3 or 2 prong on amp connection to AC

[gychang]

I have modified Helder's t-amp and will house in a wooden case. My power supply has 3 prong connected to wall and when I test the whole setup in naked fashion (out of case), it works well without hum.

Should my final project have 3 or 2 prongs?

gychang

[AndrewT]

Hi,
all exposed conductive parts must be connected to Protective Earth (PE).

[fingerboy21]

Please make sure that you know the code for wiring units. Make sure you follow safety regulations. Life can't be replaced.

Good luck and be safe!

[parb]

id also suggest you use a grounded three prong connection to the power grid.
for less than 1000VA circuits it is permissable in the US to use two prong power but special care has to be made on the power supply to construct it from electrical shock as well as from stored energy in the power supply. in the US this is regulated in article 725 in the NEC manual (which you can find here for your state: bulk.resource.org )

how about this for a simple rule of thumb: if you designed and built the power supply -you are more likely to having made a design that requires three prong outlets than not. f you got it from someone else it should be listed with a UL marking if the power supply complies with the category I, II or III standards.

[Arty]

it will not hurt to use 3 prong ones in any imaginal situation.

[gychang]

I will use the 3 prong. I recall sometime ago on another audio equipment, hum went away when the third prong on the outlet was cut off. Probably dangerous thing to do...

gychang

[Boofers]

Originally Posted by gychang

I will use the 3 prong. I recall sometime ago on another audio equipment, hum went away when the third prong on the outlet was cut off. Probably dangerous thing to do...

One good way to reduce ground loop hum is to separate earth/chassis ground and circuit/signal ground via 4 components connected in parallel between the two grounds. A resistor (~5-10 ohms), a diode from chassis to signal, another diode from signal to chassis, and a capacitor (~0.1uF). Be sure not to accidentally connect signal ground to chassis through such things as input/output connectors.