Audio Workshop AW-D2

I have been hoping to DIY a DAC but I don't have the expertise to wire up a DAC on my own.  Fortunately, one day while was browsing the web, I found Audio Workshop. Audio Workshop has a numbers of DAC PCB for sale, I picked the newest one : AW-D2. This DAC is based on the AD1955 DAC chip and the DIR1703 digital receiver. The AD1955 is being used in the Philips 963SA DVD player which was getting lots of good review. 

After I ordered the PCB and the ICs from AW, they arrived a few days later. Audioworkshop also give me some free components like capacitors and some inductors. My next step is to start ordring components, which is the most time consuming part of building this DAC.  BTW, AW sells components at a very cheap price, much cheaper than I could find anywhere else. For example, BlackGate 3300uF 16V capacitor, SSP sells at over HK$100, AW sells them for only HK$35.  

First thing I do is to go to Sham Shui Po to buy all the general components like case, transformers, cables ,connectors, and LEDs. I also tried to buy all the resistors there but some values are hard to obtain. Then I ordered the other components from Farnell. Farnell carries most non-hifi components and they do have free shipping for HK$200 order.  For hi-fi specific components, I ordered them from audioworkshop. I originally used a pulse transformer that I bought from Farnell, but I find out later that its bandwidth is only up to 1MHz, so I bought the Pulse PE-65612 from DIYZone.net to replace it.

After I got all the required components for the DAC, I start doing the soldering. The DIR1703 and the AD1955 is pre-soldered by AW. That make my life a lot easier as these 2 chips are quite hard to solder. I solder all the low profile components first, it would be easier this way. The first problem I met is I got the SMD capacitor size wrong. I ordered 2220 from Farnell but I should use 0605 type. The 2220 is a lot bigger so I have to solder them at the back of the 0.1uF pads.

I used IC sockets for all the ICs on the board. It is safer for the ICs and also I can change OP-Amps easier for sound tuning. The OP-Amps used are 4x OPA627AP for the I/V conversion and 2x OPA637AP for the low pass filter. I used mainly 3300uF Panasonic FC, Philips 0.1uF, and ELNA Starget 47uF for de-coupling. Only one blackgate 100uF is used for the AD1955’s power decoupling. So most of the capacitors I used is not really exotic.

For transformers, I used 2 R-style transformers. One for analog circuit and one for digital circuit. I use R transformers because they are smaller in size, efficient and low noise.

The aluminum case is connected to the earth of the power socket。The GND of PCB is connected to the case via a ferrite bead and a 10 ohms resistor in series.

The power regulator board I used is AW-R1. I selected using LT317/337 as the regulator ICs. The input capacitors I used is Rubycon 4700uF for its cheap price. Output capacitors are Panasonic FC 2200uF.

After everything is soldered and put into the case. I first adjusted the voltage output of AW-R1 before connecting it to AW-D2. After everything is connected, I do a double check to make sure nothing is shorted or connected wrong before powering it on. It was fortunate that I do this step, because I found the +/- 15V was connected in reverse! The coaxial cable used to connect the RCA socket and the D2 PCB need to have a good shielding if the cable length is long. Otherwise some digital noise will be coupled to the analog side. The one I am using has 100% aluminium foil plus 93% copper braid.

After power on, the LOCK led is off, which is normal because my CD player is not on yet. Then I truned on my CD player, one second later the LOCK led was on. That’s a good sign since that means the DIR1703 can lock the SPDIF signal. I play some music and then I measure the AC voltage of the audio output. I got some reading. Then I measure the DC offset of the DAC output to make sure there is no DC offset. Everything is fine then I connect the DAC to the pre-amp and turn on the power amp at the same time. I heard music from the speakers!