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.

Wednesday, October 01, 2008


Squeezebox 2 rebox part 1

So here is my SB2 rebox story.

Top still needs painting

In short, it is a SB2, with three Felix’s for power filtering, a bunch of transformers, mostly CRC filtering, a variety of regulators, a built in Burson Buffer, and provisions for adding a Twisted Pear Buffalo DAC later. Clock is a Tent clock XO3.

Here is a pic of the guts, not quite finished, but getting close

Bought a par metal 20-16165A for $64.50 for the chassis plus $15 for internal plate.
This one has “Gold/Clear alodine finish for EMI shield”. Alodine is conductive, so after you screw the thing together, the top makes electrical contact with the bottom, and front and back, as long as you don’t paint over the wrong part. And Aluminum is a good EMI shield.

It is a 16 x 16 x 5 box, so lots of room to put stuff in it, and I plan to use lots of the room

I had some different thoughts about how to handle the display.
I was going to make the entire front out of plastic, and sand everywhere expect a box for the display. I saw a thing where Peter Daniels did something like this, and it looked nice.

In the end, I got lazy. I cut a rectangular hole in the front, a little smaller than the SB2 smoked plastic display front. I then filed the hole a little bigger, until the display would just fit in snuggly, so I could “press fit” the display into the hole. I pressed the display into the front on a flat surface, then epoxyed the display in place, so it won’t come out. I also made a few cutting mistakes, where there were some gaps, and I used epoxy to fill in the gaps.

Not perfect, but it looks OK, as long as you don’t look too close ;).

To mount the actual display, I exposed flat head, number two screws in each corner. The display board has mounting holes in each corner, even though they were not used, but I thank Squeezebox for putting them there. The display is simply mounted with the screws, with a small gap between the display itself, and the smoked plastic.

The first time I tried, I did not use enough epoxy, and some of the screws came off, so this time I used more epoxy

AC Power
When I started this project, over one year ago, I was going to use a Felicia, and a REALLY big transformer. At some point, I decided to take a more “distributed” approach.

I ended up using three Felixes, and a bunch of different, smaller transformers. Pretty much dedicated transformers for different functions.

I did not use the group buy Felix cards, because they took up too much space, so I made a smaller version

Here is the at this time uninstalled IEC jack, with my “fuse” board, and the first felix. The transformer is for powering the burson buffer power supplies

Here it is, after wiring in the switch and IEC, but its harder to see stuff.

The three Felix’s are separated per below:
1. Analog circuits – Burson buffers and analog DAC supplies
2. Digital circuits – Digital DAC supplies
3. Digital circuits - +5 for SB2 and clocks.

These feed the various transformers I have.
T1 36VCT, 44VA for Teddy Reg Felix #1 (Analog)
T2 Not installed yet. Felix #1 (Analog)
T3 12.6 VCT 12VA for +5 DAC Felix #1 (Analog)
T4 12.6 VCT 12VA for Display no filtering
T5 Not installed yet 12.6 VCT 12VA for 3.3 V DAC Felix #2 (DAC)
T6 12.6 VCT 12VA for 3.3 V SB2 Felix #2 (DAC)
T7 12.6 VCT 12VA for Clock Felix #3 (SB/clock)
T8 16 VCT 25VA for 5V SB2 Felix #3 (SB/clock)

12.6 VCT 12VA = Hammond 164G12

Picture of power side of box

When the transformers are close to each other, I put them at 90 degree angles to each other, to reduce interaction between them.


Squeezebox 2 rebox part 2

This picture helped me figure out how to power the SB2

First, I built a power supply for the +5, 2A input in to the SB2, replacing the cheap walwart that come with it.
To start, the AC is filtered by Felix #3. Then, AC goes to a Signal Transformer, 16 VCT, 25 VA transformer, courtesy of my local surplus store.
I started with a Hammond 12.6V CT, 12VA transformer, but it was a little underpowered, at least I thought so. Powering a SB3 with wireless, Hammond would get to about 130f, with a room temp of 75f, so a 55 degree temp rise. Plus, with the reg I was using, the voltage was a little low. I expected it to provide 6.3*1.4 = 8.8 volts. I got closer to 7.5 volts.

With the larger Signal tx, I get around 11.5 VDC out of the bridge.
After the transformer, I have a full wave bridge, using two diodes, with the centertap going to ground. So, one diode goes to the one secondary tap, the other diode goes to a tap on the other secondary, and the two other taps are tied together, and these two taps form the ground.
This feeds a Panny, 3300uf FC cap, then a small inductor, another 3300uf cap, 0 .47ohm resistor, then a Jensen 10,000 uf cap. The Jensen cap is next to the regulator.
In general, I kept the transformers, bridges, and the first and 2nd caps in the noisy part of the box.
Not the final wiring needs to be cleaned up still.
For the regulator, I am using a PowerReg, a higher power version of the TeddyReg, from PFM.
Link here
I used these values for my PowerReg
R1 = 479R
R2 = 90R5
R3 = 50K
R4 = 100 K (added on top of board)
R5 = 50K (marked as R4)
R6 = 110R (marked as R5)
C1 = 0.1uF X7R Ceramic
C2 = 10uF Tantalum
C3 = 10uF Tantalum
C4 = 33uF Tantalum
C5 = 0.2uF X7R Ceramic
C6 = 3.3uf Wima MK4
T1 = SK117 GR
T2 = BC550C
T3 = D45H11
LR1 = LT1038

Heat sink is out of my junk drawer. Overkill, it hardly gets warm at all.
Ground is connected from the SB to the reg by a VERY short wire, it is under the yellow tantalum cap in this picture. I scrapped off some solder mask, in the ground plane, as close to my PowerReg as possible, to make the ground wire short, so the two grounds would be well coupled.
I removed the power connector, and connected +5 to a pad for an inductor right after the power connector. I also removed the inductor. I also added a 220uf silmic, close to where I wired power in. There were a couple holes, near here, a convenient place to install the cap. You can just see the top of the cap at the edge of this pic.

When I first powered up, I thought it was not regulating well, because it varied a lot over different loads. I had three 15 ohm power resistors to test with, and I would add them in parallel, so I could draw up to one amp with a 5 ohm load at 5VDC out of the reg.
Turns out, my input voltage was not as high as I expected, so the input regulator was not regulating, because I was not feeding it enough voltage. I started with a LM317, but changed to the 1038 because the 317 needs over 2 VDC of voltage difference, the 1038 is around 1.3 volts.
2nd problem I had was the PowerReg comes up too slowly, and the SB did not come up when I powered the reg up. Fortunately, Teddy came up a quick start up circuit, because other people had similar problems with the TeddyReg. adds a transistor, and a couple resistors. Resistors are same value as R3 and R4 (50K and 100K). Transistor he used was a BC639, a NPN with 1A collector current. I found a MPSA42 in my transistor box, a NPN with 500mA collector current.
Added the resistors and transistor to rear side of board, hooked everything back up, and the SB2 came on when I turned plugged in the power :).
Last problem was with tweaking the output voltage. Seems like the voltage drop from the circuit varies with the regulator output voltage, the voltage drop increases as the regulator output voltage increases.
So, I had it working, but output was around 4.8VDC to the SB. I calculated new values, to get a 5.2 V output, but it was lower, because of the increased drop. It took one more iteration to get my current values, voltage is 5.14, where my target was 5.2VDC.

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