TDA1541 - noise in one channel? - diyAudio
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Old 23rd March 2006, 08:46 PM   #1
phofman is offline phofman  Czech Republic
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Default TDA1541 - noise in one channel?

Hello, I have encountered a weird problem with TDA1541 in my CD player Grundig FineArts CD9000, after I had played with feeding the complete DAC with digital data from another transport (restored back to original status by now).

The right channel outputs a signal distorted with hiss and noise. The left channel is OK.

For testing I prepared a CD with 1kHz sine signal. The left channel outputs proper sine shape whereas the right channel sine has the upper half shifted downwards, as if the voltage produced by the most significant bit was randomly fluctuating between zero and the correct value. For a while the signal is correct sine, then the upper half moves downwards. But the shape of the upper part remains correct, it looks like cleanly cut with scissors vertically and randomly shifted down.

First I thought the analogue filter was broken. I swapped outputs from 1541, the noise moved to the other output cinch. The analogue part seems OK, voltages in measure points of both channels are basically identical.

Digital signal from SPDIF coax output is OK, I checked that too using an external DAC. I inserted an invertor to the 1541 Word Select digital input path, virtually swapping the right and left channels in the digital domain. The hiss remained in the physical right channel (pin 6). Thus, the digital data should be OK.

I checked signals at the decoupling capacitors and found the right channel MSB decoup pin 13 has random voltage noise and spikes of several tens of milivolts, whereas all other decoup pins are clean (in both channels). The spikes were correlated to the shift of the upper half of the sine shape. It looks like the MSB switch in the DAC is having problems, fully functioning for a while, then not kicking in at all, later on switching just half way etc.

It could be the decoupling capacitor. I disconnected it from the pin 13, but the random spikes remained.

As a result, I bought a new 1541A and was happy to see the problem go away. Well, just for a few minutes. The problem reappeared. The DAC can play whole CD OK. Then it goes crazy and the random distortion in the right channel starts.

The problems never appeared before playing with the DAC.

I wonder if it could be caused by a fault in the subsequent analogue filter, which perhaps damages the right output, internally in the DAC (the output goes directly to opamp input).

Solder joints look clean and decent quality. The noise appears and disappears, e.g. tonight it's gone and I am enjoying great Ray Charles hits unlike this morning

I will really appreciate any help or suggestions. I know the player is old and has almost no value, but its sound is outstanding and I do not like giving up Thanks for help in advance.
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Old 27th March 2006, 06:25 PM   #2
phofman is offline phofman  Czech Republic
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Really no suggestion, anyone?
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Old 28th March 2006, 10:53 AM   #3
ash_dac is offline ash_dac  United Kingdom
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Default Re: TDA1541 - noise in one channel?

Quote:
Originally posted by phofman

The right channel outputs a signal distorted with hiss and noise. The left channel is OK.

First I thought the analogue filter was broken. I swapped outputs from 1541, the noise moved to the other output cinch. The analogue part seems OK, voltages in measure points of both channels are basically identical.

The hiss remained in the physical right channel (pin 6).

It looks like the MSB switch in the DAC is having problems, fully functioning for a while, then not kicking in at all, later on switching just half way etc.

It could be the decoupling capacitor. I disconnected it from the pin 13, but the random spikes remained.

As a result, I bought a new 1541A and was happy to see the problem go away. Well, just for a few minutes. The problem reappeared. The DAC can play whole CD OK. Then it goes crazy and the random distortion in the right channel starts.

The problems never appeared before playing with the DAC.

I wonder if it could be caused by a fault in the subsequent analogue filter, which perhaps damages the right output, internally in the DAC (the output goes directly to opamp input).

Solder joints look clean and decent quality. The noise appears and disappears, e.g. tonight it's gone and I am enjoying great Ray Charles hits unlike this morning

I will really appreciate any help or suggestions. I know the player is old and has almost no value, but its sound is outstanding and I do not like giving up Thanks for help in advance.
Hi,

I'd say check the analogue stage after the dac. Tda1541a wants to see zero volts at it's output.

Then check the td1541a with heat gun to check it's not nearly dead. Also check link below:-

tda1541a distortion problems

Do you have the cap between the oscillator pins on the tda1541a ?
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Old 28th March 2006, 01:49 PM   #4
phofman is offline phofman  Czech Republic
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Location: Pilsen
Hi ash_dac,

Thanks a lot for the information and suggestions. I will check and report results.
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Old 1st April 2006, 07:34 AM   #5
tubee is offline tubee  Netherlands
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I have a CD 640 for testing purposes: NOS 1541A, transistor I/V (rbroertjes version) Kwak 7 combined with clock divider to dac. Sounds very good, more analog, but sometimes i feel the sound demands more from your ears. (in-ear filtering?)

What i want to say is i never hears hissing sounds, until i tried my diy cable on the NOS player, exsisting of thin 0.2mm copper wires around a 6 mm polyethylene foam tube and teflon wrapped cable core. This cable sounds rather good on standard CDP/tuners, but with NOS i hear extra hissing sounds coming around the music, on both channels. Sounds like digital noise around music information.

Its problably caused by the higher GND resistance from preamp to CDP (0.7 ohm with 0.2 gauge copper wire/ 70cm cable)

On regular RG58U diy cable (R=practically zero ohm) the hissing is over.

I have to re-design the diy cable, with a copper foil or twined/twisted GND connection to reduce resistance for NOS use.
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