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

[The Quadfather]

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

[quadsearcher]

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.

[quadsearcher]

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.

[The Quadfather]

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

[The Quadfather]

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

[quadsearcher]

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.

[The Quadfather]

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

[bob.stek]

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

[The Quadfather]

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.

[bob.stek]

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

[The Quadfather]

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?

[krkier]

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

[krkier]

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

[The Quadfather]

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.

[Russells]

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?

[scifi]

http://www.quadraphonicquad.com/foru...ht=#post174125