I just read the choice of power supplies... So let me get this straight, you're supplying 15 volt linear regulators from a 12 volt halfwave rectifier and you expect it to work at all? The instant you apply any load to that the linear regulators will stop working because the ripple voltage will be massively bellow it's dropout voltage especially from a half wave rectifier! Even LDO's wouldn't work properly in this situation you're working three volts under your regulator voltage at it's rated load! Might as well skip the regulators altogether cause they're not serving a purpose on anything other than a fraction of the supplies load at some perfect supply voltage.
Hey Sceadwian, I know what you're saying but let me try to explain myself. Although I admit to being a newbie at this.
I'm using a 12VAC-1000mA wallwart and drawing 250mA from it. Because I'm not drawing full load from the wallwart, it is outputting slightly higher voltage since it's rated 12V for full load. In my case (with our nice 122.5VAC mains supply), it is actually outputting 14.2V. This is RMS, so the peak to peak is actually about 40V (14.2 x 2 x 1.414) and measures exactly that on the scope. After diode drops on the halfwave rectifier and filter capacitors, I measure 19V and 18.5V going into the regulators with about 1V of ripple. According to the datasheets, the LM317 and LM337 require a voltage drop of about 1.6V at the load I'm putting on them, making this design totally acceptable I thought.
What I didn't account for was that a few of my customers are getting supplied with way less than the 122.5VAC I experience here. I never knew it varied that much, but thanks to this thread.. I know better.
I can't move to CT transformers as you suggested as much as I'd like to, because I'm selling these things and cannot afford any CE or UL certification (see https://www.electro-tech-online.com...tuff-that-plugs-into-mains-120-240vac.123506/).
So far the only solution I'm really seeing is moving up to a 14VAC or even 16VAC wallwart, but I'm open to any other solutions that will still let me sell these things legally.