ground bus question

[pula58]

I see a lot of the builds here with a ground bus formed by soldering a bus wire across the back (case) of all the pots on the front of the amp. The end of the bius closest to the input jack is grounded near the input jack shield.

But aren't the pots shorted to the chassis where the pot sticks through the holes on the front of the chassis? In which case, where do the ground currents actually flow: through the chassis, or through the ground bus wire, or some parallel combination of both?

[M Fowler]

Yes the pots are touching the chassis but the buss bar to back of the pots ensures the ground path of all pots flow to the ground tab bolted near the input jack area.

Ground the V1 cathode here as well.

The Komet 60 has three separate ground tabs between the pots and tone board one for low level, mid level and high level (PI).

There is a lot of different ways to run the ground in an amp.

[pula58]

Yes the pots are touching the chassis but the buss bar to back of the pots ensures the ground path of all pots flow to the ground tab bolted near the input jack area.

Why does the current flow through the bus and not the chassis? Wouldn't the currents flow through both? Unless the bus forms a much lower resistance to ground.

[M Fowler]

The buss bar has the direct path and smaller the chassis is large and strays would be my guess.

[M Fowler]

I also like Hoffman site for some good info on AC and DC paths.

[diagrammatiks]

The buss bar has the direct path and smaller the chassis is large and strays would be my guess.

huh. that's not how it works at all.

pula you make a ground loop around the pots.

usually it's not a big deal.

[martin manning]

Why does the current flow through the bus and not the chassis? Wouldn't the currents flow through both? Unless the bus forms a much lower resistance to ground.

Ground currents will flow through both paths, but the buss bar will offer the lowest resistance and be more reliable over time due to all of the connections being soldered. The buss does not need to be soldered to the pot cases, of course, and when done in that way there will be no redundant path or loops formed, and no risk of damage to the pots from overheating.

[M Fowler]

diagrammatiks

You want to avoid ground loops or multiple loops.

[pula58]

Why does the current flow through the bus and not the chassis? Wouldn't the currents flow through both? Unless the bus forms a much lower resistance to ground.

Ground currents will flow through both paths, but the buss bar will offer the lowest resistance and be more reliable over time due to all of the connections being soldered. The buss does not need to be soldered to the pot cases, of course, and when done in that way there will be no redundant path or loops formed, and no risk of damage to the pots from overheating.

I don't understand the part about the backs of the pots NOT being soldered to the bus. I thought this was the most common practice around here (i.e., at the ampgarage)?

[M Fowler]

Depends if the builder follows Mr. Aiken's star grounding rules and never solder a buss bar to the pots, tighten the pots down to the chassis and run separate wire back to the main ground terminal or star point.

Many amps solder to the pots so this has been a subject where we go back and forth. Just like some say never use a Switchcraft jack always use a Cliff isolated type jack. Some one forgot to tell that to Leo Fender and Mr. Dumble.

Mark

[diagrammatiks]

you can use a switchcraft with an isolating washer.

the pot casing will be grounded to the chassis via the nut.

so in terms of ground consider it just part of the chassis.

so if you ground the buss to the back of the pots and you connect either end of the buss to the chassis again it's kinda like connected at 2 places.

[M Fowler]

I don't understand the part about the backs of the pots NOT being soldered to the bus. I thought this was the most common practice around here (i.e., at the ampgarage)?

Yes for a Trainwreck you solder to the back of the pots and run a wire from the buss bar to a ground tab near the cap stack.

Many Dr Z amps also solder to the pots. A high gain amps like the Splawn Quickrod and Nitro also run buss wire soldered to back of the pots.

[martin manning]

I don't understand the part about the backs of the pots NOT being soldered to the bus. I thought this was the most common practice around here (i.e., at the ampgarage)?

This is where the bus runs above the pots and is supported by short wires (or is soldered directly to) the several pot lugs that are grounded. Other circuit grounds, and the single wire connection to the chassis at the input jack, are soldered to the bus.

[Andy Le Blanc]

I use a grounding block, either soldered or bolted to the chassis as a star
and then run a bus around the inside of the chassis, the powerside is
returned to the chassis out of convenience, the opt and cathode but nothing else is.

The chassis is shield and parts holder, the input is insulated from the chassis
and the pots are shielded any way, but the circuit is referenced to the bus.

I've also been surprised at some of the grounding schemes, after the
process of getting the circuit ground off the chassis, it makes for a better amp.

DIY cloning another builders solder and dress can create issues

[butwhatif]

The bus wire connects the pot ground terminals only, and is star grounded to a terminal near the in jack area on one end. Not a great idea to solder it to the pot covers, they ground to the chassis, which may have many ground currents flowing thru it.