Easy grounding questions

[Lectroid]

I'm working on an 18W amp, heavily influenced by the Hoffman Stout and by tubenit's designs.  I used the Hoffman Stout Reverb board.  I'm just about done but I realize that I am still not crystal clear about grounding.  I've read Blencowe and Aiken and try to adhere to good practices.  But I still have a couple of questions. 

I have a 14 ga. copper wire ground for the pots floating just behind them, and grounded to the chassis near the input jack.  Any pots needing a ground connect to it. The input jack is insulated from the chassis and grounded to this copper ground buss. 


1. Is there a preferred low-noise way to bring these two ground points together at the preamp end of the amp?  Where does everybody tie them together?

see the red circles on the schematic

2. The LPT ground is connected to the power supply ground, right?  Not to the preamp ground.

3. My amp has an F&T 32-32uF cap can for the A and B power supply caps.  The can is grounded to the PS ground on a transformer bolts, as is the C filter cap that supplies the LTP.  I'm not sure about the D cap though.  Should I connect it to the preamp ground or the PS ground?

[tubenit]

I think your preamp grounding should be fine given an insulated input jack.   I've grounded the LTPI with the power section and on a few amps with the preamp section.  I personally have not found much difference in noise or hum at idle with either approach.


With respect, Tubenit

[pdf64]

Michael at Modulus publishes some excellent layouts, which provide an example of how to implement the local star ground and single point connection to the chassis system described by Merlin https://files.ekmcdn.com/53d0d0/resources/other/gb-bass-kit-layout.pdf

[shooter]

pic any amp here to study, you'll be stealing pics and have amp porn displayed prominently on your walls soon after 


https://sluckeyamps.com/index.htm

[Kev-W]

pic any amp here to study, you'll be stealing pics and have amp porn displayed prominently on your walls soon after 


https://sluckeyamps.com/index.htm

And the grounding schemes work well!

[acheld]

1. Is there a preferred low-noise way to bring these two ground points together at the preamp end of the amp?  Where does everybody tie them together?

Most builders tie these together through the amp chassis.   

For example, the Hoffman scheme (which I normally use) separates the power section (eg, the PI and power tubes) from the rest of the preamp to two different grounding points on the chassis.

True "star" grounding ties everything together at one point.   And there are variations of each of these schemes.

It is good to know that there are (shall we say) devoted adherents to each variation.

Merlin has provided us with a good discussion: https://www.valvewizard.co.uk/Grounding.pdf

My perspective is that you find what works for your builds and go with it.   There is not a one-size-fits-all answer, IMO.

I love Shooter's comment about sluckey's builds . . .

Edit:   Oh, and there are NO easy grounding questions . . .

[dwinstonwood]

In my Hoffman 6V6 Plexi I grounded everything at the input jack - except for the power cord earth ground, which has it's own grounding bolt on the chassis.

Each ground star is at the ground point of each of the filter caps. So, each section of the amp has its ground star connection at the filter cap for that section.

This is probably my quietest amp.

On other amps I have connected the power amp ground and the HT CT to the cap can ground lug, and then connected the cap can ground lug to its own bolt on the chassis opposite from the input jack - so, two ground points at opposite ends of the chassis (not including the power cord earth).

These amps are also very quiet.

I've attached my Hoffman 6V6 Plexi layout showing the single input ground.

[Lectroid]

1. Is there a preferred low-noise way to bring these two ground points together at the preamp end of the amp?  Where does everybody tie them together?

Most builders tie these together through the amp chassis.  For example, the Hoffman scheme ... to two different grounding points on the chassis.

That's what I wanted to know, that two points widely separated on the chassis would constitute a valid star ground.

As a general rule, it sounds like many different grounding schemes might deliver adequate sound performance in the amp. 

Is that fair to say?

I love Shooter's comment about sluckey's builds . . .

It is so true.       

tubenit, pdf643, shooter, Kev_W, ached, dwinstonwood,  Thanks for all the tips, tricks, and help.   

[shooter]

it sounds like many different grounding schemes

grounding insures a solid pathway to return electrons back to the beginning without "adding" anything to a circuit, ie noise.
learn the basic rules for most anything, in time you might find a "better way" for you, others might not care for your creativity.


if time n efficiency are part of the goal, steal what works, ponder bigger fish latter