Computer Audio Asylum: Discrete Voltage Regulator by John Swenson

Here is the schematic for both the positive and negative regulator. I certainly did not design this myself, its a modification from someone elses design, that was a modification from someone elses etc.

CR1 and CR2 are current regulator diodes. They are a simple little CCS that is easy to use and actually works quite well. I got mine from Mouser, others carry these as well. They come in a whole range of different currents. I chose the 2.4mA version because the tempco is essentially zero for that one. You are certainly free to try different currents. There is a tradeoff, the lower the current, the higher the impedance (which is good for a CCS). I but as you go to lower currents the reference voltage is more effected by the load. The 2.4mA seems to work well.

The original version had a lot more caps in there for filtering the reference to make it even lower noise. I found it sounded better without them, and its certainly simpler and cheaper this way.

If the LED has a forward voltage drop of 2.0 volts the "reference voltage" including Q1 Vbe is equal to about 2.6V. R2 and R3 form a divider that divides the output voltage down to match the reference. If R2 and R3 are the same (as in the schematic) the ouput will be 2X the reference, in this case 5.2V. In actuality it came out to almost exactly 5.1V with the LED I was using. Its the ratio that matters not the absolute values. I like to stay in in the under 10K range. Green LEDs seem to be the darling ones these days, I tried several different ones and got very similar results, so its probably not necessary to do an exhaustive search to find the "best" LED here.

The transistors speced are TO-92 package good for 100mA and 500mW dissipation. If you need more you can go with TO-220 package transistors for Q3 or Q6, leave the others as is. I try to choose ones with fairly high Hfe and low noise.

In order for the circuit to work at its best you should have a minimum of 5V greater input than the output voltage, thus for a 6V output it should be 11V or more.

I think thats about it. Oh yeah I forgot the equation, the output voltage is:

Vout = 2.6 * (1 + R2/R3)

The output cap is no tall that critical. I'm using a United Chemicon solid polymer 39uf but just about anything will work. There should be SOMETHING there, but it can be from .1uf on up. Play around and see what works best.

John S.