TAS5558 high signal noise at bd-modulation

Hi, Bernard,

Do you have a measurement or FFT or something of the noise?

What are you using as your power stage?

-d2

Hi Don,

no I haven't measured it yet, I just listend to it and it's realy annoying. You can really hear the signal noise if the tas5558 inpute gate opens. Very bad if you're listening to small input signals.

Power Stage is a TAS5631 with BD-Mod. Filter (1:1 copy of the evm). If I use AD-Mod. for the tas5558 the signal noise disspears BUT then I have a 400kHz Switching Signal on the Speakers (because it's the wrong output filter on the powerstage for AD-Mod.).

I also tried to use 96k instead of 48k sampling rate (I thought the noise comes from the asrc of the tas5558).

Hi Don,

I made a FFT measurement of the output of the TAS5631b. You can see the 400kHz Switching Signal and the noise at about 60kHz (down to nearly 20kHz where it gets hearable). It looks not that loud on the scope but it's really annoying in real life :-/

If I mute the tas5558 the signal noise dissapears.

regards

Bernhard

Hi Bernhald,

Have you tried the AM avoidance function to change the PWM rate and see if it helps? Could it be beat noise with the power supply? Below is the FFT for TAS5558 in BD mode for reference.

reg,

Paul.

Hello Paul,

yes I tried the AM avoidance function, I also changed the frequency but nothing solved the problem.

The reason is definitely the modulation in BD Mode. The circuit is accu powered so there is no switching psu. I also changed the I2C frequency to 400kHz. 

Hope you can help me.

regards

Bernhard 

Hi Bernhard,

Did you measure the FFT plot at the TAS5558 PWM outputs or at the output stage analog output?

reg,

Paul.

Hi Bernhard,

Can you please try turn off the noise shaper and see if it makes any difference?

(Address= 0x04, Data=0x43)

reg,

Paul.

Hi Paul,

sorry for my late reply but I was busy with some other projects. I measured the FFT at the analog output of the tas5631b (I also tried tas5614a) chip.

Turning off the noise shaper has no effect. The noise disappears if the noise shaper mutes the input signal but if the input opens the noise appears. Changing the AM Avoidance mode has also no effect.

I tried following: 

Powered on the device and played some music so that the input gate of the tas5558 opens. The noise appeared after the gate opened. I stopped playing music and the noise was still present. Then I disabled the I2S bus, I even stopped the word clock, only master clock was present and the noise was still there.

Attached you can find a record of the noise. 

It's present only in BD mode, if I switch into AD mode the noise disappears. But then I get the 400kHz switching signal onto my speakers. 

Hope you can help me out.

Regards

Bernhard

Hi Bernhard,

Can you provide the I2C initialization for TAS5558 that you used for BD and AD?

reg,

Paul.

Hello Paul,

of course:

For BD Mode I use this:

{0x12,0x00}, //# Trim Register
{0x30,0x89}, //# Use BD Modulation for Channel 1/2
{0x31,0xAB}, //# Use BD Modulation for Channel 3/4
{0x32,0xCD}, //# Use BD Modulation for Channel 5/6
{0x33,0xEF}, //# Use BD Modulation for Channel 7/8
{0x14,0x04}, //# Set Automute on -90 dbFS
{0x03,0xA0}, //# Exit Shutdown

{0xCC,0x00,0x00,0x01,0x00}, //# Disable Noise Shaper
{0xd9,0x00,0x00,0x00,0x96}, //# Master Volume

For AD Mode I use this: (I keep register 0x30 to 0x33 in default)

{0x12,0x00}, //# Trim Register
{0x14,0x04}, //# Set Automute on -90 dbFS
{0x03,0xA0}, //# Exit Shutdown

{0xCC,0x00,0x00,0x01,0x00}, //# Disable Noise Shaper
{0xd9,0x00,0x00,0x00,0x96}, //# Master Volume

In my actual configuration I use Input 3 (SDIN2_1) with 96kHz fs128 Signal and Output 5/6. So no Routing is necessary. I also tried to use Input 1 (SDIN1) and PWM Out 1/2 with the same effect.

All the other registers are kept in default.

regards

Bernhard

Hi Bernhard,

I tried it on the TAS5558+TAS5614L EVM and did not see any high freq noise. I tried both AD mode and BD mode. Captured on FFT and did listening test with a 8R speaker. I'm not sure what is the cause of the noise on your board. Have you tried it out on the EVM?

reg,

Paul.

Hello Paul,

thank you for your help, I really appreciate your work.

Can you tell me where the noise at about 60kHz comes from? I think it's exactly this noise what I'm hearing on my system. The only difference is that it begins at about 10kHz in my system and at about 22kHz on you're evm board. Maybe my problem is not the tas5558 but the tas5631b?!

Confusing that I don't have these issues in AD mode, in you're fft it's not that much difference.

Is it possible that you send me a tas5558 evm board? Unfortunately I don't have one. It's unbelievable how many problems I have (had) with this chip (as you can see in my earlier posts).