Simple Class A amplifier

Discussion in 'The Projects Forum' started by Experimentonomen, Apr 25, 2012.

  1. Experimentonomen

    Thread Starter Member

    Feb 16, 2011
    I had two BD250C and two 2SA1490 PNP transistors that i dident have the NPN complement for, so i decided to make a small low power class A amplifier with them.

    the BD250C's were put to use for the constant current sources and the 2SA1490's became the audio handler.

    A few minutes in LTspice produced this circuit:

    The idling current was set to 2.5A for up to around 5 watts into 4 ohms at a PSU voltage of 16 volts.

    The psu is one 2x12V(secondaries in parallel) 80VA transformer for each channel, at the time beeing, the two transformers are wired in parallel as i used them to power a wordless drill.

    A picture of the actual amplifier:

    Simulation shows between 0.1 and 0.3% THD near full power at 20kHz and the sound is really good, especially when the source is vintage vinyl records, but the amp also have the grunt to reproduce the music of today.

    Today is day 2-3 the amp is running so i deem it stable, the heatsinks stabilize around 80 deg C judging from feel, can touch for about 3 seconds, and thats just sitting on the table with limited convection.
  2. wayneh


    Sep 9, 2010
    Touching 80°C for 3 seconds? I don't think so. Maybe a glancing touch. Few people can tolerate even 60°C (140°F).

    Anyway, was there a question you are asking? If this is sharing a completed project (thanks for that ;)), you should go post in over there.
  3. Experimentonomen

    Thread Starter Member

    Feb 16, 2011
    Its not complete until its mounted in a chassi :p Its still a WIP. ;)

    The chassi will probably just a be a few pieces of sheet metal with holes lining up with the screw holes in the edges of the heatsinks.