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Old 15th January 2013, 12:10 PM   #1
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Default Preamp grounding

Sorry for noob question, I wanted to check if my thoughts on grounding a preamp are correct. All stages are either common cathode or cathode follower.

Signal grounds are the bottom of the grid leak and cathode resistors (and bypass caps). These can be tied together, possibly with same from other stages, as a star within a star of stars, and this led back to the central grounding star on a single lead.

Grounds with ripple come from decoupling caps on the B+ and these are also gathered together as a star, and then led back to the central star.

This okay?

Last edited by Robert Kesh; 15th January 2013 at 12:12 PM. Reason: Calling the cathode the emmiter
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Old 15th January 2013, 12:18 PM   #2
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I learned a lot reading:

Audio Component Grounding and Interconnection
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Old 15th January 2013, 01:08 PM   #3
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Quote:
Originally Posted by merlin el mago View Post
That looks like cathode goes to power ground, so now i'm confused
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Old 15th January 2013, 02:16 PM   #4
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Could you post the schematic?
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Old 15th January 2013, 03:16 PM   #5
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Quote:
Originally Posted by merlin el mago View Post
Could you post the schematic?
Not right now, it's all hand scribbled, but it is three entirely conventional common cathodes, with grid stoppers, biased with bypassed cathode resistors, coupled by caps, and then a cathode follower.

It's currently breadboarded with no regard to grounding, and there is a little hum, but not much.

I'll try and get a schematic together, but I'm kind of after general principles for dummies. Most of what I read is about interconnections, or layout within a chassis, all of which I'm fine on, but little on the actual circuit layout on a pcb or matrix (mine is matrix)

Star of stars seems the only feasible way, seeing as there are about a dozen points to ground.
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Old 15th January 2013, 04:09 PM   #6
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It's probably referenced elsewhere here, but the first chapter of "The Valve Wizard" (aka Merlin Blencowe) book, on grounding, is (at the time of this posting) free for download. Go here. It's very clear and easy to follow. More info is never bad but you may not need any other reference.
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Old 15th January 2013, 04:52 PM   #7
DF96 is offline DF96  England
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On a breadboard a bus ground may be better.
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Old 15th January 2013, 08:43 PM   #8
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Quote:
Originally Posted by CarlyBoy View Post
It's probably referenced elsewhere here, but the first chapter of "The Valve Wizard" (aka Merlin Blencowe) book, on grounding, is (at the time of this posting) free for download. Go here. It's very clear and easy to follow. More info is never bad but you may not need any other reference.
Thanks, will look closer as I've half read that chapter. The one on common cathodes, right?
Quote:
Originally Posted by DF96 View Post
On a breadboard a bus ground may be better.
The breadboard I'm not too worried about, it's basically matrix board/pcb/p2p ground design that I'm interested in.
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Old 15th January 2013, 10:21 PM   #9
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I've read/thought about this a great deal recently. My conclusions: star ground everything, including pc boards and ground point of the first psu cap. It's important to isolate inputs, and star ground, from chassis. Connect star ground point to the chassis at the point where the AC ground is connected through a little circuit of 2 diodes in opposition, a 10 ohm resistor, and small film cap. While not a preamp, I did this recently on a complete ST-70 rebuild (using Classic Valve boards) and it is hum free and stable. Hope that helps?
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Old 15th January 2013, 10:51 PM   #10
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Quote:
Originally Posted by prairieboy View Post
I've read/thought about this a great deal recently. My conclusions: star ground everything, including pc boards and ground point of the first psu cap. It's important to isolate inputs, and star ground, from chassis. Connect star ground point to the chassis at the point where the AC ground is connected through a little circuit of 2 diodes in opposition, a 10 ohm resistor, and small film cap. While not a preamp, I did this recently on a complete ST-70 rebuild (using Classic Valve boards) and it is hum free and stable. Hope that helps?
Yes, thanks, I'm doing the star ground to chassis via diodes and the rest. I have no problems understanding how to ground except within the circuit board layout itself.
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