In yesterday's post I had been driven crazy by the remarkable performance improvements of a product that made no sense. A CD transport producing the bits feeding a DAC.
What in the world? Bits are bits. Every engineer and scientist willing to offer their opinion agreed. The beauty of digital is its ability to be endlessly copied without degradation—transported around the world over every means possible from telephone modems, satellite relays, and underwater cables to a new fangled optical interface. Bits are bits. Get them right and without drop outs or confusion and the only differences possible would be in the conversion process of producing analog.
Only, a new transport we had acquired was turning our world upside down. Those identical bits sounded remarkably different when played through the Jadis JD-1 transport than through any other medium we had.
And to make things even weirder it didn't matter where we had obtained those bits. Commercial CDs as well as CDr copies of those same CDs Arnie and I had ripped and then burned all sounded remarkably better.
In my investigation, armed with little more than a fancy capture scope, I narrowed down the only difference I could see. A difference that made zero sense whatsoever—in fact, so little sense that I continually rejected the observation as mere noise and clutter. Couldn't be.
When you're faced with the impossible, and it is the only option available to you, it's a good idea to let down your guard and accept it as the best possibility. Run with it to see where it takes you.
The output digital signal from the Jadis had two major differences from any other digital output I could see. Amplitude and shape. Instead of the industry standard output level of 1.2V (or so) the Jadis output a whopping 4 volts. On top of that, the output square wave shape was different. Smooth and without over or undershoot visible. It looked to me like a beautiful square wave that any analog or tube designer would be happy with if their analog circuit had output it.
But this was digital bits—bits that would never see an analog circuit—bits that were used only to trigger an input flip flop on the DAC. This could not matter!
WTF? I had to know.
It didn't take more than a day or two on the breadboard to build a little op amp circuit that would take in a standard output from a transport and amplify it up to the 4 volts to match the Jadis. This circuit got slapped onto the output of our previous CD reference transport and I pressed play. Wow. Did it have the magic of the Jadis? Yes and no. I would give it an 80%.*
This was clue number one. The output size and shape mattered. What came next was even more surprising.
*over the next few months I experimented with shape, using a softer JFET input stage op amp to round off the corners of my larger output square wave and this filled in the remaining 20% of the mystery for that transport.
