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Old 18th November 2010, 10:30 AM   #461
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Quote:
Originally Posted by Backbones View Post
Should I put in a star ground attached directly to the chassis or leave the chassis unconnected in box 2?
Leaving a metal chassis unconnected is a absolute no-go! (see the previous post...)

Quote:
Originally Posted by Backbones View Post
Or perhaps connect the two enclosures but not connect the amp ground in box 2 to the chassis. [...]
This is what I would do. Connect the enclosure of box 2 directly to the mains-Earth. Connecting the encloure of box 2 to a second GND-star in box 2 will result in a loop, which may give you trouble. You should simply try this.
Otherwise connect the GND-star of box 1 to the mains-Earth with a thermistor as recommended by NP.
This means you will have both GND and Earth running from box 1 to box 2 (plus voltage rails).

~ nightrush

Last edited by nightrush; 18th November 2010 at 10:33 AM.
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Old 18th November 2010, 10:49 AM   #462
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by Backbones View Post
These photographs have posed a question. I am in the process of putting a power supply together in a separate enclosure (box 1) but I hadn’t really thought of the grounding arrangements for the box containing the amp pcbs (box 2).
Should I put in a star ground attached directly to the chassis or leave the chassis unconnected in box 2? Or perhaps connect the two enclosures but not connect the amp ground in box 2 to the chassis.
Regards,
Chris
box 1 - chassis connected to safety gnd ; leave audio gnd floating ;

route all - PSU pos , audio gnd , PSU neg , safety gnd - from box 1 to box 2

connect safety gnd ditto to box 2 chassis

point where you connect audio gnd in box 2 - turret board or any other contact isolated from chassis is your general star ground point

then connect that star gnd to chassis (box2) via 10-30R NTC

you must remember that complete safety issues are covered only when both cases are connected via umbilical .

critical ( unsafe ) case is when you have box1 connected to mains , but unconnected umbilical to box 2 ; in that case there is no connection between safety gnd and power circuit/PSU . but I presume that you'll not using it in that way

don't forget bleeders across caps in box1 ; that way you'll not have sparks during connecting umbilical to box 2
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Last edited by Zen Mod; 18th November 2010 at 10:53 AM.
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Old 18th November 2010, 11:02 AM   #463
Tea-Bag is offline Tea-Bag  United States
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Nice work Chad and JimM.
I wish my wiring and chassis work were this nice.
Something to inspire to!
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Old 18th November 2010, 11:04 AM   #464
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That was quick, many thanks. Any talk of a live chassis is like phoning for the DIY Audio Forum emergency services, which is very reassuring. I’m often surprised how many mains electrical devices these days only have Live and Neutral mains connections and no earth wire, including my old Exposure CD player.

On a similar note the two transformers I ordered have electrostatic (ES) shields and therefore ground wires. Again my instinct is to connect these directly to the chassis earth or should I use a CL-60 between ES earth wire and chassis?
Regards,
Chris
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Old 18th November 2010, 11:11 AM   #465
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Quote:
Originally Posted by Zen Mod View Post
box 1 - chassis connected to safety gnd ; leave audio gnd floating ;

route all - PSU pos , audio gnd , PSU neg , safety gnd - from box 1 to box 2

connect safety gnd ditto to box 2 chassis

point where you connect audio gnd in box 2 - turret board or any other contact isolated from chassis is your general star ground point

then connect that star gnd to chassis (box2) via 10-30R NTC

you must remember that complete safety issues are covered only when both cases are connected via umbilical .

critical ( unsafe ) case is when you have box1 connected to mains , but unconnected umbilical to box 2 ; in that case there is no connection between safety gnd and power circuit/PSU . but I presume that you'll not using it in that way

don't forget bleeders across caps in box1 ; that way you'll not have sparks during connecting umbilical to box 2
ZenMod,
Can you tell me a little more about these 'bleeders'.
Regards,
Chris
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Old 18th November 2010, 11:17 AM   #466
Tea-Bag is offline Tea-Bag  United States
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I beleive he means using a 3-10W 2-2.2K resistor across positive to ground and from negative to ground across a set of caps in the power supply. When powered off, they will bleed down the voltage and discharge.
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Last edited by Tea-Bag; 18th November 2010 at 11:20 AM.
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Old 18th November 2010, 11:27 AM   #467
Zen Mod is offline Zen Mod  Serbia
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yup
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Old 18th November 2010, 01:40 PM   #468
Chad is offline Chad  United States
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Quote:
Originally Posted by Backbones View Post
ZenMod,
Can you tell me a little more about these 'bleeders'.
Regards,
Chris
Chris,

Attached is a picture of the placement of the bleeder resistor.


As for power and earth grounding here is what I choose to due. Please if someone sees something wrong with this please voice your concerns. I want to be safe as I have kids in the house.

The power supply chassis is directly grounded to earth. From the chassis it goes to the power rail grounds buss bar thru a CL-60. Running from the power supply to the Amp chassis are 4 wires carrying the V+, V-, Power ground and a direct earth ground. In the amp chassis the earth is hooked to the chassis and nothing else. My star ground for the pcb grounds is on a buss bar connected to the power ground. My thinking was very close to Zen Mods but I wanted the power supply to have a chassis ground at all times incase it somehow got turned on without an amp plugged in. The amp is dead silent with no ground loops. I believe this fully protects both units but please let me know if you think different.
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File Type: jpg Bleeder.JPG (131.6 KB, 297 views)
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Old 18th November 2010, 02:17 PM   #469
AndrewT is offline AndrewT  Scotland
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In a combined amplifier and PSU with a metal chassis the Protective Earth (third wire in the mains cable) must be permanently connected to chassis.

The option to use a CL60 is for the Audio Ground to Chassis connection in lieu of a direct wire connection or a Disconnecting Network.

You do not put a CL60 in the PE to Chassis connection. You are not even allowed to rely on a soldered attachment for this permanent connection.

When you separate the PSU from the metal chassis Amplifier, then my interpretation is that the metal amplifier chassis must be permanently connected to PE. Again no CL60 in this connection.

The CL60 and Disconnecting Network can be used to connect all exposed conductive parts to Safety Earth. Safety Earth is an attachment to a PE protected Chassis.
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Old 18th November 2010, 03:10 PM   #470
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OK Andrew.
Very clear. So essentially, although we are using two metal boxes they should be regarded as one and need to be electrically connected together as a single functional unit so their earthed surfaces are continuous.
Regards,
Chris
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