TL431 output filter for TDA1543 current source elimination - diyAudio
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TL431 output filter for TDA1543 current source elimination

Posted 6th September 2013 at 05:45 AM by abraxalito
Updated 6th September 2013 at 06:10 AM by abraxalito

Here's what I've ended up with in my SDcard DAC for eliminating the pull-up current sources within the TDA1543 - a heavily filtered 3.75V reference. For a single TDA1543 just connect the L and R 870R resistors to the output of this filter instead of the normal connection to 0V. Then the input's fed with the TL431 - I'm using 3k and 1k5 output voltage setting resistors. The first resistor and inductor on the left are my attempt to simulate the output impedance of the 431.

The electrolytics are Sancon 16V types with 0.1R ESR - the 440uF being made of two in parallel. The inductors need to have the right ESR (about 0,1ohm also) for which I had to wind my own 68uH - the ready made ones I have are too lossy Varying these parameters might result in a lumpy frequency response.

Attenuation is -70dB by 20kHz but almost flat to 1.6kHz and output impedance remains low down to DC.

Eliminating the current sources means that pin7 of TDA1543 now goes unconnected. This arrangement maintains the inverting characteristic of the DAC,
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  1. Old Comment
    triode_al's Avatar
    Great idea. And at what voltage is the TDA1543 running, just asking before testing myself? 3,75 bias on the AOR/AOL seems to hint at 8 VDD.
    Just noting - I remember a schema that used an opamp to get the bias with the DC on AOR/L as source as an opamp-follower design.
    Posted 17th September 2013 at 12:20 PM by triode_al triode_al is offline
  2. Old Comment
    abraxalito's Avatar
    No, its running stock at 5V (7805) - the max compliance voltage at 5V supply is 3.8V, 3.75V just happens to be 2.5V * 1.5 so quite easy to set up with the TL431.
    Posted 17th September 2013 at 03:33 PM by abraxalito abraxalito is offline
  3. Old Comment
    miklos's Avatar
    Me being a strong visual type, could you please point me to a schematic, or present one which have all that on?
    Posted 19th November 2013 at 06:52 PM by miklos miklos is offline
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