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Intro

First of all, I'm an analogue fan. However, I have over 600 CDs, so I have been thinking of building a nice DAC for a while. After attending my first VALVE meeting in 10/2002, John Tucker (aka Smoothplate) gave me the idea to build a DAC using one of Crystal Semiconductor's evaluation boards to build my own DAC. I chose the CS4397 24-bit 48/96/192 kHz, stereo, digital-to-analog converter. It works with both CD (PCM) and SACD (DSD) formats. NOTE: I have yet to see a SACD player with a DSD digital output.

The evaluation board costs $150 USD. It includes a basic power supply and a solid state analogue filter. The board includes DIP switches that allow you to switch between PCM, DSD or auto mode when used with a SACD player. In PCM mode, the stock evaluation board sounded better than the built in DAC in my old Onkyo R1 CD player.

during my research, i came across Andrea Ciuffoli's "Transformer-Coupled Tube Headphone Amplifier With Digital Input" project. After talking a bit with Doc B, he told me that he was using transformer coupling in his DAC as well. I decided to go with Andrea Ciuffoli's bandpass filter and Lundahl LL7902 1-1 transformers from K&K Audio. I also used a Lundahl LL1566 pulse transformer on the digital input to separate the transport from the DAC. Adding these transformers added even more clarity.

Start-up Delay

One problem with the CS4397 evaluation board is that upon power up, the DAC is not reset and no sound comes out. The only way to reset it is to push the DAC reset button on the board. Since I didn't want to do that after I built a house for it to live in, I decided to build a simple delay circuit using a 555 timer. I had all of the parts amongst my junk anyway. The timer holds the output low for 1.1 seconds until everything powers up. You can change a resistor value (the 1M in my circuit) to get a different delay. To install this, you have to replace R7 (a 10K surface mount resistor) on the evaluation board with the input and output of the delay circuit.

Power Supply

Both the data sheet for the CS4397 evaluation board and Smoothplate recommended that a good power supply is what will really make this thing fly. The evaluation board has terminals to hook up a +/- 12VDC supply. After adding the new power supply, the grunge went away and things really cleaned up. At this point, the DAC sounded really nice. I brought it to friend's house and hooked it to his Sony SCD777ES SACD player. We both thought it sounded better than the stock DAC.

More Mods

Upon advise from VoltSecond, I added some more filtering. This consists of:

  • the 0.01uF ceramic cap from the BNC - to ground
  • the 1k0 resistors following the LM7812 and LM7912 regulators to ground
  • the 10k0 resistors and 0.01uF ceramic caps from the output - to ground
  • updated reverse recovery spike filter

VoltSecond also suggested adding a constant current source. I have the parts but have not implemented this as of yet.