Question about ground(s)...

[Paul-in-KC]

All,

I have another dumb question that may be helpful too many readers here.

Looking at the "ODS Eyelet Boards" post by Martin Manning (Nov 13, 2016) in the "Files" board:

I see that the Power Supply Board has 3 different ground connections. One for B+1, one for B+2, and one that covers B+3, 4, and 5.

Since it would be very simple to have made these common (connect them) on the board - I am fairly certain that this separation is intentional and well reasoned.

So, may question is, "why are these separated? and why in this specific manor?" (okay, maybe two questions).

Seems to be segmented by preamp (+PI), power amp, and output transformer. And that makes some intuitive sense. Though, the PI seems more like part of the power amp than the preamp (to me).

If that previous statement is in the right neighborhood - then does it also follow that one would generally want to separate/segregate grounds by section [preamp, (PI somewhere), power amp, and OT]???

As always - many thanks to those willing to share their knowledge and make the effort to post.
Kind Regards,
-Paul

[pompeiisneaks]

That's a great question, and I'll answer now, but I'm sure someone could give even deeper meaning.

grounding is something that, if done wrong, can create ground loops and all kinds of noise in an amp. The areas that are most sensitive to those noise impacts are the first stages of the preamp, with the first stage itself being most sensitive.

The areas most prone to creating this noise are the power tubes anodes and screens. Going from either end of that scale towards the other the noise pickup and noise creation goes opposite of each other. Therefore it is best to either have only ONE ground connection point for everything, or if you're going to split them up, split up the most noise inducing and move their connection point as close to that 'source' as possible, as well as being as far away from that sensitive input side as possible.

Basically putting B+1 right next to the pwoer transformer and the power tubes means it's very close to the source of the 'noise' and can be sent to ground without incurring a grounding loop. Then the more sensitive it goes, the grounds are put farther from that spot towards the preamp/input side. Similarly B+2 is still more prone to noise but not as much as B+1, so you can put it a bit more mid level in the layout not exactly at the input but not right next to the B+1. Dumble likely experimented a lot and found this was the best way to do his grounding. From what I gather, all of the 5 or 6 grounds in this amp were carefully laid out after his years of experience understanding grounding loops and grounding techniques. I'd also recommend reading the valve wizard's document on grounding as it helps understand the 'why' better:


http://www.valvewizard.co.uk/Grounding.html

~Phil

[Paul-in-KC]

That's a great question, and I'll answer now, but I'm sure someone could give even deeper meaning.
...

I'd also recommend reading the valve wizard's document on grounding as it helps understand the 'why' better:


http://www.valvewizard.co.uk/Grounding.html

~Phil

Thanks Phil - and funny you should reference that - I had printed and was (am) reading Chapter 15: Grounding - as I see your response.