A story of mysterious interaction between a diy tda1543 dac setup and the human body.

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Bartb

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Joined 2017
#1
Hello everbody!
Maybe someone could kindly explain what exactly is going on... 🙂
I am testing a diy 16xtda1543 based dac.
The dac is running on a 12V power supply and feeds a Primaluna Valve amp. The dac is connected via i2s to an sd card reader running on 4x1.5V AA batteries. There is so much noise that the music is hardly distinguishable.
BUT.
If I touch one battery with a finger (mind you: the outside plastic wrap, not the wires) the noise is reduced by 25%. When I add a second finger on the 4th battery the noise is down 50%. If I lift the battery pack and wrap my right hand around it, down 80%. With my left hand, I place a finger on each RCA jack exiting the dac, and the noise is virtualy gone. Listening to music this way is quite unconfortable. I am wondering what circuit my body is simulating in this setup and how can I replace it? (my body) 🙂 🙂
Thanks !!
 
#6
Hello !
Whilst the previous problem was easily solved (grounded 🙂 ) thanks to your suggestion, there is another little problem with the sd player/tda1543 combo.
I am experiencing a short burst of static in between tracks...Any idea where that might come from? ( SD card player playing .wav on 4x1.5V batteries, connected via I2S to single TDA1543 with passive IV conversion, @8V and straight to valve amp )
Thanks, Bart
 
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#12
I didn't know the answer, had to look it up. Its at least 100 in practice - though that's not guaranteed, just a typical at 25oC. If you want the ultra-conservative 100% guaranteed figure, its 35.

The data you need (in particular the buffer's output drive characteristics) isn't shown in the Nexperia 74HC125 datasheet, its in the HC/HCT user guide.
 
#13
Thanks for checking that out. This surely simplifies the design in case I go with 32xTDA1543.
( DDDAC 2000 says a good balance between improvements and power consumption is 60x but I definitively want to stay lower 🙂 )
To date I've made a 16x TDA1543 and I am very happy with the sound. It has a punch and consistence that I like very much. Somewhere I read this chip's sound (with passive i/v) is addictive... and I'm starting to believe that.
 
#14
Yeah its addictive all right with passive I/V but goes up another level (think crack cocaine) with active I/V preceded by a fairly steep filter. Then you'll not need to use as many chips as 32. Have you tried TDA1543A incidentally? It has at least one problem on the older version fixed.
 
#15
Ahaaa I'll try the active setup as well then 🙂
It started as a car audio project, and I was attracted by the relatively simple setup.
I compared my 2cent dac (16xTDA1543) with the (acclaimed) DCT-Z1 Denon, the (respected) Pioneer DEX-P9R and the Shanling CD T-80 (tube-home), well... they're all headed to the dustbin, 😀
No haven't tried the TDA1543A, what problem did they fix?
 
#18
Single PNP transistor in common-base mode. DAC output goes to emitter, I/V resistor between collector and 0V. Base is fed from a reference voltage (TL431 works fine). Think I've posted up the schematic before trouble is I can never remember where...
 
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