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building a TPA3255 260-2-29A, and need some guidance
- Thread starter nick650
- Start date
Hi Nick, can you please explain in details how did you resolve it? I have probably the same issue with 2*TPA3255 boards connected directly to 4 signal outputs of one ADAU1401 DSP board.
HW configuration:
- TPA3255 boards are powered from the same DC source. Each of them has only unbalanced 2-channel input with ground pin.
- Coaxial cable from each of TPA3255 boards goes to ADAU1401 where their ground wires are connected together and linked to the grount pin of ADAU, 4 signal wires are connected to ADAU signal outputs.
Issue description:
- 1. Only DC power connected to TPA3255 boards - no hiss at all.
- 2. Main power ON and only one TPA3255 board connected to ADAU (ADAU powered ON or OFF) - no hiss at all.
- 3. Main power ON and two TPA3255 boards connected to the input cables. Cable ground wires are connected to each other. No connection to ADAU - slight hiss.
- 4. Same as 3, but cables connected to ADAU (ADAU power OFF) - stronger hiss.
- 5. Same as 4, ADAU power ON - strong unacceptable hiss.
- 6. Better result when ADAU is powered from 3255 audio ground pin and +3,3V LDO. If powered from main DC ground and 3,3V LDO - hiss is ~10 times stronger.
PS. Oscilloscope connected between DC ground and audio ground of 3255 board shows 500mV high frequency noise with the peak at 450kHz.
Dear forum members, your ideas will be highly appreciated. I gave up.
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As an option - have you thought about abandoning the analog signal? If you have only digital sound carriers, then today you can refuse to use a low-power analog signal.
Thank you. I've already purchased upgrade kit to switch system to i2S internal audio transport. Hope it will help )
Meanwhile, people say some popular studio monitors are based on digital amp + i2S internal transport from ADC and they may also hiss... Anyway i will try.
Meanwhile, people say some popular studio monitors are based on digital amp + i2S internal transport from ADC and they may also hiss... Anyway i will try.
Most studio monitors use class D amplifiers with an analog input, or class D amplifiers with an I2S input that have their own DAC inside the chip. The problem is that class D amplifiers generate a lot of electromagnetic radiation that very easily gets into a weak analog signal because the interference generator is quite close to the analog signal. If you are ready to give up the analog signal, then for the sake of interest, consider using an amplifier that does not have an analog signal.
I gave up the analog signal quite a long time ago and thereby got rid of the problems of ground loops and similar problems. My amplifiers have a weighted average noise at the output of a 100W amplifier, no more than 100 µV. Other measurement results can be seen in this thread.
https://www.diyaudio.com/community/threads/3-way-dsp-amp.415065/
I have received PCM5102A boards and replaced audio transport with I2S line. PCM5102A DACs are now soldered to the 3255 boards and they likely work correct. Correctly terminated I2S bus connecting 2 boards (3255+5102A) with ADAU MP6,7,10,11 GPIO. So everything seems correct. But i got even more HISS from this new configuration. Surprisingly, adding MUTE box in SIgmaStudio and software muting ADAU completely stops system hissing. Power line is absolutely perfect. I've even tried power it from the battery.... nothing helps. Idle hiss is quite strong. I thing it is slightly stronger than in "analog" version based on ADAU internal DACs. I'be tried to disconnect everything from ADAU except I2S and power and it is still hissing on I2S. I can't understand what i did wrong.
PS: ADAU1401 is small board from AliExpress (China). May be it is not the best one, but i can't understand how can it work absolutely good with one 3255 AMP using ADAU DACs and hiss like a crazy on I2S out.
Any ideas will be highly appreciated.
Attachments
Even if i feed sound from ADAU DAC to 3255 - no hiss unless i connect 2 3255 boards at the same time. 3255 boards don't hiss if i use only one of them.
By the way, just did some tests.
1) Hiss level grown by 5dB after change from ADAU DAC and analog wiring to I2S and PCM5102A.
2) In any of 4 channels hiss can be cancelled by soft mute in SigmaStudio
3) Disabing ADC in HW configutation or just muting them stops hissing issue
4) Changing word length of I2S output in HW configuration does change hiss level. Changing from 24bit to 16 increases hiss level by 50% approx.
5) Changing other parameters only stop normal operation of I2S bus.
By the way, just did some tests.
1) Hiss level grown by 5dB after change from ADAU DAC and analog wiring to I2S and PCM5102A.
2) In any of 4 channels hiss can be cancelled by soft mute in SigmaStudio
3) Disabing ADC in HW configutation or just muting them stops hissing issue
4) Changing word length of I2S output in HW configuration does change hiss level. Changing from 24bit to 16 increases hiss level by 50% approx.
5) Changing other parameters only stop normal operation of I2S bus.
No. It is not that simple.
In "analog" version - Yes. It is interference noise. Switch off one 3255 board and hiss is gone. Meanwhile, software MUTE of ADAU ADC or Output doesn't change hiss volume.
Then i changed to "digital I2S" to get rid of hiss.
In "digital" version it is not interference between two 3255 boards. Disconnecting one of them doesn't change nothing i.e. there is a HISS. But this hiss can be removed by software MUTE of ADC or Output on ADAU1401.
PS: 3255 boards have syncronized clock. And it has absolutely no effect on hiss in both version (sync/no sync/450kHz/600kHz - all the same).
In "analog" version - Yes. It is interference noise. Switch off one 3255 board and hiss is gone. Meanwhile, software MUTE of ADAU ADC or Output doesn't change hiss volume.
Then i changed to "digital I2S" to get rid of hiss.
In "digital" version it is not interference between two 3255 boards. Disconnecting one of them doesn't change nothing i.e. there is a HISS. But this hiss can be removed by software MUTE of ADC or Output on ADAU1401.
PS: 3255 boards have syncronized clock. And it has absolutely no effect on hiss in both version (sync/no sync/450kHz/600kHz - all the same).
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