CD-4 adjustment question

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proufo

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Most systems have the side imaging problem, including all discrete quadraphonic systems. Special recording tricks would need to be used to prevent the side-imaging problem. QS, EV, DQ, SQ, BMX, and H also have this problem.
If I get it right, the problem is not the system. The more flexible (that is, the more discrete), the more the producer is able to use any technique to improve the end product to his heart's content.
 

Sonik Wiz

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BTW, there are a lot of internal adjustment potentiometers in JVC 4DD5 demodulators. I believe my 405 Technics only a pair.

Would love comments about the Output Matrix Balance section. TIA.
Very interesting how to article. A lot of good advice. In regards to the matrix modifications I can see why the problem he described & the approach taken would be of benefit. There is some leeway on adjusting carrier level but the separation pots must be adjusted as correct as possible. As was said perhaps it was aging components. But also it could have been that way brand new. Most people would have just accepted it. The quality of component parts compared to today was dismal. Carbon comp resistors at 5% were considered good, nowadays 1% metal film is the norm even in SMD. The power supply xfmr& caps are had their problems too and now you can get really good electro caps with low ESR & low leakage. Every time I revisit the legacy gear I think how much better it could be today building an identical circuit with better parts, PCB lay out, etc. Allowing for proprietary parts that may or may not be available.

I note that the matrix circuit shown in the PDF outputs Front & rear so there must be another matrix section after that to derive the 4 corner signals.
 

par4ken

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I note that the matrix circuit shown in the PDF outputs Front & rear so there must be another matrix section after that to derive the 4 corner signals.
The matrix circuit shown would be duplicated for the other channel. A bit confusing but it's showing lets say Lf+Lb mixing with Lf-Lb (the demodulated carrier signal). The same goes for the right channel.
 

Sonik Wiz

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My old CD-4 demodulator didn't have a carrier level adjustment, so I didn't need to do that. I just had to adjust front/rear separation for both left and right. Easy peasy.

But my Sansui QRX-7001 has this adjustment and it seems to do little as I turn the knob.

If I have the knob turned all the way to the left I definitely notice it's incorrect. But as I start to turn it to the right, once things start sounding okay, turning it any further to the right doesn't seem to make any difference. And it starts to sound correct only about a quarter of a turn from left to right into the adjustment.

My question is, do I turn this dial to the right just until everything sounds okay? Or do I turn it further? Does it really make any difference?

Also, I have two different CD4 cartridges. Shure and a JVC. Do I need to readjust everything when I switch to the other cartridge?

I appreciate your help! Good morning
Shout out to gvl_guy!
How are the adjustments & CD-4 adventure going? And thank you for your patience on wide ranging subjects have gone. You really started quite the thread!
 

gvl_guy

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Well, things are okay I suppose -- for CD-4. 🤪 It's sounding better when I play albums I purchased new years ago (rather than the used stuff off Discogs.) But I got a few good used ones.

I think the demodulator is having issues. For some reason, all of a sudden, the vocals seem to be coming out of the rear. I thought it was the Tony Orlando and Dawn's Greatest Hits album (which I read isn't that great when it comes to quad) But my Eagles On the Border seems to be doing the same thing.

At this point, it's probably the demodulator in my Sansui receiver more than a cartridge/stylus issue. I'd love to have someone look at it, but I don't think the shops around here would understand quad.

I recently purchased a NOS JVC demodulator, cartridge and stylus. Brand new. Never used. But it wouldn't turn on when I got it. ☹ It's been in a local shop for two months for repair, but they have been super slow at getting parts. (Pandemic issues, they tell me.) We'll see what happens when I get that back and try it.
 

par4ken

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The side-imaging problem is the problem that, when a part is panned between the side speakers on one side, the human hearing system locates the speakers instead of interpolating a position between them. This is because the close ear gets a signal from each speaker and the far ear gets a delayed and diminished signal from each speaker. The delays are correct to locate both speakers, but are incorrect to locate the side image between the speakers.

In order to hear the part in the correct place, the listener must turn his head.

If a system does not have the side-imaging problem, the part can be panned smoothly around the listener with no breaks in continuity caused by a jump in the image when the part goes to either side.

The problem does not appear in front of or behind the listener.

Most systems have the side imaging problem, including all discrete quadraphonic systems. Special recording tricks would need to be used to prevent the side-imaging problem. QS, EV, DQ, SQ, BMX, and H also have this problem.

Systems that do not have the side imaging problem include DD (Dynaco diamond), Denon QX, Dolby surround, Pro Logic, Pro Logic II, and 7.1 (I haven't heard that yet). I also made an octophonic system that does not have it. In all of these, panning a part all the way around the listener is done very smoothly. I have done it many times.

I designed a microphone system that eliminates the side-imaging problem. I tested it by having someone walk around the mics and talking (He kept saying "can you hear me now" like the ad). When I played it back through a QS decoder, I heard him all the way around without a jump, and at the distance he was from the mics.
While I don't consider side imaging in a quad system to be a problem (there is enough going on in a good quad mix that imperfect side imaging is easy to overlook), I am intrigued by your claim to have solved the problem. It sounds a bit like Ambisonics.
 

par4ken

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Well, things are okay I suppose -- for CD-4. 🤪 It's sounding better when I play albums I purchased new years ago (rather than the used stuff off Discogs.) But I got a few good used ones.

I think the demodulator is having issues. For some reason, all of a sudden, the vocals seem to be coming out of the rear. I thought it was the Tony Orlando and Dawn's Greatest Hits album (which I read isn't that great when it comes to quad) But my Eagles On the Border seems to be doing the same thing.

At this point, it's probably the demodulator in my Sansui receiver more than a cartridge/stylus issue. I'd love to have someone look at it, but I don't think the shops around here would understand quad.

I recently purchased a NOS JVC demodulator, cartridge and stylus. Brand new. Never used. But it wouldn't turn on when I got it. ☹ It's been in a local shop for two months for repair, but they have been super slow at getting parts. (Pandemic issues, they tell me.) We'll see what happens when I get that back and try it.
If the vocals are coming from the rear then your cartridge is either wired backwards (phase reversed) or I've heard of the magnets of some replacement styli being reversed (N to S) which will also cause a phase reversal. Front and rear outputs of the demodulator will then be reversed. I had the same thing happen with a moving coil cartridge connected to a single tube based pre-preamplifier; it caused a phase reversal which cased the front and rear outputs to be reversed.
 

MidiMagic

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I have one record made on the late 1950s with the channels out of phase with each other. When played in QS, the orchestra is behind me.

Reversing the magnet polarity would not affect the sound of stereo playback or matrix playback. But until today, I never though about it affecting CD-4 playback. Wiring the cartridge backwards could also do this to CD-4, but not stereo or matrix.

I have a special headshell with one channel wired backwards for playing vertically recorded records from before 1930.
 

gvl_guy

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If the vocals are coming from the rear then your cartridge is either wired backwards (phase reversed) or I've heard of the magnets of some replacement styli being reversed (N to S) which will also cause a phase reversal. Front and rear outputs of the demodulator will then be reversed. I had the same thing happen with a moving coil cartridge connected to a single tube based pre-preamplifier; it caused a phase reversal which cased the front and rear outputs to be reversed.
This is very strange. You may be onto something. Using my old (and original) Shure M24H cartridge, the vocals seem to come from the rear. I never, years ago, had an issue with this cartridge. But when I use my JVC 4MD-20X I recently purchased, (new old stock,) the vocals are correct. The mainly come from the front. BUT looking at the wiring, all the connections seem correct on the Shure. (Colors all match up.) I did recently get a new stylus for the Shure. But can a stylus do that? Any other thoughts?
 

par4ken

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This is very strange. You may be onto something. Using my old (and original) Shure M24H cartridge, the vocals seem to come from the rear. I never, years ago, had an issue with this cartridge. But when I use my JVC 4MD-20X I recently purchased, (new old stock,) the vocals are correct. The mainly come from the front. BUT looking at the wiring, all the connections seem correct on the Shure. (Colors all match up.) I did recently get a new stylus for the Shure. But can a stylus do that? Any other thoughts?
With a moving magnet cartridge the magnet(s) are attached to the stylus via the cantilever. Reversed magnetic pole is the only thing that could cause the phase reversal short of reversing the coils. In another thread somewhere here someone had that happen with a replacement (unbranded or generic) Audio-Technica stylus. Both channels will be phase reversed so will go unnoticed in stereo or matrix playback. The difference (sub-carrier signal) doesn't care about the phase of the carrier and so always demodulates with the proper absolute phase.
 

MidiMagic

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I can imagine a substitute stylus made by a manufacturer that had no connection to CD-4 reversing the magnet polarity and not seeing any difference it would make.

If the magnet polarity is reversed and the cartridge has no grounding strap, it can be fixed by reversing the + and - leads on the cartridge.
 

The Quadfather

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My old CD-4 demodulator didn't have a carrier level adjustment, so I didn't need to do that. I just had to adjust front/rear separation for both left and right. Easy peasy.

But my Sansui QRX-7001 has this adjustment and it seems to do little as I turn the knob.

If I have the knob turned all the way to the left I definitely notice it's incorrect. But as I start to turn it to the right, once things start sounding okay, turning it any further to the right doesn't seem to make any difference. And it starts to sound correct only about a quarter of a turn from left to right into the adjustment.

My question is, do I turn this dial to the right just until everything sounds okay? Or do I turn it further? Does it really make any difference?

Also, I have two different CD4 cartridges. Shure and a JVC. Do I need to readjust everything when I switch to the other cartridge?

I appreciate your help! Good morning
What you do is use your worst CD-4 album (if you have Cat Steven's Greatest Hits" that's a good one to use. Turn down your separation pots so that you only hear the subcarriers. It will sound hollow, that's normal. Play the record and adjust for the best fidelity. I would turn it up until it clears up and go no more. If you have trouble cleaning it up, adjust for the least distortion. If the clean area is wide, then find the edge points and go in between. Then bring up your separation pots and adjust for max separation. If it sounds clean over a wide range, then that's a good sign that you have a very good CD-4 cartridge/stylus.
 

The Quadfather

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I can imagine a substitute stylus made by a manufacturer that had no connection to CD-4 reversing the magnet polarity and not seeing any difference it would make.

If the magnet polarity is reversed and the cartridge has no grounding strap, it can be fixed by reversing the + and - leads on the cartridge.
This would create an imaging problem with stereo as well as a bass cancellation problem.
 

The Quadfather

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😳 ......... or you you could just get that authentic CD4 sound by rubbing sandpaper against a microphone :devilish::rolleyes: 🥴 (with apologies to Top Tips from Viz magazine! though you probably can't get it anywhere other than the UK)
If that's your impression of what CD-4 is like, you need a better cartridge. I suggest the Audio Technica AT440MLb.
 

gvl_guy

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What you do is use your worst CD-4 album (if you have Cat Steven's Greatest Hits" that's a good one to use. Turn down your separation pots so that you only hear the subcarriers. It will sound hollow, that's normal. Play the record and adjust for the best fidelity. I would turn it up until it clears up and go no more. If you have trouble cleaning it up, adjust for the least distortion. If the clean area is wide, then find the edge points and go in between. Then bring up your separation pots and adjust for max separation. If it sounds clean over a wide range, then that's a good sign that you have a very good CD-4 cartridge/stylus.
I have that album and will try it!
 

MidiMagic

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This would create an imaging problem with stereo as well as a bass cancellation problem.
No it won't.

You are thinking of reversing only one channel. I meant to reverse both channels.

Most people can't tell if the stylus motion toward the outside of the record causes a compression or a rarefaction on both channels. In fact, they often can't tell which their speakers are doing because some stereo amps put out a signal to the speakers that is opposite in phase to the input signal and some put out the same phase.

There is no "standard phase" because the difference is inaudible. The only requirement is that both channels have the same phase (for center stability and bass strength, as you said).

This is why you have to check speaker phase if you have a different kind of amp for the back channels. One amp might invert the output signal while the other does not.

One time I had even more fun because the tape out and monitor were in the opposite phase from the tuner in and the line out. When using a matrix decoder in the tape monitor loop of this receiver, the front speakers were out of phase with the back speakers when the monitor switch was in the source position.

I often reverse the cartridge connections to one channel to play vertically recorded records.
 
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