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Tweeter DAC

Posted 22nd June 2014 at 04:24 AM by abraxalito
Updated 25th June 2014 at 05:49 AM by abraxalito

Hexacaps have their limitations - they provide a great low impedance for lower freqs but according to my LCR meter, turn inductive for frequencies in the mid-single digit kHz. Which is about the lower edge of the passband for a tweeter. So what to do to get a low impedance power supply to a DAC chip from 4kHz and up? Here's my first attempt - there are 7 TDA1387s each sandwiched between two low ESR 4700uF lytics. Sandwiching them together is an attempt to get the inductance as low as possible - the loop area can't practically get any smaller than this. Getting the wires in has tested my patience and that's even before powering the beast up....

Update - well I could have been knocked over with a feather - this worked first time I plugged it in. So now I'm thinking about how to build a markII version, considering if I can get more decoupling close in....
Oh I'm now not sure that my bandpass tweeter filter is really delivering the goods as per its simulation. Connecting the bandpassed output to the bass/mids reveals rather more bass than I'd like so some investigation is in order. Overall though very pleased indeed with the improvements that have arisen from activating the whole system - my 228rmb speakers now are sounding like mini-horns. More results in accord with the hypothesis that dynamics is amps, not speakers....

Update2 - here's a pic of the next insane decoupling arrangement taking shape. Let's call it the DACupine for now. Each of the six DACs will be mounted on its own octagaonal PCB, at right angles to the board. Thus there will be around 35,000uF per chip within about 1cm of the power pins. I'm building this with 1oz copper but would like to get some 2oz double sided PCB material to try....
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Comments

  1. Old Comment
    fas42's Avatar
    Richard, can't but repeat that your energy and enthusiasm is very impressive ...
    permalink
    Posted 23rd June 2014 at 12:01 AM by fas42 fas42 is offline
  2. Old Comment
    abraxalito's Avatar
    Thanks Frank! Certainly I'm passionate about getting the very best sound....
    permalink
    Posted 23rd June 2014 at 12:52 AM by abraxalito abraxalito is offline
  3. Old Comment
    fas42's Avatar
    Richard, just refresh my memory on how those multiple TDA1387s are working; IOW, what the circuit for the above is, please ...

    Thanks,
    permalink
    Posted 23rd June 2014 at 11:36 PM by fas42 fas42 is offline
  4. Old Comment
    abraxalito's Avatar
    They're working as DACs, connected to 51R resistors (left and right) which then lead off to the bandpass tweeter filter. All 7 are paralleled, summing their currents together.
    permalink
    Posted 24th June 2014 at 07:33 AM by abraxalito abraxalito is offline
  5. Old Comment
    fas42's Avatar
    Ahhh, dear - I think we're about ready for a TV cartoon series, peopled with all your critters ...

    Though, your latest "creation" reminds me of my mains DC blocker, has the same, spokes of a wagon wheel construction, .
    permalink
    Posted 26th June 2014 at 10:21 AM by fas42 fas42 is offline
  6. Old Comment
    fas42's Avatar
    Richard, you appear to have disabled comments for your latest blog, the XO-centric setup - accidental or intentional ... ?
    permalink
    Posted 5th July 2014 at 03:59 AM by fas42 fas42 is offline
  7. Old Comment
    abraxalito's Avatar
    Accidental, thanks for the heads up! I will go investigate now.... Found an unticked box, its ticked now. Let me know if you get problems.
    permalink
    Posted 5th July 2014 at 02:53 PM by abraxalito abraxalito is offline
    Updated 5th July 2014 at 03:00 PM by abraxalito
 
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