Wiring DPDT switch for internal channel jumper

Ronno25

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I just wired up a two channel, two input amp with a channel jumping dpdt switch. The switch works as it should when I have a guitar plugged in. When channel jumping is engaged and nothing is plugged in to the amp there is a loud buzz/hum. I'm using switchcraft shorting jacks. Did I wire this up wrong, and if not, is there a solution to this problem? See my diagram below:


Screen Shot 2022-04-03 at 10.51.15 AM.png
 

Wally

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It appears to me that as drawn your shorting tabs are not shorting anything out. I would think that you need to have a connection from the shorting tab to the ground tab on the Jack on the right as we view them. This would in effect short both jacks to ground with nothing plugGE’s in. When you plug into that Jack on the right, that shorting ground would be lifted from both jacks. You would always have to use the Jack on the right as we view them above when plugging in, or both jacks would be shorted to ground.
 

Ronno25

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@Wally The problem I'm running into is that the jack on the right is the normal channel and the one on the left is the bright channel, so not being able to use the bright channel wouldn't work. I suspect that if there is a solution to this it is very complicated. I'm wondering if just removing the switch and putting in a 3rd jack would be the best solution. That way I can manually jump the channels if I want. The buzz is annoying as is, although it's not like I have my amp on with no guitar cable plugged in often. It mostly bothers me because it's poor design on my part.
 
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Ronno25

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Just realized I can’t add another jack as the turrent board is in the way.
 
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Ronno25

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Ensure the switch ground goes to exactly the same point as the input jack ground!
The switch ground and both input jack grounds all go to the ground bus bar close to each other, but not exactly at the same place. Would this really make a difference? It seems that the problem is an open circuit, I'm not understanding how the placement of the grounds would affect this. Could you shed more light?
Screen Shot 2022-04-04 at 11.31.11 PM.png
 
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Jon Snell

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Your drawing looks like the ground points are different but the photo shows correct placement.
To clarify; If a signal ground has a chassis ground point as well as another ground point, there can be tiny voltages set up between them, these can be amplified and cause unwanted hum/noise.
 

Ronno25

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I was digging around some of Steve Luckey's schematics and found his Supro build. He used a single input jack with an on-on-on switch to go between two different channels or both. There's my solution. Super simple. Now I just have to figure out what to do with this ugly hole in my chassis where the second input jack used to be 😭. It's a 5e3 so not sure what mods I would even want to do to it. Was thinking I could try a PI grid stopper potentiometer, or "sweet pot" as robrob calls it.
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