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Building the ultimate NOS DAC using TDA1541A
Building the ultimate NOS DAC using TDA1541A
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Old Today, 01:20 PM   #6931
koldby is offline koldby  Denmark
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Join Date: Jun 2003
Location: Ruds Vedby
Quote:
Originally Posted by Hanze Khronye View Post
It is the AC signal current through the DCR which performs the function of IV conversion. AC impedance is the same as DCR for a resistor. AC impedance of a transformer varies with frequency.

So you see what you write cannot be correct.

WRT comment re 25mV and datasheet, this is DC voltage compliance, 25mVDC, and not an vRMS value or anything else.

These are fundamental misunderstandings which have gone unchecked.

HK
Turns out you are not even right WRT output compliance:
What is meant by the DAC output voltage compliance range? | Analog Devices
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Old Today, 03:35 PM   #6932
lcsaszar is offline lcsaszar  Hungary
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Default TDA1541A output voltage compliance

Now I am a bit confused. The data sheet recommends +/-25mV. Even John/ecdesigns say so, e.g.:

Faulty TDA1541A?

Building the ultimate NOS DAC using TDA1541A

Building the ultimate NOS DAC using TDA1541A

There is some diode at the output that gradually begins conducting, if I understand correctly. I will measure THD vs. I/V resistor and maximum allowed value soon.
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Old Today, 04:18 PM   #6933
batteryman is offline batteryman  United Kingdom
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Building the ultimate NOS DAC using TDA1541A
Quote:
Originally Posted by lcsaszar View Post
Now I am a bit confused. The data sheet recommends +/-25mV. Even John/ecdesigns say so, e.g.:

Faulty TDA1541A?

Building the ultimate NOS DAC using TDA1541A

Building the ultimate NOS DAC using TDA1541A

There is some diode at the output that gradually begins conducting, if I understand correctly. I will measure THD vs. I/V resistor and maximum allowed value soon.
Has anyone been able to measure the distortion caused by not meeting the + -25mv specification?

I must say that my dac is sounding better than its ever done since I fed in a current to the CT and adjusted it to 0mv at the dac output pins. I'm sure it also sounds maybe 3db louder which could be due to ALL the dac current flowing into the transformer instead of some going through the I/V resistor? (which are still connected)

However I was looking at the spectrum of a 1Khz sine wave at -10db (as used on previous testing) and there was no 2nd or 3rd harmonics visible and distortion was around as low (.2%) as grounding the CT, but there were two significant spurious non harmonic spikes at about 5.6K and 8.5Khz @-40db which were not present before. I haven't yet investigated what has caused them. They did not seem to be amplitude related and there are no switching spikes on the signal - its completely clean.

Last edited by batteryman; Today at 04:21 PM.
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Old Today, 04:51 PM   #6934
batteryman is offline batteryman  United Kingdom
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Building the ultimate NOS DAC using TDA1541A
Quote:
Originally Posted by koldby View Post
Turns out you are not even right WRT output compliance:
What is meant by the DAC output voltage compliance range? | Analog Devices
Must be some mistake here - HK cannot be wrong, he's never wrong - Google supplies all his knowledge and we know how reliable it is.....!
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