Power supply

[brucetassin]

Hello

I need help, I'm not the brightest lite in the room.
I'm building an RIAA pre amp and I need a good clean power supply.
I found this circuit (Schem A below) in an old issue of Popular Electronics (June 1972). Its a NEG reference (I don't know if that's what to call it). I want to change it to a POS reference, (Schem B below).
The reason I want to change it is because I may have noise problems when I use it to power my pre which has a POS ref.
Q2 is what gives me the biggest problem, should it be a PNP?
Thanks for your help.

 

[Mooly]

I would say Q1 in the second image should be the PNP. Emitter to pos input.

How much current do you need ? The 430 ohm and 220 ohm series resistors seriously limit the ability of this one.

 

[Michael Bean]

I'm not the brightest lite in the room.

That's a pretty old and archaic design, maybe it's time to step into the 21st century.

First, what are the voltage / current requirements of the preamp? It's probable that a much better solution is possible using modern parts and circuit design.

Mike

 

[Mooly]

If its a low current single rail phono stage then a simple one or two stage shunt zener supply could give outstanding results. Dead simple too. All depends on the current needed and how much headroom there is (unregulated input to regulated output) as to whether its feasible.

 

[woody]

Or you might look at fig. 9.2 in the Tl783c application notes. My math isn't all it should be but I think R2 will end up being about 2.7 k and it's going to be dissipating about .6 W so I would think about using a 2w one there. If you want to try this I might mail you
one seeing as we are almost neighbors.

http://www.ti.com/lit/ds/symlink/tl783.pdf

 

[Ketje]

Hello

I need help, I'm not the brightest lite in the room.
I'm building an RIAA pre amp and I need a good clean power supply.
I found this circuit (Schem A below) in an old issue of Popular Electronics (June 1972). Its a NEG reference (I don't know if that's what to call it). I want to change it to a POS reference, (Schem B below).
The reason I want to change it is because I may have noise problems when I use it to power my pre which has a POS ref.
Q2 is what gives me the biggest problem, should it be a PNP?
Thanks for your help.

Since the supply is foating you can connect to ground whatever you wish.By puting the ground on the top the other side gives positive voltage(s).
Mona

 

[brucetassin]

Hello All
Thank you for your help.

Woody, very generous offer, but I would just get one if I source this project. If I build a PS using this chip, will it be quiet enough to power a phono pre-amp?

I built the pre-amp shown below. I'm using batteries for now but I want a full blown PS. I've tried several wall warts but most of them are noisy and none have the voltage I would like.

Ketje, My first though was to do as you indicate but then I became concerned
that it would be noisy. I will use a three prong socket for AC mains input and earthing where necessary. I dont want the PS or pre-amp floating.
I want the turntable ground going to earth also. Just trying to keep things quite.

 

[Mooly]

This preamp only draws around 12 milliamps when run on a voltage of around 40 vdc. I would suggest somewhere around 30 to 36 volts as a good choice of supply value.

That brings you into easy build territory A small 15:0:15 Vac transformer will give around 45 volts DC at light loading.

Something like this,
CTFE10-15 - CAMDENBOSS - TRANSFORMER, PCB 10VA 2X 15V | CPC

You then have lots of simple options to add a regulator such as zener shunt or even a three terminal voltage reg IC.

Come down a little on DC voltage such as using a 24 volt rail and you could use a 7824 reg (you would need a 12:0:12 tranny for that)