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Old 12th August 2003, 05:34 AM   #1
Jay is offline Jay  Indonesia
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Default Is this monoblock common?

I'm building a "monoblock" amplifier in one box. I'm separating the ground for both channels by letting one of the channel ground floating. Is this wrong approach?
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Old 12th August 2003, 06:41 AM   #2
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As long as the cases are both safety grounded to earth, leaving a signal ground floating is perfectly valid.
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Old 12th August 2003, 07:44 AM   #3
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Quote:
Originally posted by pinkmouse
As long as the cases are both safety grounded to earth, leaving a signal ground floating is perfectly valid.
This might be questionable. There is no shielding effect if PCB "floats" against case. You will lead capacitive coupled EMI inside the case, just along signal cables. As a minimum, signal gnd should be connected via capacitor with the case.
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Old 12th August 2003, 07:56 AM   #4
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If your pcb has groundplane you have rather good sheilding but I would connect the case becuase it's good in almost every sense. I can't see why you shouldn't if the case is of metal.
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Old 12th August 2003, 08:06 AM   #5
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Per,

the reason may be ground-loop problem. In case that both cases are connected to protective earth (PE), you create ground-loop by signal cables shields and two monoblock cases connected to PE in case that you interconnect signal GND to the case at both monoblocks.

Pavel
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Old 12th August 2003, 08:07 AM   #6
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Quote:
Originally posted by PMA


This might be questionable. There is no shielding effect if PCB "floats" against case. You will lead capacitive coupled EMI inside the case, just along signal cables. As a minimum, signal gnd should be connected via capacitor with the case.
Sorry, a bit early in the morning for me, I didn't make myself clear, I was talking about the ground in the signal cable. After reading about this in Self's book, I always connect mains and signal ground at the input socket, and it seems to work well.

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Old 12th August 2003, 10:10 AM   #7
Jay is offline Jay  Indonesia
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It was not about fighting the circular ground.

Circular ground (hum) was what I didn't expect from trying to do what I'm going to do (Safety is not a big deal).

I wanted to have the lowest degree of crosstalk between channels.

I wanted to test the validity of monoblock concept from economy perspective.

Distance between channels (especially the power supply) does count indeed, but often there is something more serious than just about distance.
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Old 12th August 2003, 10:21 AM   #8
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I can guarantee that consequentional monoblock solution leads to best achievable localization in the soundstage.
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Old 12th August 2003, 10:50 AM   #9
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Quote:
Originally posted by PMA
Per,

the reason may be ground-loop problem. In case that both cases are connected to protective earth (PE), you create ground-loop by signal cables shields and two monoblock cases connected to PE in case that you interconnect signal GND to the case at both monoblocks.

Pavel
There is no need to connect to protective earth as long as the mains circuitry is OK, just let the case haven the same potential as the signal ground.

NOTE: This is only valid if you don't have a mains filter which has it's case connected (normal mains filter).

(Why: If an apparatus has mains filter and the case is floating you will get 115 VAC (or 55 V) in the chassis, not good.)
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Old 12th August 2003, 01:25 PM   #10
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Quote:
Originally posted by peranders

There is no need to connect to protective earth as long as the mains circuitry is OK, just let the case haven the same potential as the signal ground.

NOTE: This is only valid if you don't have a mains filter which has it's case connected (normal mains filter).

(Why: If an apparatus has mains filter and the case is floating you will get 115 VAC (or 55 V) in the chassis, not good.)
Any metal chassis containing points at mains potential must be securely connected to mains earth. I don't understand what you mean about mains filters.

Sorry if that sounds harsh, but this is an important point.

Cheers,
Tim.
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