wavelength brick power supply
Power Supply for
Wavelength Brick USB DAC
Built 2-2009
Wavelength's website is USBDACs.com and is highly recommended for its wealth of information on USB DACs in general as well as setting up and configuring a PC based music server. Gordon Rankin also deserves thanks for his frequent contibutions to the on-line community at Audioasylum.com.
Between the time I started this project (at my usual slow pace), and the time I completed it, Wavelength released its own upgraded power supply for the Brick called the Mortar. I suggest you check it out.
MPB's High Current Power Supply
I've found that wall-wart power supplies often present an opportunity to improve audio circuits by replacing them with well regulated high current supplies. So, I decided to build a new supply to replace the Brick's stock supply.
I based this design primarily on the article entitled "Preamp Power Supply" by Gary Gallo in The Audio Amateur magazine, issue 4/90, p.47. In that article, he indicates several key changes from the datasheet recommendations to optimize simple three terminal adjustable regulated power supples for audio use, all of which I incorporated into this supply. They include:
1. Use of a much higher current transformer than traditional, I used a 15V 100va transformer from Antekinc.com, part number AN-1215. The stock wall-wart is 1000mA at 13.5volts, or 13.5va.
2. Use of very large output capacitors (typically data sheet recommendations are much smaller than the input caps).
3. Use of divider resistor values around the regulator IC that are several times the typical values, dramatically reducing output impedance and ripple rejection.
4. The use of Linear Technology LT1085/LT1033 series adjustable regulators instead of the common LM317/337s. This supply is only positive, so there is no LT1033 used here to created a negative supply.
Most of the parts, except where noted, are from Mouser.com or Digikey.com.
I used a PCB from Peter Daniel, of AudioSector.com, who is very helpful and highly recommended. The PCB is actually one half of an F3 power supply PCB, designed by Peter for a wide variety of power supply uses, and perfect for use here. As an aside, the F3 is a variant of Nelson Pass's Zen amps.
Above: Views of the unstuffed PCB, showing bottom view at the top, and top side below. Peter's PCBs are always works of art with gold plated thru holes. Click on any photo for an enlarged version.
Above: Populated PCB, before wiring it up (click to enlarge). The regulator is actually an LT-1086, the 1.5 amp version of the 3 amp LT1085. I used two Nichicon KG filter caps: 4,700/50V before the regulator, and 5,600/35V after. Rectifiers are MUR860s. Output voltage is set to 15.0V with dividing resistors around the regulator of 1K and 10.5K. I also added small 0.1/160 Vishay 1837 bypass caps on each of the big caps.
Above: Partially assembled chassis from the rear, before the PCB was installed. The chassis is a two part aluminum case bought on ebay. Search using "Aluminum Project Box Enclousure Case", note the mis-spelled version of "enclosure".
Above: Completed top view, showing general layout. Click to enlarge. The regulator PCB is to the right, meter to the left, power transformer in the center.
Above: I found a beautiful old 15 volt Simpson model 125 meter in my parts bin, so I added it to the front panel.
Above: Rear view of the power supply. Pretty simple: hardwired output cable (to avoid another connector), IEC and power switch. The switch is on the back as I expect to leave the unit on all the time. Note that there is a 1A slow blow AC line fuse, located inside the chassis on the rear panel.
The power supply and Brick draw only 2.3 watts when the Brick is not playing (in standby mode), and 8.8 watts when it is playing.
Above: Finished unit, front view. The faceplate is from FrontPanelExpress.com. Just remember to specify that you want the grain of the panel to go horizontally.
Above: OK, I couldn't resist. "Brick on a Brick" or "Brick Squared". This is not my usual setup, but shows my power supply, along with the Wavelength Brick, along with a VPI "Magic Brick" (normally used on my amp, mostly to dampen chassis vibration).