Thursday, October 02, 2008


Squeezebox 2 rebox part 4

Part 3
So, I decided to upgrade the +5 DAC power, to use a separate transformer/bridge/caps/regulator.

For this +5 DAC power, again using a Hammond, 12.6 VCT, 12VA transformer, filtered by Felix #1.
This is full wave rectified with two diodes, then to a CRC filter with 3300uf FC caps and a .47 ohm R.

Regulator is a single voltage version of this
They no longer have the model I bought on their website.
I was buying some discrete buffers from them anyway, they had a 2 for 1 deal going, so I decided to buy one of these regs, it was only $10.

Based on the PCM1748 datasheet, I need 13mA max of +5V, and 10mA max of 3.3V for the DAC.

+5 is now set up for 50 mA, so I need to change some resistors for a lower current, or add a load to it, to draw more power. I added a load
40 mA
R = 100 ohms gives a load of 50ma + the 13ma, max load of 63ma
But the transistors were getting kind of warm, so I disconnected the load resistor.
I am going to try a 200 ohm resistor, and see what happens.

I put a little piece of perf board under the regulator, to keep it from shorting anything else.

I used one of the screw holes for the transistor, to help hold it down. That, and the wires are holding it down.

I hooked up ground to a pad for a connector I removed.

Power is hooked up to a via, next to a cap on the +5.

I mounted it like this, to keep the wires as short as possible.

Before I made this change, the sound was detailed, but could be a little fatiguing.

After this change, the detail is still there, but sound is more relaxed, no fatigue anymore. Not sure why, I am happy with it.

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