Noise problem on TDA1541A output - diyAudio
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Old 18th May 2004, 07:46 PM   #1
Peter K is offline Peter K  Netherlands
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Question Noise problem on TDA1541A output

Hallo,

My DAC (2 x TDA1541A S1) that worked perfect for 9 months has been starting to generate some noise. The noise is quite low (but disturbing) level maybe -40 dB (as far as it is possible to guess this!) it sounds like a sort of wisper. I have heared it on both channels but never on both channels at the same time.

My system setup is as follows:
- CDPRO 2 with I2S output.
- DAC: 2 x TDA1541A S1 like the diagram of Pedja, I2S in.
- Passive I/V, output stage like diagram of TNTAudio.
- Output of the outputstage can be swithed to my headphone amp or my GainClone.

When I connect the CDPRO audio out to my GainClone the signal is clean.
When I listen to the output of the DAC with both the headphone amp or the GainClone I hear the noise.

The noise is only there from the moment that a track is playing. When a PAUSE the music there is no noise. My conclusion so far is that it must be one of the TDA 1541A chips.
The next thing really makes me wonder what is going on:
I have a Denon test CD, on all the test tracks with music and tones I hear the mentioned noise. However on the track with absolute silence I do not hear the noise when the track is playing.

I hope one of you can explain me what might be the problem. I can imagine that one of the chips is creating the problem. But why, might it be the temperature. The DAC is on 24 hrs a day and is getting quit hot. I have switched the DAC off for some time to cool down but this did not solve the problem.

I would very much appreciate some input,

Thanks,

Peter K.
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Old 18th May 2004, 08:36 PM   #2
Zodiac is offline Zodiac  United States
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Default Soldering?

Could be a dry solder joint, esp somewhere on the ground circuit. Check for joints that look dull or alternately just blanked resolder everything....
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Old 19th May 2004, 06:07 AM   #3
Peter K is offline Peter K  Netherlands
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Zodiac,

Thanks for the tip, I will check this out.

Peter
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Old 19th May 2004, 06:49 AM   #4
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Why leave it on 24 hours when it becomes hot ( which it need not to be anyway ) ? Since I learnt of TDA1540 that they fail after much hours of service I stopped leaving DAC's/cdplayers on. When broken in it takes 15 to 30 minutes to sound right so what's the point of creating useless heat, using power and having a risk while you're away ( certainly if it really becomes *hot* and is DIY ) ? It also helps to measure when you want to solve a problem. Gear should be measured when taken in service too ( again, especially if it's going to be on all day ). Show us a picture for clarity please.

2 x TDA1541A-S1 like in piggybacked ? Try it with one chip, maybe that solves the problem ( if one is defective ) and/or swap it for the other one to see if the noise disappears. What becomes hot, the DAC chips or power supply ? I could imagine one chip too fail when heat is too high. In this case I suspect one of the TDA chips to be defective. Dissipation of TDA1541 is high compared to modern chips so the upper chip will become hotter than normal when stacked. I understand from your post that they're stacked, if so I'd remove the upper one and test further. Don't expect the problem to go away now when you let it cool down, one is defective already. I know the whispering of defective chips, followed later by one channel distorting or failing.

Again I think that paralleling *bipolar* neanderthaler DAC chips by stacking them is not clever but who am I ? Fashion is fashion and if people keep telling it sounds better others keep doing this.
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Old 19th May 2004, 07:24 AM   #5
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Default Heat........

Blast it with your heat gun, and I bet it gets much worse.

Then hit it with freeze spray. That will prove my point.

(That is what they do before they fail.)

Jocko
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Old 19th May 2004, 07:44 AM   #6
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Quote:
(That is what they do before they fail.)
Absolutely.
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Old 19th May 2004, 11:06 AM   #7
Peter K is offline Peter K  Netherlands
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Jocko and Jean-Paul,

Thanks for your information.

The 2 TDA chips are not piggy backed, they both are on PCB and build as parallel circuits, separate TL431 regulators, decoupling capacitors, etc. The outputs come together at the I/V resistors.
I am not sure about the amount of heat (temperature) that is produced by the chips, I am however quit convinced that it is not extensive. It does not burn the fingers anyway...
The PSU is cool. The temperature T amb. in the cabinet builds-up to about 40 deg C, the TDA temperature might be to high because of the high T amb. This will cause the aging.

I think I will drill a pattern of small holes in the top cover of the cabinet to ventilate it. This will solve the temperature problem. Additionally I will indeed switch of the DAC when it is not used.

So if I have understood you both right it is to be expected that the noise that I hear I a pre-failing sign of one of the TDA chips.

I will check out the individual chips and the PCB soldering tonight or tomorrow. I will post the results.

Thanks again,

Peter
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Old 19th May 2004, 11:43 AM   #8
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My bet would be a solder joint or (very important) try to put new 470pf caps between pins 16 and 17 on both chips.
When these are not ok the sound gets the way you say.
Maby the heat killed them...

And power that thing down when not in use.
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Old 20th May 2004, 05:36 PM   #9
Peter K is offline Peter K  Netherlands
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Default The results of my tests

I did the tests on the DAC based on the different suggestions, the results are as follows:

First I must mention that the mentioned noise, could better be called "distortion of the lowest audio levels".

- No bad soldering on the PCB, checked and resoldered.
- No bad TDA chip, replacement did not change it.
- The problem appeared to come from the DAC at the right part of the PCB (see picture). I replaced the 470 pF without results.
- I removed the OS-CON 15uF that are on the highest bits, this improved the situation a bit.

IMHO, it is not the chip but something around it.

I ended up with removing the TDA (and I/V resistors) at the right part of the PCB and to my supprise I liked the sound of a single chip more than the dual chip version.
IMHO the sound is more detailed (especially the voices). The sound stage is some steps back which makes the overall picture more relaxed.

So up to now I did not solve the problem, maybe it is a bad decoupling cap or so (??).
On the otherhand I like the single chip version, so I think I will keep it this way.

Hereby the picture of the DAC PCB:
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File Type: jpg dac.jpg (60.5 KB, 855 views)
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Old 20th May 2004, 05:37 PM   #10
Peter K is offline Peter K  Netherlands
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An other picture with the output stage on top of the DAC:
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File Type: jpg dac_iv.jpg (60.7 KB, 815 views)
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