TDA1541 - lots of sibilance on vocals - Sony CDP227ESD player

[audio_tony]

I have recently bought a Sony CDP-227 (with dual TDA1541).

I used to own one of these a few years back, and that one was fine.

But this latest one suffers badly from sibilance.

My initial thoughts were to simply recap the entire DAC stage, but then I thought I would ask first - to see if anyone else has experienced this kind of issue with the TDA1541.

On well recorded CDs, the quality is superb - but the vast majority of "regular" CDs have this sibilance issue.

All other frequencies are fine - in fact the bass and midband are actually the best I've heard in ages.

I have tried different amp / preamp combos and that has made little difference.

Looking at the internals of the player - it doesn't look to have had much use, despite being 20+ years old.

Any suggestions would be gratefully received.

TIA.

I have attached a snippet of the schematic of the DAC / o/p stages.

 

[DF96]

Check C414/514 - the caps at the opamp input. These divert some of the HF current from the bare waveform edges away from the opamps. If these caps are missing or faulty then the opamp gets fed a lot of HF energy it can't cope with. This would be more noticeable at the treble end of the audio spectrum, as the edges are bigger there.

 

[audio_tony]

I checked those caps, they're ok.

Whilst I was in there, I removed C413 / C513 (I've never been a fan of putting caps of different types in parallel) and I bypassed R408 / R508 and increased R407 / R507 to 560 ohms.

The cables I'm using are fairly long, and I did wonder if I was getting some oscillation in the o/p stage due to the cable length / capacitance.

I know that many designs suggest that you should have 470R -> 1K series resistance to protect against oscillation with capacitive loads.

I also fitted some sockets for the opamps, but clearly FET opamps don't work too well here lol

I'm guessing I need a bit of biasing on the input from the TDAs, and I don't want to start messing about with that.

So I guess my next upgrade will be a couple of LM4562s.

 

[percival007]

Could it be that the Spindle Motor could be running slightly slow?

I have had faulty Motors causing distortion in the past, admittedly it often causes no play or very bad distortion but I have had on occasion it causing slight HF distortion.

I am not saying it will definately be this but it may be worth a try.

James.

 

[percival007]

Also the RF output from the Laser could be falling to the threshold of acceptability, I have had this causing slight HF distortion.

James.

 

[audio_tony]

Thanks, I'll do some checks according to the manual.

 

[lcsaszar]

On well recorded CDs, the quality is superb - but the vast majority of "regular" CDs have this sibilance issue.

This might indicate permanent error correction (interpolation between good samples) so hard working that the resulting waveform hardly resembles to the original. You need to check the eye pattern with an oscilloscope.