Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Johntb on June 02, 2020, 07:44:24 pm
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Is it better to have a single grounding point or multiple throughout the chassis?
What are the advantages/disadvantages to each?
Thanks
John
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Bookmark this website...
http://www.valvewizard.co.uk/
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Is it better to have a single grounding point or multiple throughout the chassis?
What are the advantages/disadvantages to each?
Welcome to the dark side John! Kidding...sort of. Most have no idea of this concept and it's importance. Using boating in the ocean as an analogy - most can't wait to get the motor started or sails up and off they go. But when they get to where they want to go they have no real clue about anchoring safely and securely. Grounding to amp building is analogous to anchoring.
Merlin Blencowe has the most complete information but Aiken's is also very good. It takes many readings of both and many amp builds to get it all completely understood thoroughly inside out. Especially if you do not simply copy people's builds or do a lot of modifying. In a nutshell, in lower gain amps it's not nearly as critical. But the higher the gain, stages, complexity, etc. it increases in importance exponentially. They both agree that the star method is best with one grounding point for the circuit. But UL says to have a separate ground with it's own bolt to the chassis for the line voltage side to the primary of the power transformer (I say it this way to help avoid confusion). So essentially there are in reality 2 ground points.
The way Merlin explains it is to think of the input as being the small stream high up in a mountain. It flows slowly making it's way to another (first part of the preamp) and joins. Then the stream gets a little bigger and flows into a larger one (2nd part of the preamp - think after a couple more stages/cathode follower, reverb, etc), then eventually flows into a river (joining the phase inverter). Now eventually the river flows into the lake or ocean where the biggest currents flow (output jack, power tube's cathode bias resistor/cap if cathode biased, and reservoir filter cap) - this is your main ground point. Everything ends up here (your main star point).
Another important consideration to all of this: Do not mix up your chassis grounds with your signal grounds. Signal grounds are a RETURN PATH for your signal. Keep these guarded and controlled never being allowed to connect to chassis ground - this is the primary cause of ground loops. And if this mistake is made early in the circuit it gets amplified and re-amplified again and again along with the signal as they make their way through down through the circuit to the power tubes. This is a large cause of oscillations of all types where some are audible and many are not within our hearing range but wreak havoc on our tone, sustain, and very odd noises which can sound like cabinet and speaker buzzes, mosquitos on a particular fret/note, etc.
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Bookmark this website...
http://www.valvewizard.co.uk/
Read quite a bit there not so much on the grounding as of yet. Thank you.
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Bookmark this website...
http://www.valvewizard.co.uk/ (http://www.valvewizard.co.uk/)
Read quite a bit there not so much on the grounding as of yet. Thank you.
http://www.valvewizard.co.uk/Grounding.html
download the document.
--pete
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Another thing to allow for is the idea that even with the most "perfect" grounding scheme, you can still have pesky ground loop problems. I can do nine builds with no issues whatsoever and then a tenth will have a ground loop. Get good at finding them and fixing them because they will happen.
The problem that I most frequently have.... one random cathode resistor/bypass cap in the preamp section just doesn't like being grounded the same way as all the others and just won't be happy until it gets its own ground.
You can't be afraid to snatch out the offending connection and do something else with it even though the resulting ground connection does not conform to the scheme that you are using.
Dave
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Welcome to the dark side John! Kidding...sort of. Most have no idea of this concept and it's importance.
So essentially there are in reality 2 ground points.
Another important consideration to all of this: Do not mix up your chassis grounds with your signal grounds. Signal grounds are a RETURN PATH for your signal. Keep these guarded and controlled never being allowed to connect to chassis ground - this is the primary cause of ground loops.
Thank you for the information.
I have about 6-7 amps under my belt. Mostly high gain.
I personally use at least 3 separate grounds. One for each CT on HV and 6.3 CT (when there is one) then one on the signal side. I have used a couple on the signal before without noticing any issues.
Just getting some different opinions and education. Plus I have quite a bit of grounding on my current build.
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Bookmark this website...
http://www.valvewizard.co.uk/ (http://www.valvewizard.co.uk/)
Read quite a bit there not so much on the grounding as of yet. Thank you.
http://www.valvewizard.co.uk/Grounding.html
download the document.
--pete
Better yet, buy the book! Wouldn't be without it.
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Bookmark this website...
http://www.valvewizard.co.uk/
Read quite a bit there not so much on the grounding as of yet. Thank you.
Maybe you missed the link called "Grounding and Ground Schemes".
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Bookmark this website...
http://www.valvewizard.co.uk/ (http://www.valvewizard.co.uk/)
Read quite a bit there not so much on the grounding as of yet. Thank you.
Maybe you missed the link called "Grounding and Ground Schemes".
To be specific
Click here to view the article (360kb PDF) (http://www.valvewizard.co.uk/Grounding.pdf)