wall wart power supply for ssl comp ??

I want to power my next ssl comp with an external power supply
it has 18V AC / 1A at the output

can I use it to power the ssl comp??

there are just 2 leads at the connector (no "center tap")
so how do i get the 0V potential ??


thanks
mat

Use a doubler? I guess the SSL needs +/- something?

If it does, just use a 2 diode doubler instead of a rectifier bridge.

Best regards,

Mikkel C. Simonsen

I don't have much experience in building power supplies...

is there a simple way to convert the two ac leads coming from the external trafo into 3 leads (2x ac 18V , 1x 0 V)

so I can leave the pcbs "as is" and just connect the 3 leads

here's the schem. from the ssl ps :

Hi Matthias,

Peter Purpose linked to this schem from Roll Music a while back:

Roll Music +/- and 48V PSU

Just ignore all the +48V stuff at the top of the picture- look at the bottom circuit. And take the output from after the rectifiers. You may want to use larger smoothing caps than in the original SSL schem because this is only half-wave rectification. This schem has disappeared from the Roll site, so I've bunged it up for a while.

Also, have a look at this Rane schem:

Rane PSU example

Your 18Vac transformer may not get you all the way to +/-15V because of half-wave rectification. The smoothing caps will only be charged half as often, and depending on the no-load voltage of your "18Vac" transformer, its output current rating, and the size of the smoothing caps, your output voltage may not be enough to supply the +/-15V regulators (they need a good volt or so of "dropout" voltage to function correctly)

It may be an idea to knock up the half-wave rectifier and add some smoothing caps and see what sort of voltage you get under no-load and load conditions.

Mark

It looks like just connecting one wire from your transformer to the center tap, and the other to one of the remaining terminals should work. But increase the smoothing caps to double size. And remove the meter light.

Best regards,

Mikkel C. Simonsen

thank you mikkel !!

I'll try it tomorrow..

increasing the caps to 4700µ should be enough...


mat

I'm not sure that this will work.

There is a wierd issue with regulator latch-up if one side comes up before the other - which it does with single-secondary double single-rectified supplies.

Try it, if you really need to use external transformer, but don't expect predictable results.

You should rather build an external trafo box with a suitable transformer - or try sourcing a symmetrical wallwart

Jakob E.

here is my ssl ps circuit for powering from wallwart. slowstart neg. voltage to prevent regulator latchup. works fine!

steff

http://home.t-online.de/home/micro.wave/forum/ssllatchup.gif

Yes, something like that will do it..

Jakob E.

I have used the circuit with LM317/337s and have never had any unstability. I do remember reading about the 78xx/79xx problem here before though. I seem to remember that some brands worked and some didn't?

Best regards,

Mikkel C: Simonsen

thank you all!!

I'll just try it the next days and post the result...

I just set it up like mikkel said and it works fine... no problems at all...

Try switching the power 25 times. If it works every time then it's OK.

Best regards,

Mikkel C. Simonsen

yes. And let it discharge completely between tries - some 30-40 sec. Make sure that it still compresses every time - it will probably still pass audio even if psu is halfway hanging..

Jakob E.

I tried it more than 20 times... no problems at all...

maybe the problem only occurs with some special 79xx regulators ??

a few months ago I had some problems with 79xx regulators that I bought
at "reichelt electronics" here in germany...
now I'm using some regulators from "SEC"....

Yes, some 79xx's are clearly much more sensitive than others. So is most of the 78LXX and 79LXX's I've tried..