footswitch question

[Belva]

I plan on building a 3 way footswitch for gain, reverb & chorus on an old Hohner amp. I also plan on running one 4 pin plug instead of the 3 seperate plugs in has now. The type of wire needed is the question. Every factory footswitch I've seen has shielded wire. Is shielded wire really necessary for this app.? I've built singles before with lamp cord without a problem.And my local hardware store has some 5 wire 20AWG. @ 17 cents a foot. Do I run any noise/crosstalk risks using this type of wire? I can use the xtra wire for ground or just not use it. Common ground of course Thanks in advance.

[amp_surgeon]

If audio signal is going through the cable then you want shielded cable. If it's just grounding part of the circuit that controls an on/off type function, then it probably doesn't matter if it's shielded.

 

The point being that an unshielded cable is going to pick up noise that a shielded cable wouldn't pick up, so the question is whether that noise is going to affect the way the circuit works, or make it's way out the speaker.

[Belva]

Thanks. Stands to reason that, with these being simple on/off switches, shielding isn't needed. Why do factory footswitches almost always use shielded? I've only dealt with 2 button type with shield being the common ground & this must make it easier, therefore cheaper.

[amp_surgeon]

It could also be said that the footswitch on an effects pedals is also an "on/off" switch, but the signal generally does actually pass through the switch. I wouldn't make a remote footswitch for an effect pedal without using shielded cabling.

 

You mentioned a Hohner amp in your first post. The Hohner CA200 has a couple of external switches; one for reverb, and one for tremolo. Both use shielded cable, even though the audio signal doesn't pass directly through them. The reverb switch is used to ground the output from the reverb tank, so any noise on this line is going to be passed back into the reverb tank amp, and may be heard at the speaker, depending on the setting of the reverb intensity knob. The tremolo switch grounds the cathode of the tremolo oscillator tube. It would take a pretty significant amount of noise here to cause any noticeable change in the current through the tube, and any change it did cause would only change the waveshape of the tremolo oscillator. In other words, you could probably get away with an unshielded cable for the tremolo without any serious problems.

 

Look at the schematic for your amp, and determine if noise at the point where the switch is connected to the circuit might cause problems.

[WRGKMC]

I'd stick with whatever the original switches were. If they were grounded theres a reason for it so stick with it. Any kind of grounding switch will have a hot wire in its core to apply the ground at the switch. If the amp uses and SSR or relay type switch in the circuit that is activated by a switch it may be a different story but even there shielding may help block emf caused by the inductance of the cable.

[Belva]

Getting a schematic aint gonna happen. And no footswitches came with it. It was a yard sale find that needed some cleaning. Hohner Marlin. It has three 1/4" jacks for footswitches. One for gain, one for reverb & one for chorus. I've used my tuna can footswitch with each and had no problems. Used lamp cord to build that footswitch. But I want to combine all jacks into one to reduce hassle. I don't know if using a 4 wire cable with a common ground would create problems. 4 pin plugs & jacks are available. I also thought about going 5 pin & running the guitar signal as well. Then I know shielded would be required.