Fender 2 button Amplifier footswitch with diodes - electrocution question

[macjohn]

I have a Boss ES-5 and am trying to wire up a little converter box to send it's control jack signals to my amp.  Unfortunately, my Fender Blues Deluxe has the Fender 2 button footswitch with a couple of diodes that have complicated things a bit.  Here's what I did and it works:



I can send a signal to switch the channels or turn the reverb on or off. My only problem/question is this - when testing it, as I plugged the TS cable in that connects to my amp, I had my arm resting on my guitar strings.  I felt a bit of electricity in my arm and quickly removed it from the strings. Everything worked and once it was fully plugged in, there was nothing shocking happening. 

Should I be concerned?

[thermionix]

I don't know anything about the Boss ES-5, but I don't think there's any potentially harmful level of power in the regular FBD footswitch circuitry.  Surprised it's anything you could feel.  I think you're safe.

[Transmogrifox]

My only problem/question is this - when testing it, as I plugged the TS cable in that connects to my amp, I had my arm resting on my guitar strings.  I felt a bit of electricity in my arm and quickly removed it from the strings. Everything worked and once it was fully plugged in, there was nothing shocking happening. 

Should I be concerned?

The Blues Deluxe feeds 39 VAC (RMS) to the switch circuit.  I didn't see any place it could get what UL would consider to be a hazardous voltage (>42 V RMS), but given how close to the line they push it not a surprise you can feel a sensation of shock.  Other agencies consider 80V RMS to be potentially lethal so that gives you an idea of the risk level with 39 VAC.  The product would not be able to bear the UL mark if there was a user-accessible voltage > 42 V RMS under a single fault condition

Perhaps a more fool-proof way to do this would be to hard-wire the cable from your converter box to the amp sort of like the Fender switch box would have, with the male end on the end of the cable that you plug into the amp.

That way your converter box is grounded as soon as the sleeve makes contact with the amp and then I don't think there is as much opportunity to accidentally touch (the hot) tip to a grounded part of your box before the box itself is grounded.

A more complicated way to do this would be to implement the switching function with relays using an isolated wall-wart supply for coil power, which would be switched from the ES-5.  This would allow you to maintain galvanic isolation between the ES-5 and your amp.  I don't think this is warranted, but it's an option if you're particularly concerned about getting 39VAC where you don't want it.  39VAC would likely destroy your ES-5 if you accidentally connected it into one of the loop inputs or outputs.

Hope that makes sense.

[macjohn]

Perhaps a more fool-proof way to do this would be to hard-wire the cable from your converter box to the amp sort of like the Fender switch box would have, with the male end on the end of the cable that you plug into the amp.

Thanks for that in depth answer!  I think I'll go with the fool-proof but somewhat lazy option and just always leave the male TS cable plugged into the converter box.  I'll have this mounted under my board so it'll be easy to just roll up the cable and throw it on my board when packing it up.

[macjohn]

another thing I noticed with this, I put this into a standard pedal enclosure and mounted it under my pedaltrain pro (which is metal as well).  It seems that there's a grounding issue when it's screwed into the pedalboard.  I get a very loud buzzing and the switches no longer function.  Using velcro to attach it, rather than screws, alleviated this problem.

Is there something about the ground circuit of the pedal switch that can't mix with the ground coming from all the pedals and my guitar signal?

[slacker]

According to this schematic the sleeve of the footswitch jack isn't connected to ground that would explain the problem you're having. I'm guessing your pedaltrain is grounded though its power supply so when you screw your box to it that becomes grounded and in turn grounds the sleeve of the jacks.  I would either use a plastic box for your converter box or use plastic jacks or isolate them from the box in some way.

http://support.fender.com/schematics/guitar_amplifiers/BluesDeluxe_Reissue_2004_schematic_Rev-A.pdf

[macjohn]

According to this schematic the sleeve of the footswitch jack isn't connected to ground that would explain the problem you're having.

http://support.fender.com/schematics/guitar_amplifiers/BluesDeluxe_Reissue_2004_schematic_Rev-A.pdf

Sorry if this is an ignorant question but if I have the black wire connecting both of the sleeves, how is it NOT grounded?

EDIT:  by 'this' did you mean your attached schematic?  if so... never mind.  stupid question answered.

[slacker]

Yeah sorry I meant the attached schematic, should have made that more obvious. The sleeves of your converter box aren't grounded they're just connected to each other with the black wire, they're only grounded if the thing you plug into them has its sleeve connected to ground. Your control jacks on your ES-5 are probably "floating" so the sleeve just connects to either the ring or tip depending on the setting, it isn't connected to ground or anything else. So when you plug everything together the sleeves of the amp footswitch jack, the converter box and the ES-5 are all connected together and are at whatever voltage the amp footswitch sleeve is at but they're not connected to ground and everything works as it should. If you connect the sleeves of the converter box to ground via the box and the pedaltrain then that also connects the sleeve of the amp footswitch jack to ground which it isn't supposed to be and that's why it doesn't work,

Hope that makes sense    

[PRR]

This was a fairly rude way for Fender to do it.

Simplified:


The shell of the jack/plug is NOT common to the rest of your system. There is most of 2V AC on the shell !! in 3 of 4 conditions. If the shell touches any "grounded thing", the switch will not work AND you are injecting 50/60Hz BUZZZ at 10 times larger level than guitar into system ground.

I would use isolated jacks and NOT bond any part of the switch guts to metal.

[StevetheWebb]

Hey MacJohn,

I have a BOSS ES8 and I have been trying to switch my Fender Deluxe through the ES8 settings. I can get it to channel switch but not do the drive/more switching. Has anyone had any experience with this. I would like the ES8 to do all the switching and not have to have my Fender Footswitch on my pedal board as well.

[macjohn]

I don't have this footswitch but from a few quick googles, it appears to be wired similar (a couple of diodes controlling whether drive or channel is getting switched).  A stereo cable would run from the ES8 to a switchbox, and then mono out of the box to your amp.

There's not a way without creating your own custom switching box unfortunately due to the diodes.  It's cheap and fairly easy to build though.  If you post a few pictures of the insides of your pedal, I can tell you for sure if a switchbox would handle it or not.

[redbagy]

The way the Fender switch works is by detecting the peak voltages on the trough or peak?