Transformerless Bipolar Power Supply?

[sta63bmx]

The Question: Can you use a full-wave bridge rectifier with the 120VAC coming out of the wall, attach the neutral and hot to the AC pins, and then get positive and negative rectified electricity on the other side, and then feed it to your filter stages to make a bipolar power supply?

Another Question: Would the earth ground act like a center tap and be about in the middle of those two voltages?

Or does this not work because you only have one "leg" of AC instead of the two coming off a center-tapped transformer?

I want to build a circuit with the LM3876 audio chip and it needs bipolar power.  The voltage available from 1:1 transformed wall power is more than enough, and it could be filtered, rectified, and then set up with voltage regulators.  What am I missing about the procedure of rectifying AC into a bipolar power supply? 

[Joecool85]

Not totally sure how to answer this one, but over at ssguitar.com we have a couple people that are actually experts in power supply building/design and I'm sure they could answer your questions easily.

[The Tone God]

The Question: Can you use a full-wave bridge rectifier with the 120VAC coming out of the wall, attach the neutral and hot to the AC pins, and then get positive and negative rectified electricity on the other side, and then feed it to your filter stages to make a bipolar power supply?

NO!!!!!!!!! You should not and cannot connect directly off the AC supply without a transformer. You need some kind of galvanic isolation from the AC supply or bad things WILL happen.

Andrew

[jrem]

The Question: Can you use a full-wave bridge rectifier with the 120VAC coming out of the wall, attach the neutral and hot to the AC pins, and then get positive and negative rectified electricity on the other side, and then feed it to your filter stages to make a bipolar power supply?

NO!!!!!!!!! You should not and cannot connect directly off the AC supply without a transformer. You need some kind of galvanic isolation from the AC supply or bad things WILL happen.

Andrew

You need an isolation transformer to "disconnect" your power supply from the mains.  Look at it this way . . .   without the transformer, if you're hanging onto the strings, and your amp is grounded (real ground, the three prong type) and you're non isoloated ps has a short to hot (or if it shorts to hot and your neutral isn't isolated, pretty much the same thing), you are making a direct connection with the hot lead.  The transformer isolates you from the mains. The ground is ground, and has potential with neutral, but both can carry the hot main.  Use the transformer.

Second question:  no, you can not use ground as your center tap with a 110VAC single phase circuit.  Black is hot, white is neutral, green is ground.  110VAC is between black and neutral, and between black and ground, but what's the diff?  Ground and neutral may have potential between them, check it with an ohm meter.   Ground to ground should never have any potential, white to white may have several volts from point to point in your house.

Use a transformer, they're cheap.

[Processaurus]

I played through an old "airline" tube amp at a friend's house that shocked the hell out me because it had a "hot chassis", ie no power transformer.  Made back before UL... anyway, don't do it.

[sta63bmx]

Thanks for the info.  I really appreciate it, guys.  So at the very least you need a 1:1 isolation transformer so you aren't directly coupled to the mains?  And if you're gonna use a transformer, might as well look for one closer to the voltages you want.  LOL @ the hot chassis.  You mean like the polarity switch on my Ampeg?  Scary stuff!