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Lou Dorren: 2007 CD-4 Papers (5)

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JonUrban

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QQ member rolvkarsten has provided copies of Lou Dorren's papers regarding his proposed CD-4 demodulator for posting here. As many of you know, it was Lou's dream to create a modern CD-4 demodulator for the membership. Unfortunately that never came to pass, but here are the 5 papers he created that we can read through and see how far he actually had gotten in the design. The last time I spoke with him he said he was very close to creating the prototype and was going to send one to me for an official forum evaluation. How close that came we'll never know.

View attachment cd-4paper1.pdf
View attachment cd-4paper2.pdf
View attachment cd-4paper3.pdf
View attachment cd-4paper4.pdf
View attachment cd-4paper5.pdf
 

rolvkarsten

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I took the time to go through Lou Dorrens latest - revision 5 - published schematic set of his "High Performance 2007 CD-4 Demodulator", starting here .
(https://www.quadraphonicquad.com/forums/showthread.php?9035-Lou-Dorren-A-new-CD-4-Demodulator!!!&p=164167&viewfull=1#post164167)
Reading through the thread, the five PDFs and some of Kristian's post (forum user "krkier") I extracted most of the B.O.M. (Bill Of Material):

  • U4/U18/U24/U31/U44/U50 - (analogue mux) - Analog Devices DG 5209 or Intersil DG409
  • U17/U43 - (14 stage binary counter) - 74HCT4060 or On Semi MC14060 (or equivalent)
  • U16/U42 - (ANRS - compandor) - On Semi NE570 available at DigiKey (NE570DGOS-ND) or Youwang Electronics UTC571
  • U10/U36 - (FM-PM FSK Demodulator/Tone Decoder) - Exar XR2211A obsolete, but NJM2211 from "New Japan Radio" seems like a drop-in replacement
  • U8/U34 - (limiter) - NXP SA606 (with ability to drive the RSSI meters directly
  • U55/U56 - (NOR gate) - e.g. two single gates 1G02
A good choice for opamps is the Linear technology LT1115 which can run from +/-22V rails and is well suited for moving coil and moving magnet cartridges. Most like also strain gauge cartridges.
Also remember this CD-4 demodulator has a"wide bandwidth" input suited for external RIAA or strain gauge amplifiers.
Regulators and transistors are known and availlable from many sources.

Which leaves the analogue filters. Not much has been said, but it seems not to be a DSP so I think these are built around switched capacitor filters, e.g. Linear Technology LTC1064 or "Active RC" filters like again Linear technology LT1562. These have the advantage not needing a clock located around 800kHz.

  • FDB1/FDB4 - 30kHz BP filter ~40dB out of band attenuation, ref Installment III figure 23.
  • FDB2/FDB3/FDB5/FDB6 - 15.667kHz 8th order LP filter
The filter symbols in the revision 5 schematics are 10 pins and I speculate that Lou Dorren made modules with switched capacitor filter ICs and supporting circuitry like buffer opamps. I.e. small PCBs. Ref to post 986 where the picture of Lou Dorren's PCB shows six daugther boards. Speculation again, two are larger, probably they are the BP-filters and the four smaller PCBs the LP-filters.

What I do not like particularly is the use of analogue switches (the muxes) and switched capacitor filters. The switched capacitor filters require good layout of the PCB, there is a possibility for unacceptable clock bleed through, but they also provide for steep filters without a dedicated DSP. Analogue opamp based filters with resistors and capacitors are also a complex task.
What is possible is to renounce on the filter performance and use e.g. 4th order filters. These will probably be better than the old demodulator designs anyway.

One note on the strain gauge (SG) cartridge input: The design differs between left and right channel design as the opamp U5b for the left channel is inverting while the corresponding U29b is non-inverting. This has to do with the biasing of the SG cartridge, as explained by Lou Dorren in the original thread.

This is my analyzis of the design and project so far.

Regds
Rolv-Karsten
 
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maspadaro

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Hi everyone, I haven't been on this forum for a while.. it doesn't mean I haven't been listening to quads.. got a quad Pioneer 8 track 2 months ago.. not bad.
But I was going to bring up 'Kickstarter', If someone was willing to start it I assume you would get funded pretty quickly, if this idea wasn't brought up before of course. It seems it would be a promising way to get this going but of course I am not a technical person to figure out and carry on what Lou started. But there were a few people here that have looked into the technical data.
I would definitely put money just because I do have a quad system set up and I still prefer to listen to LP's (its easier to find them than RtR or in better shape than 8 tracks). I also have 3 CD4 modulators from Pioneer to JVC to Panasonic. all working.

Regards,

Miguel
 

4-earredwonder

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I guess there has never been a software solution for decoding CD-4?
And even if there was it's all dependent on the quality of the vinyl. As we're all spoiled today with sparkling Quad SACD transfers with, IMO, ultra quiet backgrounds, negligible print through and absolute discrete placement of instruments, vocals, etc., unless the vinyl is in pristine condition, and a LOT of the US vinyl at that time was hardly prime quality, a 21st century custom designed CD~4 demodulator would still be at the mercy of not only the vinyl itself but careful selection of the turntable, tonearm and cartridge and I'd go so far as to add interconnects joining all these components to your pre/pro. I'm sure Japanese pressed CD~4 vinyl would be somewhat superior to its US counterpart.

A far fetched dream would be to repress onto 180/200g virgin vinyl which might be viable if the CD~4 stampers [?] still existed but that would probably be akin to finding a needle in a haystack and the cost and expense of 'attempting' to create new master CD~4 stampers would be cost prohibitive and prove what when one has incredible digital technologies at one's disposal.

I used to spend a fortune attempting to create full length motion pictures utilizing Super 8mm film. Today, An iPhone X [and equivalent] can create an entire production in 4K resolution with 5.1 sound.......my point being, it's charming revisiting the past but advances in ALL aspects of technology sometimes render that past charmingly obsolete. Not to in any way denigirate those images we captured in Super 8 which were lovely but only a smidgen of the 35mm film quality we beheld on the big screen, a perfectly well designed 2018 CD~4 demodulator could not possibly give us spoiled hi res SACD, DVD~A, BD~A geeks that same sensation of hearing these QUAD treasures remastered from the original master tapes transferred to these digital mediums.....unless, quite possibly, CD~4 demodulator, TT, tonearm, cartridge, interconnects and vinyl were in perfect alignment.

Being a hoarder, I have quite a large collection of CD~4, SQ, QS records in pristine condition, a $5K turntable sitting in mothballs and they all reside beside boxes of Super 8mm film....hundreds of laserdiscs including elaborate Japanese box sets, QUAD Open Reels, hundreds of Stereo ORs and what I find ironic......a little 5" disc blows away all of those formats....of yesteryear!
 
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markshan

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Believe me, the preference would be for all of these relics to come out on Blu-Ray. That said, I'm pretty well versed in the art of needledropping.
 

TVB

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I would purchase this unit in a second if it became reality, especially if it was around the original $500.00 agreed on price ( but I would probably pay more because I have a large collection of discs). Remember, this was a CD-4 design using using modern technology and components much improved upon as compared with components which were available when quad was first developed. Not to mention it was designed by the guy who was at the forefront of CD-4 technology (which I consider an ingenious design). However there are probably to many hoops to jump through to make it happen. As another person we all know would probably say......Sad...
 

proufo

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Last edited:

proufo

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And even if there was it's all dependent on the quality of the vinyl. As we're all spoiled today with sparkling Quad SACD transfers with, IMO, ultra quiet backgrounds, negligible print through and absolute discrete placement of instruments, vocals, etc., unless the vinyl is in pristine condition, and a LOT of the US vinyl at that time was hardly prime quality, a 21st century custom designed CD~4 demodulator would still be at the mercy of not only the vinyl itself but careful selection of the turntable, tonearm and cartridge and I'd go so far as to add interconnects joining all these components to your pre/pro. I'm sure Japanese pressed CD~4 vinyl would be somewhat superior to its US counterpart.
IMHO, the right way to do CD-4 rips is via half-speed playback.

Both the AM and the FM portions of the discs could be cleaned just as Lp rips are enhanced today.

The result, I have no doubt, would be more than acceptable.
 

markshan

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IMHO, the right way to do CD-4 rips is via half-speed playback.

Both the AM and the FM portions of the discs could be cleaned just as Lp rips are enhanced today.

The result, I have no doubt, would be more than acceptable.
Half speed playback takes the bass notes and drops them below the noise floor. It's the opposite of half speed cutting. However, I often take a regular speed file and work on it at half speed. But at 96k, the 30k-ish carrier signal is retained with no problem.
 

rolvkarsten

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Hi, the papers are still available, but Lou’s original link has been archived, and can be found here:
 
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