randytsuch's audio page

5VDC for the DAC

The 5VDC analog power for the DAC comes from a linear reg, but the linear reg is powered from a switching reg on display card. I decided to supply my own power to it, but for the time being, I am still using the little 5v reg on the SB board.

To do this, I removed R29, shown in this pic. To get to R29, you need to remove the wireless board (if you have one) and the processor card. R29 is under them.

Then, I just connected a wire to the positive lead of the "big ass" cap, which is to the right of R29 in this pic.

For now, I supplied a voltage of around 11.5 volts, unregulated. Its the same power I feed to the PowerReg, which generates the 5VDC input for the main SB board.

It made a small improvement, I was actually expecting more. Things sounded a little cleaner, and I think the highs improved the most.

This turned out to be a temperary solution, I will explain the more permanent change later.



5VDC for the Display board
Since I was not using the +14 from the display board anymore, it was time to feed the Display a different +5. In the stock SB, the display board is powered from the same +5 that powers the main SB board.

This involves isolating the display board from the main +5, and generating a seperate +5 to power it.

You need to remove the processor card to make this cut.

To power the display board, I used a seperate 6.3V, 12VA hammond TX. This TX does not go to a Felix, it is powered directly from the fuse board.


I connected the secondaries of the TX in parallel, so it generates the 6.3VAC at 12VA, and then ran two wires to a bridge. The bridge is next to a cap, as shown here. And both of these were glued to a heatsink, which is in the corner by the display card.





On the other side of the heatsink, I have a generic 7805 regulator, to take generate a regulated 5VDC. It puts out 5.1VDC, which is good enough. After hooking up the regulator, its a good idea to check the regulator output before connecting it to the display :)










All that's left now is to hook up power to the display board, which is easy because there are test points you can just solder wires to.






The ground test point is labeled J3


The +5 test point is labeled J17.
They are right next to each other, on the left side of the display board looking from the back.


This change had a bigger difference then I expected, I thought the background noise dropped, and things got "blacker" after making this change. I think it keeps noise generated from the switching regs on the display from getting into the main SB.