DIY Power Supply for Gram Amp 2

Hi GrahamD, Good job making a power supply. Most people are afraid of working with mains voltages.
 Be sure to have a 0.5 amp fuse on the mains input for safety.

For improved clarity, add a 10 ohm (5 watt, wirewound) resistor in series to the input to the rectifier and a 0.002 uF (100v) disc directly across the transformer secondary. After the rectifier, put a 0.1 uF (100v) ceramic disc across the input to the LM317. These added filter components strip away almost all the noise from the mains supply.
 The output voltage will be very stable with the LM317 regulator, it is one of my favorites.
Be sure to put in the manufacturer recommended reverse biased diode across the output for large filter capacitors, it is described in the LM317 datasheets for National Semiconductors.
As time passes, the trimmer potentiometer will be a weak link, replace with suitable 1% resistors if possible.
Note: more than 1000 uF (100v) filter caps is overkill, and may be stressful on the LM317.

Here to help,
Bruce


Edited by BAK - 18 Mar 2015 at 12:53pm

"It uses a quality 240/24 volt transformer, diode rectifier set, followed by a LM317 voltage regulator and 4 1000uf caps."

Your description led me to believe the 4 each, 1000uf caps, were on the output of the Lm317.
If on the input (or before the regulator), no more than 100 to 330 uF would be required, 500 uF would be OK.
The LM317 is so good at rejecting input voltage fluctuations, larger capacitors are not needed,
  but a 0.1 uF ceramic disc is a very fast capacitor needed to filter the RF and EMF noise on power lines.
I would still use 330 to 500 uF on the final output, after the regulator, for stiffening the voltage for the varying current load.
Still a reverse biased diode across the output for large filter capacitors is recommended.

If you wish, I can send you a pdf file of the datasheet for the LM317.
It completely covers the circuit design requirements and has example schematics.

Another of National Semiconductors' design hints is to put a 10 uF, 50v cap across adjustment pin to ground for added noise reduction and stability.

I have used this regulator in many designs. It has better noise and ripple reduction figures than a standard TO220 style LM7805, 7812, 7824...etc.

Here to help,
Bruce


Edited by BAK - 18 Mar 2015 at 12:09pm

This is the circuit used ( sorry about the crappy drawing) which includes the reverse bias diodes not mentioned in my original brief description.
If you can provide any suggestions to further improve or modify it please feel free to offer them.
Cheers
Graham