TDA1541 and TDA1543 questions
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 12th January 2009, 01:41 AM #21 Gabdx1   diyAudio Member   Join Date: Jan 2009 Ok, what is sure is that this is proly better than what i/v i had in mind... I saw also there is this ultimate dac ? based on the same schematics... very interesting...
lcsaszar
diyAudio Member

Join Date: Mar 2004
Location: Budapest, Hungary
Quote:
 Originally posted by revintage Hi Oshifis, To check I have understood this right: About 1541, 25/2=12,5ohm is the highest allowable resistor? Output with 6 ohm will be 6*2=12mV? A parentesis: About the CD 2V out std I find this unnecessary as not even a poweramp needs this much. Wouldn´t 0dBu=0,775V be enough? Or why not the semiprostd 300mV/10k? If we go for 6ohm load and 0,5V out we then only need 40x gain.
The output current is actually 0 to 4mA, i.e. DC shifted. So the highest allowable resistor is 25/4=6.25ohm.
The resulting voltage drop is 0 to 25mV, that is 12.5mV peak (8.84mV RMS) sitting on 12.5mV DC.
In order to get 2V RMS (2.83V peak) from 8.84mV RMS (12.5mV peak), one needs about 226x gain. Of course, for 0.775V you need 88x, and for 300mV you need only 34x voltage gain.
The DC component must be blocked or shifted.

What I am not sure about, how hard is the +/-25mV compliance limit. How does the distortion increase when it is exceeded? Is there a diode to the substrate inside, a base-emitter diode or what? Is the output current modulated somehow by the output voltage? Questions, that maybe the designers of the chip are able to answer. Or perhaps someone who has measured the distortion vs. load resistor characteristics.

 13th January 2009, 01:18 PM #23 ccschua   diyAudio Member   Join Date: May 2008 So Can I borrrow the thread. I am currently running a diy tda1541 with input isolation transformer using DV709. The output IV is using 4xNE5534 and the DC block by 10uF WIMA MKP4. I wonder will the discrte output such as OPA Sun V2 / HDAM will improve the sound further.
 13th January 2009, 01:23 PM #24 ccschua   diyAudio Member   Join Date: May 2008 So Can I borrrow the thread. I am currently running a diy tda1541 with input isolation transformer using DV709. The output IV is using 4xNE5534 and the DC block by 10uF WIMA MKP4. I wonder will the discrte output such as OPA Sun V2 / HDAM will improve the sound further.
 13th January 2009, 03:32 PM #25 Gabdx1   diyAudio Member   Join Date: Jan 2009 Try replace 4ne by 4 x AD8599, Best op amp so far.... If you still want more you can check regulator/clock/output caps to like 22 uf and bypass... If you still want more then discrete opamp/tube There is no limit to what you can spend !!!! Ok, seriously if you have a tda1541 made in 1987 it is worth it because they are as good as the new tda1541as2, just maybe a little wilder
 27th February 2011, 02:30 PM #26 Gregje   diyAudio Member   Join Date: Oct 2009 Location: London Hi, Does Philips mention 25mV limit for the passive conversion in 1541? I am aware of such remark in the documentation of 1541A. Having said this, the question is whether I should lower my passive I/U resistor which is now 100Ohm. I know that people suggest something like 30Ohm, but I am not sure whether they refer to 1541 or 1541A.
rafbraw
diyAudio Member

Join Date: Jan 2009
Location: the body
Hi All. I am new here and fan of TDA 1541 like many here... I'd like to thank Icsaszar for this info:
Quote:
 Originally Posted by lcsaszar The output of the TDA1541 is sinking 2mA at zero analog output. This current varies between 0 and 4mA from negative to positive analog output peak.
This info is not given in any of TDA1541 datasheets. This 2 mA current generates about 4 Volts DC on output of the I/U op-amp converter (1,8kOhm x 4mA), therefore the output electrolyte caps can be correctly polarized. However that makes the next filter op-amp operating around 4 Volts DC instead of nice 'zero' (maybe it's good because allows to avoid some op-amp "around zero output" distortions?)
In my Marantz CD56 I applied a simple low noise transistor based 2 mA current source to feed directly the output of DAC. In this way I could eliminate output decoupling capacitors. It just works, but I am looking for better sounding solution.
Regards Raf

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