much ANY cable with 3 means of conduction could be used (it doesn't matter whether the 3 lines are all sheathed conductors, or 2 sheathed conductors plus a plain, unsheathed shield brade).

Lastly, in all probability, your footswitch casing will be connected to shield/ground even if you do connect the shield brade directly to the sleeve lug of the TRS socket (instead of to the casing), because the sleeve part of the jack socket will actually be in contact with the casing purely by being mounted through it. You'll see what I mean. This is fine by the way, but I thought I'd mention it.

[iShawn]

Okay, okay I get it.

Just need to buy a TRS plug and I'll be set then.  I didn't a microphone cable is the same as a TRS cable.

[axg20202]

Okay, okay I get it.

Just need to buy a TRS plug and I'll be set then.  I didn't a microphone cable is the same as a TRS cable.

Well, technically, it's not. Mic cable does indeed use 2-core plus sleeve cable, but it's not called a TRS cable - TRS refers to plugs/jacks, which you generally wont find on a mic cable. Mic cables generally use XLR (which has 3 pins). Not being pedantic, but buying correct cable and connectors depends on getting these distinctions right.

Hope this helps.

[iShawn]

Ah, I didn't know what to call the actual cable part, thus I called it what the plug is called.  Oops.  Anyways, thanks for all the help, when the parts come in and I get it done I'll let you know how it goes... 

[iShawn]

I got it finished, and although I don't have  drill I have a box ready for it too...  Works well, however there's an issue with my amp that won't let me switch with the reverb (This was the issue on the old footswitch, and so I assumed it was footswitch, seems to be the amp).  So I'm waiting on advice or a fix from my local amp buddy, or else I'll drop the reverb switch and make it solely a vibrato switch.  Even if so, the momentary vibrato switch is awesome!  May post some pics when it's finished...

[iShawn]

Oh, and by the way, thanks for all the tips and such.  I would have probably messed up something without you.  According to my amp I'm still wrong, according to my multi-meter I'm still right.   

[jakenold]

Hi Shawn,

Be sure that your reverb unit is plugged in correctly, that the driver-tube (12AT7) is OK (it probably is) and that the wires at the plug hasn't snapped.

My 70's SuperReverb had a reverb that didn't work. Turned out to be a mr. smartypants who had modified it and got it all wrong.

Be careful when messing around inside your amplifier, high voltage inthere!

Kind regards, Jake

[iShawn]

Yeah, I read that warning about capacitors still retaining current, and touching could kill you.  So I was very careful.  I looked inside of it, the soldered joints seemed fine, so I am really in the dark.  It's okay though, I'll just make the footswitch control the vibrato, the reverb is usually always on anyways... The reverb works just fine, I just can't get it to turn on via footswitch, but that's about 20 minutes from not being a problem anymore...

[iShawn]

Okay, if it matters, pictures.  The wiring inside is absolutely identical to how fender has it, except the hold switch is wired in parallel and the ground is simply connected to the sleeve. 

I put some clear tape on the enclosure and drew with a Permanent Marker, but I don't like my penmanship enough to do more than label the switches.  The footswitch is completely passive, running off of the amp knowing if something is grounded or not, but I noticed a slight pop especially when engaging the momentary switch, can that resistor mod work on such a thing, or would it be the switch itself.  It's not loud enough to be audible in a live setting, just something I noticed (which may or may not have been present with the original footswitch).