Potentially daft question - TRS cable for Fender footswitch

Haych

So, yeah, think this is going to be a daft question but somebody once told me the only stupid question is the one you didn't ask!

Fender Hot Rod amps have a TRS cable that connects the footswitch to the amp.  When I bought mine a while ago this cable was missing.  I suppose I could have constructed one but it's probably less hassle, not much more expensive and probably far more reliable to buy one.

The only aftermarket TRS cable I can find is a shielded audio cable.  I presume there should be no issue using this, it's not carrying high voltage or current and is only used to switch a couple of relays inside the amp, right?

I know, say, using a guitar cable in place of a speaker cable is a big no-no, but am I right in thinking there should be no issue using an audio cable for this application?

TIA

Ducks for cover.......

Danny1969

No
Use a mono non shielded cable
The circuit uses AC and diodes to achieve different states from one mono non shielded cable

Shielding will add reactance and screw the circuit up in some cases 

Danny1969

The cable Fender supply is rubbish but a speaker cable like this is ideal

https://cpc.farnell.com/pro-signal/psg01301/loudspeaker-power-leads-6-35mm/dp/AV14469?st=speaker cable jack

Haych

Righto, thanks @Danny1969 I am genuinely both surprised and appreciative.  As usual I have overthought and over complicated the matter!

Cheers

ecc83

I have found this schematic for amp and foot switch.https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Hot-Rod-Deluxe-Schematic.pdf

I can see nothing in there that would be in the least bothered by a screened cable? The jack shown is a TS form.

BTW, in extremis a decent guitar cable will work fine from amp to cab. A bit marginal for a 100W+ amp and a 4 Ohm speaker but still ok to get you through the night. A very long curly cable on the other hand might just melt! I have old XLR mic cables that could comfortably handle 2kW!

Dave.

ICBM

It’s a TS cable, not TRS. (Although TRS will work, just not necessary.)

I did some testing and a shielded cable works fine as long as it’s less than about 6m/20’, depending on the capacitance per metre - beyond about 9m/30’ it won’t work. So you can use a short guitar cable if you have to, but if you want a proper long cable, use old mains cable or something similar - even cheap 2-core ‘bell wire’ speaker cable will work, although it’s not very robust. There’s no minimum current rating, the current in the circuit is tiny.

Haych

Thanks all. I wrongly assumed it was TRS since all the other similar amps I’ve ever used were all TRS. 

Every day is a school day, eh!

snowblind

I have a fender footswitch and cable which is of no use to me so if you want a spare let me know.

DartmoorHedgehog

ICBM said:

I did some testing and a shielded cable works fine as long as it’s less than about 6m/20’, depending on the capacitance per metre - beyond about 9m/30’ it won’t work..

While the chances of ever playing anywhere that means I'm more than 20' away from my amp are somewhere between extremely unlikely and no chance, just out of interest do you know if that applies to the channel switching circuit in a Rocker 30?  I've always used an instrument cable (probably a 10' one I think but it's never anywhere near needing to be that long). I don't think even my longest lead is as long as 30' so I can't very easily try it myself but would be interesting to know.

In fact at the place we usually record the amp is shut in another room with a long cable. None of our songs have ever needed channel switching mid-song so it's never been an issue, but if it did then that's when I might need to use a massive footswitch cable.

ICBM

DartmoorHedgehog said:

just out of interest do you know if that applies to the channel switching circuit in a Rocker 30?

No, the Rocker is a simple DC-operated relay circuit so you can use an (effectively) unlimited length of any type of cable.

DartmoorHedgehog

ICBM said:

DartmoorHedgehog said:

just out of interest do you know if that applies to the channel switching circuit in a Rocker 30?

No, the Rocker is a simple DC-operated relay circuit so you can use an (effectively) unlimited length of any type of cable.

Thanks @ICBM - good to know for when we get offered that stadium gig  

ecc83

I recently made relay box to effect switching of two active monitors (killed when using a mic) and used two DPDT 5V min relays which power easily from any USB 5V sources.

A similar circuit could be used to extend a foot switch almost ad.inf.

Dave.