Turntable / cartridge selection for CD-4

[Colin Dunn]

I have the same problem as flavio81. The difference signal is very faint. If I bring up the separation controls beyond about 25%, I get no front-back separation. If I back them down lower, there's still no front-back separation, but also not enough signal to drive my pre/pro's input stage.

I don't have the tools/know-how to determine if the capacitors are bad.

If indeed they are ... about what would it cost me to have someone re-cap the unit?

 

[Doug G.]

Perhaps this is good time to stress the importance of low capacitance cables between the turntable and demodulator because the 30kHz modulated siganls will get attenuated if the cables have too much capacitance.

Going by memory, less than 100pF is ideal. The lower, the better.

Doug

 

[Colin Dunn]

Perhaps this is good time to stress the importance of low capacitance cables between the turntable and demodulator because the 30kHz modulated siganls will get attenuated if the cables have too much capacitance.

Going by memory, less than 100pF is ideal. The lower, the better.

Doug

How would I know the capacitance of my phono cable?

I have two turntables I've tried with the JVC demodulator - a Sansui SR-636 and a Technics SL-1200. Both these tables have hard-wired cables going into the case; the cables are not user-replaceable.

Before I spend $175 to have KAB rewire my tonearm on the SL-1200, I'm just trying to figure out where the issue lies ... too much capacitance? Or a defective demodulator? Or both?

 

[The Quadfather]

You guys with the low difference signals should recap your units. The difference signal should be just as loud as the main audio. It is when they are precisely matched in level that you get the best separation. Without sufficient difference signal, you have just a phono preamp. It will sound hollow, that's normal. And you will hear it in all the channels equally if the amp is adjusted equal. The best separation will normally be about halfway on the pot, well, maybe a little less. If the difference signal doesn't sound sand papery, then you need not worry about cable capacitance, it's apparently not causing a problem. Good Luck, and happy listening.

The Quadfather

 

[flavio81]

You guys with the low difference signals should recap your units. The difference signal should be just as loud as the main audio. It is when they are precisely matched in level that you get the best separation. Without sufficient difference signal, you have just a phono preamp. It will sound hollow, that's normal. And you will hear it in all the channels equally if the amp is adjusted equal. The best separation will normally be about halfway on the pot, well, maybe a little less. If the difference signal doesn't sound sand papery, then you need not worry about cable capacitance, it's apparently not causing a problem. Good Luck, and happy listening.

The Quadfather

Quadfather,

I get a very very very faint difference signal. But it is there and i can get full 4-channels if i adjust the separation pots. The problem is than then the signals at the out are immensely faint because of this. Have you any idea which capacitors can be more at fault? There are a LOT of electrolytic capacitors in this unit, and i don't have an ESR tester.

 

[The Quadfather]

Have you got an oscilloscope? You can use it to check the signal before and after the coupling caps. Good signal before and bad signal after equals bad cap. Note that not all the caps are coupling caps, some are filters, and their negative leads will be grounded. You probably will not be able to check caps in the preamp section this way, because the signal will be too weak. However, preamp problems would affect the main audio as well. Capacitors are not that expensive if you buy them from an electronics supply house. Might as well replace them all. (just the electrolytics). Get a schematic, that will be helpful in identifying the caps. Good Luck and Happy Listening.

The Quadfather

P.S. By the way, what demod do you have?

 

[flavio81]

Have you got an oscilloscope? You can use it to check the signal before and after the coupling caps. Good signal before and bad signal after equals bad cap. Note that not all the caps are coupling caps, some are filters, and their negative leads will be grounded. You probably will not be able to check caps in the preamp section this way, because the signal will be too weak. However, preamp problems would affect the main audio as well. Capacitors are not that expensive if you buy them from an electronics supply house. Might as well replace them all. (just the electrolytics). Get a schematic, that will be helpful in identifying the caps. Good Luck and Happy Listening.

The Quadfather

P.S. By the way, what demod do you have?

Quadfather, i do have an schematic. My demod is the Fisher badged version of the JVC 4DD-5, identical. That's why i ask.

Yes, i do have an oscilloscope, i'll have to fetch it. I know i can trace the signal and replace caps, it's just that i wanted a suggestion on WHERE on the circuit the caps are most likely to fail IF the difference signal is weak (and everything else is OK). This thing has MANY coupling caps, and most of them are electrolytics. Yes, they are cheap, but replacing all or most of them would take me a lot of time, and i don't have so much time. Plus of course there is always the risk of damaging nearby components (or the PCB) every time you are desoldering and soldering back again.

Anyway, it seems that i will just have to do it the old, time-consuming way. There's also a Pioneer CD4 demod on sale locally but i don't want to spend more money again.

 

[quadsearcher]

To follow up on my CD-4 experience, the stock Dual turntable with (Empire ?) M+ cartridge I had in for repair was plug-and-play with both my 4DD-5 and borrowed Marantz 400, except for multiple copies of one Hugo Montenegro LP and the worst abused and scratched demonstration LP. The cart I own does not have the frequency response needed, in another post here I sort of mistakenly assumed it was good enough because it had a Shibata.

 

[maspadaro]

Have a question to the group. I managed to get my quad set up not too long ago.. maybe 2 months. I have quad Pioneer (amp/preamp)set up with a Dual 1249 TT with a JVC needle that I got from Canada and a Pioneer demodulator, not the cheap one the bigger one that Pioneer made (I also have a Panasonic one). It’s nice to have the controls in the front to switch but since I have multiple TT I use the mention for cd-4 only and my other for matrix (SQ/QS), to my question ( I know this is not a new post) can someone tell me the procedure one needs to get good separation from the demodulator (steps). There are 3 knobs Back/Front separation and Level.
I do have a test record but I heard you should try to set the back first. Why and what other steps are the best way to do it.
Most of the knobs are set to at 12 o'clock and I do hear separation, but is it the optimum? How can one check this?
By the way I fell in love with Quad Music. Wish there were more music done in LP's
On a side question, how about matrix set up procedure?
Regards,

 

[The Quadfather]

Dear Maspadaro:
You should have two separation pots and one (or two) for carrier level. First, realize that a CD-4 demodulator is actually two demodulators inside the box. One is for the left channel and the other is for the right channel. Separation between left and right is maintained by the vector modulation scheme of the record, just like a stereo record. The demods provide front to back separation for their respective channel. Start by turning both separation pots all the way counter clockwise. Put on a CD-4 record known to have good separation such as Doobie Bros "Toulouse Street". We will adjust the carrier level first. Listen. That hollow sound coming from the speakers is the signal from the 30 kilohertz carrier, demodulated. It is a difference signal used by the demodulator to cancel the unwanted signals in the front and back speakers. It may have some distortion or splatter. We want to get rid of that. Adjust the carrier level control through it's range until you find the sweet spot where the splatter is mostly gone. It will still sound hollow, that's normal. Then make small adjustments stopping to listen to get rid of what is left. Note: If you cannot eliminate the splatter, then you may have a dirty stylus or you need a better phono cartridge. I recommend the AT440MLa made by Audio Technica, but there are other fine carts availlable that will work as well. If your demod has two carrier level pots, then adjust your amplifier balance controls so that you hear only the audio from the side you are adjusting at the moment. Then repeat for the other one. The two pots should wind up in about the same position. Note: If you have your balance controls set equally for all speakers and there isn't audio coming from all speakers at the same level, then there is a technical problem with the demodulator, assuming the system is good. Now you should have hollow audio with no distortion. To adjust your separation on the left channel, adjust your amplifier balance controls so that only the left front is heard. Now turn the left channel separation pot slowly clockwise. You will notice that as some instruments in the audio will get louder, others will diminish. find the sweet spot where the instruments that diminish are mostly faded away. That is maximum separation. Now you have a choice to make. Do you want to leave it there for maximum separation, or you can take it up a little further and sacrifice some separation for better fidelity? If you do sacrifice a little separation, you will still have a lot, and it will sound sweeter. It's your call, you might want to try it both ways. Anyway, whatever you do, repeat the procedure for separation adjustment for the right side. When done, adjust your amplifier for equal balance and enjoy the quad!
The Quadfather

 

[maspadaro]

Morning Quadfather:
Thank you for the detail procedure. I have not been able to test it this weekend but I will this week, I had to install 2 speakers up on a wall. Now I can go back and test the channels. I don’t have the Doobie Bros "Toulouse Street", but I do have test lp for cd-4 and I am waiting to receive one for SQ. The JVC 4MD-20X cart/stylus that I have had no problem picking up the cd-4 on the first try and to verify I put a regular lp and the CD-4 light didn’t go on. So I know it’s working fine, I think I got lucky since there are so many things that can go wrong with these old systems. But I also took the time to set up the TT correctly (down force/anti-skating).
I admit I am not sure how good the pioneer qd-240 Demodulator is or even if I can take it to the next level with your detail explanation, but I will try. I do have the Panasonic SE-405 waiting in the wings.

So what the differences from the JVC 4dd-5 and 4dd10 beyond the adjustments being up front or on the back? I am not looking to buy one yet, but if I do I would like to know what the differences are. I personally like having the controls up front and I also notice that most if not all demodulators don’t have a carrier level adjustment like the Pioneer QD-240. Is this actually good or a sales gimmick?
Regards,
maspadaro

 

[flavio81]

Morning Quadfather:
Thank you for the detail procedure. I have not been able to test it this weekend but I will this week, I had to install 2 speakers up on a wall. Now I can go back and test the channels. I don’t have the Doobie Bros "Toulouse Street", but I do have test lp for cd-4 and I am waiting to receive one for SQ. The JVC 4MD-20X cart/stylus that I have had no problem picking up the cd-4 on the first try and to verify I put a regular lp and the CD-4 light didn’t go on. So I know it’s working fine, I think I got lucky since there are so many things that can go wrong with these old systems. But I also took the time to set up the TT correctly (down force/anti-skating).
I admit I am not sure how good the pioneer qd-240 Demodulator is or even if I can take it to the next level with your detail explanation, but I will try. I do have the Panasonic SE-405 waiting in the wings.

So what the differences from the JVC 4dd-5 and 4dd10 beyond the adjustments being up front or on the back? I am not looking to buy one yet, but if I do I would like to know what the differences are. I personally like having the controls up front and I also notice that most if not all demodulators don’t have a carrier level adjustment like the Pioneer QD-240. Is this actually good or a sales gimmick?
Regards,
maspadaro

Masdaparo,

I have the JVC and the Pioneer you have. Both have carrier level adjustments. The JVC has it on the bottom of the unit. The carrier level meter isn't so useful. The Pioneer is a mediocre demodulator, sometimes it loses carrier. On the other hand, i haven't replaced a component and definitely more than one capacitor is dead. So perhaps when new it was a decent demodulator.

Which brings us to... you ought to test these units before buying. The best unit is the one that works.

You shouldn't need to fiddle with the "separation" and carrier level adjustment once everything is correctly set-up, so i don't think there's a big need to have these controls at the front.

 

[maspadaro]

Morning Flavio81.
Well I can't test them before buying them.. got them both through ebay. I heard the JVC is the standard, and that you can still get one for $100. The Pioneer seems fine, but that is why I would like to set it up optimally before I pass judgment. Will try the Panasonic next, but I need to make sure the set up is correct. I got separation almost right away, heard it but I would like to refine the sound coming out from each channel, the reason for my original post. Can you get the same separation from these systems as the new systems in surround?
I am grateful to all for the replies. I always liked tinkering with stereo systems and once I went back to TT's, Quads were the next logical step. Now that I have a few CD-4 LPs and SQs the sound beats the stereo ones almost always. I have a friend now looking into SACD for music.
Wish I could upload to iTunes SACDs for surround sound. But that is another subject. I am techy at heart too. So I have new and old technology working together.
Regards,
maspadaro

 

[Doug G.]

As far as separation, with a CD-4 system, yes, you should be able to get equal results to a modern surround system. There is likely to be a bit more noise due to technology limitations but that can be minimized with careful adjustment.

The adjustment with a CD-4 setup record is thus: With the balance controls set to the back channel you are adjusting (right or left), play the separation track on the record for that channel. Adjust the separation control for that channel for a minimum output from the back speaker. The output will never be zero but just get it to a minimum and that will result in satisfactory separation in normal play.

Repeat the same for the other channel.

The carrier level adjustment isn't all that critical but set it for a minimum of distortion while the carrier level track on the record is playing.

If you have problems with spitting or "sandpaper" sounds, it is due to poor tracking at the cartridge/record groove interface. Carrier dropout may be due to too high capacitance in cables from the turntable to the demodulator.

It make take a little time to get everything dialed in but once you do, it will be glorious. And, as you said, you are a techy anyway and like to "tinker".

Doug

 

[The Quadfather]

The JVC 4DD5 is well known for it's reliable service and performance. The 4DD10, from what I remember had a discrete phono preamp instead of an IC amp. It was supposed to be their upgrade unit, but I cannot vouch for it's performance, for I have not heard one. I can tell you that the 4DD5 was sold rebranded as other brands, in appearance, remarkably the same. The boards were also sold to other manufacturers such as Marantz, who didn't want to go to the trouble to develop their own product (they did later). Like all Marantz components of the era, they came packaged in fine wood and brushed aluminum "gold" finish. I believe the number was CD-300. Note that the CD-300B is not a 4DD5. The Panasonic demod is a good sounding demod I hear, but I also hear it's adjustments are more finicky. I have never listened to one. However, most CD-4 units, even sorry ones can achieve good separation. Happy Listening!

The Quadfather

 

[maspadaro]

Thank you for all the replies and info. knowledge is power as they say. Loking forward to a few hours to recalibrate the demod.
I have a few sytems in the house and in theory I can set up a second quad on another room with the panasonic demod. But I need to give it time.. My wife is a very understanding woman.. dont want to push my luck.

regards,
maspadaro