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

  1. #26
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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    Malcom:
    Without getting out my schematics and going into what you are doing, You should be aware that if you are using one of the JVC test discs, the older version has a defect. That disc is labeled with the number 4DE-202. I have one of these, it is the small disc that came with the demodulator. Not too long ago, I read of this defect and had remembered that I had made a note on the jacket many years ago about what I then perceived as a defect. I had noticed that the behaviour of the disc did not match what it should have been with a correctly working demod. I pulled the disc and this is what I had written on the jacket:

    (At band 2) Right channel recorded wrong: adjust for low output on (right) rear channel

    This notation matched what I had read that day. Of course, if you are using a different alignment disc, or are using the later version where this problem was corrected (I believe it was 4DE-203), this does not apply. You can still do the test by switching the input connections to the demod so that you are using the left channel test tones on band 1. Hope this helps.

    The Quadfather

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    I've looked for one of the test discs and it appears they go for more than I can justify for myself right now.
    Using tones from Malcolm's test disc would be a work around and if accurate, the only thing not accounted for would be slight variations from turntable set-up or cartridge channel matching.

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    The Quadfather: thanks for your good description: http://www.quadraphonicquad.com/foru...-4-demodulator . Now I know how it is supposed to work and and mine seems to be OK, the separation pots acting like level controls confused me until I read it. I heard Superstition by Montengro for the first time without too much distortion. Now I just have to clean the record to hear it even better.
    Malcolm: After reading the Marantz manual it looked like (for a different adjustment) they were using TP304 and TP303 as monitor points and TP302 and TP301 as signal injection points. I tried it this way and the input levels weren't padded, and the new back channel trimpots nulled nicely not far from center using back panel outputs as monitor points. The back panel controls still nulled at full ccw, it works out fine however, set up by ear.

    Using a Yamaha PX-2 TT and AT125LC stylus/cart.

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    Quadsearcher:
    Remember that if you are using a new stylus, they have to be broken in. I use a modern AT440MLa cartridge. It performs well without breakup. Just music and separation. This particular stylus has lasted quite awhile, much longer than what my previous trackmaster 8 stylii lasted. I have been going for about five years with it now. I'm still using the stylus that came with the cart. I break them in by playing about five stereo or SQ records. You can use CD-4 records, but until it's broken in, it won't give optimal performance. With stereo or SQ, it doesn't need optimal performance. Clean records definitely play better. If I pick up an old CD-4 record, say, at a used record store, I usually find that although it looks clean, it has to be dredged by a linear contact stylus a few plays before it gets really clean. I would have to stop play after about two songs to clean the stylus. Anyway, I'm glad that my writings were of help to you. It is sometimes difficult for an engineer to explain something that is technical in non technical terms so that (I am assuming) a non engineer can grasp it. It sounds like I suceeded.
    The Quadfather

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    Y'all:
    I just went back and read that post. It's funny how similar my wording with what I wrote today, is to what I wrote then. I see that some of what I said in the last post was covered in the early post on CD-4 demod alignment.
    The Quadfather

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    Definitely worth covering again, I read it and hadn't thought about the stylus & cart until you mentioned it in the above post. The AT125 was on the table when I got it (used), I haven't inspected it with the microscope. If it shows wear I'll look into the 440.

    "Just music and separation", that is encouraging!

    I am an elect. technician and can follow the signal flow in the schematic, just don't have the skills to see why Malcolm's out-of-phase/in-phase test tones didn't result in null on the back panel separation control. Maybe I was looking for too pronounced of a change which is why I went too quickly to full CCW. Now that I have it very close by ear I'll look at it again before I close it up.

    Thanks again for the help.

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    Quadsearcher:
    It does help to be knowing about the electronics. Here are some tips:
    If you pot down the separation control for a side and hear nothing, then the signal from the pll circuit is not getting through. Troubleshooting is in order. Bad demod!
    Most problems will be due to bad electrolytic capacitors. Next most will be transistors. If your unit has the earlier PLL chips, you might want to replace them with new ones. Yes, they're still availlable, last I checked.
    The cartridge and stylus is the main factor in good CD-4 performance. Granted, if the demod is working properly. How the stylus tracks is everything. I track the AT440MLa at 2.0 grams. The recommended 1.5 is just too light for CD-4 with that cart. Of course, I don't know about yours.
    Good Luck!
    The Quadfather

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    I have recently decided to try to recapture the glory of my misspent youth and set up a quad system again. I found a almost-NOS 4DD-5 and a used Technics SH-400. I have been a tinker-er in the past - can tell + from - on caps and usually don't grab hold of the hot end of my soldering iron. But my fine motor skills have deteriorated over the last year or two and I am reluctant to try the mods to the 4DD5. Mechanical board replacement and occasionally soldering RCA plugs seems to be my limit. So I decided to find a reputable audio dealer/repair person who could come to my rescue.

    I finally found ONE local electronics repair place which would even work on older equipment. However when I brought my 4DD-5 to them with a printed copy of the mods, they informed me that 1) they would charge a MINIMUM of 2 hours at $80/hr (plus parts), 2) would consider any work they did as 'experimental' and would not guarantee it would work, 3) if it did not work they would remove the mods (at $80/hr) but not guarantee its performance after the removal, and 4) they had a backlog of 124 units which they would prioritize ahead of mine as well as any new 'normal' repairs. Also I would need to bring my calibration disk and a CD-4 cartridge and be there when they calibrated the 4DD-5 because they would not guarantee their loss if they were misplaced or damaged.

    You can imagine my excitement at having finally found someone to mod my JVC. {sarcasm off} I didn't even ask them about the Technics.

    So to the point of this message: HELLPPPP! I don't mind paying a reasonable amount to a competent techie to make the mods, especially if he/she has the experience to work with CD-4 equipment. I am fine with mailing it off (though GB and Germany seem unrealistic!). I won't even complain over how long it might take. Any suggestions or takers?

    BTW, a little off topic. I happen to have visited grandchildren over the summer in Wayne, NJ, the east coast headquarters of JVC. As a lark I went there and happened to meet the JVC vice-president, Bob Nizza, in the parking lot. Specifically I asked him if there was any old CD-4 documentation (or even equipment) available at JVC. When he stopped laughing, he did tell me about some of his old equipment which he still has - 2 top-of-the-line CD-4 receivers (4VR5456X) and a pair of JVC Nivico HE Series 5340 speakers, 3 JVC QLY5F TT's, and 4 ECA102 quad "Radar Screen" reverb amps. I told him to contact Lou Dorren and offer to manufacture his new decoder - he smiled and politely did not laugh out loud (again).

    Dr. Bob, pun aficionado and admirer of the original 'Dr. Bob' of the Muppets

  9. #34
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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    Dear Bob:
    What I would do if I were you is to try to get the demodulator working in it's stock state. It (the 4DD5) is a good performing demodulator when it is right. Then wait for Lou's demod, while you enjoy very good quad. The SH400 is a beautiful demodulator, I know, I have one, but it does not perform as solidly as the 4DD5. I know, I have a 4DD5 also. While I am capable of performing the work, these days I have so little time. I am a landlord and I have a full time job as a broadcast engineer. I can't even catch up to what I need to do on my own house. I wouldn't however, use those people whom you spoke of. Just keep looking. Look for an old timer who worked in consumer electronics during the quad era. the right person might even be proud to work on your demod.

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    Quote Originally Posted by The Quadfather View Post
    Dear Bob:
    What I would do if I were you is to try to get the demodulator working in it's stock state. It (the 4DD5) is a good performing demodulator when it is right. Then wait for Lou's demod, while you enjoy very good quad.
    Thanks for your comments, Quadfather. Not long after I posted my message, I went over to see if there was any new activity on Lou Dorren's new demodulator thread. I hadn't been over there for several weeks, having become discouraged at the lack of progress or information. Then I found his post of 2 1/2 weeks ago - "It's alive, it's alive!" (Young Frankenstein) Glad to hear he is almost fully recovered from his medical issues and the demod will be produced. I put my name on the list some time ago but almost gave up.

    So I do have my name on the list, and getting the 4DD-5 modded is now less important. Once I get the new Dorren demod, I may even risk burned fingers and try to mod it myself since it will be a backup.

    Dr. Bob

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    Yeah, Lou had us worried for awhile. He kind of dropped off the radar for awhile. We didn't even know he was ill. There was a lot of speculation, but the consensus was that the project was dead for whatever reason. And now good news. Of course, I will rejoice when I have the demod in my hands. For until then, anything can happen. Let's hope a bunch of demodulators get built.
    The Quadfather

    P.S. I wonder if Lou intends to build a CD-4 modulator after the demodulator project is done?

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    Quote Originally Posted by The Quadfather View Post
    P.S. I wonder if Lou intends to build a CD-4 modulator after the demodulator project is done?
    For what reason? You want to press some homemade vinyl?

    -Kristian

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    BTW: Malcom's page seems to be down. Anybody knows what happened?

    In addition to the modifications Malcom made I suggest to check the supply voltages at the various ICs. Get your Oscilloscope and tie it AC-coupled to the supply pins of the ICs, then choose something like 50mV/div or even 100mV/div. You will be suprised how much "dirt" you will see there.

    Choose ceramic capacitors, 100nF to 220nF, and solder them with as short leads as possible directly to the IC pins on the bottom side (solder side). This will reduce noise considerably.

    -Kristian

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    No, I don't want to press homemade vinyl. It is for those in the industry like himself that want to do it. Of course, he wouldn't need as many, maybe 1 or two.

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    This link no longer works. Is there a new link?

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

    Also, I posted this on another thread but someone may find it useful here...

    I read about these mods at the end of 2012. I have a Pioneer amp without a phono input and I wanted to use my Technics SL1200 Mk2 turntable because I play a lot of records. I had a cheapo pre-amp bought with Magix Analog to Digital converter software (which is very good, BTW) and wanted a superior replacement.

    I had an old JVC 4DD-5 on a shelf in the man-cave. Last used about 1980.

    I did the mods and put a DPCO / DPST switch on the right hand side (I cut a slot into the casing and glued the switch into place so just the tip of the switch sticks out - looks OK and works very well).

    I was very happy with the result, BUT...
    ...the right front channel kept fading out after a while of playing.

    I resoldered input connections, poked around with screwdrivers and pondered why, when the channel faded out, almost any tap on the case would bring it back again.

    I discovered that one of the two adjustment pots on the back - which hadn't been touched for thirty years - was obviously quietly oxidising and going o/c whenever it warmed up. I merely put a screwdriver into the pot's slot and turned it back and forth a few times (ending in the same position as it started) and, lo and behold, the problem was cured.

    I am now a happy bunny. I hope this helps someone else to do what we did...

    Oh, and where can I find a suitable, inexpensive cartridge/stylus for CD-4 records?

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400


  17. #42
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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    I just wanted to post information about my experience in modifying my marantz cd400 here, so that others can have this information if it helps.

    I had a tech do the modification of adding the trimpots, and calibrating according to the instructions of the modifications, so I didn't do the calibration myself and can't speak to what exactly happened with that process, but I've known the tech to do good work and feel he should have been able to follow the instructions properly. What I've noticed ever since the modification though is that, while adjusting the demodulator to have very discreet rear channels, the fronts have been seeming to get some bleedthrough. I've also noticed that much of the bleedthrough can be cancelled out by mixing in the rears at -4dB...but not always, sometimes it adds bleedthrough of things not in the front. Really odd. I wasn't sure if maybe things were mixed that way, so I pulled up some of my past conversions, and I confirmed my fears...there was rear info bleeding into the front currently, which hadn't in the past. I also ran the channel id portion of a test record and found there was definitely something wrong.

    Ugh...

    When I first had my suspicions, since I don't have the test equipment required, I played with the trimpots with the test tones to adjust the separation knobs, and I did find that the spot the trimpots were adjusted to allowed the most discreet rears, once I had adjusted the separation knobs. I also found adjusting the trimpots did nothing for the fronts.

    What to do?

    My biggest struggle was a lack of clear back information...calibration records give you test tones in the front to adjust the rears to be silent, but not the opposite. So, I went to ebay and found one of those Project 3 test records for cd4, the one that came out in all 3 formats. I know from my SQ copy that it has a portion where it puts pink noise alternating in the front and rear, to help balance your front and rear channels. I've not gotten this yet, but I think this will help me zero in on the best setting.


    But, I wanted to play around some more, so I opened the thing up again, and went looking for a record that would have a simple mix with stable parts, so I can listen to the front and hear those parts cancel out as I adjust. I went with Average White Band. So, I cue up pick up the pieces, listen to the fronts only, and hear the guitars bleeding into the fronts. Adjusting the added trimpots did nothing. But, turning up the separation knobs on the back, made the guitars drop out. Continuing to turn up the knobs didn't result in the guitar coming back up, it wasn't a null point. So, I figured, ok, probably best to just turn it up to the point where it's fully dropped, but not further, so I went back and did that. Then, I put the test record back on, put on the test tones, and of course I had more sound in the rear than before on the test tones. But, adjusting the added trim pots allowed me to find a null point on those. Was it as quiet as before? I don't know....I guess I should have recorded all this testing.

    Anyways, after this, I was left with a setup that was performing right when playing the channel id portion of the record. I'm not sure how scientific it is, or if it's fine tuned as accurately as possible, but now I know I'm on the right track. I also don't know if this is the norm for this modification, and if the calibration procedures in the instructions are flawed, or my tech goofed something...but I'd suggest anyone doing this mod pay close attention to their front channels, and have a project 3 record on hand. I plan on doing some more thorough calibrating once my project 3 record shows up. I'm thinking what I found above is the best procedure to calibrate with added trimpots....adjust the front to have the rear info just cancelled out with the separation adjustments, then find the null point on the rears on the trimpots.


    Just wanted to share this because, with so few people doing this, it really helps for those of us playing around with these things to post our findings and experiences. I know it would have helped me greatly if while i was going a bit out of my mind wondering if I had a problem or not if I found a post of someone having a similar experience.

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    Just to let you know
    The Project 3 CD4 LP does not have a test tone on it
    I don't know why it would seem if you were using it as a set up
    it would be normal

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    I think you've misunderstood my post. My point is, with the added trim pots, in addition to the normal test tones that a normal test record has (which I do use), it would be useful to have a test that is supposed to be only out the back, and not out the front, to make sure your calibration is good all around. The project 3 record will offer me that.

    Adding the trimpots has added an additional adjustment that cannot be done with a normal setup record. And I certainly wasn't suggesting using the project 3 record in place of a setup record.

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    One little heads up...the cd-4 version of the Project 3 test record doesn't have the pink noise balancing track. It instead has different frequencies played in all channels in equal volume to adjust the balance. But, the channel id track does give me tones in each individual channel. Anyways...my calibrating method is still sound, adjust the separation knobs to make sure there is no rear information bleeding into the front, then adjust the added trimpots to find the null point on the channel separation test on a normal cd4 test record.

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    Just like to know has anybody ever tried and took a CD-4 demodulator out of a Sansui QRX-9001 and made a free standing unit out of it? I have read threads here that said it is one of the best demodulator ever made because i have 3 that i could use.

    Jay

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    Default Re: Modifying the JVC 4DD-5/Marantz CD-400

    Quote Originally Posted by JR Hearne View Post
    Just like to know has anybody ever tried and took a CD-4 demodulator out of a Sansui QRX-9001 and made a free standing unit out of it? I have read threads here that said it is one of the best demodulator ever made because i have 3 that i could use.

    Jay
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