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

[ress4278]

This is interesting. I'm having almost the same issue with my SH-400. I'm using - believe it or not - an AudioTechnica eliptical stylus w/ matching cartridge and it gets BETTER CD-4 results than my Ed Saunders Shibata/Cartridge.

Regardless, I get the same odd readings from the dial on my SH-400. I've found that decreasing carrier level on both channels clears up much of the distortion while still giving excellent separation.

I have a funny feeling that the dial on the SH-400 is calibrated more for it's matching cartridge and is pretty much rendered moot (or unreliable) with any other cartridge.

I have been using the AT 440ML cartridge successfully with the SH-400 and the JVC 4-DD5 which is in-line now. The JVC is not showing any playback problems.

I don't think the problem is cartridge related. The 440ML is not a Shibata. If memory serves there is another member that has the SH-400, uses the 440ML, and is not having set-up problems.

 

[Doug G.]

The demodulator doesn't care what cartridge it gets the carrier from as long as it is at the correct level. That is what the meter is for on the SH-400.

The determining factor is if the recorded level on different calibration records is the same. Is the JVC level the same as the original record that came with the Technics SH-400? I don't know (I don't have an original record for mine). If it is, the level is to be adjusted until the needle on the meter is within the thicker part of the line around the "0" mark. Since I don't have the Technics record, I just turn the level up until I get reliable demod. without distortion.

What Lou is getting at by switching the cartridge leads around is to see if the trouble stays in the right channel or goes to the left. If the trouble stays in the right channel, the trouble is with the demodulator. If the trouble switches to the left channel, the trouble is with the cartridge or turntable wiring.

Doug

 

[ress4278]

The demodulator doesn't care what cartridge it gets the carrier from as long as it is at the correct level. That is what the meter is for on the SH-400.

The determining factor is if the recorded level on different calibration records is the same. Is the JVC level the same as the original record that came with the Technics SH-400? I don't know (I don't have an original record for mine). If it is, the level is to be adjusted until the needle on the meter is within the thicker part of the line around the "0" mark. Since I don't have the Technics record, I just turn the level up until I get reliable demod. without distortion.

What Lou is getting at by switching the cartridge leads around is to see if the trouble stays in the right channel or goes to the left. If the trouble stays in the right channel, the trouble is with the demodulator. If the trouble switches to the left channel, the trouble is with the cartridge or turntable wiring.

Doug

Doug,
The SH-400 was working fine for weeks after repair and I used the JVC set-up record. The Technics record is rare as hen's teeth. If the trouble was in the wiring, wouldn't it show up w/ the 4DD5?
This problem has happened twice in the same channel. I think the person repairing it didn't know enough about the unit.

 

[Bob Romano]

You can add me to the list! I like my Marantz but a spiffy new one would be most excellent!!

 

[Doug G.]

Yes, if the only variable is which demodulator is in place and the problem stays in the same channel each time with the SH-400, it's a good bet that the SH-400 is where the problem lies.

I have a question for Lou. I was measuring voltages in my SH-400 and all of the DC levels on the QS15022s were very close to the values given on the schematic except for pin 23 which calls for 5.7 volts and I measured 7.0 volts in mine. I see this pin goes to the pre-amp in the chip but what is its function?

I also measured about a volt low in the power supply at the regulator output (about 12 and 13 volts at the emitter and base instead of the indicated 13 and 14 volts) so I have to look into that too. The 18 volts at the collector was normal. The unit seems to function OK though except I have to have the carrier level controls set lower than what I would expect to be normal to eliminate all distortion.

I would appreciate any info you could give me regarding the pin 23 thing. Thanks!

Doug

 

[loudorren]

Hello everybody,

ress4278, Yes. If you reverse the phono input leads and the problem goes from right to left then the problem is in your cartridge. Speaking of cartridges, the AT440-ml is not satisfactory for CD-4 playback. This cartridge cuts of at 32 KHz which means that the sub-carrier system is trying to demodulate an SSB-FM SSB-PM SSB-FM signal instead of the FM PM SSB-FM signal that is suppossed to be there. Loosing the upper sideband of the 30 KHz signal is very detrimental. Getting any kind of usable results with this cartridge says a lot for the QSI5022.

Doug G. Your premise is incorrect. The cartridge frequency response, distortion, and high frequency separation are quite critical to proper CD-4 performance. Turning on the carrier indicator or seeing carrier level on the meter means only that the cartridge is good enough to pickup the 30KHz carrier but does not indicate if it is indeed getting the upper sideband.

What is the voltage at pin 24 and pin 27? What is the exact voltage at the base of transistor TR701? What kind of cartridge are you using?

Lou Dorren

 

[Malcolm2010]

Hello You All,

Pickup cartridge to be announced. For every ones information. The Signetics CD4-392 and the CD-894 chips are actually a Signetics (NXP) NE565 or a National Semiconductor LM565. Still in production by both!

Lou Dorren

Lou,
it was my understanding that the Signetics CD4-392 was a dedicated CD-4 demodulator chip similar to the QSI5022. It did not contain a phono stage but certainly contained sections of the ANRS circuitry normally separate in demodulators, and the output matrix was on chip.

Malcolm

 

[The Quadfather]

You would be surprised at how well an AT440MLa does work. But it's certainly not perfect. I suspect this is because the cutoff isn't that sharp. I used to use a Trackmaster 8, it worked very well, and wasn't shrill like the 440MLa They were cheap, and at 20 bucks a pop, I could afford to keep a good stylus on it. But, alas, Audio Technica quit making them, and now won't even make the replacement stylus for them. I have an AT14s, but Audio Technica long since quit making stylii for that one. I wish I could get a linear contact stylus for that one, since it's a true quad cartridge with full frequency response. I do believe a linear contact stylus performs better than a shibata for CD-4 playback. Case in point: The Ed Saunders cart is essentially a Trackmaster 8 with a shibata stylus. However, a Trackmaster 8 with a linear contact stylus will walk all over the Saunders cart. But those of you who bought the Saunders cart can always play your stereo records with it. Ha Ha! But I guess a true test would be to take the stylus off the Saunders cart and put it on the Trackmaster 8. I believe it does fit. If it performs well, then maybe the insufficiency is in the cart itself. If I ever get some time, I might try that. If it works, then I have a stylus source for my Trackmaster 8 and the same for the AT331LP cartridge.

The Quadfather

 

[Bob Romano]

You would be surprised at how well an AT440MLa does work. But it's certainly not perfect. I suspect this is because the cutoff isn't that sharp. I used to use a Trackmaster 8, it worked very well, and wasn't shrill like the 440MLa They were cheap, and at 20 bucks a pop, I could afford to keep a good stylus on it. But, alas, Audio Technica quit making them, and now won't even make the replacement stylus for them. I have an AT14s, but Audio Technica long since quit making stylii for that one. I wish I could get a linear contact stylus for that one, since it's a true quad cartridge with full frequency response. I do believe a linear contact stylus performs better than a shibata for CD-4 playback. Case in point: The Ed Saunders cart is essentially a Trackmaster 8 with a shibata stylus. However, a Trackmaster 8 with a linear contact stylus will walk all over the Saunders cart. But those of you who bought the Saunders cart can always play your stereo records with it. Ha Ha! But I guess a true test would be to take the stylus off the Saunders cart and put it on the Trackmaster 8. I believe it does fit. If it performs well, then maybe the insufficiency is in the cart itself. If I ever get some time, I might try that. If it works, then I have a stylus source for my Trackmaster 8 and the same for the AT331LP cartridge.

The Quadfather

Not to threadcrap here but I don't know much about needles for CD-4 but you might want to check here:

http://www.needledepot.com/listproductsofbrand.aspx?brand=AUDIO TECHNICA

 

[loudorren]

Hello People,

Malcom you are correct. The CD4-392 is a combination chip of the NE565 and the NE570. The CD3-392 itself is not available anymore but can be easily replaced by a small daughter board using these chips. So many chips, so little time.

Quadfather, The cartridges that have given you some performance do not do justice to what CD-4 is capable. A cartridge for CD-4 should have a frequency response to at least 50KHz with 12 dB of separation at 50KHz. Audio Technica has only 1 cartridge in their current product line that is CD-4 capable. It is the AT-OC9ML/II. It is very pricey at $599.00 MSRP.

By the way the Shibata tip and the line or Microline tips all have essentially the same contact area in the groove wall. THe slight manufacturing differences are to avoid having to pay royalties. Dr. Norio Shibata, inventor of said stylus tip is a brilliant scientist and really nice guy!! The cartridge that I will use with next demodulator has a frequency response of 57KHz and a separation of 17 dB at 50 KHz.

Lou Dorren

 

[proufo]

Hello, Lou.

Would it be too difficult or expensive to include SQ decoding capabilities, using current Dolby chips and the such?

QS would be icing on the cake.

 

[ress4278]

Part of the reason I use the AT 440ML is the sonics. If you are one of those using it for CD-4 playback, have you heard a Shibata that sounds as sweet?
The separation is spot on, so I'm not missing that.

The AT OC9MLII can be had for $299.00 at LP Gear, but I don't see any reviews. Is anyone here using this cartridge ?

 

[loudorren]

Hello Again,

Proufo, This is a subject that grinds my molars. We, the NQRC (National Quadraphonic Radio Committee) worked for 13 years to get discrete Quad 4-4-4 set as the national standard of the United States. We did acoustic listening, double blind tests with over 2000 auditors to determine if people could tell a significant difference between Discrete 4-4-4 Quad, Matrix 4-3-4 Quad (RCA), Matrix 4-2-4 Quad (Sansui QS), Matrix 4-2-4 Quad (CBS SQ), including all of the enhancers (Vario Matrix, Tate, etc). The result was overwhelming. Discrete 4-4-4 performance won out over all others. Now I know that there are a lot of you that have a great amount of 4-2-4 and it's synthesis effect on a 2 channel recording can be interesting, but it is not true Quad. On any of the 4-2-4 systems, you can not put in 4 individual signals at the encoder, one in each channel, and have them come out of the decoder in each of the for channels without severe crosstalk (very poor separation). On the enhanced systems, if only one channel is sent, the decoders turn the level down on the 3 channels that are not supposed to have any output. Under those conditions the Matrix system can synthesize the channel position. Try to send any more than one channel and all bets are off.

The numbers tell the story and the story is the Information Theory. It states, that for a given number of input channels, there must be the same number of carrying channels, to deliver to the same number of output channels. 4-4-4 means 4 input channels, 4 carrying channels, 4 output channels. 4-2-4 means 4 input channels, 2 carrying channels, 4 output channels. I encourage everyone to enjoy all of their Matrix systems and Matrix record content but when they want to hear true Quadraphonic reproduction, Discrete is it. The new CD-4 decoder will just demodulate CD-4 signals.

ress4278, don't go spending any money on cartridges just yet!

Lou Dorren

 

[Q-Eight]

The numbers tell the story and the story is the Information Theory. It states, that for a given number of input channels, there must be the same number of carrying channels, to deliver to the same number of output channels. 4-4-4 means 4 input channels, 4 carrying channels, 4 output channels.... when they want to hear true Quadraphonic reproduction, Discrete is it.
Lou Dorren

Amen, Brother!!

Sing it loud.... I'm Quad and I'm proud! :banana:

CD-4, Q8, Q4 all the way!!

 

[ress4278]

QUOTE: ress4278, don't go spending any money on cartridges just yet!

So, it sounds like we will be treated to a new level of performance, perhaps to the point that your cartridge is matched to your demodulator better than to any other. Is it the combo that will be partly responsible for the updated performance?

If that is the case, it will be the first time I've tried CD-4 that way.

 

[loudorren]

Hello CD-4 Fans,

Installment II is now at the link http://www.johana.com/~johana/dorren

Lou Dorren

 

[Quadro-Action]

I may think wrong, because the answer from Lou is till now not written, because I think, the new Demodulator will also work with well (WELL) extant pick ups. But we have read sometimes, that some CD-4 fans are working with those cartridges, which are not really suitable to tracking the CD-4 signals. For those a well working cartridge is of course wellcome. By the way -and for another answer of Lou - I work with MC cartridges from Elac (EMC-1 - which are unfortunately no more produced)) which have a frequency range up to 60 kHz with no fall off at the end. The channel-separation by 20 kHz is like individual measurement around 22 dB, so it may by 50 kHz at least 15 dB. The tip is one of van den Hul. So the CD-4 reproduction with my demodulators SH-400, 10 S, 1000 is very clear und satisfying. When Lou is answering of the ask before about the cartridges, he may also tell, if my cartridges are further on suitable to the new demodulator.
By the way, I am of course also very interested for the new technic and the demodulator and I think, as written before, that there are here in Germany an around some more fans, who are interesting for a new CD-4 Demodulator.

Dietrich

 

[The Quadfather]

Hey Lou:
Yeah, when I got my first demodulator, a cheap Claricon unit, quad had gone asunder, and price was very much an issue for me. I had a good cartridge and couldn't even afford one new stylus for it. I was very poor in those days. But I couldn't even find a good quality demodulator at any price. So I suffered very poor performance and finally gave up on CD-4. The one good thing I had was a good turntable, a Marantz 6300 direct drive. So I started from a perspective that CD-4 didn't actually work, and that was reinforced by what I had heard others say. Many years later, one day I was walking through an Alabama flea market, and there on the shelf was a JVC 4DD5 for $15.00. So I said, what the heck, I'll try again. I put the demod on the bench and replaced some blown transistors and capacitors, and I got it functional. But I could not find a good cartridge, so it still sounded like sandpaper scratching, a sound that everyone here is familiar with. An electronics dealer I talked to suggested that the Trasckmaster 8 might do the trick. He had some so I bought one. I turned down the separation and adjusted the carrier level to a point where I heard very little distortion in the difference signal. I set the separation pots for best separation using headphones and a Doobie Bros album, (the Doobies seem to be real good for this) and went into the other room where the speakers are. It was amazing! No splatter, Great separation. I walked out of the room (where I couldn't hear separation) and I could not even tell the demod was on! CD-4 was clean for the first time ever! Most records would play well, but not all. It's not that I couldn't afford the high dollar cart now, it's that I wouldn't want to afford the high dollar replacement stylii, which have to be replaced often. Worse, I would hate to spend all that dough and still not get a noticeable improvement in sound quality. But I have been reading your technical papers and it sounds like you're on to something. I have decided that if you can bring it in for as you say well under a grand, and it works well, and you supply the cart and stylus, I will be willing to ante up and give it a shot and go for 100% performance instead of 90% that I have now. I don't believe that the AT440MLa that I am using now is as good as the Trackmaster 8 I can no longer get stylii for. Although I am not a "golden eared audiophile" I do have four ears, actually a fifth ear and a big ol' bass ear have recently grown in, but I shouldn't be too hard to please. I have an SH400 I'm using now, but the JVC wasn't bad at all.
I await in anticipation for the new product.

The Quadfather
P.S. will there be a test record with it or if not, will a standard test record suffice?

 

[winopener]

After reading the second pdf i wonder just one thing... will it be cd-4 only or will be possible to use it as a regular stereo phono preamp too?

 

[kfbkfb]

Will there be a way to adjust the delay between the
LF+LB/RF+RB Base Band(s) and the LF-LB/RF-RB Carrier(s)?

Kirk Bayne