Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mason on May 11, 2021, 08:00:22 am
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Hey yall, I'm trying to debug an issue with my Soldano clones footswitch. The channel switching works fine when using the front panel toggle switch. However, when using a footswitch it doesn't work. I'm using a switchcraft 12a shorting jack for the footswitch jack. The way it's wired up is as follows. From the PCB there are two wires, when they're shorted the amp is in the clean channel, when open the amp is in the overdrive channel. These two wires from the board go to the footswitch jack. The ground wire goes to the sleeve lug, the wire carrying power goes to the tip lug. The front panel spdt is wired so the middle lug goes to the footswitch sleeve, and the top lug goes to the footswitch middle lug, which when no footswitch is plugged in gets shorted to the wire from the board carrying the power.
I can confirm that the toggle switch does what it's supposed to by checking continuity, and I can confirm the footswitch also opens/closes the circuit as well *when the amp is off*. However, when I turn the amp on the footswitch no longer properly closes the circuit. I read a resistance around 500 ohms between the tip and the sleeve of the jack with the footswitch plugged in. When I use a smaller 6 inch cable to run from the footswitch jack to the footswitch then it works, but using a longer 10-foot cable causes it to not work.
Does anyone have any ideas for what's going on? For reference, I've used multiple 10 foot cables with the footswitch with the same results, and I've made sure the footswitch jack is properly grounded to the chassis. Attached is the schematic for the switching power supply and footswitch circuit. The footswitch i'm using doesn't have the led or extra resistor.
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I read a resistance around 500 ohms between the tip and the sleeve of the jack with the footswitch plugged in.
Disconnect the FS plug and connect your ohm meter to the tip and sleeve of the FS plug. Do you measure zero ohms when the switch is closed and infinity ohms when the switch is open?
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I read a resistance around 500 ohms between the tip and the sleeve of the jack with the footswitch plugged in.
Disconnect the FS plug and connect your ohm meter to the tip and sleeve of the FS plug. Do you measure zero ohms when the switch is closed and infinity ohms when the switch is open?
Yes, it's zero ohms when closed and infinity when open. And with it plugged into the jack I get the same reading as well. The issue arises when the amp is turned on and power is going through the switch.
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When power is turned on there is voltage across the switch if it is open so don't try to measure resistance with power on.
Use a gator clip test lead to short the FS contacts. Does this work?