Lou Dorren: A new CD-4 Demodulator!!!

[The Quadfather]

Dear Lou:
Apparently I missed the auction. If you have one left, I can just send you a check, and you can send it directly. If you like this idea, contact me privately. If not, let me know the item number when you repost. Oh, and for some of the guys here that like to fool with computers, it might be an interesting idea to offer a output-input loop between the preamp and the demod itself. If not in the base price, maybe as an option. It also would be cheap to do.

The Quadfather

[loudorren]

Hello to all,
Since it does not affect the design except for two holes and a couple of RCA jacks, I will include a direct output for left and right at line level. This will also give any that want a great phono preamplifier. You all contributed to this design addition, so I will call it the QQ Forum Direct Stereo Output! Thanks Cai, Tad,!!

Alaudra,
Mike, No carrier level controls, no AGC. All unnecessary! The problem with your other request is the R.I.A.A. eq. At half speed with the standard curve, severe overload at the low frequencies would occur. Adding switchable R.I.A.A. eq curves creates a mess with the preamplifier. Sorry.

Quadfather,

The new ebay listing for the remaining 9 test records is 330202788081.

Lou Dorren

[kfbkfb]

Regarding the Base band/Main channel (contains
LF+LB or RF+RB) and the Carrier/Sub-channel
(contains LF-LB or RF-RB) delay issue:

I'm getting my information about the delay from
the paper (48th AES 1974-05-07) entitled:
"The CD-4 Mark-II Modulation System"
in the section:
"Delay Relationship Between Carrier and
Base Band"

A High End JVC CD-4 Demodulator included a delay
adjustment, apparently (CD-4 approved) phono
cartridges differ in the amount of delay they
have in the 20kHz to 45kHz frequency range.
A special CD-4 test record had to be used to
optimize the delay adjustment.

Kirk Bayne

[aludra]

Hey Lou,
Thank you for your response...

"Mike, No carrier level controls, no AGC. All unnecessary! The problem with your other request is the R.I.A.A. eq. At half speed with the standard curve, severe overload at the low frequencies would occur. Adding switchable R.I.A.A. eq curves creates a mess with the preamplifier. Sorry"

I use the computer to double the speed of the 1/2 speed recording back into demodulator circuits..1/2 speed recorded flat without RIAA eq....software LO eq RIAA curve applied before return to demodulator...I have had excellent results using this technique...and have the added advantage of click removal before return which eliminates ANRS pumping on clicks and mute circuits false triggering...

Also how do you compensate for inner groove carrier level drop??...hence channel separation decreases??? I have always found in my CD-4 transfers if I gain ride the carriers as the record plays (Very easy with the SH-400) I can maintain the full channel separation till the end of the record although the noise increases somewhat...

And you are very correct about the CCC circuit in the SH-400...useless and I have removed that daughterboard in my SH-400 and bypassed it completely.
Big improvement!!!

I hope you will consider this simple loop for us 1/2 speeders... sure would LOVE to take advantage of your super preamp...at the minimum at least a line input to the demodulator. Thank you for your genius!!
Warmest Regards,
Mike

[aludra]

I also forgot to add I have rebuilt my SH-400 and inserted my own line inputs past the preamp stage to avoid the mediocre preamp
and LO RIAA eq stage....But would sure love to get an advanced 2008 demodulator for my collection...Count me 1st in line with my checkbook!!!

[loudorren]

Hello again,

It is nice to have a computer dedicated to the web close to my lab bench!

kfbkfb, Ah yes, the infamous JVC AES paper. Written when CD-4 was still a lab curiosity. About a year before it was presented. At the time of the paper, JVC was using a Foster/Seeley discriminator for the FM detector. No Limiting!! They wanted RCA to adopt the system but it suffered from several problems. I was asked to look at the problems and I developed the CD-4 FM Phase Lock Loop receiving system. If working correctly,the small diameter variation in carrier level will be taken care of by the limiter. Delay variations in early CD-4 pickups was pretty bad. This was because they were just figuring out how to make them. With the advent of the Shibata low tracking mass stylus, higher compliance cantilevers, and precision generator coil matching, hitting the CD-4 pickup specification became quite easy for the cartridge manufactures. The cartridges of today that are CD-4 compliant are an order of magnitude better then the 1970's. Main channel to Sub-channel cartridge delay is very accurate.

Aludra, The preamp in the SH400 is the QSI5022. By the way if you put the cartridge select in the semiconductor position and either capacitively couple the cartridge inputs or remove the DC bias from the input you will have a great flat preamp.

Lou Dorren

[kfbkfb]

CD-4 *Automatic* Channel Separation:

The product information about the Technics SA-7300X receiver
states that "Separation and carrier levels are automatically adjusted
to each cartridge characteristics, ensuring a very carefree operation."

How did Technics do CD-4 automatic channel separation and could
the method be used in your new CD-4 Demodulator design?

Kirk Bayne

[The Quadfather]

Dear Lou:
Can we avoid surface mount components, especially the capacitors which have a short lifespan? Also, multilayer boards that are impossible to trace and repair? This stuff is used now-a-days even when it is not necessary, and it's a nightmare to work on it. Panasonic had a major problem with surface mount capacitors in their broadcast DVC Pro gear. Also, some of their early DVD players had the problems with what we came to call "capacitoritis". At least the quad era gear is easy to work on, which is good, because I've had to work on my stuff many times over the years. I hate to keep going back to the well on this, but we do need gear that is easily repaired. And we need the schematics and service info. It was a long time before we got prints on our Tate Audionics units which were regarded "Top Secret" for years. Still haven't seen them on the Fosgate units. It was all so unnecessary, because all the secret stuff was in the chips. But I guess if the industry has left the old construction methods too far behind, and surface mount is unavoidable, at least stick to single or double side board only with components on one side only and all conductors on the surface of the board, not inside, and all electrolytic capacitors lead mounted (better quality capacitors). Also, screw Rohs compliance. Use real leaded solder that does not require special super hot soldering gear, and doesn't grow conductive "fingers" that short out the gear over time. We don't have to worry about lead in the landfill, because this gear will never be thrown away! The danger of lead contamination is way over rated anyway, like most "dangers" we are warned about on products we buy. I guess that's all from me. Thank you for the opportunity to input on this project.

The Quadfather

[krkier]

Also, screw Rohs compliance. Use real leaded solder that does not require special super hot soldering gear, and doesn't grow conductive "fingers" that short out the gear over time. We don't have to worry about lead in the landfill, because this gear will never be thrown away! The danger of lead contamination is way over rated anyway, like most "dangers" we are warned about on products we buy.

If Lou likes to sell his decoder comercially, then he has to use RoHS leadfree components and solder!

Nowadays it is much harder to find components with lead than without. Nearly all manufacturers of components have changed their program to leadfree, only offering "green" products. It would be difficult for Lou to get these leaded components since he sure does not intent to built millions of his decoder.

And the change in soldering temperature is not that much, from 230°C to 260°C. Every professional soldering iron can be regulated up to 400°C or beyond.

The whisker problem (your "conductive fingers") is something that the industry is aware of. The problem is the surface of tin-plated materials, and their compounds. Think IC-pins, or component pins in general. Also printed cirquit boards with galvanic tin covering of solder pads, pins, and areas. But the industry has already methods to prevent this phenomenon.

-Kristian

[Quadzilla]

.

[loudorren]

Hello Folks,

It's soap box time!!! As one in this industry for more years that I wish to quote, these are my opinions. You all know the saying "that opinions are like ..." Anyway, as to the construction of the new demodulator. I, unfortunately, have no control over the semiconductor manufactures packaging. 94 % of all new and even some legacy chips are in surface mount. I'll try to avoid these where ever possible, but it is a losing battle. Having said that, RoHS components are just fine so I don't mind using them. Lead free solder is another mater. It represents to the current industry the biggest failure mode of the "green" changes. It crystallizes, making diodes where diodes are not supposed to be. Parts do not re-flow well and tend to fall off in vibration tests. This industry is far from having solutions to all of the problems. Take Swatch for instance. They have gotten a waver to use leaded solder in there product because normal wristwatch abuse was causing massive product failure. Off the soap Box.

I am not going into large scale production on the demodulator. I intend to have built what this "club" of CD-4 fans needs. How many will be determined by all of you!

Double sided G-10 or FR4 printed circuit board with plated through holes, solder mask, and legends for easy servicing and components on only one side is the order of the day! Axial lead resistors, radial lead capacitors, and DIP chips with sockets where possible. I would not do it this way for large scale production, but for servicing purposes (I hope the users will never have to), I think this is the only way to go. I will also make available a package of critical replacement parts so if one needs to fix something you can. Schematics, definitely, plus a users and a service manual.

kfbkfb
Kirk, Automatic separation was a way of saying that they chose a fixed separation because everything would work OK, but not optimum. There is no good way to make a long term automated separation system, with out having to use wide dynamic range gain cell circuitry. The problem here is that the gain cell gets very expensive if you want ultra low distortion. You must have ultra low distortion to have great separation. Then you must have some way to store the control value for the gain cell, other wise you must set it up with a test record every time you turn the unit off and on. Having said all that, I like to adjust the separation controls manually, it gives me the sense of power (something I can do better than the machine)!

All for now,

Lou Dorren

[Quadzilla]

.

[The Quadfather]

Hey Lou:
Ok, A parts kit is an excellent idea and I was going to suggest that. You beat me to it. I have a technical idea you might want to try. I don't know if it would work well, but you might want to test the idea. Instead of brick wall filtering the main audio, why couldn't you bandpass filter the carrier and then feed the carrier back into the main audio 180 degrees out of phase in order to cancel the carrier in the main signal. You would have to maintain cycle to cycle phase relationship to make sure that no modulation products got through the cancellation process. The main carrier could then be presented to the matrix with no bandpass filtering. Is it worth a shot?

The Quadfather

[loudorren]

Hello Quadfather,

For phase cancellation to work the two signals being algebraically differenced must be identical in amplitude and 180 degrees out of phase. For others, this means that when one signal goes positive the other must be a mirror image going negative. That is the problem. When the 30 KHz sub-channel is passed through a bandpass filter, the filter modifies the amplitude and phase just enough to make the algebraic differentiation unsuccessful. So, although an interesting idea, unfortunately, in this case it will not work.

Lou Dorren

[The Quadfather]

Hey Lou:
Yeah, I thought it was an interesting idea. But you're probably right. You're getting a lot of feedback here. You will have your pick of the best ideas. There are certainly some good ones. Will the new demod be rack mountable?

The Quadfather

[loudorren]

Hello Quadfather,

The final unit is going to be pretty small. I suppose you could mount it on a 19 inch rack shelf. My friend Mike (wa6ubw) suggested using Velcro mounting strips on the bottom so that the unit could be easily attached and removed. Not a bad idea!

Lou Dorren

[The Quadfather]

The Rohs requirements are European Union law, not U.S. so if the demod was not Rohs compliant, it would only affect the ability to sell in Europe. Not that I mean to dump on our european friends, but it would be better to make a better product. These demods will be in service for a very long time, far beyond the normal lifespan of a piece of electronic gear. Europeans would just have to import them from the U.S. I don't know what would be the situation with Canadians and Aussies. But where there's a will, there's a way.

The Quadfather

[The Quadfather]

Small will work. I'll just get a single RU rack shelf and put it on that. I haven't had much luck with Velcro, the glue keeps coming unstuck. It can share a shelf with my Laserdisc Dolby AC3 demodulator after I get all the sticky goo off of it.

The Quadfather

[wa6ubw]

,,,after I get all the sticky goo off of it.

there is a liquid cleaning product called "Goo Gone" which might be useful.

[callmez]

there is a liquid cleaning product called "Goo Gone" which might be useful.

Or good old fashioned acetone!

Mark Z

[Cai Campbell]

Or good old fashioned acetone!

Which disolves everything, including the silk-screened lettering, the case, and your kidneys!

Ronsonol lighter fluid is the way to go...

[Quadzilla]

.

[Philip Spinner]

ahh, Goo Gone. Used it to remove many stubborn seals on Silverline discs.

[The Quadfather]

Aw, come on, all you guys got to talk about is Goo Gone?

The Quadfather

[callmez]

Aw, come on, all you guys got to talk about is Goo Gone?

Pretty lame, eh? Things should pick up a bit when we all have our new demodulators...

Mark Z