Toroidal Transformer hook up.

[fschris]

I have a noob question ...I want to hook a 25VA 15V toroidal transformer to a PCB for a Audio amplifier. The input on the PCB board has 3 pins. The center pin seems like a ground. The transformer only has 2 wires for the 15V ... Do I need to have a 3rd wire coming off the transformer?

[thaumaturge]

IF the current draw is low (Like for driving op amps) then you can use a rail splitter circuit to create a virtual ground. National makes an IC for that specific purpose. I wouldn't try to use one to drive a power amp though. Also 15VAC split and rectified would only give you like +/- 10.5 VDC rails. If you still wish to try do a google search on rail splitter circuits.
Doc

[fschris]

I have no idea what you are telling me... lol

[DF96]

What does the circuit expect? Does it have positive and negative rails, with ground in the middle? If so, it may be that it expects a centre-tapped secondary on the transformer. Have you bought the right transformer?

[thaumaturge]

Originally Posted by fschris

I have no idea what you are telling me... lol

Likely the circuit you are attempting to hook to is probably expecting plus and minus DC voltages and a ground... A transformer outputs AC. Simple answer; It's not going to work.
Doc

[fschris]

Okay help me understand this for instance... For example if you look at this basic amplifier board on ebay and scroll down to the pics... for the input it states 26v-0-26v ... and the PCB states 26V GND 26V...

However I have looked on Antek and other sources for Toroidal Transformers and none have outputs with a ground... that is my confusion.... I Have not found one. I see the AC iputs for the transformer and the out puts are always like 2 or 4 or 8 wires but none are a ground? I am missing something.

Example PCB board:
150W+150W TDA7294 X 4 BTL+Speakers protected board | eBay

help this Noob!

[CanAm Man]

Yes. You probably have the wrong transformer. You need a transformer with two secondary windings. The required output voltage of these windings will be dependent upon the amp you select. If the amp needs a +V, gnd and -V you get this through the two secondary windings (four wires), by connecting one wire from each of the secondaries together (effectively giving you THREE output wires from the transfomer) and then connecting these PAIRED WIRES TO THE GROUND TERMINAL.

Will be very difficult to answer your question more succinctly, unless you provide the specifics on the amp you intend to build--photos of the specific PCB and the schematic would be very useful.

Are you certain the amp PCB has an "in-board" rectifier and PS filter caps? If it does not, you will need more parts to provide DC to the amp modules.

You're asking a VERY ELEMENTARY question--you certain you want to play around with possibly lethal transformer wiring?

[audiofan]

I saw the picture ....

I tink you need a transformer with a " center tap " it is a third wire that comes from the middle of the winding.

This way you get one common point ( the center tap ) and from this common point you get 2 equal voltage.

if you can post a picture of you transformer it may help somebody to help you.

I your transforme has no center tap ( only 2 wires ) you may connect it betwen common point and one side ( leave the third screw with no connection ) The amplifier will turn on and work but DONT LOAD IT use only one chanel at low level .... you will have a chance to test the unit . DONT expect tu use it this way all the time, you will have to get a transformer with a center tap and of correct voltage. ( unit will be working on half wave rectification )

[audiofan]

ONE MORE NOTE did somebody told you something about HEATSINKING this unit will not work without a proper heatsink .........................

[fschris]

Okay so what you are saying is that "center tap" transformers have a ground !

also , no I am not going to wire anything up that could be lethal!

As for trying to figure out what I wanted to do I am not going to do it becuase it is above my level of understanding. I had a AV123 plate AMP that I want to use and it needed a Toroidal transformer, however as you can see I cannot find the proper power source.

Here is what I was looking to power.... I am selling it on ebay now.

https://skydrive.live.com/redir.aspx...78B797AFB!1649