Cgs synth

>I'm going to be using the +/-15v psu's to supply some of the digital
>modules in my system to keep noise away from analog module power
>rails. Is there any reason why I couldn't attach the regulators to
>the pcb with short (50 to 100mm) flying leads so that they could be
>remotely mounted on a single large heatsink, with insulation washer
>kits to keep them electrically isolated from each other. I'd guess
>that they could be good for 600 to 800ma per rail in this
>configuration.....

You need to keep the 100n capacitors physically close to the regulator, so
if you remote mount them, solder the 100ns directly to their pins.

>Also, could you explain more fully why I would need to go up from
>15v-0-15v to 18v-0-18v transformer for higher current outputs? I
>thought that with full wave rectification you get a higher DC
>voltage than AC anyway - somewhere near 1.3 to 1.6 times higher?

square root of 2 is the figure. The problem is you lose a lot of voltage in
the process - 1.2 across the diodes and another 3 across the regulator. Also
the output from the capacitor is not a straight line. The higher the load,
the more it droops between cycles. The BOTTOM of this droop must be higher
than 18V for the regulators to work propperly.

Also, the no-load output of the transformer is irrelevant (apart from
determining the minimum voltage for the electros), as you won't be running
no-load.

If you really wanted to, the use of low-drop voltage regulators and schottky
diodes would save you a couple of volts of losses, allowing a greater load
to be taken from a 15-0-15 transformer.

Ken
_______________________________________________________________________
Ken Stone sasami@... or sasami@...
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
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