Red Light District Amp Screen Reg

[mach1]

On the face of it, a simple TL783 (150v zener limited ) screen reg would seem a more elegant solution than the TIP50 / LM317 Maida reg employed by SY.

Given that SY is infallible, what am I missing ?

pm

[SY]

I used TIP50 (or any other similar HV bipolar or FET) and the 317 because they're cheap and easy, and it performs well. I've also never lost one in actual use, just in doing stupid things poking around with probes. I do these things in order to show my fallibility.

There are a lot of other good regulator solutions. I've never used the TL783, but it would probably work OK if you could arrange it to survive turn on and turn off. The sweet thing here is that the screens are high level and common mode. Makes life easy.

[mach1]

Thanks - I'll give the TL783s a try.

pm

[alexmoose]

Hey SY,

I have been meaning to impliment your regultor in a phono preamp design, I need to regualte 300v at 4-5ma, how would I modify your design to fit my needs? or do I just have to mess with the pot in the circuit. Thanks so much

-Moose

[SY]

You'll want something a bit quieter for phono use. But that's easy to do with just a few extra caps and diodes. Have you seen the original Maida National Semiconductor applications note from where this design derives?

[alexmoose]

yes, actually, I read it right before I posted,

so you are seggesting that I use something closer to what is in documentation?

http://www.national.com/ms/LB/LB-47.pdf#page=1


I liked yours because it seemed to make more sense to me as I have a limited knowladge of semiconductors. but the way I see it, your design does not have the error correcting feedback created by the diodes, am I right? also, adding more caps, should I just put two caps on either side of the regulator circuit? I have (at least) thirty 680uf 200vac capacitors (the fruits of disecting 20+ computer power supplies) I could put two of those in series on each side of the regulator.

Would all the resistor values stay the same? I am still sketchy on what some of them do, but I really want to learn how to harness the power of Linear regulators.

The orignal design uses a 5W pot where yours does not say, is this because of the resistor network that you have implimented?

Thank you so much, you've already been extreemly helpful

[SY]

Actually, the diodes aren't for feedback, they're for protection. Nominally, anyway; I've still popped lots of devices during testing and probing around, though I have never lost one in normal use. The feedback is from the resistor going from the sense terminal to ground and the resistor going from the output terminal to the sense terminal.

Yes, you can use something like figure 1. The caps you have are probably way too large for this- you want values like 10-50uF. You can also get by without the Darlington; a reasonable-hfe pass device like TIP50 or even the NSD134 (no longer made) will do fine for low current service. You could even use a MOS device like IRF820. I'll sketch up something suitable later tonight.

The other alternative is to use a simple two transistor regulator. For a phono stage, the load is constant (class A), so you don't need fabulous dynamic regulation, just a good, steady, low-noise rail. See my article on the Heretical preamp for an implementation that will work fine for you.

[alexmoose]

Thank you very much for using your friday night to help out a punk college student!

-Moose

[SY]

I always liked Ann Arbor.

[alexmoose]

Its a Rockin' town, My brother goes to school there, but I am 530 miles north west of there in Lovely Houghton, at Michigan Technological University. 6600 students, 4000 in engineering, 1500 students are women.....