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  1. Old Comment

    And now for something completely different...

    I just finished a new layout which includes base resistors on each of the output devices. I am not sure whether these will be essential to achieving stability, but I figured that if I included (all 104) of these resistors in the layout, I can load them. If they prove unnecessary, then I guess I could put zero ohm links in - but I honestly think that is a fond hope.

    Yep, I have a few reels of both NPN and PNP small signal transistors (mostly 549/550/559/560) which will without a doubt still be mostly full when depart this world.

    For a headphone amp, a small handful of these would do. Their power dissipation is somewhat less than the TO92, which would be a limitation in this - admittedly ludicrous - application.

    I will make a test board this weekend. The front end works fine, so the testing will be all about the output stage.

    My plan is to start with a single pair of output devices, get the ting running and work from there watching to see what happens with stability in particular as the output devices and current scales up.
    permalink
    Posted 20th May 2016 at 09:35 AM by googlyone googlyone is offline
  2. Old Comment
    abraxalito's Avatar

    And now for something completely different...

    If you get it working I shall be very interested as SOT-23 transistors are really so cheap - I shall be inclined to try a higher powered headphone amplifier with multiple output devices for a start. In the meantime though I'll play safe and use SOT-223s.
    permalink
    Posted 18th May 2016 at 10:45 PM by abraxalito abraxalito is offline
  3. Old Comment

    And now for something completely different...

    abraxalito, yes, this is no doubt a likely area of misery in this Ill-considered undertaking. But then, it wouldn't be fun if it just worked.

    If you hear lots of cursing and shouting coming from down under it will be a fair bet that this has got the better of me!
    permalink
    Posted 14th May 2016 at 10:46 PM by googlyone googlyone is offline
  4. Old Comment
    abraxalito's Avatar

    And now for something completely different...

    Getting small signal transistors to play well together when maralleled I gave up on. But then I was using them in a classA design, you may have more luck in classAB. I think Doug Self found the same - parasitic oscillations are a devil to overcome.
    permalink
    Posted 14th May 2016 at 04:57 AM by abraxalito abraxalito is offline
  5. Old Comment

    High Sample Rate PCM

    Quote:
    This approach has interesting repercussions: I will let you ponder them for the time being.
    17 bits worth of monotonicity, and uselessly high sample rate, that won't help it ?
    permalink
    Posted 11th May 2016 at 12:40 PM by tritosine tritosine is offline
  6. Old Comment
    abraxalito's Avatar

    High Sample Rate PCM

    There's no shortage of multi-bit DACs that go faster than the PCM1704, they just happen not to be targeted at the audio market. AD768 is one such, a fairly ancient design which runs up to 30MHz.
    permalink
    Posted 2nd May 2016 at 04:11 AM by abraxalito abraxalito is offline
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