Transformer Newb Help

[nsimon]

Hi everyone. I just got interested in analog electronics/amplifiers. I bought a kit, soldered up my amplifier and rectifier; was all set to buy the proper transformer... But I can't seem to find a transformer that meets the specifications anywhere... (Also, I am slightly confused about the transformer terminology)

The instructions say I need a 60VA transformer with a 35V center tapped secondary winding. Am I to assume that the primary voltage is 120 V? Also, some sites just give current ratings and winding ratio. Would the equivalent winding ratio and current be 4(ish):1, and 2 amps?

Is 35V a strange transformer voltage or am I just bad at searching?


This is a link to the kit, which specifies the transformer.
http://www.electronickits.com/kit/complete/ampl/k50.pdf

Thanks in advance!

[mjf]

hello.
this kit uses a lm1875......there are many threads in the forums with examlpes......you can use the search button
or look in chipamps forum for lm1875.
or have a look at the datasheet.

.......the transformer is 36Vac centertapped (2x18Vac, this gives you around +-25Vdc)
or 30Vac(2x15Vac). powerrating 60va..........80va or more.
greetings

[tomchr]

Hi,

The AN-3218 from Antek Inc. would work. Though, being a 300 VA transformer, it's a bit overkill for your application. It wouldn't hurt any - well, other than your wallet...

You could also use an AN-1215. 100 VA at about half the cost of the 300 VA. It's a 2x15 V transformer so your max output power of the amp will be slightly lower than with a 2x18 V.

Typically, transformers have two independent windings rather than one winding with a center tap. Connect the two windings in series to form a center tapped winding. You have to watch out that you connect the "bottom" end of one winding to the "top" end of the other. If you connect them incorrectly, you'll end up with about 0 V out. And if you short out the windings, you create a short circuit (no surprises here).

As for the primary voltage. Well... That depends on what voltage you plan to connect the transformer to. If you're in the US or Canada with 120 V mains voltage, you need a transformer with a 120 V primary. 115 V would work too... If you're in Europe or elsewhere, where 230 V is the mains voltage, you'll need a transformer with a primary rated for that.
If you look at the Antek transformers, you'll see that they have two 115 V primary windings. Connect them in parallel for 115 V operation, and in series for 230 V operation.

Remember to include a fuse in the primary circuit.

By the way, I'm not associated with Antek Inc. in any way, shape, or form. I've just used a couple of their products and have been pretty pleased so far. You can find similar products at DigiKey Corp. | Electronic Components Distributor | United States Home Page, Mouser Electronics - Electronic Component Distributor, US - Electronic Components Distributor | Newark.com, www.jameco.com, and other places.

~Tom

[nsimon]

Thanks for all the advice! I'm going to go with the AN-3218 and hopefully, I can get the wiring right :0)