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Old 12th June 2006, 07:58 PM   #1
zuus is offline zuus  United Kingdom
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Default TDA1543 - Has anybody else had this?

I have a Derek Shek NOS DAC and got curious so I thought I would remove the ref resistor (a variable one on this DAC). The data sheet says it is optional, but when I remove it, despite getting music at much reduced volume I also get a kind of digital noise. The resistor is set to 1.47kohm and gives 4.35v at the output pins, perhaps a little high??
Does anybody have any thoughts on this, do I have a faulty DAC?.
Regards,
Mark
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Old 12th June 2006, 10:31 PM   #2
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Location: osorno , Chile
Hi Mark:
I'm not a technical guy but I'll try to help
Quote:
The data sheet says it is optional
Which data sheet? Philips data sheet or your DAC's data sheet?
AFAIK, Rref is mandatory for the DAC to work. It must fix Vref between 2 and 2.2VDC for proper functioning and lack of (excess ) HF noise. Maybe it says "variable R is optional IF you swap it for a fixed one!". For fixed Rref I believe it got to be between 0.6 and 0.7/Rload.
If you let it without Rref you will get oscilation and much HF noise. (Did I say it well, guys? )

Use hi quality R for Rref and Rload. I use Riken-Ohm (it is said that they sound warm due to higher noise but I don't care!)

Quote:
The resistor is set to 1.47kohm and gives 4.35v at the output pins,
Do you mean Rload (signal to ground) is 1K47? Yes 4.35 is a bit high. Something between 3.6-3.85VDC looks better to my non-expert eyes (and even that could throw UHF noise to the next stage) .
There is plenty of info here. Also search for Philips TDA1543 data sheet.

Good luck.
M

PS: you have your output DC blocking cap, don't you?
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Old 12th June 2006, 10:54 PM   #3
zuus is offline zuus  United Kingdom
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Join Date: Apr 2006
Location: Swindon
Quote:
Originally posted by maxlorenz
Hi Mark:
I'm not a technical guy but I'll try to help


Which data sheet? Philips data sheet or your DAC's data sheet?
AFAIK, Rref is mandatory for the DAC to work. It must fix Vref between 2 and 2.2VDC for proper functioning and lack of (excess ) HF noise. Maybe it says "variable R is optional IF you swap it for a fixed one!". For fixed Rref I believe it got to be between 0.6 and 0.7/Rload.
If you let it without Rref you will get oscilation and much HF noise. (Did I say it well, guys? )

Use hi quality R for Rref and Rload. I use Riken-Ohm (it is said that they sound warm due to higher noise but I don't care!)


Do you mean Rload (signal to ground) is 1K47? Yes 4.35 is a bit high. Something between 3.6-3.85VDC looks better to my non-expert eyes (and even that could throw UHF noise to the next stage) .
There is plenty of info here. Also search for Philips TDA1543 data sheet.

Good luck.
M

PS: you have your output DC blocking cap, don't you?

The TDA1543 data sheet (the DAC doesn't have one), says Rref is optional (if I read correct). I gather from what you say that if I replace the adjustable with a fixed one, that would be an improvement. Rload is (for left and right) 2.7Kohm (to give standard output level I guess). So the 4.35 on these is too high then?
Also yes I do have dc blocking caps (3.3uF RIFA (whoever they are)), too low??
Kind Regards,
Mark
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