Recommend me a transformer

[ed8150]

I was having trouble locating a transformer for a project(see http://sound.westhost.com/project04.htm) it needs to be a 28-0-28v center tapped transformer that has a 120vac @ 60hz primary winding. I have searched digikey and mouser without success, but perhaps this is due to my own incompetance and novicehood in the sphere of electrical engineering. Thanks in advance for your help,
Edward

[Tweeker]

Starscream is teh win!

Not the cheapest answer, but close to what you asked for. You might try Plitron.

[xplod1236]

Try partsexpress.com

Here is one that should work.
http://www.partsexpress.com/pe/showd...number=122-625

[AndrewT]

Hi,
the tweeker suggestion is shown as a 30V centre tapped. This is 15Vac & 15Vac connected together. Wrong voltage.

You need a 28Vac + 28Vdc or 56Vac centre tapped.

Note that project 04 reminds you that 28V is a bit low so you may need to up your voltage slightly.
Try 30Vac + 30Vac or 60Vac centretapped. You will find that 300VA 2 * 30Vac a lot easier to source.
This higher voltage will give 41Vdc to 44Vdc at the PSU, so watch your component ratings.

When you measure the AC voltage across the windings with no load you will find a voltage that is a lot higher than the manufacturer's rating due to transformer regulation. This can vary from as low as 4% to over 20% for small transformers. Your 300VA will probably be about 5% to 6%.

[AndrewT]

Hi,
the parts express should be AVEL Y236751 330VA 30V+30V TOROIDAL TRANSFORMER
The 25+25 is just a bit too low.
If you want to use the 60W amp into 4ohm speakers you should up the transformer rating to match.
60W8R mono needs 90VA, stereo 180VA.
120W4R mono needs 180VA, stereo 360VA.
So, that 330VA 30+30 will drive a pair of 4ohm outputs.

[Tweeker]

Ack!

I looked through the PE site trying to find something but didnt have luck. Couldnt directly navigate to those transformers. Should have searched.

I'd probably go with one of the 330VA transformers for $47.67. Either 2*25VAC or 2*30VAC. 2*30VAC matches project most closely. 6% regulation is claimed. Dual secondaries are fine, you dont need a center tap.

If your planning to make an unregulated LMxxxx series chip amp use 25VAC, 30VAC would require regulating it.

[Tweeker]

Note that Parts Express has a $50 minimum order on International shipping. USPS is probably the best choice for shipper, UPS charges outrageous brokerage fees.