Building a dual rail supply from a 64VCT trans

Discussion in 'General Electronics Chat' started by kevinwil, Feb 22, 2005.

  1. kevinwil

    Thread Starter New Member

    Feb 22, 2005
    Hey everyone,

    I am new to the group and I have a question. I bought some Alesis amp/crossover boards from many moons ago, and I am finally getting around to using them. They are using the LM3886 and LM2876 chips (i'm removing the 2876 since it tops out at an even lower voltage!) I have never built a power supply before, I usually find something I can use as a power source for my projects. This time, I wanted to get my feet wet with some real voltage!

    Anyway, I tore apart a Harmon Kardon 680i from my junk pile which has been dead for many years to see if the transformer was still good. Sure enough, it's fine. It has two 64VCT secondary taps which MAY be a little too much. I got 32.9 volts with the meter on each. Did I mention this transformer weighs 11 lbs? :D

    So I calculate this will give me a dual rail voltage of roughly +/- 45 unregulated.

    So, the LM3886 will accept up to a 84 volt swing (thermal Spike protection starts kicking in @ 80), but looks like it will be happiest around +/- 35volts.

    Now clearly 45 volts is unloaded and I know this will flucuate wildly. I have two questions:

    1. Will this overvolt the LM3886, or will I just need a heatsink the size of Texas?
    2. Could I use a LM338 to create a regulator for this? Or is 45v too much for the 338 as well?

    I found this:

    Which has a 60VCT with LM338's. Could I do this with my 64vct transformer? It's funny, I usually have too little power, not too much. I'll try my best not to electrocute myself!

  2. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    hi kevin

    if you desire to have a regulated output why not. just pay close attention to your ground layout. use the star topology for your ground layout of the power supply. :)