CD-4 - The thin line between success and failure, but still in the fight!

[edisonbaggins]

My Technics produces minor hum, which disappears when music is present.
Little bit hummier when my can lights are on. I have lamps I switch on during most music listening. No hum from those bad boys.

 

[fredblue]

just to put my serious stetson on for a sec., i found certain model CD-4 demodulators quite sensitive to noise from particular gadgets.

for instance, i couldn't bring my old iPhone (think it was an 8 but may have been the 6) anywhere near the 4DD-5 when it was up and running without weird pinging and interfering noises coming through the speakers.

fwiw my current iPhone (12) doesn't seem to have the same issue for some reason? idk if it's a red herring or not but just thought i'd mention it?

 

[Sonik Wiz]

I used to have close friends that worked at Hi-Fi-Fo-Fum ("the stereo store with the funny name").

Anyway they always refereed to CD-4 as Compound Distortion to the Fourth Power. But they didn't mind selling & making money from it.

 

[4-earredwonder]

My Technics produces minor hum, which disappears when music is present.
Little bit hummier when my can lights are on. I have lamps I switch on during most music listening. No hum from those bad boys.

Dimmer switches sometimes do produce prodigious HUMMING ....... that's why dedicated outlets are HIGHLY recommended. And grounding one's mains to a copper spike!

 

[4-earredwonder]

I used to have close friends that worked at Hi-Fi_Fo-Fum (the stereo store with the funny name).
View attachment 90320
Anyway they always refereed to CD-4 as Compound Distortion to the Fourth Power. But they didn't mind selling & making money from it.

My local snob Audio Salon did embrace SURROUND but never bothered with CD~4 .... WAAAYYYYY too problematic out of the gate!

 

[edisonbaggins]

Dimmer switches sometimes do produce prodigious HUMMING ....... that's why dedicated outlets are HIGHLY recommended. And grounding one's mains to a copper spike!

I recently replaced my can bulbs with better matches for my ballasts. That completely eliminated hum from the cans themselves, and their dimmer switches.
Just a lil bit when running certain, usually vintage gear.
All my gear runs through line conditioners.

And I don't mind using lamps while listening. They create a chill vibe.

 

[Quad D]

NO!

Then probably your demodulators pick up noise somewhere, you can try power conditioners or even ground loop insulators, but maybe that's just how they are. I am using different demodulators (Sansui) and getting the CD-4 playback to work well was quite easy, no problems with hum or RFI interference. QRX-5001 receiver is not expensive and outputs demodulated CD-4 playback through tape outputs, so in essence it might be used as an external decoder (its phono input). No automatic carrier level adjustment, though, all manual.

 

[J. PUPSTER]

Then probably your demodulators pick up noise somewhere, you can try power conditioners or even ground loop insulators, but maybe that's just how they are. I am using different demodulators (Sansui) and getting the CD-4 playback to work well was quite easy, no problems with hum or RFI interference. QRX-5001 receiver is not expensive and outputs demodulated CD-4 playback through tape outputs, so in essence it might be used as an external decoder (its phono input). No automatic carrier level adjustment, though, all manual.

Yeah, come to think of it I used to Demod. through my QRX-8001, & don’t recall hum from back then…

 

[quadsearcher]

Yeah, come to think of it I used to Demod. through my QRX-8001, & don’t recall hum from back then…

That implies you might have a ground loop now. I haven't run into a ground loop at home but I have at work.
In no particular order:
I ran both ground leads (receiver and TT) to the demod ground.
An adapter made for plugging in a 3-prong plug into an old 2-prong is a "ground lift". For testing, I'd try lifting grounds on both the TT and RCVR if they have 3-prongs..
Try everything plugged into a strip so it is all sourced from one outlet.

Other stuff: A nearby router can cause noise through the phono.
Even experienced electricians have missed this one:
If a coax cable for cable TV is connected to your system, try disconnecting it to test. Even if it is a TV with cable on the tuner, it might still be connected to the system via hdmi, or to a cable box with hdmi to the receiver.

 

[Sonik Wiz]

Yeah, come to think of it I used to Demod. through my QRX-8001, & don’t recall hum from back then…

So then... I might ask if you were demoding ok through the 8001, why did you start trying other sources?

 

[J. PUPSTER]

So then... I might ask if you were demoding ok through the 8001, why did you start trying other sources?

I documented that already, as the 8001 started having issues overall of some weird hum and the rear left channel cutting out. That's the main reason I purchased the Involve Amp Master to keep rolling until I decide if I'm going to send that beast back to qrxrestore. I've already dropped some serious coin on getting it reconditioned the first time, which I'm sure you remember.

 

[par4ken]

Just a side step in threads here from Mr. Baggins' thread here.

My latest Panasonic SE-405 (as with all my Quad gear) is hooked up with Blue Jean LC-1 cables. I consider these to be pretty good quality shielded cables. The hum is not found with my other gear, like my Surround Master v2 etc.

I'll soon record in the hum I currently have in the Pany SE-405 and post here later for folks to listen to it. As I said before, I can usually hear voices in the background if cranked up; it could very well be some kind of local Radio interference IDK.

@barfle mentioned a part called a “power supply filter capacitor”, don't know if @Sonik Wiz replaced that one in my Marantz or not? But, all three Demodulators I now own have the same type of hum: Marantz CD-400B, JVC 4DD-5 & now the Panasonic SE-405. So even if it's that “power supply filter capacitor”, and you could find old one's out of a parts Demodulator for replacement, you'd still be using really old and unreliable parts IMO. So, are these “power supply filter capacitors” available new that would work in the Demodulators?

I probably mentioned this before, but when converting some of these 70's Japanese Cd-4 LPs I have to raise the recording-in amplitude by about 12-16 dbs to get a decent level with my current cart., an AT-15S. That just raises the levels across the board for stuff like hum to come out and it's very difficult to reduce after the fact. It might take 3 passes with Noise Reduction software to quiet it down which isn't good because I believe it is taking some dynamics out of the music and mudding it up a little IMO.

Are you sure that you have a good ground connection from your turntable? Remember Sonic had the same trouble with his turntable and finally found that the ground connection was bad. Power supply capacitors can go but it is unlikely that they would be bad in all three demodulators.

 

[barfle]

Just a side step in threads here from Mr. Baggins' thread here.

My latest Panasonic SE-405 (as with all my Quad gear) is hooked up with Blue Jean LC-1 cables. I consider these to be pretty good quality shielded cables. The hum is not found with my other gear, like my Surround Master v2 etc.

I'll soon record in the hum I currently have in the Pany SE-405 and post here later for folks to listen to it. As I said before, I can usually hear voices in the background if cranked up; it could very well be some kind of local Radio interference IDK.

@barfle mentioned a part called a “power supply filter capacitor”, don't know if @Sonik Wiz replaced that one in my Marantz or not? But, all three Demodulators I now own have the same type of hum: Marantz CD-400B, JVC 4DD-5 & now the Panasonic SE-405. So even if it's that “power supply filter capacitor”, and you could find old one's out of a parts Demodulator for replacement, you'd still be using really old and unreliable parts IMO. So, are these “power supply filter capacitors” available new that would work in the Demodulators?

I probably mentioned this before, but when converting some of these 70's Japanese Cd-4 LPs I have to raise the recording-in amplitude by about 12-16 dbs to get a decent level with my current cart., an AT-15S. That just raises the levels across the board for stuff like hum to come out and it's very difficult to reduce after the fact. It might take 3 passes with Noise Reduction software to quiet it down which isn't good because I believe it is taking some dynamics out of the music and mudding it up a little IMO.

Power supply filter capacitors are pretty generic parts. They are still being manufactured, because power supplies are still being manufactured. But in the other thread, @Sonik Wiz mentioned that he had replaced them, so since that's been addressed, I'd guess it's not the problem.

https://www.newark.com/nichicon/lkg1h102mesabk/capacitor-alum-elect-1000uf-50v/dp/26T4985
Phono preamps are notoriously finicky devices, and CD4 demods all have phono preamps, as far as I know. They have high gain and are prone to interference. Sometimes that's a grounding issue, other times, it's electromagnetic pickup. I've seen turntables with separate ground wires, and even in some of my old designs, I experienced ground noise, and it wasn't easy to track down. Electromagnetic pickup can be helped with shielding.

Another possible issue is the old, and likely corroded, RCA connections on that beloved old equipment. It's possible that one of the ground (shield) connections is weak, and that can allow all sorts of interference into your circuitry. A good scrub with a contact cleaner won't hurt anything, and might fix it all.
https://www.grainger.com/search/cle...dabd4a&gclid=bf9ece07a53411d128efaa28dcdabd4a

 

[J. PUPSTER]

Are you sure that you have a good ground connection from your turntable? Remember Sonic had the same trouble with his turntable and finally found that the ground connection was bad. Power supply capacitors can go but it is unlikely that they would be bad in all three demodulators.

Pretty sure they are fine, I typically switch between the Demods., a Rotel TT preamp into the SMv2 or just straight into the Rotel for regular LPs. They never have any issues other than the Demods.

 

[J. PUPSTER]

Another possible issue is the old, and likely corroded, RCA connections on that beloved old equipment. It's possible that one of the ground (shield) connections is weak, and that can allow all sorts of interference into your circuitry. A good scrub with a contact cleaner won't hurt anything, and might fix it all.
https://www.grainger.com/search/cle...dabd4a&gclid=bf9ece07a53411d128efaa28dcdabd4a

All these Demods. I've been trying looked pristine, like they were NOS fresh as a newborn's arse.

 

[Quad D]

I documented that already, as the 8001 started having issues overall of some weird hum and the rear left channel cutting out. That's the main reason I purchased the Involve Amp Master to keep rolling until I decide if I'm going to send that beast back to qrxrestore. I've already dropped some serious coin on getting it reconditioned the first time, which I'm sure you remember.

I am pretty sure you can use the 8001 in passive mode, just as a phono preamp, tape outputs will have processed CD-4 signals. The issues are probably in power amp and/or preamp, or eventually SQ/QS boards (CD-4 signal is not going through them).

 

[jupp369]

Quad D said:

Are you getting the same hum when using a regular phono stage (not CD-4)?

NO!

Thousend possibillities

No hum with another cardridge !!! so you found already the black hole!
That means: TT, 405 and receiver are OK! All cartridges use the same preamp. Try the AT15 with a normal stereo LP, so the decoder part is not involved.
I had also such problems: cleaning the connector of the headshell and the contacts inside the tonearm with a glass brush or fine sandpaper (at work we had also such problems at golden contacts). I removed also the rubber ring at the headshell, so the pins get deeper and give contact.
Try if the contacts in the tonearm are moving with a nail. And you can try another headshell.

The extra ground wire on the SL's is only chassi.
Now I faced similar problems with china cables: grounding is only a parallel wire, no shield/screen. Also the 3.5mm jacks had always bad grounding on computer.
(Stopped also all tests with needle drops, because I heard neighbors cellphone.)

I had to do a lot with searching for errors. Only helps a step up. Disconnect and switch off everyting except receiver and 405. Even the TT off. and then add one after next.
Sorry that I can't pass by ...

 

[proufo]

See page 4 of this service manual to get an idea of how complex the adjustment ("alignment") of a CD-4 demodulator is.

 

[par4ken]

See page 4 of this service manual to get an idea of how complex the adjustment ("alignment") of a CD-4 demodulator is.

Best not to touch it or you may never get it to work right again!

 

[fredblue]

Best not to touch it or you may never get it to work right again!

ahh.. i did that with one of my 4DD-5's, played around with some pots and it went totally goofy!

although it wasn't working properly in the first place, which is why i took it apart and started tinkering with its' innards!

lesson learned; leave the fiddling about to the experts. oh and Uncle Ernie. he's an expert at fiddling about, fiddling about!