Re: DELTA - New PS-fixed ground or iso switch?


"Frank Stearns"
> "Phil Allison"
>
>>> It's finally time to wire up the new International Power linears I
>>> picked
>>> up to replace the original, now rather feeble Soundcraft supply feeding
>>> my 16 frame Delta.
>>
>>> I have two new open frame supplies (+,- 24V @ 2.5 amps each side dialed
>>> down to 17V, plus a 1A 48V supply).
>
>
>>** The makers data only specifies a +/- 5% adjustment range - but you
>>are claiming - 30 % ???
>
> Actually, the specs for this particular supply say "18-24V";


** How about you post the model number them ??.

Your claim above that it was 24V, 2.5 amp one is false.



>>Also, Soundcraft PSUs have a "voltage tracking" circuit in them, to
>>prevent the positive and negative DC voltages getting significantly out of
>>balance during switch on or switch off cycles *OR* if one DC rail goes
>>out due to thermal overload etc.
>
>>Without this tracking circuit, it is possible to seriously damage the
>>desk.
>
>
> This particular original Soundcraft supply is pretty simple. It uses 317
> and 337 regulators in TO-220 cases with the standard half dozen or so
> caps, diodes, and resistors around each device.


** So it is a POS baby size PSU - not a real one.

The CPS 150 and larger ones have a tracking circuit.


> I'm not sure that the new supply offers cross tracking either,


** Better ask.


> but they do mention their "anti-latch" circuit which is supposed to
> prevent uneven
> startup problems.


** Right, like when the + supply forces voltage into the - one.


>
> I know what you mean about damage to the desk -- in some of their later
> consoles Quad Eight strapped across a pair of Lambda +/- 15 supplies,
> floating the commons and making a common from the plus rail of one supply
> tied to the minus rail of the other to develop +/- 30 V. They'd adjust
> them down a touch to get 28.6 V. (Every module had the rails pass through
> 1N4002 diodes.)
>
> If the positive box shut down the coupling caps were reverse biased and
> you'd find capacitor confetti all over the inside of the console. Kinda
> sickening to pull a module and see a bunch of naked leads sticking up in
> the air and no sign of the 330 uf cap that used to be there except,
> perhaps, a few scraps of the thing dangling off one of the lead stubs, or
> the more hearty ones simply blown apart but most of the material was still
> there, just no longer tucked inside the little can. (These were the
> Sprague "Atoms" in the orange/yellow cases.)
>
> This happened to me once during a mix session, and happened to at least
> two other QE clients when I was at QE. I got only a cold stare when I
> suggested to the chief engineer that some sort of protection should be
> installed if they were going to use supplies in this configuration.



** At the VERY least, fit reverse polarity protection diodes across each
rail.





............. Phil





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