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Grounding with separate enclosures?
Grounding with separate enclosures?
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Old 4th February 2018, 07:58 PM   #31
TheNuge is offline TheNuge  Germany
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Hi Guys!
Better give you an update on the amp: it's finished, doesn't hum and performs as it should (I'd say it sounds excellent, but don't want to start a debate on whether or not an amp should "sound" like anything).
I followed the advice on hooking up the caps correctly, and have twisted the wires wherever possible. There's a central "function" ground (0V) in the amp enclosure (towards the front plate in the middle), which in turn is connected to first the amp enclosure and then the PSU enclosure where it also runs to ground.
Click the image to open in full size.
I decided not to run the secondary voltage for the inputs, but it doesn't seem to be lacking anything!
It's now got 60.000uF (the silver caps) per rail in the PSU enclosure and another 13.600uF (the orange caps) per rail in the amp enclosure.
The two enclosures are connected with a shielded cable carrying -DC, OV and +DC plus an additional cable for safety earth.
DC is switchable (actually on the primary side) between +-72V and +-88V, but I've only been listening with the +-88V so far.
Click the image to open in full size.
Excuse the mess!
And this is how the whole setup now looks:
Click the image to open in full size.

Next project will be some Pass First Watts for the horns

Cheers
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Old 4th February 2018, 11:26 PM   #32
forr is offline forr  France
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Quote:
Originally Posted by AndrewT View Post
The Protective Earth wire gets connected to the mains Chassis/Enclosure. That is a SAFETY connection and has absolutely nothing to do with obtaining a good working audio system.
There is a second rule: All exposed conductive parts should be connected to the Protected Chassis/Enclosure. Again this has nothing to do with obtaining good quality audio. It is purely SAFETY.
However, both the PE connection and the extra "All exposed parts" connection can give an additional route for interference reaching the audio circuitry.
Scott has mentioned
I plan to test a power supply (probably regulated) in a separate enclosure from the one of the amplifier. There will be a safety earth connection for the power supply chassis but the power supply 0V will not be connected to it.
The power supply will be floating down to the inside of the amp enclosure. I wonder about screening the cable between the enclosures, the screen being connected to the power supply chassis with a cap.
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Old 4th February 2018, 11:41 PM   #33
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by forr View Post
There will be a safety earth connection for the power supply chassis but the power supply 0V will not be connected to it.
It should be so the fuse blows if mains voltage gets into the circuit
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Old 5th February 2018, 05:58 AM   #34
forr is offline forr  France
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Quote:
Originally Posted by scottjoplin View Post
It should be so the fuse blows if mains voltage gets into the circuit
A fuse blows for an excess of current. The protection of persons is achevied using a circuit breaker based on the difference between the currents in the live and neutral wires of the mains (for more than 30 mA in France).
Lab power supplies have their output usually not connected to the chassis and earth and people using them are more exposed than users of standard audio devices.
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Old 5th February 2018, 09:03 AM   #35
scottjoplin is offline scottjoplin  Wales
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Meanwhile the amp bursts into flames. I'm guessing lab power supplies would be double insulated.
Why not connect the 0 volts to the chassis?
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Old 5th February 2018, 09:30 AM   #36
AndrewT is offline AndrewT  Scotland
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Lab power supplies are not double insulated, i.e. not ClassII
They are connected to PE making them ClassI

The outputs are isolated.
And usually with a connection to PE protected chassis if required.
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Old 5th February 2018, 12:18 PM   #37
bluerooster is offline bluerooster
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As to the mutual grounding of two seperate chassis, what I did was to simply connect the two together via a heavy lead. That way they are mutually grounded.

On the shelf to the left is the amplifier, on the right is the 4kv power supply. Both are kinda big, but the supply is also pretty darn heavy. The power supply is controlled remotely from the switches on the amp, and the mains feed also comes from the amp to the HV supply. They are electrically bonded with a 10 gauge cable between both chassis.
While this may not be an audio amp, it uses electrons just the same.
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Old 5th February 2018, 02:41 PM   #38
forr is offline forr  France
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Quote:
Originally Posted by AndrewT View Post
Lab power supplies are not double insulated, i.e. not ClassII. They are connected to PE making them ClassI
The outputs are isolated.And usually with a connection to PE protected chassis if required.
As you say, the chassis of a lab power supply is connected to earth for safety reasons (only). The outputs are isolated and supply current to devices which schield of do not need to be connected to earth for best EMI rejection, even more, should be avoided in absence of hazards, according to EMC specialists.
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Old 5th February 2018, 02:55 PM   #39
scottjoplin is offline scottjoplin  Wales
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Ok, you don't want to connect 0V to chassis because PE may be noisy, fair enough. On a side note, oscilloscope 0 volts/reference is usually connected to PE, why is that done?
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Last edited by scottjoplin; 5th February 2018 at 03:09 PM.
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Old 5th February 2018, 03:17 PM   #40
AndrewT is offline AndrewT  Scotland
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Maybe because you are holding the probe and it has exposed metalwork as well as metal on the connectors. You and the exposed metal need to be at the same voltage. PE does that for us.
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