power supply problem

[Harry Bissell]

Benefit of switching regulator...

Very small size of magnetics (transformers need MUCH less core at 100KHz than
60Hz)...

Very high efficiency (often +90%) so there is very little heating...

Ripple is a very high frequency so filter components can be smaller...

BUT!   That ripple is almost impossible to stop... it may get into high
gain audio, make VCO's sync to subharmonics of the switcher frequency...
generate RF that clobbers radio receivers nearby (like wireless mics...)

So most of the DIY types prefer the heavy and predictable linear power
supplies....

H^) harry

BTW... i regularly use a SWITCHING power supply on my bench... its an enclosed
frame Lambda supply, + / - 12V at 1A each.  I do not usually have any problems
tracable
to that switcher... so if you have a high quality supply you may have no
problems at all...

Kenneth Martinez wrote:

> > Replace the 7912 with new one. Also check those 15uF caps (I guess they
> > are tantals wich are prone to failure). I'd replace all elcos in PSU
> > (hey how old they are? - they go dry over the years)...
>
> how long do they usually last?  this synth's about 15 years old and all the
> parts look to be original
>
> > ... add some 10-100n ceramic caps...
>
> ok, I'll "refurbish" this PSU by replacing & adding parts as you
> suggest...local stores don't stock the 7912 so this'll have to wait while I
> order the parts :-(
>
> Also...I'm curious - what's the benefit of this "switching" type of power
> supply versus just having the first transformer with all the needed
> secondary windings?  Does it just replace the 60 Hz ripple with a 30kHz
> ripple (or whatever frequency it switches at)?  The voltage regulators
> still have heat sinks on them, so what's the advantage?