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Old 3rd March 2009, 05:31 PM   #1
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Default Bias Ground

Hi, I was wondering if somebody would be able to advise me on the best place to ground my biasing circuit for a fixed bias power stage. I have two ground points - one star ground for the power stage smoothing caps and cathodes and a bus ground for the phase splitter and preamp.
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Old 3rd March 2009, 07:58 PM   #2
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Use the star ground from the power supply for the bias supply. But I'm scratching my head here on the use of two different ground points. Why? Surely the buss must be connected to the star in some fashion otherwise it won't work.

Victor
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Old 3rd March 2009, 08:06 PM   #3
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Hi, I was referring to:
http://www.aikenamps.com/StarGround.html
and some of the ideas he uses particularly addendum 3 and the second section "what is "star grounding"?". I might have misunderstood though and would be very grateful if you could send me the right direction!
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Old 3rd March 2009, 08:20 PM   #4
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Oh OK, I see what you mean. Ultimately the grounds are connected together. He's talking about "branching" (at least that's what I call it) to keep progressive stage grounds together. Try to keep then as short as possible for best results with lowest hum. And use a heavy copper line (#14 at least) for the buss.
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Old 3rd March 2009, 08:40 PM   #5
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I see, I'm not entirely sure whether my plan is correct or not! At the moment I have a bus (1.5mm copper wire) running 2/3 of the chassis with components in order from input to phase splitter and then i intended to ground. On a separate board further along I had the power stage parts connected to a star ground and to a separate ground (on the same chassis).

Is it ok having these two points which is what i gathered from that website, or should the bus point also connect to the star ground?
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Old 3rd March 2009, 10:59 PM   #6
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Quote:
Originally posted by AmpBuilder225
Is it ok having these two points which is what i gathered from that website, or should the bus point also connect to the star ground?
The buss line should be connected to the star ground. That's what a star ground is all about. Having all grounds meet at a single point on the chassis. It may make a slight difference, hum wise, just where the buss ground wire is connected on the buss itself. Experimentation may be necessary to find the quietest point be it the center or one end of the buss line.

In the case of Aiken's two point ground scheme, this "may" be helpful if individual filter capacitors are used. However, in the case of a mutiple "can" electrolytic capacitor, it can't be implemented and is generally not necessary anyway. This should be borne out by the countless thousands of commercial amps already out there with multi-section PS capacitors.
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Old 3rd March 2009, 11:47 PM   #7
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It all appears to make good sense now - thanks for clearing that up. I have got individual filter caps but I think I will add the buss to the star ground as you say. The way I have layed it out, i think I will have the star ground of the power stage as a continuation of the buss so that the amp is in order of currents flowing. If it is noisy I might try a separate buss ground to the chassis etc. Thanks for your help!
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