Grounding Question

[Diyengineer]

Hi,

If I’m doing a sort of a star grounding system located at the input jack, is it ok for cathode resistors and grid leak resistors to share the same wire back to the jack? Or should they have separate wires?

Similarly, is it on for preamp tube cathode resistors and power tube cathode resistors to share the same wire back to the jack as well? Or should those be separate as well?

Thanks

 

[rayma]

is it ok for cathode resistors and grid leak resistors to share the same wire back to the jack?
is it on for preamp tube cathode resistors and power tube cathode resistors to share
the same wire back to the jack as well?

Think of each stage as a sub-circuit, and run one ground from each stage (grid and cathode).
This especially goes for the output stage, which has larger current and more ripple noise.
But keep all those ground wires short, by good layout. Post some photos.

 

[Diyengineer]

Great, thank you!

 

[cerrem]

Keep in mind there are AC signal loops and DC loops ..... Just remember to keep it short and return it back where it came from... Personally I never use the chassis for current return .... I only ground the chassis in one location for shielding purpose.. The whole concept of using the chassis for return currents was to save on copper wire $$$ and sometimes weight as in some air-frame wiring systems..

 

[Merlinb]

If I’m doing a sort of a star grounding system located at the input jack,

That's not normal. Why are you sending noisy currents back to the input jack??

is it ok for cathode resistors and grid leak resistors to share the same wire back to the jack? Or should they have separate wires?

Theoretically they should share the same wire but it's unlikely to make much difference.

Similarly, is it on for preamp tube cathode resistors and power tube cathode resistors to share the same wire back to the jack as well? Or should those be separate as well?

Theoretically they should be separate, but if it may not make much difference.

 

[Diyengineer]

That's not normal. Why are you sending noisy currents back to the input jack??

I'm am using the jack only because I have read about that method elsewhere. The scheme that I planned to use and have used in a couple other amps I built is the following: I bussed the secondary 0R OPT to the input jack with a 12ga wire. Then tied all P.S. grounds together on the P.S. board and ran 1 wire back to the jack. The P.T. center tap is grounded on the P.S. board at the filter caps. Then tied all of the active circuitry together and ran 1 wire to the jack as well. Then I ran 1 wire from the jack to the IEC ground terminal passing through an X2 cap & low ohm resistor. Then bonded the chassis to the IEC as well. I will separate the active circuitry by stage now, each with a separate run to the central node. If not the jack, where would be the ideal place to locate the central grounding point? And what might the ideal scheme look like? I have read about so many grounding schemes, everyone seems to do it a little different.

Thank you!

 

[scottjoplin]

You have confused the star with connecting the amp ground to the chassis at the input socket.

 

[Merlinb]

If not the jack, where would be the ideal place to locate the central grounding point? And what might the ideal scheme look like?

http://valvewizard.co.uk/Grounding.pdf

 

[cerrem]

http://valvewizard.co.uk/Grounding.pdf

The input jack is actually a really good place to ground.... This article is very useful for those learning to ground properly... When designing mixed-signal circuitry, a common node for grounding is at the ADC input..

 

[Diyengineer]

Thanks for the input guys.

 

[Chris Hornbeck]

http://valvewizard.co.uk/Grounding.pdf

What an excellent piece! Thanks very much for posting this; it'll be where I'll point folks from now on.

All good fortune,
Chris

 

[Diabolical Artificer]

"What an excellent piece! Thanks very much for posting this; it'll be where I'll point folks from now on." Merlin's site is invaluable for builders of valve amps, I'd have struggled without it.


Andy.

 

[Chris Hornbeck]

Issues of "grounding" are subtle, maybe in some large part because we believe schematics, where elephant-in-the-room assumptions are the usual case. Merlin B's piece is crystal clear in breaking down the assumptions into good mental models. Once you have a good (and real) model, you can fly on your own.


Bob Cordell's book (highest possible recommendation) additionally discusses the signal ground to chassis ground connection in detail. And JNeutron has posted some ground-breaking (NPI) next-gen thoughts about system wiring issues in the John Curl Blowtorch thread, mostly lost in the noise there, but well worth the effort.


All good fortune,
Chris

 

[David Davenport]

Audio Component Grounding and Interconnection right here on diyAudio.