# Thread: Anyone here understand volt-amps?

1. ## Anyone here understand volt-amps?

I hate to admit it, but its something I dont have a firm grasp of. I bought a 2.1 Yuanjing amp kit. I think its 28 X 2 and 68 X 1. I want to use a toroidal transformer for power.

I dont have much info on the amp, I want to use the right transformer.

Well .

2. I may be a bit rusty on this but I believe they rate transformers in volt-amps instead of watts because the voltage can be out of phase with the current. In that case P = I X E wouldn't be accurate. In your case if its feed by your local hydo, current and voltage should be in phase and you could just use P = I x E. Power (Watts)= Current (Amps)x Voltage (Volts). Power in equals Power out in a transformer, ignoring the little bit of lose. I hope that helps.

3. Dude thanks for the answer.Something static like a light builb watts roughly equals volt/amps, something dynamic like the amp where the voltage and current is always changing it has a lot to do with phase. A/C isn't my forte, DC I know really well. I could stick a big one in there to cover my ass but I'm trying to keep the amp as small as possible. I guess I need to look around the net and study some more.

4. If I read your post correctly you're going to use this transformer to step the AC mains down and then convert that to DC to run your amp. You'll need a bridge rectifier that can handle what ever current is needed by your amp and a big honking filter capacitor. Some kind of DC voltage regulation would be good too. If you know the DC voltage output of the bridge rectifier there is a formula to figure out what AC voltage the transformer needs. Once you have the AC voltage and current needed on the secondary of the transformer you have your volt-amps. You'll want some extra room to play with so the transformer should be rated higher than your calculated values. Like I said though, I'm pretty rusty with this stuff, its been a long time since I ever had to sit down and design a power supply circuit. I've built a few low power units to replace dead power packs and pretty well just used what I had in my electronics junk drawer.

5. It has a 25 amp bridge rectifier on board. The amp will operate from 5 to 26 volts. I'm looking for a 26 volt transformer with a center tap so I can have the positive and negitive rails. This is the amp, Yuanjing I paid around \$26.00 from ebay.

6. OK, there you go, most of your work is done for you. All you have to do is look though the specs for the maximum current it might draw.

7. All you get is the amp. No schematic, no specs. no wiring diagram, no box.
Oh well.

8. Looking at the picture, I'm thinking you may want to put some heat sinks on those IC's mounted vertically along the back side.

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