Placing a voltage doubler after a regulated power supply?

I was looking at this new 500 series preamp from Shadow Hills and am curious as to how they convert the 16v standard of api 500 series racks up to 24v. Do they just place a voltage doubler on the preamp card along with 24v vreg's and associated circuitry?

you can check it out here...

http://www.vintageking.com/s.nl/sc.18/category.533/it.A/id.5730/.f

Looks like an interesting year for 500 series rack owners. A-Designs and Purple are also in on the action it appears.

Some switch-mode step-up converter would be the easiest and most efficient way to do this..

Jakob E.

Hmmmm. Something not quite right here.
It's unlikely that the designer would use a switch mode supply right next to the mic amp; he seems to know the difference between steel and mu-metal lam transformers, so he should know all about spurious interference from switch-mode power supplies, and the switching of 16V up to 24V is hardly worth the trouble.

Please tell me I'm wrong! :roll:

To get decent overload margin on class A (or class A/B as they state)descrete amps it's a whole lot easier to use the 48V phantom power rail.

Im not sure what the API 500 series power supplies consist of... i'd be hesitant to try and run 11 modules off the 48v rail alone but maybe thats what they have done.

Would it be feasible to even consider a voltage doubling circuit with vregs to obtain 24v off the 16v rails?

Voltage doubling can only be done from AC or a pulsing DC signal. you can't charge a cap higher than the DC rail feeding it without going with a flyback setup or the like.

As Svart says, you can't "double" DC unless it's pulsed. You can increase DC using a charge pump circuit (which uses pulsing). I've not seen them used much, but they're out there.

Hmmm, beats me! :?

Peter or Pucho should be here shortly...

Peace,
Al.

I can't guess how there could be anything other than a cleanly isolated little switcher in there.
Oh... NOW I get how they've done it...
YOU supply a 9V cell in the back ! Right ? ! ! :wink: :green:

I investigated the idea of running single ended 24 off of bipolar 16 for this very purpose and a well implemented switching chip from N*ational Semi seemed to be the only reasonable way to do it. I really don't think you could run anything off of the phantom supply and there are per-module current limits on the main bipolar supply as well, so efficiency is definitely a factor to consider. Some of switcher chips are excellent in this regard - even if you need to invest more money in suppressing the noise. Anyway, here are the other ideas I toyed with - some seem very silly, I know.

1) If you call -16V your 0VDC reference then you have +32 which can be clamped down with a zener. Simple enough until you try and interface with the rest of the world (and the rest of the units in the rack :shock whose ground potential is 16 volts higher than yours! Floating is not an option

2) With an op amp circuit it is not hard to reconfigure it from running on positive only to bipolar supply, since it is in many cases the potential difference between the two rails that matters most. 16 plus 16 equals 32VDC. That's more headroom than +24, yet close enough that you probably don't have to rebias or pick higher voltage devices. Just remove a bunch of the ground connections and replace them with a negative rail, re-do the coupling and power application, and so on...

Naa, I don't think that is what they do - it would be gross misinformation to claim that single-24V is "better" than dual-16V. At least I hope this isn't it.

btw: The improved max-out-before-clipping-headroom in running +-24 over +-16V is only a meagre 2.5dB or so. Hardly any reason for going through all this trouble for that amount of extra output level (which is probably not even used after all)?

Jakob E.

buck/boost/flyback converters can be implimented to do the job cheaply and easily... just separate the ground plane and make sure you filter the output heavily. I use these in sensitive video amplifiers and they work just fine.