Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Nathan on October 24, 2023, 02:20:36 pm

Title: Grounding Theory
Post by: Nathan on October 24, 2023, 02:20:36 pm

Howdy kind folks,


I am strategizing a layout for my next build and I am 'somewhat' unclear on grounding paths.


I heard somewhere (probably here?) that the power section should be grounded together and the preamp section grounded together as far away as possible to ensure the signal path does not pick up any AC.


So first question: are all the filter caps considered part of the power section? Or are the caps supplying B+ to the preamp tubes considered preamp section? In other words, is it ''better'' to separate grounding points?


Next question is related: does the order matter when grounding? ie. does filter cap '2' need to come before filter cap '3' when using a ground bus?

Title: Re: Grounding Theory
Post by: shooter on October 24, 2023, 02:52:05 pm

PA caps and preamp caps are grounded separate.  there are many schemes, best to surf up something like "understanding grounding in audio circuits"
I like to take ALL preamp grounds to 1 point at or near the input jack.
My PA gets grounded at or near a bolt for the OT
I create a ground buss on the turret board for pre, a separate one for PA, then run 1 wire to the 2 points mentioned above.


I prefer to spread my caps out near the point they will be used.

Title: Re: Grounding Theory
Post by: kagliostro on October 24, 2023, 03:32:53 pm

Ciao Nathan

(https://el34world.com/charts/images/ChassisGrounds2.png)



and read also here
http://www.valvewizard.co.uk/Grounding.pdf (http://www.valvewizard.co.uk/Grounding.pdf)

Franco

Title: Re: Grounding Theory
Post by: labb on October 24, 2023, 04:58:48 pm

I pretty much follow the Hoffman plan with the exception that I separate the preamp stuff from the power stuff and ground all of the preamp on a ground lug located at the input jack. The ground lug for the power I install close to the first power cap and the ground for the mains( green wire) I put on a ground lug of its own where the mains enter the chassis. That gives me three ground points and there is a lot of knowledge that says that is too many. This has always worked for me. I always lock tight any bolts on the grounds.

Title: Re: Grounding Theory
Post by: acheld on October 24, 2023, 06:27:33 pm

+2 on the Hoffman scheme.   It works.

I also use a separate bolt near the power cord as my safety ground.   (This is NOT part of the circuit -- present only "in case").

Title: Re: Grounding Theory
Post by: PRR on October 24, 2023, 07:14:17 pm

Quote from: Nathan on October 24, 2023, 02:20:36 pm

...does the order matter when grounding? ie. does filter cap '2' need to come before filter cap '3' when using a ground bus?

"Ground follows signal."

That's not universally best but usually a good start.

Title: Re: Grounding Theory
Post by: labb on October 24, 2023, 07:40:51 pm

If you have a free hand with the layout put some thought into mounting each filter cap with the section it powers.