+/-12V, 1A from Futurlec Board - Tell me how I screwed up...

[mydementia]

Hey guys.
A few weeks ago I was placing a futurlec order when I stumbled upon this:
http://www.futurlec.com/Mini_Power_Dual_12V.shtml

It looked like exacly what I needed to power my LXH2 (charge pump only provides 10mA - this circuit needs more like 30mA...).
I got it in the mail yesterday and fired it up this morning.  First I used a 16VDC wall wart for the input power - plugged into the LXH2 I saw +/-11.98V - pretty good.  Then I turned on the amp - all sorts of cyclic whining and buzzing... but excellent tone when I played a little...  So I tried a 12VAC wall wart I have lying around (unloaded ~16VAC).  I plugged it into the circuit and got +/-12V - cool.  When I turned on the amp there was a loud constant hum...

Am I underpowering the board for +/-12VDC?  Do I need to add more filtering?  Should I scrap it and use a RS tranny (http://www.radioshack.com/product/index.jsp?productId=2102494&cp) and call it a day?  (I got 6 of these trannies in a surplus enclosure I picked up recently).

Here's the schematic for reference:

What do you think?

Thanks for looking.
Mike

[Paul Perry (Frostwave)]

Well, 12 v AC is going to rectify to 16.8V peak - less say 1.6 for a couple of diode drops in the rectifier - now you have 15.2 peak - that gives you 3.2V headroom for the regulator.
Now I don't know whether your mains might be down 5 or 10% - or whether your mains sine wave is squashed by all the other switch mode supplies & crap hanging off the line - but it IS getting kind of marginal.