Grounding as well as securing them in addition to the hardware.
The housing of a pot is clamped around the front onto the bushing and the bushing is bolted onto the chassis and the chassis is grounded.
So why is there bus wire soldered to the backs of pots?
I just don't think the pot housings or even the chassis should be used for any other than a shield. So if the pots are like some Alpha pots that I have that have continuity through the bushing, they should not be used as a ground. Some grounding methods I've been looking at violate some basic rules about low noise amplifier design. And in a high gain / high current amp like a Marshall, I would think a star of stars style grounding scheme would be important. Meaning there should be separate grounds for each filtered section, separate ground for the chassis / shielded wires and of course the most important is a single thick ground wire from the power tube cathodes to the star. And using shielded cable in strategic locations (like inputs) might also be important. But I'm asking because this will be the first high gain guitar amp build for me. So as Fonzie would say, I could be "wro-wro-wrong".
Because oxygen, between dissimilar metals:
works it's way in over time and causes loss of continuity.
After a few years the pot is no longer solidly grounded. The noise starts to increase.
ground.
But I would still argue that it should only be on the shield ground.
FYI
star grounding is not the quietest method.
This is because of AC ripple in the ground connections of the power supplies.
Not being a tech, I'm a little confused. For a pot to be a shield against noise, doesn't it have to be grounded? And aren't all the grounded components common to each other even if they're connected to the chassis at different points? So what's a "shield ground"?
Your comment implies separate grounds...
"Chassis connected to just about any ground", can be a real good way to end up with ground loops, and increased noise.
What about the grounding method used in this build? Looks really neat and cool.
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