Modifying the JVC 4DD-5/Marantz CD-400

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Malcolm2010

300 Club - QQ All-Star
Since 2002/2003
Joined
Dec 9, 2002
Messages
359
Location
Durham, England
I have a JVC 4DD-5 demodulator and over the last few weeks have carried out modifications to improve its performance. Most of what I have done is common sense and may seem trivial to the more experienced of you.
As there are no “How To” documents available, I decided to put together a small article describing the changes so we can all enjoy the best performance from this demodulator.


You can find out what I did here :-

http://www.grizwald.plus.com/quad/JVC_4DD5_mods.pdf

This is part 1 of an irregular series of modifications, based on the JVC 4DD-5 and clones like the Marantz CD-400.

Malcolm
 
Dear Malcolm:
That is a very interesting article about modifying the 4DD5. I knew I wasn't dealing with a novice when you pointed out that the brown streak on the capacitor was glue, not leakage. (it was originally a yellowish color) . I have two of these demodulators, so one can go to the bench while the other is in service. These are good demodulators, but yes, they can and should be improved. I will look forward for more.

The Quadfather
 
I have often wondered if a more modern PLL chip could be employed to demodulate CD-4, and would perform better? On the other hand, would an entirely vacuum tube (valve) approach to CD-4 demodulation work better? Would an old fashioned coil type discriminator perform better than a PLL circuit, which was relatively new at the time. I someday may have the time to play with these ideas, but for now, they are only ideas. If CD-4 had suceeded and stayed with us in the market place, I have no doubt that research would have improved it's performance to the point that it would be a very fine system. Fortunately the line contact stylus was developed before it was completely dead, paving the way to the current level of performance. However, I suspect that better performance is obtainable. Hopefully Malcolm can find more ways to do this. He apparently has the time to devote to it. Thanks Malcolm!

The Quadfather

proufo said:
Many thanks Malcom!
 
The Quadfather said:
I have often wondered if a more modern PLL chip could be employed to demodulate CD-4, and would perform better? On the other hand, would an entirely vacuum tube (valve) approach to CD-4 demodulation work better? Would an old fashioned coil type discriminator perform better than a PLL circuit, which was relatively new at the time. I someday may have the time to play with these ideas, but for now, they are only ideas. If CD-4 had suceeded and stayed with us in the market place, I have no doubt that research would have improved it's performance to the point that it would be a very fine system. Fortunately the line contact stylus was developed before it was completely dead, paving the way to the current level of performance. However, I suspect that better performance is obtainable. Hopefully Malcolm can find more ways to do this. He apparently has the time to devote to it. Thanks Malcolm!

The Quadfather

Well, some of the later CD-4 designs employed a Phase Tracking Loop (PTL) instead of a Phase Lock Loop (PLL) to improve performance. But I don't know how you'd graft that on to an existing demodulator like the 4DD-5.
 
bmoura said:
Well, some of the later CD-4 designs employed a Phase Tracking Loop (PTL) instead of a Phase Lock Loop (PLL) to improve performance. But I don't know how you'd graft that on to an existing demodulator like the 4DD-5.


I have the AES paper on the PTL demodulator, but have not researched it well enough to comment, however it would not be worthwhile to graft a new PLL (PTL) system into the 4dd5, that level of complexity would warrant a new build from scratch........ Hmmmm there's a thought !!

Malcolm
 
proufo said:
Hello again, malcom.

Check the comments in this post. Maybe it would proviode ideas for part two or three.

https://www.quadraphonicquad.com/forums/showpost.php?p=15948&postcount=12

This is the full thread:

https://www.quadraphonicquad.com/forums/showthread.php?t=2598

I read that series of posts a while back, it interested me as I found the 4DD5 to be a good demod, certainly there are better ones around, but it is low cost and can be upgraded cheaply and easily. I decided to see what could be done to improve its performance, as I could not afford anything more exotic.
As far as future articles are concerned, I have a few modifications for the PLL and the ANRS circuitry that require further testing. The PLL mods improve the lock range and frequency response in the subcarrier channel, the ANRS mods improve tracking. These require a reasonable level of technical skill as they involve setting up the lock range and the VCO free running frequency as well as the ANRS tracking. All the alignment information is in the service manual here http://www.grizwald.plus.com/quad/SManual.pdf . Unfortunately I do not have limitless time on my hands, so the additional modifications will arrive as and when I can, hopefully within the next few months.

Malcolm
 
Malcolm2010 said:
I have the AES paper on the PTL demodulator, but have not researched it well enough to comment, however it would not be worthwhile to graft a new PLL (PTL) system into the 4dd5, that level of complexity would warrant a new build from scratch........ Hmmmm there's a thought !!

Malcolm

Could be. I'm not familiar with the CD4-10 and the studio unit you mentioned. But I did have a CD4-50 back in the Quad era. When you teamed that demodulator with one of the better recorded and mastered CD-4 discs - like some of the Enoch Light discs -- Wow !
 
Actually the discriminator is but a small (but important) part of the overall circuit. The idea would be to build a circuit board with the updated discriminator, and patch it into the circuit using wires to holes where the old chip resided. Also, I wonder if replacing the old chip with it's modern equivalent would yeild an improvement. Maybe the chip design has been improved over the years. Discrimination is the weak point in CD-4, that and stylus tracking. They are interrelated. If the stylus tracking is good, then the discrimination is acceptable, but if the discriminator was more forgiving, it wouldn't require as perfect of a signal to make it work right. You get the picture.

The Quadfather



however it would not be worthwhile to graft a new PLL (PTL) system into the 4dd5, that level of complexity would warrant a new build from scratch

Malcolm[/QUOTE]
 
There is a possibility of doing this using a CD4-392 chip as used in the CD4-50 and QRX8001/9001 demodulators. A lot of the on board circuitry of the 4DD5 would be redundant, the CD4-392 contains almost everything but the phono stage !. It has ANRS and output matrix on board, carrier limiter (no separate carrier level adjustment) and a very good PLL/VCO combination. So you would not be able to simply "drop in", it would require a separate PCB. My comments on building one from scratch were simply that if you were to go to this level of modification, you will be replacing most of the active circuitry within the demodulator. Why not then build one from scratch using an existing design as a starting point, re using hard to get components such as the roofing filters etc. It would be about the same amount of work, and the existing case could be used to house it.

my .02

Malcolm
 
Hello.
Let me first present myself.I am an electronic engineer with music, audio and audio design as hobbies (among others). I am new to this forum. But via ebay I have recently purchased some vintage four-channel equipment (JVC SEA-V7E, 4VN-880, 4VR-5445, 4DD-5 etc) and some CD-4 LPs. I wanted very much such equipment more than 30 years ago, but it was too expensive (or I hadn't enough money).
Anyway, now that I got this equipment I of course want to improve on it.
The 4DD-5 is an unit that can be plugged right into a 5.1 preamp/AVR. I read through the mods described in http://www.grizwald.plus.com/quad/SManual.pdf , and of course these seems absolutely worthwhile and necessary.
But I think also phono stage design/RIAA-preamps have improved since the early seventies.
The TA7122 should in my view also be a candidate for upgrade (I haven't been able to find the datasheet of this op-amp, but I will be very surprised if nothing better can be designed today).
Improvements to the power supply should also be possible.
But first, one should do the upgrades proposed by Malcolm.

Best regds
Rolv-Karsten
 
You can find out what I did here :-

http://www.grizwald.plus.com/quad/JVC_4DD5_mods.pdf

This is part 1 of an irregular series of modifications, based on the JVC 4DD-5 and clones like the Marantz CD-400.

Hi Malcolm,

I'm currently working on a 4DD-5. I read your technical paper about modifying the unit. So far recapped it, and am about to replace all those trimpots since they do not look good anymore. All oxydiced (sp?) and black.

However, one note about your output matrix mod: From my understanding you replaced R136/R137 with a trimpot to remove "Front" information from the "Rear" channels. But then you also have to replace R135/R138 with trimpots, too, to get rid of "Rear" information from the "Front". From the signal "Front - Rear" feeding the transistor you get "Front - Rear" on its Emitter and "- (Front - Rear)" on the collector. From IC103/IC104 you get "Front + Rear", which is feeding R135/R137 (R136/138 respectively) to get

1.) Front + Rear + Front - Rear = 2 x Front
2.) Front + Rear - Front + Rear = 2 x Rear

out of the resistor matrix. (Actually they are only adding signals, not matrixing) So I think your modification is only half the truth. You trimmed the signal ratio between R137 and R141, but nothing between R135 and R139. (And there's also some signum failure here since from your description of signals in your paper either "Front Out" and "Rear Out" are swapped, or the transistor has to be fed with "Rear - Front". Anyway, it doesn't matter as long as one knows what this "resistor matrix" is doing here...)

Another clone of the 4DD-5 is the Dual CD40.

-Kristian
 
Is someone still working on a PC-based demodulator?

I think we should aim at a workflow that involves half-speed playing and RIAA/demodulation in software. Any cartridge could be used and there would be no tracking issues.

Maybe the FM part could be done in hardware, after retrieving the pure FM signals from the digitized channels. It would involve several A/D and D/A steps but may be worthy even so.

This could be a beautiful project for those that know how to do such things. In theory I'm working on a half-speed turntable but that is the easy part and I have no time to work on that.
 
A half-speed turntable isn't so hard to get nowadays, if... you're looking with a open mind.
No way to get now a new deck with 16 2/3 rpm, but there are plenty of DJ deck that has "+-50% speed control". 33 1/3 rpm minus the 50% makes 16 2/3 rpm.

RIAA in software is trivial.

The hard part is the demodulation. The only thing that i can think of that could be very useful is to stabilize the recording, using the 30khz carrier as a tone reference. A kind of variable resample as in a PLL circuit. That will ease up the later decoding process, getting rid of any off-center issue.
 
The TA7122 should in my view also be a candidate for upgrade (I haven't been able to find the datasheet of this op-amp, but I will be very surprised if nothing better can be designed today).

I don't think it's entirely necessary to have the original datasheet. To understand the operational amplifier you might look for TA7120. The TA7122 may have better specs, though.

-Kristian
 
So I think your modification is only half the truth. You trimmed the signal ratio between R137 and R141, but nothing between R135 and R139. (And there's also some signum failure here since from your description of signals in your paper either "Front Out" and "Rear Out" are swapped, or the transistor has to be fed with "Rear - Front". Anyway, it doesn't matter as long as one knows what this "resistor matrix" is doing here...)

Correction: You don't need the second trimpod, the path R135/R139 has to be balanced with VR1 (R138/R142 with VR2). Locatet before the input of IC103. That's why JVC included just one trimpod for finetuning their CD4-50.

Sheesh, it's always dangerous to deep fly over cirquit diagrams... :eek:

Another improvement: Replacing those 0,22µF electrolytics with foil capacitors. The capacitors are marked LLC which probably stands for Low Leakage Current. If, due to age, the ESR of these caps gets too low they might affect the operating point of the input of the operational amp, since R123 near IC103 is of higher ohmic value.

Those can also be found in the ANRS, where high ohmic resistors might be affected by lower resistance of these capacitors.

-Kristian
 
The hard part is the demodulation. The only thing that i can think of that could be very useful is to stabilize the recording, using the 30khz carrier as a tone reference. A kind of variable resample as in a PLL circuit. That will ease up the later decoding process, getting rid of any off-center issue.

Most of the process should be done in the PC but if needed, the FM signals could be retrieved by feeding the appropiate points in a demodulator with the output of a PC soundcard, playing back just the FM part of the digital recording and capturing it back.
 
I don't think it's entirely necessary to have the original datasheet. To understand the operational amplifier you might look for TA7120. The TA7122 may have better specs, though.

-Kristian

That is true. What I really was after was more to see the data to be able to compare this amp with e.g. the NE5532 or the OPA2604/OPA2134.
Of course, such modern opamps does not fit right into the 4DD-5 board.
As others have mentioned, audio coupling capacitors could be changed also.
I would also guess resistors are 5%, and critical one could be chaged to 1%.
Maybe also the power supply could be improved upon, maybe better stabilisation.
There was a comment in a posting that if quad had become more of a hit than it did, and CD-4 had prevailed, the CD-4 system would have been improved. That is probably entirely correct, however, I feel ultimately that CD-4 is flawed by a too limited frequency response. But of course, if ONE system (CD-4) had "won" in the 70ties and 4 channels had been the standard by 1980, the CompactDIsk system would have had to relate to this, and it too would have been a 4-channel system. (An intersting thing is that the "Red book" standard specifies flags in the bitstream for just that, 4 channels. This has never been utilised, no disks and no players. But I think it is still in the "Red book". Now we have DVD-A, SACD, DTS and all that of course.)

Best regds
RK
 
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