CD-4 Disc Demodulator JVC 4DD-5 . Please help.

I'm a lot better than yesterday. Still sick. Dragged myself into work anyway.

If cleaning it doesn't help, I would try to return it. Ive seen used 4dd5's on ebay and craigslist as low as $40. There used to be a Canadian seller on ebay that had a stock of brand new old stock ones complete in the box for about $100 plus shipping. Thats how I got mine. They have been selling them for what seems like years, but now as of late, I have seen no more. Maybe they finally sold them all

That's why I kinda used to scoff at people selling used ones for $100. Why would someone buy a used one for $100 or even $75 when you can get a brand new one in the box with the test record and cables and paperwork for $100. One could say that they may be bad from sitting, but I have yet to see a post by anyone saying that they were anything but working perfectly out of the box. Some of the test records were warped though.

But if that one is broke, I would try to return it. You could probably get another one for less than it would cost to repair that one.

That sounds like good advice. There's still on on eBay. Thatnks to the magic of mobile internetm I just bought it en route to LAX airport. Now if this doesn't work, there's gremlins in my system, but I have hope that this will "perfect" my quad setup.... after 8 heartbreaking months of triumph and tragedy (mostly tragedy).

Until I decide to spend the dough on a tate or Lafayette SQ-W. I just don't know abou this SQD-20202 business. Front and back sound basically the same to me, though less basically the same than the built-in decoders on my HK 800+.

Have you been reading the threads about the Reality Technology Surround Master? It already has equal or better QS decoding than the best Sansui, and they will be making a version with QS and SQ, hopefully the SQ will be as good as or better than the Tate. Expensive little box, but well worth it if it decodes better than $2000 worth of hardware for $500

I didn't see that. I'll keep my eyes open for that. But that's about the most niche product I've ever heard of. How big can the audience be for a modern QS / SQ decoder?

Well, the original purpose of the box was for using the principles of QS for synthesized quad/surround, not decoding formats. They are making the special SQ box for us.

When I found mine in an Alabama flea market, it had a bad cap and a leaky transistor. While I can't vouch safe your skills, as repairs go, capacitor replacement is not that difficult. You need a good quality soldering iron, rosin core lead and tin solder, or what used to be referred to as radio and TV solder. You will also need some good quality solder wick. It is used to soak up the old solder to make part removal easy. Put the wick on the joint and heat until the solder melts, and the wick will soak up the solder. If needed, move to an unused portion of the wick so more solder can be soaked up. once the solder is gone, it should be easy to lift the leads of the capacitor, and then pull it off the board from the other side. It is important to note the position of the black stripe down the side of the cap, as this is the negative marking. It will have minus signs on it. The new cap needs to be oriented the same way, or it will go pop! (explode). Make sure the replacement cap is the same uf (microfarad) value. The voltage value can be a little higher if you can't find the exact same, but never lower. The higher voltage value is possible because modern capacitors are often smaller than those of the day the demod was made. Electrolytic capacitors are small aluminum can shaped components, with a plastic sheath, with two leads, both coming out of one end in this case, usually brightly colored but can be brown or black. They will have the stripe down the side of the sheath indicating the negative lead. They have a capacitance value and a voltage rating. The smaller ones are usually the coupling capacitors, the bigger ones are usually filter caps to remove AC ripple from the DC. These filters are probably not the problem. When resoldering, heat the work, not the solder. when the work is hot enough to melt solder, touch the solder to the work, and allow it to flow onto the work. Once the joint is made, remove the iron. The joint will harden in about 4 seconds. If you are not practised at this, get an old junk circuit board and practice before attempting it on a valuable demod. Remember go slow and careful. Make sure the demod is unplugged when replacing components. And do not overheat the board. It will cause the copper land to lift from the board. If the first one doesn't look good after it's done, let a pro do it before you mess up a perfectly good demod. Good Luck
The Quadfather

I like to chime in here, and note that I have acquired 2 more CD-4 demodulators since my original post. The JVC-4DD5 has horrible high frequency response compared to my SE-405 Panasonic and my SH-400 Technics. When listening to normal stereo it's best to just not use these units, and go directly to your receivers phono input. The JVC-4DD5 'direct' out input goes through the cd-4 filter that cuts audio above 15k.. Actually, the 4DD-5 starts cutting frequencies way before 15k. Hell, I own 8-track players that sound better than CD-4 played through the 4DD-5.

Great. Now I'm regretting my decision to return the one I bought and buy a new one on eBay. Oh well. I think I'll hook my NAD preamp to the direct out on the JVC and then into my receiver. Something is messed up on the receiver preamp board.

Appreciate all the technical info though.

Nonsense! I don't know about the Panasonic demod, but I have a Technics SH400. I tried it out back awhile ago replacing my 4DD5. guess which one now sits on the shelf? (Hint, It's not the 4DD5) I own the Akai CR80DSS eight track player. It does not sound better than the 4DD5. And as for the direct output going through the filter before it exits the demod, that's just plain false. I am looking at the schematic now. The direct outputs come from a switch that is connected directly to the inputs. No filter, not even a coupling capacitor. Just the switch. The filter is way down the chain and is past the preamplifier. However, it does affect the main outputs of the demod, even when the demod is in the stereo mode. Perhaps this is what Surroundme33 meant. it would not be difficult to install a switch to bypass the filter if it bothers you that much. Of course, to be fair, I have to admit that my hearing isn't what it used to be. But then it wasn't a big deal to me when my hearing was good. I stand by the JVC 4DD5.

Glad to hear a differing opinion. I still might use my NAD in conjunction with the JVC. Whatever sounds better.

I don't think any demodulator puts the signals through anything other than maybe a switch before the direct output jacks. That is THE purpose of those jacks - to get signals directly from the cartridge to whatever preamp you are using. No influence from the demodulator.

We also have to remember that you cannot necessarily compare these old units as if they were new. There may be components not in spec. anymore and that negates any assertions as to which unit may be better or sound better than another. The only way to do that is to be sure each unit in any comparison is completely restored to original specifications.

An example is comparing my SH-400 and SE-405. The SH-400, in magnetic cartridge mode, is not so good. The right channel is fine but the left channel is weaker and the separation is not the best. Now, I'm sure it didn't leave the factory like that. It is age. In semi-conductor cartridge mode, it sounds fabulous. Obviously, components involved in that mode are still all OK.

The SE-405, on the other hand, sounds fabulous in magnetic cartridge mode and, while it is OK in semi-conductor mode, the performance is somewhat lacking compared to the SH-400. The highs are a bit muted in comparison. Is it just that way by design or are there components and/or adjustments which need attention?

The only way to tell would be to completely dismantle it and test all components and replace any bad ones. And then completely recalibrate it afterwards. Both units, as a matter of fact. Even though I am capable of doing just that, I am content to just use the SH-400 for my SC cartridge and the SE-405 for MM cartridges. Laziness, I guess.

It just illustrates why one cannot just take vintage units of any type and compare them without restoration.

Doug

The Quadfather said:

Nonsense! I don't know about the Panasonic demod, but I have a Technics SH400. I tried it out back awhile ago replacing my 4DD5. guess which one now sits on the shelf? (Hint, It's not the 4DD5) I own the Akai CR80DSS eight track player. It does not sound better than the 4DD5. And as for the direct output going through the filter before it exits the demod, that's just plain false. I am looking at the schematic now. The direct outputs come from a switch that is connected directly to the inputs. No filter, not even a coupling capacitor. Just the switch. The filter is way down the chain and is past the preamplifier. However, it does affect the main outputs of the demod, even when the demod is in the stereo mode. Perhaps this is what Surroundme33 meant. it would not be difficult to install a switch to bypass the filter if it bothers you that much. Of course, to be fair, I have to admit that my hearing isn't what it used to be. But then it wasn't a big deal to me when my hearing was good. I stand by the JVC 4DD5.

Click to expand...

I actually read the 'filter' phenomena on a site that explains how to modify the JVC 4DD-5. I can't find the web page now, but it was very informative on how to improve the unit. I believe it was something like 'malcom's quad page' - something like that. Any way, one of the mods illustrated how to bypass the filter that cuts audio above 15k.. Somehow the JVC keeps the filter on even when listening to the 'direct' stereo out.

As far as 8-tracks concerned. I own 3 quadraphonic tape decks (wollensak 8060, Akai CR80DSS, and Marantz TD-48). The Akai and wollensak sound way superior to my JVC 4DD5 unit ( i own 2 of these as well).

I own a 4DD-5 (Sylvania DQ-3700) and CR-80DSS. The Akai never sounded as good or better than a 4DD-5. I've had both since they were new in the box. Something is very wrong.

On my old Quad system, the 4DD-5 on the 2ch pass-through mode and direct into the phono input from the turntable sounded exactly the same. Back then, I could hear to 19khz with no problem. My hearing was tested.

Yes, the age of the equipment is definitely a factor. A complete recap should restore a demod to factory specs, and it's alignment would probably be closer to factory specs after you were done even without aligning it than if you aligned it without renewing it. The SH400 might actually be a better demod with a recap, without doing it to both devices one would never know. I have not had the time to do this kind of overhaul, I just repair my equipment when it breaks. Maybe after I retire. I have a 4DD5 I keep on the shelf that doesn't perform as well as the one in my system. It works, but not as well. Probably because it still has the early phase lock loop chips in it. I put modern ones in the other one. Still, I like the 4DD5.

Also, the direct output of a demodulator is not the same as two channel output from the normal output jacks. The direct output jacks are connected directly to the cartridge outputs when switched in. This is so you can send the cartridge signals directly to your amp/receiver to use matrix (SQ, QS, etc.) decoders if you are playing records of those formats. Two channel output from the demodulator, whether manually switched or automatically switched by the demodulator detecting the carriers or not, still routes the signals through some of the demodulator circuitry, probably the filters.

surroundme33, I believe the latter is to what that article is referring. The bypass of the filters would be so you can still use the JVC as a preamp without the 15kHz limitation. If the article is, in fact, referring to the demodulator output as "direct output" it is incorrect in that aspect.

EDIT: Oddly enough, I just noticed the SE-405 does NOT have direct output jacks but DOES have 4 channel auxilliary input jacks which you can select on the front. The SH-400, on the other hand, DOES have direct output jacks but does NOT have 4 channel auxilliary input jacks.

Doug

Doug G. said:

surroundme33, I believe the latter is to what that article is referring. The bypass of the filters would be so you can still use the JVC as a preamp without the 15kHz limitation. If the article is, in fact, referring to the demodulator output as "direct output" it is incorrect in that aspect.

Doug

Click to expand...

Yes, this is what that mod was referring too. It was a special mod to bypass the demodulators filters for the purpose of regular 2-channel mode. I just can't find that web page anymore. Btw, I was just referring to the JVC 4DD-5. My other demodulators have true bypass switches.

surroundme33 said:

I just can't find that web page anymore.

Click to expand...

It was "Malcom's Quad Information Page". Now defunct. If someone is interested I may have the article about the 4DD-5 mods he developed at home. And yes, he shortened the filters with two relays when demodulator doesn't detect the carrier signal.

-Kristian

Let's see if I can upload these files.

scifi said:

http://web.archive.org/web/20070629060439/http://www.grizwald.plus.com/quad

Click to expand...

Yep, that's the page, but unfotunately the documents weren't accessible from archive.com.

-Kristian