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And then there were two... Amps of 100 Transistors

Posted 28th May 2016 at 06:39 AM by googlyone

And then there were two! A lot easier simply loading just the "output devices" and testing.

The second one initially looked super stable, but after I got it quite warm by running an almost clipping sinewave into a 4 Ohm load, I did find just a tough of oscillation on negative excursions.

The first amp had envelopes of oscillation at 3MHz. The frequency of the second amps oscillation was 13MHz.

In the end removing the capcitor between the bases of the output devices (what was it there for anyway?) tidied things up.

These Amplifiers of 100 Transistors seem to breed!

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  1. Old Comment
    Did you HFE match the transistors?
    Posted 3rd June 2016 at 08:22 AM by erik777 erik777 is offline
  2. Old Comment
    No, not specifically. I did test their operation, as I did not want to be searching through all those output devices looking for which one was misbehaving.

    They all came from one batch each of NPN and PNP.

    During the measurement process, I noticed that the HFE were all very close for each of the PNP and NPN groups.
    Posted 3rd June 2016 at 02:03 PM by googlyone googlyone is offline

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