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Maida BIAS regulation grounding question
Maida BIAS regulation grounding question
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Old 29th December 2017, 05:08 AM   #1
ahanuban is offline ahanuban  United States
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Default Maida BIAS regulation grounding question

I'm looking to set up regulated B+ and bias supplies on my power amplifier. On Page 41 of the 21st Century Maida Regulator thread, Tom states:

Quote:
Originally Posted by tomchr View Post
You should be able to generate a positive and a negative voltage with two Maida Regulators in series if the conditions below are met.

Conditions: The two Maida Regulators must be fed from separate transformer windings, separate rectifiers, and separate reservoir caps. Basically, the input circuits must be completely separate. You then put the two regulators in series on their outputs and ground the centre point between the two.
My understanding is that when the signal ground is taken to be the point between the two regulators connected in series (and not connected to anything else), the signal ground is at a positive potential with respect to an earthing rod (or human skin, under realistic conditions).

Given that fact, I would assume safety ground (earth/chassis) should be kept separate, i.e. disconnected, from signal ground in this configuration. However, I'm wondering what the ramifications would be when connecting other devices to the tube amplifier. Wouldn't that raise their signal ground voltage to that of the bias supply (not only causing a ground loop but also causing a safety hazard if their chassis is connected to signal ground)?

If my understanding is correct, this would be very dangerous when using a preamplifier without safety ground, for example. And if the signal ground is to be connected to mains safety ground, the chassis would be live at a DC potential if the safety ground connection fails.

Last edited by ahanuban; 29th December 2017 at 01:13 PM. Reason: Clarification
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Old 29th December 2017, 06:23 AM   #2
leadbelly is offline leadbelly  Canada
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Maida BIAS regulation grounding question
No, no, and no to each of your last 3 paragraphs.
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Old 29th December 2017, 06:34 AM   #3
ahanuban is offline ahanuban  United States
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leadbelly, can you please explain your reasoning so I can understand?
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Old 29th December 2017, 06:39 AM   #4
leadbelly is offline leadbelly  Canada
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Maida BIAS regulation grounding question
tomchr describes how it must be built isolated. If the supplies are isolated, the have no ground reference. You establish that ground reference. You are probably not understanding tomchr's instructions and imagining multiple ground connections.
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Old 29th December 2017, 06:42 AM   #5
ahanuban is offline ahanuban  United States
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I understand that the bias supply and B+ supplies are isolated from each other. My question pertains to the function and safe use of the signal ground point developed where those two supplies are connected in series.

Essentially, if you build an amplifier around this power supply and the signal ground is not connected to a proper earthing rod, when you touch an RCA connector on the amplifier, you will be touching the output of the bias regulator.

Last edited by ahanuban; 29th December 2017 at 06:44 AM.
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Old 29th December 2017, 06:45 AM   #6
leadbelly is offline leadbelly  Canada
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Maida BIAS regulation grounding question
Again, if you follow tomchr's instructions, there is no problem connecting safety ground to signal ground. That's the whole point of an isolated supply.
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Old 29th December 2017, 06:48 AM   #7
ahanuban is offline ahanuban  United States
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Right, but what I am asking is not whether they can be connected; rather, I am asking what will happen if they become disconnected, for example in the event of faulty mains wiring.
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Old 29th December 2017, 06:49 AM   #8
leadbelly is offline leadbelly  Canada
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Maida BIAS regulation grounding question
Don't ********, just try to learn.
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Old 29th December 2017, 06:58 AM   #9
ahanuban is offline ahanuban  United States
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Pardon?

I was really hoping for some constructive help in understanding and mitigating risk here, not vague and unexplained answers.

Last edited by ahanuban; 29th December 2017 at 07:01 AM.
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Old 29th December 2017, 07:45 AM   #10
kward is offline kward  United States
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Quote:
Originally Posted by ahanuban View Post
Essentially, if you build an amplifier around this power supply and the signal ground is not connected to a proper earthing rod, when you touch an RCA connector on the amplifier, you will be touching the output of the bias regulator.
Whenever you have two independent electrical components connected together where signal grounds on each component are at different potentials, you create conditions for a ground loop. In other words, current will flow through the connecting cables from the one ground potential to the other. This situation is not specific to just this type of pos/neg power supply scheme.
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