Mini DAB Walk Radio DAB-P9

Since I had the radio opened for analysis, I took no chances of wasting time trying to attach the carry handle into the tiny "U" aperture of the cabinet, and therefore I have just put the handle thread loop into its allocated position in the cabinet corner before setting the back cover in its place.

The battery indicator had two bars out of three when I got the radio new in the box. 

After closing the back cover it was time to do some more relaxed listening to my FM favorite stations and see if my inside analysis job did not break the radio. 

After some hours of listening, the battery indicator was flashing and empty. 

I plugged a USB AC charger using the supplied USB cable and I left it charging in the power off state for around 4 hours. Initially the charging indicator blue LED was lit and then went off after the charge was alleged complete.

I suspect the current consumption is on the heavy side when using the built-in speaker, as after a couple of hours of listening at moderate level, the battery is again with only two bars. I still have to use it on earphones but it is expected to have a longer battery life as the load is much lower.

Either that or else the 1000mAh battery is on the weak side; maybe it just needs a few discharge/charge cycles to get its full performance. I reckon now that I forgot to take battery current consumption measurements, so probably that would be one of the next steps to further document this radio .

As expected, the FM reception was unaffected with RF interferences while using the USB charging

However, when sitting the radio close to my LED workbench lamp it reduces the receiver sensitivity considerably, losing quality and the RDS data is lost as well. In this respect, the double priced Sangean DT-800 is no better here, showing the same results. I see this behavior in most DSP radios.

 

Jose Mesquita, 06.Nov.22

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General remarks on build design and operation performance

I was looking to acquire this little pocket radio sold by several Chinese sellers under different brands, namely the well known Sihuadon, where the common identification was the back label calling this radio as DAB-P9.

Also I was unable to find any technical details of the chassis setup, even pictures of the internals were unavailable on a extended search. 

The build construction looks good for the price. On the outside, the cabinet feels solid, and the six self tapping screws on the back cover are hidden under six plastic caps of the same cabinet color.

For some reason, they ship the carrying handle apart as an optional accessory. Some reviews I saw from owners complain about this, as apparently it is not so easy to attach the handle to the radio. I didn't try yet to insert it in cabinet dedicated aperture, but I suspect it will require a needle to pick and pull the thread and some patience to do it.

The LCD screen is small but the indicators and text show strong contrast, easy to read despite the small font used. 

The FM band sensitivity and selectivity looks fine to me, and I am currently in a remote location dozen of kilometers away from transmitting towers. Also the FM-RDS seems to be working fine, on pair with my double priced Snagean DT-800. 

There is no DAB transmitting stations in my country, so I can't comment about it. 

In addition to the telescopic antenna, the earphones wire acts as antenna as well.

The sound quality is acceptable for this kind of product, both on the built-in speaker and earphones. My Sangean DT-800 may beat it but not by much.

 

Internals view

After opening my radio unit, I could finally see what were the design choices. So much miniaturized hardware in so small PCB sold at a modest price.

There is only one PCB assembly and the Display unit.  The built-in speaker is not glued to the front cabinet,  being fixed in place with the help of rubber foam. The Li-Pol battery however is fixed using a strong double-sided glue tape.

A powerful audio amplifier XS9971 IC is used to drive the built-in speaker to more than acceptable sound pressure levels for such a tiny 2.3cm driver. The driver speaker uses a long excursion throw voice coil able to handle up to 2W. The datasheets inform that this IC is able to deliver 1.8W to a load of 4Ohm when running at 3.7V operating in class AB setup. 

I found an interesting design choice inside. Several features are overlap between the AP8048A MCU IC and the AC6905A MP3 playback IC, among audio codec and playback, LDO power supply regulators, earphones output, SD card support, file system, and so on. 

As I see it, there is nothing in the AC6905A IC that the AP8048A could not handle. But for some reason they used a dedicated AC6905A to handle the SD card and MP3 playback functions. This forced to use an additional 24MHz TCXO crystal, increasing the production costs even more.

Also the AC6905A supports features not enabled in this chassis, like FM radio or Bluetooth (this radio model does not offers BT). 

As a side note, JL (Zhuhai Jieli technology) obtained the AC6905 (AC690X series) Bluetooth 4.2 certification in 20-Dec-2016, but later on in 2021 some vulnerabilities were found that forced JL to replace these IC series with updated versions. These issues can be found at the CVE REPORT website, look for CVE-2021-31611, 31612, and 31613.

The JL (Zhuhai Jieli technology) curious case

One final note on JL (Zhuhai Jieli technology) IC designation. They mark the IC's with such references that makes it impossible to find any specifications. After much searching, I found I was not alone, several people were baffled by this JL approach. 

Then I accidentally found pictures on AliBaba and AliExpress showing a AC6905A  label associated with the reference AC21BP0A902-5A8 that I have on my radio unit for the JL IC.

After some more time searching images and associated text, I realized that only the first two letters and the last group of digits/letters would designate the IC reference.

However the story is more complex as the other digits/letters do have a meaning not disclosed, probably some of them refers to the loaded firmware, and I believe the two digits after the two initial letters may refers to the production date. Some examples:

• AC19AP1Q796-25B4 == AC6925B
• AC20BP01111-28B4 == AC6928B
• AC218P02509-55F4 == AC6955F
• AC21BP0B057-65A == AC6965A
• AC21BP0G282-65E4 == AC6965E 

• AC1649AP0V934-5A8 == AC6905A  -> year 2016?
• AC21BE00716-5A8 == AC6905A -> -> year 2021?
• AC1649AP0V934-5A8 == AC6905A
• AC19AP1Q769-5A8  == AC6905A
• AC1714AP0Z242-5A8 == AC6905A

In the present case of the AC6905A, belonging to the 690X series, it seems that it is the base general designation of a specific features set. Then there are different versions of it depending on the loaded firmware that will enable/disable/configure the final feature set.

 

Partial parts listing

The diodes, resistors and capacitors were not included in this listing. The components labels were set arbitrary as I could not see silkscreen labels for them.

The PCB shows the Ref. "LT-DAB-P9 0925"
 

PCB underside: Control and Power Supply

Q1    A1SHB  HM2301B 3-pin SOT-23 Power P-MOSFET - Power switch 
Q2    1AM M  MMBT3904L 3-pin SOT-23  NPN 200mA 40V 200mW
Q3    1AM M  MMBT3904L 3-pin SOT-23  NPN 200mA 40V 200mW
Q4    1AM M  MMBT3904L 3-pin SOT-23  NPN 200mA 40V 200mW
Q5    1AM M  MMBT3904L 3-pin SOT-23  NPN 200mA 40V 200mW
Q6    1AM M  MMBT3904L 3-pin SOT-23  NPN 200mA 40V 200mW
Q7    2A  MMBT3906L 3-pin SOT-23  PNP 200mA 40V 220mW
IC1    DW01-A  6-pin SOT23-6 4.3V One Cell Li-ion/Polymer battery protection 
IC2    8205A  6-pin SOT-23-6L Dual Power N-MOSFET -  Used with IC1 

PCB Top side: Receiver stage R-WB sub-assembly

X1     4-pin 24.576 MHz TCXO
IC3    S79  AS179-92 6-pin SOT-363 3GHz FET SPDT RF switch
IC4    8035  QN8035 10-pin MSOP10 Stereo FM RDS/RBDS receiver by Quintic
IC5    FC8080Q  32-pin QFN by FCI - T-DMB DAB OFDM RF Tuner/Demodulator

 

PCB Top side: Audio amp stage for built-in speaker

IC6    XS9971  8-pin ESOP8 Class AB/D Audio Power Amplifier 

PCB Top side: MCU stage

X2    2-pin 32.768 kHz
IC6   AP8048A  48-pin LQFP48 ARM Cortex-M3 by MVsilicon Audio Application Processor
IC7   25Q16ESIG SOP8 8-pin by GigaDevice 16Mbit serial flash memory
LCD LCD assembly with LED back light - 12-pin interface cable

PCB Top side: MP3 Player stage

X3     4-pin 24.000 MHz TCXO
IC8    AC21BP0A902-5A8  AC6905A 24-pin SSOP/QSOP-24 by JL Zhuhai Jieli Technology
SD1  SD Card Socket Adapter 

 

 

 

Jose Mesquita, 03.Nov.22

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