Saturday, 19 May 2012

Digital rail cap swaps.....OsCon SEPC

Reverse Engineering the power rails!!!!

Spent a fair bit of time identifying various devices on the main board
There are 3 linear voltage regulators related to the DAC, clocking and audio processing.
U18 voltage regulator for the codec chip U12 Wolfson WM8974
U20 is the 3.3v voltage regulator for the clock section including U14,U15 and U33 which are generate and buffer both clocks and using logic switch the active clock frequency. U34 is buffer logic for the SPDIF out which also shares this regulator.
U21 is the 5V voltage regulator for the AKM4420 DAC both analogue and Digital. Its also provides the 5v feed for the touch screen.
I'll fit 470uF OsCon SEPC solid polymer caps where possible on the digital supplies.
C144 is the main 5v rail cap (Replace the original cap)
Directly to the supply pins of U15 and U33 clock select logic (not in photo)
Directly across C133 & C131 for the DAC
Directly across U34 SPDIF Buffer logic (not in photo)
Output side of 3.3v reg across C106 (not in photo)
Output side of 5v reg across C135
Finally, the output of the DAC itself has caps in the signal path which are not required as there is no DC present on the audio output which can be seen as wire links in the above picture.

Saturday, 5 May 2012

Hardware Mods part 1 - External PSU (historical)

Squeezebox Touch Hardware Mods

I've been running squeezeboxes for a good few years now and I still own and original SB and modified SB3(blog here). I've always been interested in the Transporter but I don't think it would be any better than the modified touch I'm using now.
Like most of these things, the place to start is at the wall wart switched mode power supply. These are used as they can be made very cheaply and can effortlessly provide higher current requirements.
Having experienced excellent results with over specified linear power supplies and my own low noise voltage regulator in various applications including the SB3 this is where I started.
50VA toroidal transformer, Hexfred high speed diodes and 2 x 22,000uF Panasonic TSUP capacitors provide approve 11v DC unregulated which can provide in excess of 5A. Ultimately, the Touch will need a few power supply rails. The main 5v regulated rail and an unregulated rail to feed the clocks and new internal regulators.
Initially, the power supply with its low noise 5v regulator can supply the whole Touch in place of the original wall wart PSU