TDA1543 output unbalanced... - diyAudio
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Old 25th April 2007, 08:15 PM   #1
wmincy is offline wmincy  Malaysia
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Unhappy TDA1543 output unbalanced...

Hi All,

Finally I pull out the TDA1543 NOS DAC! Years ago, not aware the difference between TDA1543A and TDA1543N or TDA1543, I brought lots of A types home, of course they were useless. Recently I got some 50 pcs of TDA1543 and this time it does work. Sound great, but honestly high frequency is its weak point, cannot compare with DAC inside my Sony CDP557ESD.
Actually I have a problem with the output. I noticed it just when I put it in comparison with my Sony: the DAC sounds unbalanced, volume came from PIN8 was lower than normal, I can't figure out why. Then I measured the voltage on both output (PIN6 and PIN8) and found 4,89V on PIN6 and a higher 4,95V on PIN8. Has anyone dealt with this kind of problem? How to solve it? Please help....

* attached here with some pictures.

Mincy
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Old 25th April 2007, 08:17 PM   #2
wmincy is offline wmincy  Malaysia
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Old 25th April 2007, 08:20 PM   #3
wmincy is offline wmincy  Malaysia
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last one.
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Old 26th April 2007, 12:13 PM   #4
digifun is offline digifun  Ukraine
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Maybe you has a problem with power unit. Chek capacitors in power circuit and voltage.
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Old 26th April 2007, 01:43 PM   #5
lucpes is offline lucpes  Europe
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I'd say to check if the IV resistors are properly matched.
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Old 26th April 2007, 05:55 PM   #6
PSz. is offline PSz.  United States
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Those voltages will never be equal, but I am not the best person to explain why...

I would suggest that you read up on biasing the 1543 as the voltages you have on the output seem high to me. I found http://www.dddac.de/ to be a wonderful reference. Start by clicking "DDDAC1543" at the top of the page, then click "DIY-Support" on the left side. You will find a link titled "Make sure to adjust the correct DC Bias ...."

good luck and best regards,
psz.
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Old 26th April 2007, 06:58 PM   #7
wmincy is offline wmincy  Malaysia
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thanks guys,

but none of these are the causes, power supply works well, voltage remain stables at 8,3 V. The I/V resistors values are 671ohm and 673ohm, better than this.

I checked the output with oscilloscope then everything is clear! too clear. One of the output decreased with high frequencies, so probably the low-pass filter had some problem, should double check.
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Old 26th April 2007, 07:12 PM   #8
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a) This is a cheap, super budget chip. Of course the sides are unbalanced. Try another one until you find one that is matched.

b) the slight imbalance in I/V resistors may well be enough to cause the very slight (0.06V) imbalance.

c)All NOS DAC's roll off over 16KHz. There are filters you can build to "correct" this, but most people feel that they do more harm than good.
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Old 28th April 2007, 10:21 AM   #9
wmincy is offline wmincy  Malaysia
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I tried with other 4 DACs from the batch, under oscilloscope the signal from PIN8 started to roll off from 1KHz above while the signal amplitude from PIN6 remained quite constant: at 5KHz PIN8 output almost half the PIN6 output... so weird, I'm so frustrated...
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Old 29th April 2007, 12:19 PM   #10
dddac is offline dddac  Germany
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Quote:
Originally posted by wmincy
I tried with other 4 DACs from the batch, under oscilloscope the signal from PIN8 started to roll off from 1KHz above while the signal amplitude from PIN6 remained quite constant: at 5KHz PIN8 output almost half the PIN6 output... so weird, I'm so frustrated...
Why don't you be a bit more factual ? roll off at what slope? where is the -3dB point ? Where is the circuit you built ? For sure your bias is too high, but may be you found my site useful in that point.

Further more, the differenece is soo small between channels, more than normal !! The difference has no influence on the sound, as you block the DC any way with hte output capacitor ......

Too high or too low bias in absolute sense, makes both measurable as audible a big difference, so you might want to tweak this to somewhere round 3.8 to 4 volt (imo the optimum)

Do not forget to have the right mix between Rref (pin 7) and Rload (pin 6 and 8) you need to find the optimum between max output voltage and lowest d2 d3 distortion.

as said, why don#t you publish your circuit, that we can have a look (and advise if you want )

best regards

doede
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