I bought an amplifier board too, it ("BLAMP-50W-V3",
http://www.ebay.com/itm/281967072104 ) is built around the TDA7492 50W class-D amplifier and a CSR8635 bluetooth module (without antenna). The main board is populated with a a DC socket for power (center positive). Pairing went without problems ("M-DIY-AUDIO-"). At 12 V it draws less than 100 mA with "JBL Control One" (~10 yrs old), and I don't need it much louder. The AUX input (3.5 mm stereo) has a contact to detect if something is plugged in and it seems to be routed via the nearby SGM4717 analog switch. Volume control is digitally controlled via pushbuttons and I suspect that everything goes through the bluetooth module. Unfortunately, there is quite a bit of quiescent noise. It's tolerable at room level but not suitable if you want to listen to something very quietly (e.g at night). Dialling down the amplifier gain level via DIP switches helps a bit, also making the source louder and the module quieter seems to help a bit.
Actual problems however are the default volume level and the startup sounds. Powering the board, one is greeted with a loud "du du du da - blip" followed by aforementioned audible white noise. It takes 6 "volume -" button pushes to get that down to bearable. So I am trying to figure out how to change that.
I seem to have found the pinout of the module in question, "F-3288":
http://www.aliexpress.com/item/New-Arrival-Bluetooth-4-0-Stereo-Audio-Module-Control-Chip-CSR8635-Stereo-Bluetooth-Module/32308035803.html http://www.dhgate.com/product/bluetooth-stereo-audio-module-ble-4-0-module/241472833.htmlTrying to figure out the audio signal paths:
MIC -> C82 -> SGM4717 Pin 2 NO1
GND -> C86 -> SGM4717 Pin 5 NC1
SGM4717 Pin 3 COM1 -> BT-Module Pin 27 LINE / MIC_AN
MIC -> C87 -> SGM4717 Pin 10 NO2
TRS Audio jack Tip (left channel) -> C81 -> SGM4717 Pin 7 NC2
SGM4717 Pin 9 COM2 -> BT-Module Pin 28 LINE / MIC_AP
TRS Audio jack Ring (right channel) -> C80 -> BT-Module Pin 31 LINE_BP
TRS Audio jack Sleeve (GND) switch contact -> BT-Module Pin 19 RX (PIO0/PIO1?*)
BT-Module Pin 30 LINE_BN -> C88 -> GND
BT-Module Pin 18 TX (PIO0/PIO1?*) -> SGM4717 IN1&2
*note that the schematics differ from pinout
So the analog switch normally routes the audio jack to the IC's Line in pins, but the IC detects if no plug is present and then has the choice of using the microphone as input (for the bluetooth hands free function). So the audio is ADC/DSP/DAC'ed and I think that might not help with the noise.
So I am thinking about bypassing/mixing the jack input directly to the amp input, which should be accessible at the filter capacitors next to the BT-Module outputs. However, to be able to use the Bluetooth audio as well, I need to at least change its startup volume and sound. So ...
The BT-Module has 4 undocumented pads on top, near the GT4128 "2-WIRE 128 K Bits Serial EEPROM" (
http://www.giantec-semi.com/upload/datasheet/GT24C128_DS_Adv.pdf) :
1 (module corner) EEPROM Pin 7 WP - CSR Pin PIO12 Pin 22 (SPI flash chip select)
2 CSR8635 Pin 31 - PIO13 (SPI flash data bit 1)
3 VCC / 1V8
4 GND / GND
What could this be used for?
Found the datasheet:
http://www.datasheetcafe.com/csr8635-datasheet-csr/ ->
http://www.ndatasheet.com/datasheet-frame/300/mdownload.php?id=869877EEPROM connections (see pads above)
1-4 GND
5 SDA <-> CSR Pin PIO11 Pin 26 (SPI flash data bit 0)
6 SCL <- CSR Pin PIO10 Pin 25 (SPI flash clock)
7 WP <- CSR Pin PIO12 Pin 22 (SPI flash chip select)
8 VCC (1.8 V, up to 5.5 V for GT4128 only!)
So reading this directly is not out of the question but the work is probably the same.
This leaves digging out an unreliable FT232RL board I made years ago...
On this module, PCM needs to be pulled high to enable the debug SPI interface (and I think released again, to test the new settings).
So far I have been able to change the device name but my changes have always caused problems (and suspected bricking, but then after a few trials, reading/writing was possible again) . At the moment, I cannot connect to the device at all; the programs just freeze at "communicating with device". Buriedcode might be right. I think the last I tried was "Merging" a ConfigTool .psr file into the connected device in PSTool... Maybe my FT232RL wires are falling apart.
I have written a small Python script that reformats the ConfigTool .psr into something more similar to what PSTool generates. Makes it much easier to compare. Will publish that soon.