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Vibrato footswitch popping

3/13/2006 5:19 PM
Vibrato footswitch popping
I have a SF Twin Reverb that makes a loud popping sound everytime I switch on the vibrato effect with the footswitch. I have the original pedal, but not the original cable. I am using a twisted pair for the center RCA connectors with the shield as the ground for the switches. There doesn't seem to be as loud of a pop if I just use a shorted RCA plug to turn the vibrato off and on, but this defeats the purpose of the footswitch. I would like to know if anyone else has/had this problem and what I can do to fix it. I find it hard to believe that this amp left the factory like this. I really don't want to get too crazy modifying my amp, though.  
I posted this in the Mods& Tweaks forum also, but I guess this is more of a repair issue after all.
3/13/2006 8:35 PM
Rick Erickson

It sounds like you are inducing a spike in the Reverb line when you switch the Tremolo. (Vibrato) This is why Fender shielded the Reverb footswitch lead in the first place and ran the Vib hot lead outside the shielding. You might try looking at the Vibro-King schematic "Vibrato" circuit. They added a resistive divider to drop the voltage at the footswitch jack in the "off" mode. This might help reduce the problem. It could also be a faulty component somewhere. SF Fenders are getting rather old and need a bit of TLC before they perform to spec..  
3/27/2006 6:24 PM

Problem solved, sorta. I finally received the correct cable from Ampwares and that all but eliminated the pop. There is still a little pop when I switch the Vibrato on, but it's nowhere near as loud as it was.
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