Lou Dorren: A new CD-4 Demodulator!!! [ARCHIVE]

[Quadro-Action]

Hello Kristian, I know from my own listening, that there exist quadraphonic mixes for 2 titles from the "Spectrum"- One is released with the Samper "Quadraphonic Experience" and the other has existed (or extist further) only by a rerecording among sound-engineers. May be also, that there have been only two titles mixed in 4-channel for a pick out, which is suited for the sampler. Because the "stratus" runs 7 minutes, the shorten other "Quadrant 4" is taken.

Dietrich

 

[Quadgirl]

Hey, all.
Quadfather gave me a heads-up on this now quite fascinating 6 page thread. Lou Dorren - if you are keeping count, count me in for your new demodulator. I don't understand the ins and outs of all the tech talk, but get the gist totally. This is just so great and previously, to me anyway, unthinkable!!! I love CD-4 and would love to take my system to the next level with this. I use the AT20 cart and enjoy it for CD-4 on my Marantz 6300 table, but it will be wonderful to bring modern technology in. Or, maybe even consider downsizing to one turntable for all quad and using the Rega. Either way, this is truly exciting!

Now on an unrelated note just out of curiousity. Since you really know this stuff inside and out, Lou, if you have an opinion and feel like answering, I'm trying to master a good protocol on record care and would like to know if you have any tips in this area. I do use a VPI record cleaning machine (wet cleaner), but use it on noticeably dirty-ish records. Once clean, I just handle with care and use nice inner sleeves. I do brush the record when starting the turntable and even spray static guard on the floor in front of all the equipment before a record playing session, so now that I may become even more addicted to CD-4 with the forthcoming demodulator, I want to make sure to protect my investment. Thanks for all you are doing and for all on this forum who are contributing ideas.
Quadgirl (Laura):banana:

 

[rustyandi]

Lou
I will be ordering one of your units when you build them
will you be haveing power switching for Australia 240 Vts
if not i will buy a transformer
Just to be different
would you unit be able to do any good for UD4?
Ron

 

[loudorren]

Hello Quad People,

It has been a few days since my last posting. I have been busy mixing the final tracks for one of the artists on my label. Besides electronics, sound recording, music mixing, and music production are the other loves of my life. Installment III is now available at http://www.johana.com/~johana/dorren. It gives some good history of Disk recording and CD-4 system implementation.

Quadgirl, Thanks for the nice words, Installment IV has a humorous true story that resulted in RCA and Warner Bros. endorsing
the CD-4 system. This leads to the proper care and feeding of CD-4 and stereo records. This should prove to be useful for everyone.

rustiandi, Hey Mate, universal power supply, 100, 105, 110, 120, 200, 220, 230, 240 VAC, 50 or 60 Hz. This is CD-4 only.

To all who asked, TAAS is a multichannel acronym!!!

Everybody have a good weekend and if there are any questions I will be monitoring the thread.

Lou Dorren

 

[bmoura]

Hello Quad People,

It has been a few days since my last posting. I have been busy mixing the final tracks for one of the artists on my label. Besides electronics, sound recording, music mixing, and music production are the other loves of my life. Installment III is now available at http://www.johana.com/~johana/dorren. It gives some good history of Disk recording and CD-4 system implementation.

Quadgirl, Thanks for the nice words, Installment IV has a humorous true story that resulted in RCA and Warner Bros. endorsing
the CD-4 system. This leads to the proper care and feeding of CD-4 and stereo records. This should prove to be useful for everyone.

rustiandi, Hey Mate, universal power supply, 100, 105, 110, 120, 200, 220, 230, 240 VAC, 50 or 60 Hz. This is CD-4 only.

To all who asked, TAAS is a multichannel acronym!!!

Everybody have a good weekend and if there are any questions I will be monitoring the thread.

Lou Dorren

Speaking of the Phase Lock Loop (PLL) what ever happened to the Phase Tracking Loop (PTL) which was in one of the later generation CD-4 units?

 

[callmez]

Great stuff Lou -- you have a real knack for explaining the finer details in ways that an audio ***** like me can understand. Much too early to clamor for installment 4, so I'll just add a big THANKS for #3!!

While we're waiting, how about a catchy name for the new unit -- something flashier than "high performance 2007 CD-4 demodulator"?

Mark Z

 

[jefe1]

How about the Dorren QQ CD-4 Demodulater???


Count me in for one of these! :banana:

 

[kfbkfb]

Regarding "worn" CD-4 discs:

The product information from Sansui
on their QC-04 CD-4 Demodulator states that:
"Further, since CD-4 records have a life
of about 100 playings, you may notice that
if played beyond this point they will begin
to lose front/back separation."

In the 1973-08 issue of Popular Electronics:
(using a Technics 460-C phono cartridge)
"After 100 plays, the level of the carrier was
fluctuating slightly, down by 3 dB at times."
"Obviously, wear is no more a problem with
CD-4 pressings than it is with any other
current type of disc."

Were any tests done to see how many times
CD-4 discs could be played on regular mono
or stereo record players (spherical stylus,
high tracking force etc.) and still decode
when used with a CD-4 phono cartridge?

Kirk Bayne

 

[Quadro-Action]

In an issue of the "Funkschau" Germany - in that time the leading journal here, there was reported around 1975 such a test with microscope fotos from CD-4 grooves after playing many times (100?)with conventional stereo pick ups with ellyptical and conical needles and a pressure of 3-5 gramm. And logical there was seen trails in the groove (and how by stereo and matrix records?). But this was not a real problem, because the contact area in the grooves by tracking with stereo-systems was very small. Because the Shibata contact zone is bigger and beyond this, there is a real tracking and reproducing of the CD-4 ( 30 kHz) signals further on possible. May be, that also many playing with a shibata needle can produce a few tracks in the groove walls. But, as commented before, for CD-4 was taken therefore an especially and harder Vinyl compound - and beside this - no one will play a record 100 times ore more. I have played my "best" CD-4 records only 10 or maximal 20 times - always and further on with best results.
The statement of Sansui is of course only an attempt to make any unsure by the consumers for the unliked rivalry CD-4 system.

Dietrich

 

[The Quadfather]

I suspect I've played a few of mine more than a hundred times.

Hey Lou:
I have another couple of ideas to fly by you. How about a separate separation control for each channel. That would ensure the optimum separation. Sure, it would take longer to set up, but once done, it would be worth the effort. A delay adjustment might be worthwhile as a internal technician adjustment to make sure the opposing waveforms line up (timewise) in the output matrix. That would also have the effect of maximizing separation.

The Quadfather

 

[loudorren]

Hello and Good Morning (Afternoon and Evening to some of you),

kfbkfb, Quadroaction,

Mark and Dietrich, The story about record wear, stereo and CD-4 records is an interesting one. This story starts at the number of times a CD-4 disk could be played without noise and breakup. The Sansui comment as the say is bogus. The sub-carriers of the CD-4 system are FM-PM-FMSSB. Their statement "CD-4 records have a life of about 100 playings, you may notice that
if played beyond this point they will begin to lose front/back separation." is incorrect. Fluctuations in the carrier level do not change the recovered audio level in an FM-PM-FMSSB system. as long as the audio level, and phase are intact the separation does not change.

The 100 play criteria was set by RCA as the number of plays that would be commercially viable. It was actually that a CD-4 record at 100 plays should not sound any different than at 1 play. This is where Dr. Shibata's development became so important to both stereo and CD-4 records. A typical conical or elliptic stylus in a cartridge, tracking and 1.5 grams, puts a surface pressure of 15000 lbs.per square inch at the stylus to disk contact. This is because of the point contact made by these type styli. At this tracking pressure, the stylus eventually gouges a trough in the groove walls. The Shibata stylus has a groove contact about 40 times larger than the conical or elliptical ones. Instead of a point contact, it is a line contact, which reduces the surface pressure from 15000 lbs per square inch to 150 lbs. per square inch. This extends the number of plays to over 1000. This makes the CD-4 disk as durable as conventional stereo disks. The Shibata stylus also has a unique feature of it's own. Disks that have been damaged by conical or elliptical styli, will play like a brand new disk. The Shibata stylus, because of it's wide surface contact area plays the undamaged surface not touched by the other styli. As I wrote in my last post, a humorous incident happened on the way to RCA and Warner Bros. CD-4 support and I describe this in installment IV. By the way, the technics 450c, 451, 460, were the best CD-4 cartridges. The were all semiconductor type.

bmoura, The Phase Tracking Loop detector was a great theoretical idea on paper and as a lab proof of concept system did work The problem turned out to be modulation deviation greater than 1 radian (360 degrees) was too large for the tracking filter and the Hilbert Transform. It does work well with lower ratio deviation. The NXP TEA5767 FM stereo radio chip is a fine example.

Quadfather,

Manual separation controls are mandatory. Delay are internal precision matched.

Lou Dorren

 

[kfbkfb]

Regarding the Sum Signal LPF
in your new CD-4 Demodulator:

I couldn't see exactly what the corner frequency
of the (DSP) LPF is from the graph, if it's 15kHz,
could it be raised to 16kHz or even 16.5kHz
(thereby allowing minimal attenuation of 15kHz,
which is apparently the maximum frequency allowed
to appear in the Sum Signal) and still meet the
requirement for carrier filtering?

Kirk Bayne

 

[winopener]

For the record, one of the german-pressed cd4:
http://i20.ebayimg.com/02/i/000/d1/b6/e9d9_1.JPG

 

[loudorren]

Hello kfbkfb,
Kirk, The filter pass band is flat within .1 dB to 15.5KHz, and is -86dB at 18 KHz with an average stop band attenuation of 60 dB down. This accurately matches the filters in the record system. This filter is used in the main channel and sub-channel audio chains to insure filter delay matching.

Lou Dorren

 

[BD-4 CD-4]

Lou,

Put me down for one of your New CD-4 demodulators. I read the enitire thread for the first time & would appreciate hearing your new demodulator in my den.:banana:

 

[kfbkfb]

Regarding the "Hi-Blend" switch on some
Technics CD-4 Demodulators (SH-400 etc.):

From the Technics SA-7300X product information
about the "CD-4 Hi-Blend" switch:
"With this switch on, an excessively worn-out
CD-4 disc can be reproduced clearly if it
should bear noise."

Some CD-4 difference signal recovery issues:
1. Low carrier level.
2. High noise in the 20kHz to 45kHz frequency
range.
3. Distortion products in the 20kHz to 45kHz
frequency range due to problems below 20kHz.

I don't understand how reducing the front to
back high frequency channel separation will
help mitigate issues 1,2,3.

Will your new CD-4 Demodulator include anything
to help make "an excessively worn-out CD-4 disc"
more listenable (perhaps an option to limit the
bandwidth of the demodulated difference signals
to, for example, 8kHz)?

Kirk Bayne

 

[loudorren]

Hello kfbkfb,

Kirk, This technique was borrowed from making FM stereo car radios. If you reduce the Front to Back separation of the demodulator, it is like turning down the audio level from the sub-carrier detector. If noise and distortion were coming from the sub-channel, then by reducing it's level into the sum and difference matrix, the noise and distortion is reduced at the sacrifice of Front to Back separation. Most of this problem starts out at the higher audio frequencies, so in addition the "blend" is made frequency sensitive. The CD-4 records that are "worn", probably are not! There is a technique that I describe in installment IV which yields amazing "worn CD-4 record" recovery results. As they say in Radio, "Stay Tuned".

Lou Dorren

 

[surroundophile]

Hi Lou,
What kind of TT do you reccomend for playback (tone arm of S-shaped, straight, linear tracking)? Most people here have recomended a linear tracking TT. I used to have sporadic success playing back CD-4 with a 70's quad-equipped TT (Dual). Whan it died, I replaced it with a Mitsubishi linear tracking TT (from Ebay) and CD-4 playback improved immensly! Are any of todays TT good (but now they are SOOOO exspensive!) ?
Will this demodulator require low capaitance cables? Will they come with the demodulator (or an option of them) ?
Thanks

PS I WILL be buying one or two demodulators.

 

[rolvkarsten]

I am impressed by Mr Dorren making this State of The Art CD-4 demodultor 33 years after his last attemp, and around 30 years since quad died (more or less). But there are lots of CD-4 records around, so for the collectors and enthusiasts this is a good thing. Especially as many of these recordings do not seem to end up as e.g. 4.0 recordings on SACD or DVD-Audio.
Still, we must remember that CD-4 is compromised with a limited frequency response (maybe that does not matter for us +50 years old). So the best thing would be digital versions. In the mean time we can enjoy Mr Dorren's demodulator.

I scanned an old JVC paper for you all:
http://www.yousendit.com/transfer.php?action=download&ufid=270F9B9A6078DE44 (Introducing_JVCs_CD-4_Record_System-The_Only_Discrete_4-Channel_Record_System.pdf)
Please feel free to downlaod and distribute.

Best regards and looking forward to Mr Dorrens Installement IV!
Rolv-Karsten

 

[The Quadfather]

I will take discrete surround recordings any way I can get 'em, but it looks like there may be problems getting DVD Audio and SACD players repaired or replaced 20 years out, And CD-4 equipment is simple and repairable, and will be for years to come. Hopefully, including Mr Dorren's. So new CD-4 recordings might just be the way to go for quad longevity. It looks like the stylus industry has survived the demise of the turntable, and so have turntables. So if there were new CD-4 recordings, I would be willing to purchase them providing they were of good quality. Apparently, getting back a production capability wouldn't be that monumental of a task to someone already in that business. And anyone still in the LP business is familiar with small scale production and wouldn't consider it a loss. I think a lot of times the major record industries don't want to do surround because they don't make tons of money on it. But someone used to making the kind of money a successful local business would make, would consider it OK. There are a lot of CD-4 records out there, and Mr Dorren might get business outside of the Quadraphonic Quad community that he didn't anticipate if word gets out. Wouldn't that be great?

The Quadfather