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Class D Switching Power Amplifiers and Power D/A conversion

SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix
SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix
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Old 18th November 2016, 12:27 PM   #21
ratep2001 is offline ratep2001  Denmark
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I bought it from here:
TDA7492P Bluetooth 4.0 CSR8635 Audio Receiver Digital Amplifier Board 50W+50W | eBay

But it has a red PCB and looks similar to the photo in the text, not like the photos attached to the ebay posting. Difference to what has been delivered is that e.g. the top of output chokes on mine is whole blue and not only the rim, compared to the photo. Gain setting around NE5532 is still done with 22k and 75k resistors.

In my SPI programmer I have put a 10k resistor from SPI/PCM pin to 1.8V in order to put it in SPI mode. Can this be overriden/locked in SW? Is there any other programming interface?
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Old 18th November 2016, 12:42 PM   #22
doctormord is offline doctormord  Germany
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No, only if they use a stronger pulldown (in HW). Have you measured the voltage at the pin?

Edit: The TDA7492P boards are more noisy than the 3116/3118 boards, thats what i also have noticed. If it is "digital" noise, comming from the module, i'd suggest to change the elyt cap after the 100R resistor for an MLCC, say 10-20uF for a way lower ESR which dominates the attentuation of the filter. You may also try to change this cap for a low-esr elyt or polymer cap. (1000uF) (I'd suggest the latter first)

Last edited by doctormord; 18th November 2016 at 12:49 PM.
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Old 20th November 2016, 10:45 PM   #23
ratep2001 is offline ratep2001  Denmark
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It seems that the differential signalling to TDA7492 and the replacement of R22 and R21 with high ohmic values made this Bluetooth amplifier sound decently without any pop-and-click at turn-on. However as mentioned in another post, there is still an annoying problem with pop-and-click at turn-off.

Can you explain how R22 and R21 affect the turn-on pop sound and why they are not capable of supressing turn-off pop sound? Disabling the amplifier at turn-off was mentioned as a solution to the aforementioned problem - is there a possibility to do this change on the existing board? And what does it take to perform the mod?

By the way, does anybody have a principle schematic of this board?

I have also measured with multimeter the resistence to ground of SPI/PCM pin and in both amplifiers the value is in MOhm range. So I would suspect that there is any physical external pull-down resistors on either of the amplifier boards. There is probably some active pull-down in the chip. I need to mount programmer again and try to measure the voltage during programming...
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Old 21st November 2016, 08:11 PM   #24
doctormord is offline doctormord  Germany
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R22 and R21 only affecting the power-on time-constant at the Mute/Reset Pin. To finally fix this, a SVS (system voltage supervisor) can be used which monitors the supply rails and mute the amp at power-up/down.
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Old 21st November 2016, 09:50 PM   #25
ratep2001 is offline ratep2001  Denmark
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I hear a pop-and-click noise not only when turning off the power supply but also when muting. I.e. when streaming music from smartphone via bluetooth, the amplifier is first unmuted and this does not produce any pop-and-click sound anymore, after increasing R21 and R22. But this does not work for muting - how can this be, if R21 and R22 are affecting the time constant on the Mute/Reset pin?
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Old 21st November 2016, 10:08 PM   #26
doctormord is offline doctormord  Germany
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Because the resistors limit the capacitors charge current, the voltage rises slowly, increasing the time for unmute. This doesn't work the other way around like it actually is implemented as the resistors also limit discharge rate. The value of the coupling caps is part of the problem to. I'll check for a better fix when i get some spare time.
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Old 21st November 2016, 10:21 PM   #27
ratep2001 is offline ratep2001  Denmark
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When comparing with your photos, my bluetooth amplifier seems to have also some SOT-23 components close to the muting RC-circuits. After you mentioned the discharging problem with the big resistors, I believe that this could be diodes making it possible to bypass the big resistors and mute the amplifier fast. I am not sure though and will need to check the layout and do some measurements.
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Old 22nd November 2016, 06:57 PM   #28
doctormord is offline doctormord  Germany
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Are you able to do some high-res pictures?

To get rid of the "popping" you may adapt an MCP121 for the reset handling.

http://ww1.microchip.com/downloads/e.../20001906D.pdf
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Old 27th December 2016, 07:06 PM   #29
wesjuhdabomb is offline wesjuhdabomb
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Just performed this mod, works like a charm! The volume output of this board is quite high by default (most likely by the 32dB gain). This is especially noticable when the board powers up, as the start-up sound is very loud. This is also my primary concern, as the volume buttons on the board allow to lower the volume after power-on.

Am I correct that I can perform one of the following:
1. Place a stereo pot between output of CSR8635 and RINP and LINP pins.
2. Reduce the gain by replacing R27 (32K) and R28 (75K) resistors with 20K and 100K respectively.
3. Mod the CSR8635 chip output volume(not really an option by reading experiences on the internet, and 20USD SPI-USB chip required).

I am a bit confused with option 2, since the combination of 32K and 75K resistors is not an option in the TPA3116 datasheet for 32dB gain, so maybe I require different resistors?

Last edited by wesjuhdabomb; 27th December 2016 at 07:18 PM.
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Old 2nd January 2017, 12:29 AM   #30
fixedcoil is offline fixedcoil
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Default CSR8635 Alert Tone "Noise"

Hi,

DISCLAIMER: Everything written below is information I have gleaned from reading CSR documentation, blog posts and related comments. It is offered in good faith with no promises. What I relate worked for me, your mileage may vary but BEFORE changing any PSKey parameters you should DEFINATELY BACKUP your modules by dumping/writing their initial settings to file using both PSTool and the ROM Configuration Tool.

I recently bought a Sanwu Audio Bluetooth Audio Amp module on Ebay and was disappointed to find that it played loud discordant event tones when powering up, pairing, connecting and when the volume was changed. I just wanted to put it in to the ceiling void of my bathroom to be able to play music from my phone with better sound quality than that provided by the phones speaker.

The Bluetooth chip is by Cambridge Scientific Research (since bought by Qualcomm) CSR8635, designed to be used in a hands free a car phone, or similar, application. Searching online I not come across anyone also finding these features unwanted and solving the problem of removing them. I did find CSR information and programming software not easy to obtain but it is available if you look.

This document is written for a different device but the parameters seem identical:
http://read.pudn.com/downloads166/so...User_Guide.pdf

This is the PSTool Users Guide:
http://www.52bluetooth.com/csr/adk3....lUserGuide.pdf

To communicate with the module you need a USB/spi module. It is possible to DIY one but a CSR module can be found here:
CSR uEnergy SPI Programmer Board Kit - Broadband

There are spi lands on the Sanwu module to which fly leads can be soldered.

The 8635 configures itself when it boots by reading default parameters, called Keys from ROM. It can be customised by writing modified parameters into EEPROM which then mask and overide the corresponding default parameter. These modified parameters are called persistant store keys (PSKey). PSKeys are split into three groups. The first are fully locked down from manufacture, they configure the bluetooth radio and other regulated features. The second group contain the user configurable PSKeys; those from 0 to 24 are secure keys and need the CSR86xx Series ROM Configuration Tool to write to them. The keys from 25 to 49 can be written to using the PSTool.

The event tone parameters are stored in PSKey USR26. The format is four hex digits:
xxyy xxyy, where xx is the event and yy the tone to play. Setting all the yy digits to 00 removes the tones.

The Hands Free Profile is stored in USR3 and can be removed by simply deleting all between USR3 up to USR4. Alternatively the ROM Config Tool can be used to unselect the HSP and HFP profiles under the HFP tab.

Finally to change the module name from SanwuAudio use the PSTool, search for name, type in the new name and press Set.
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