Help with choosing a transformer?

[CarsonPratt]

Hello all!
I'm currently working on my first stereo amp, the gainclone design from this website PA100 DIY 2x LM3886 in parallel gainclone audio amplifier. I am a beginner with diy audio, but am familiar with digital electronics as well as some analog. I have all the parts chosen for the amp, and designing my own boards was fairly easy compared to some of my past projects.

My only problem so far has been with the selection of the transformer to use for the power supply. I understand the requirements for the transformer as stated in the schematics on the website, but I haven't the slightest idea of where to look for actually purchasing one! The range of selection prices are immense, and I don't really know where to start.

If someone could point me in the right direction, or is familiar with this amp, please let me know.

Thanks!

[CanAm Man]

Originally Posted by CarsonPratt

My only problem so far has been with the selection of the transformer to use for the power supply. I understand the requirements for the transformer as stated in the schematics on the website, but I haven't the slightest idea of where to look for actually purchasing one! The range of selection prices are immense, and I don't really know where to start.


Thanks!

You can't go wrong with an Antek torroid transformer--lots of variations to purchase, at good prices. Same goes for Piltron.

Look for a dual 120vac primary (so that you can also use it for 240vac if needed). Also look for dual secondaries, so each winding can drive it's own respective power rail. Depending upon the speaker impedance you'll be driving (4 ohm or 8 ohm), 20-22vac secondaries are OK. I'd recommend at 300VA current capacity for a dual LM3886 amp.

[CanAm Man]

This is a good candidate, among others:

Antek - AN-3220

[CarsonPratt]

Thank you for the fast reply!
Ill take a good look at them and see what seems appropriate.

As for the current-cap, is 300VA enough? The one in his design is 500VA, but he did say that the power supply was a little over-kill. I will be doing the same layout with a total of 4 lm3886's (two per channel)

Again, thanks for the help!

[geraldfryjr]

I would go with at least AS-3428 with a dual PA100 design.
You won't get a full 100 watts at 8 ohms on a lower supply voltage.

This is something that gets a lot of debate as it is just my opinion.

Generaly you want at least 50% more power rating on the transfomer than the total amount of power that you wish to operate at.

So 300VA should be enough, anymore is over kill and a waste but if you plan on using a 4 ohm load then 400VA would be a better choice to allow for the extra current demand.
The AS-4428 would be the one I would choose.


jer

[Firebat]

I was looking at the 4428, seems like a good choice.
Ill probably wait a couple days before picking it up, but in the mean time thanks! Your help is much appreciated

[CanAm Man]

I must have missed that part of the discussion, where you talked about going with bridged chipamps. I'd forego my comment about a 300VA transformer, and I'd go to something heftier, like a 400VA or 500VA model.