Simple/dumb question here..
I am building a low (24vdc) voltage hybrid tube headphone amp. I am mounting the board in an aluminum case. The power supply is stand alone (like a printer supply) so input is just 24vdc and gnd.
Should I tie the dc gnd to the metal box or leave the board and dc isolated from the box.
Looking for safety and noise reasons. I know its only 24v, but dont need any tingles, especially if its humid, damp, etc..
Thanks!!
I am building a low (24vdc) voltage hybrid tube headphone amp. I am mounting the board in an aluminum case. The power supply is stand alone (like a printer supply) so input is just 24vdc and gnd.
Should I tie the dc gnd to the metal box or leave the board and dc isolated from the box.
Looking for safety and noise reasons. I know its only 24v, but dont need any tingles, especially if its humid, damp, etc..
Thanks!!
Not a dumb question at all. Definitely tie the ground to the box. Not only will that provide you protection, it will also dampen electrical interference. Look up Faraday Shield or Cage. As a side point, all MR Scanners have a copper box that is totally sealed around the scanner to keep out stray RF Signals
Stan
Stan
One does need to be careful when it comes to input jacks and such - the case must not be connected to star ground more than once (except at RF).
Good to know, thanks. I was pondering that. I can Isolate the jacks from the case and maintain one ground point.
The Chassis MUST be connected to Protective Earth (PE).
This is compulsory for all class1 equipment. i.e. those fed with a three core cable.
All conductive exposed parts should be connected to Chassis.
This too is compulsory but very often is ignored.
The phono/RCA socket for the inputs and low level outputs has an exposed metal barrel.
It is required that we protect users by connecting those exposed metal barrels to Chassis and thence to PE.
This is to help prevent fatal accidents.
This is compulsory for all class1 equipment. i.e. those fed with a three core cable.
All conductive exposed parts should be connected to Chassis.
This too is compulsory but very often is ignored.
The phono/RCA socket for the inputs and low level outputs has an exposed metal barrel.
It is required that we protect users by connecting those exposed metal barrels to Chassis and thence to PE.
This is to help prevent fatal accidents.
I feel bad for guys like AndrewT as he has to just go from forum to forum on this site to answer my dumb questions 😀 thanks by the way!
Question on this though.. This is being powered by a wall wart / brick style premanufactured 24vdc smps supply. The AC side of the brick has a earth pin for the wall, which will obviously be used, but the dc out cable to it's typical dc wall wart style barrel plug is only +DC and -(GND). How can I tie the chassis to PE when it doesn't exist?
I intend to connect the DC GND to the chassis as if it was a PE line, and star the board and all components from there. I will not isolate rca barrels from the chassis if it is unsafe. Is this not correct?
So like this? (forgive the kindergarten level drawing..)
The only thing I was going to do different was take the (-) of the rca jacks back to the board, isolated from the chassis at their mounting point, as the (-) (dc gnd) on the board will still be tied to the chassis, along with all other dc gnds.
The only thing I was going to do different was take the (-) of the rca jacks back to the board, isolated from the chassis at their mounting point, as the (-) (dc gnd) on the board will still be tied to the chassis, along with all other dc gnds.
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Your bit of equipment is not mains powered. You have used a piece of manufactured equipment that gives you an isolated low voltage supply. Your piece of equipment is powered by a "deemed to be safe" LV supply.
Your equipment does not need a Mains PE connection, if it is not connected to the Mains Power.
Now to the exposed Metal parts on mains powered equipment.
These are usually part of another circuit or knobs & screws.
The circuit parts must remain part of the circuit. Get the audio circuit working, that means isolated from the Chassis.
Then look for a method of complying with the safety requirement.
I use the Main Audio Ground (MAG) as my sole link to the Chassis and thence to PE. That one link ties in all the other Grounds and Returns that take a reference from the MAG. But with one important proviso. All the subsidiary links must, if exposed to Fault Current, be capable of passing that Fault Current until after the Mains Fuse has ruptured and the arc extinguished.
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So I am understanding correctly, the DC gnd from the SMPS is the same as the MAG, as it is shared with the same plane, so find one point to tie the audio grounds and dc ground to the chassis, and ensure all ties to this point are heavy enough to last longer than the fuse, correct?
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