I’ve been aware of this product since its intro and glowing review in 1996 (Stereophile, Robert Harley) . Never could afford it, tho. And even eBay prices on vintage gear is quite high.
To that end …
I would like to build something similar for my older DACs in the house. Just a block diagram or (optimally) a service schematic would be handy. Please help if you can. Thx!
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Not an easy project for a DIY. Basically, the DL (designed by our chief engineer, Bob Stadtherr) is a 500kB RAM buffer FIFO. The output of that buffer is clocked by a low jitter ultra-low noise/phase clock running at a fixed frequency and controlled by a crystal oscillator.
The idea was that if you can clock the digital data stream with a low noise fixed clock, there will be essentially no jitter. Then we added a sweet output stage that had no hard edges, and that worked great.
The trick was the input stage.
Because a CD transport (or any digital source) does not use a fixed low jitter clock, its output was all over the map—hence the problem. Loads of jitter.
So, how do you load the DL buffer FIFO so it doesn’t over run or under run the buffer?
Bob came up with a “simple” solution. A bit of logic that turned the FIFO into an intelligent buffer. By monitoring the input and calculating its speed (too slow or too fast), he set the buffer length accordingly.
Within the limits of the device, that meant a steady output stream without hiccups or burbs of data.
Hope that helps.
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@ hanz,
check out this thread, it’s long, but lots of good learning material.
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Yes, I am aware of that diyaudio thread. Also there are others threads on that forum about FIFO RAM buffers …
NOTE: the PSAUDIO weird forum engine will only allow one external URL link per post. So I had to break this reply into three posts.
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There was a Technics -1000 MASH CD player from 1989 that used FIFO. It was full of those gazillion 74HC logic devices as well.
NOTE: the PSAUDIO weird forum engine will only allow one external URL link per post. So I had to break this reply into three posts.
And …
The Mark-Levinson 30.5 (1995 dac) also used similar FIFO RAM. But perhaps the most interesting application is in Chord’s original DAC 64 (2002). Note what John Atkinson wrote about the RAM buffer … paragraph two in the Listening section…
NOTE: the PSAUDIO weird forum engine will only allow one external URL link per post. So I had to break this reply into three posts.
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The posting limitation is for new users.
Hmmm … even back in the mid-90s, when I assume the DL was designed, there were monolithic IC devices that could do FIFO RAM inside that single chip.
Also, low-noise clocks (osc circuits) have been circulating in the Ham magazines since radio began.
I assume there is quite a bit of art to getting the jitter and distortion down to “audiophile” levels. Tweaking the design with o’scope and SA. Hence the DL with all those gazillion 74HC chips and independent power regs. Egads!! using all those sensitively tuned components, on a mass production device, and maintaining the consistency of the orig design specs in the mass production must be quite a challenge. Issues/snags with that approach may indeed be what JA, in the 2002 Chord DAC64 review, seems to have run into.
An interesting PS Audio product for the modern age might be DL Mk2, and different from AL. As I noted earlier, vintage gear demand and respective pricing is (and has been) high.
Yes, a product such as DL Mk2 will be controversial on forums like ASR and HydrogenAudio. But … that still brings attention and debate to audio – important, because the Cosmos hates the vacuum of boredom 
And there does seem to be a healthy market: Schiit released their URD cd transport. And non-over-sampling and discrete R2R – all ancient digital technology – has its share of supporters.