Double Regulated power supply for Mic Pre

Ok,
I am going to be building some mic pre's with +24V single ended power supply (guess which! ) The plan is to have a separate power supply that feeds +24V, +48V, maybe +5v to any number of cards that may fit in one chassis. My questions is: After the regulated "outboard" power supply, does it make sense to have another set of regulators on the mic pre board itself? More is better? I seem to vaguely remember hearing something about this...

If this is a good thing to do, how would I go about it? Since the input voltage should be reasonably regulated already, do I just duplicate the entire supply on the board? I would think that I might be able to just toss the regulator and maybe a couple smaller filter caps, plus a couple R's and diodes...

What do ya think?

Ian

if you decide to go down that path, you will have to find higher voltage regulators for the first stage - if you are using 78XX series regulators they need to have a supply voltage that is higher than the output voltage or they will drop out of regulation, so you would need for instance to put a 9 Volt regulator in the first stage, followed by a 5 volt regulator on the mic pre board, for the 5 Volt supply. This of course may also mean upping the transformer secondary voltages to feed the first stage regulators, and if necessary the filter cap voltages as well.

You may get lower noise by using two cascaded voltage regulators - assuming the noise of the regulator itself is low... The LM317/337 should be better than the 78/79XX regulators to use on the individual boards. Remember that you need 3-4V to drop accross the regulator.

Best regards,

Mikkel C. Simonsen

You can also get better sound/lower noise by using emitter followers with a big cap. You only loose 0,7V by this.

Yes, multiple Vregs are a good idea. The LM3X7 are as good as the more expensive LTs in my experience. And much better than the 7XXX series. They work best with a healthy drop between 'em, at least 4 volts. so you need to feed a 24V Vreg with 28V. Maybe start of with a LM317HV or TL783C (max 700mA! And NO cap on the regulator leg!)

The closer the Vregs are to the circuit/amp the better. Decoupling and grounding scheme are just as important, if not more, as the choice of the Vregs.

A circuit is only as good as the power feeding it. After all an amp is nuffin' more than a modulated powersupply :wink:

You can compensate for the voltage drop of an emitter follower by floating the earth of the voltage regulator up with a diode.

Right. But loosing 0,7V rarely makes any practical/audiable difference.

Check out this idea:
http://www.wenzel.com/documents/finesse.html

Its a shunt regulator for low current stuff. Cool idea, idunno how well it will work.

That's great Brad :thumb:

A good and easy way to clean up a Vreg..

I think Tim of SCA is doing this on his N72 kits these days. I think the onboard regulation is for use with the PS02 which is a bi-polar +-27V. The PS01 is +24 only.

You can check out his forum for details.

Steven