Digging into old gear can be quite the adventure! I'm glad to see you're making progress on this project.
Bose 4401 CD-4 Demodulator?
- Thread starter Asklia
- Start date
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Asklia
Well-known Member
Merci! Still some problems unsolved (or tasks ahead). The poti must be replaced, although its still working without problems. Replacements are already on my desk.
There is (or has been) a red LED for CD-4 detection (called "radar" by JVC in the old days) on the CD-4 carrier board. But this will be invisible, when the BOSE is closed. So I modified the board by adding a third pin acting as power for a red/green duo LED. This will replace the old 6 Volt lamp inside and its red plastic cover simulating a red LED on the front. Common Anode for the duo LED, of course :~)
Biggest task currently is cleaning all (!) of the PCB connection bars and angled connectors to get rid of the tin coating for galvanizing with gold afterwards. I took them from a second BOSE in spare, so no need to worry
There is (or has been) a red LED for CD-4 detection (called "radar" by JVC in the old days) on the CD-4 carrier board. But this will be invisible, when the BOSE is closed. So I modified the board by adding a third pin acting as power for a red/green duo LED. This will replace the old 6 Volt lamp inside and its red plastic cover simulating a red LED on the front. Common Anode for the duo LED, of course :~)
Biggest task currently is cleaning all (!) of the PCB connection bars and angled connectors to get rid of the tin coating for galvanizing with gold afterwards. I took them from a second BOSE in spare, so no need to worry
audiomaster
Senior Member
The big problem with the CD-4 board is that to adjust anything, or check the carrier light,you have to take the cover off. With my unit in a rack, that involves unplugging everything, removing it, then replugging the phono to set the carrier etc. I did drill a hole in the cover so, with a small mirror, I can see the light while it is in the rack. But I do like the 4ch tape inputs and EQ bypass on the unit. If they ever make a Surround master with CD-4 option I may go to that. To remote the carrier light and adjustments to front or rear would be a chore.
After some research, I found a japanese page (thanks to Google translation) with a TDM-20 demodulator, which seems to be a compatible, but slightly simplified version of the TDM-19.
These japanese guys took the TDM-20 board from an unnamed receiver to repair an older JVC CD-4 demodulator:
http://tangodelic2.cocolog-nifty.com/tangodelog/2021/04/post-983096.html
View attachment 90353
If anybody knows more about a receiver with such a board, please let me know
Asklia
Well-known Member
I found the idea to have a hidden LED for the CD-4 carrier very strange. But with a little bit of soldering, you can use a duo LED at the front for power and CD-4 instead the red power lamp.
The two poties of the Bose carrier board can be easily mounted as a stereo poti on the back. I do not like to drill additional holes in historic equipment, but the useless remote control DIN socket can be removed. And the hole used for a suitable stereo poti, with the same values of course.
The JVC TDM-19 board needs some preservation as well: The ELNA capacitors might be excellent, but the transistors used should be replaced. In tape recorder as well as reel-2-reel tape machines like Akai, they are known to degrade and be noisy.
You might have a deeper look at the picture: Its high resolution and shows the component exchangecquite well.
And yes, if these incredibly guys from Involve will make a CD-4 demodulator, I will like to test this as well. I tried to animate them to enhance the layout of their existing development boards, so these boards will fit directly into a Bose 4401.
The two poties of the Bose carrier board can be easily mounted as a stereo poti on the back. I do not like to drill additional holes in historic equipment, but the useless remote control DIN socket can be removed. And the hole used for a suitable stereo poti, with the same values of course.
The JVC TDM-19 board needs some preservation as well: The ELNA capacitors might be excellent, but the transistors used should be replaced. In tape recorder as well as reel-2-reel tape machines like Akai, they are known to degrade and be noisy.
You might have a deeper look at the picture: Its high resolution and shows the component exchangecquite well.
And yes, if these incredibly guys from Involve will make a CD-4 demodulator, I will like to test this as well. I tried to animate them to enhance the layout of their existing development boards, so these boards will fit directly into a Bose 4401.
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- Joined
- May 24, 2014
- Messages
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I have a dead Bose 4401, of course its missing its demodulator... I was looking for a reference to a particular issue on demodulator crosstalk. Remembered a mention. II dug up someones scan of Audio Magazine November 1976. I actually bought this copy in paper. I had the entire PDF, but I've sliced out just the article. Its on Building Latest CD-4 Demodulator.
JVC created a TDM-29C and with outside help, supplied it as a kit to electronic enthusiasts. A fully assembled JVC TDM-29C card was included with a circuit board for a high gain phono preamp to match its latest CD-4 Demodulator. I've never seen mention of the TDM-29C. I thought to myself this thread might enjoy this PDF.
JVC created a TDM-29C and with outside help, supplied it as a kit to electronic enthusiasts. A fully assembled JVC TDM-29C card was included with a circuit board for a high gain phono preamp to match its latest CD-4 Demodulator. I've never seen mention of the TDM-29C. I thought to myself this thread might enjoy this PDF.
Very interesting article, thanks for the post!
I had never heard of the TDM-29C chip. Wow I've never seen a CD-4 circuit so simple. It must be an amazing chip. I wonder if it made its way into commercial equipment?
There's been a Compcor (Wireless World) & SWTP CD-4 kit so it's been done before. That gives the potential if you can't buy a perfectly working vintage CD-4 unit, build one. If you can find the right demod chips.
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- Joined
- May 24, 2014
- Messages
- 45
Kinda cool. The preamp board with the RIAA limits... its finding that kit, built or unbuilt. I looked up the later models from Victor-JVC. The Victor/JVC CD4-50 (1980 with TDM-27) and Victor CD41000 (unknown, suspect TDM-29C?)
It really annoys me that while quad equipment was starting to mature and beginning to get really good it was suddenly abandoned by most equipment and record labels. What were they thinking?! Again think of the colour tv analogy. We would still be living with black and white TV if the industry would've gave up so fast!
Hi,
I'm also refreshing my Bose 4401 and I'd be interested in knowing the RCA sockets reference you have been installing, along with the Molex multiple pin connectors, if a male rhodium (golden aspect) plated exists. After 50 years, the nickel plated ones tend to suffer from corrosion.
Thanks !
- Joined
- May 24, 2014
- Messages
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So many factors, but it is the record business. Their goals are pretty well communicated... its about money.
That Pink Floyd song where he sings the line; "Which ones Pink"? I always figured that pretty well summed it up for Mr. Waters.
I've read where witnesses described the end of Quad where executives were really angry and going nuts. When the decision to pull the plug was finally made; I've read one account where a high ranking guy had some very costly equipment destroyed with sledge hammers. So dramatic... idiots.
Now, vinyl got popular again... still hoping Matrix will be back. Labels are sitting on all those masters, trickling out specialty SACD, DVD-Audio & Blu-ray with those 4 channel releases.
While I was searching found another CD-4 doc put out by JVC that I hadn't found before. I've attached. Bet someone regretted the title years later...
That Pink Floyd song where he sings the line; "Which ones Pink"? I always figured that pretty well summed it up for Mr. Waters.
I've read where witnesses described the end of Quad where executives were really angry and going nuts. When the decision to pull the plug was finally made; I've read one account where a high ranking guy had some very costly equipment destroyed with sledge hammers. So dramatic... idiots.
Now, vinyl got popular again... still hoping Matrix will be back. Labels are sitting on all those masters, trickling out specialty SACD, DVD-Audio & Blu-ray with those 4 channel releases.
While I was searching found another CD-4 doc put out by JVC that I hadn't found before. I've attached. Bet someone regretted the title years later...
- Joined
- May 24, 2014
- Messages
- 45
Attachment failed. Next try...
That’s going to take a bit of study on my part, but it looks pretty interesting.
I believe it was about 50 years ago (criminy, am I that freaking old?), I went to an AES trade show and picked up a CD-4 circuit board and chips. There were apparently some filters that were also necessary, and that kit has been moved about eight times, with nary a soldering iron applied to it. When I last checked, the filters hadn’t miraculously appeared, so it seems I won’t be attempting that build any time soon, either.
And there was a format war for that, too! CBS had a system that was out before WWII, but RCA’s NTSC got the nod here. Of course, PAL and SECAM never went away until the world went digital. Somehow we got color TV.
So colour started before WWII, was introduced in Canada in the mid sixties but not really a thing until the early 1970's! An extremely long run until it was finally accepted!
I don’t really know about Canada, but WWII pretty m uch brought consumer electronics to a halt world-wide.
Star Trek debuted in the mid 1960s, and it was in color.
Bonanza was colour in the late 50's, pushed by NBC. CBS was more reluctant. Superman as well switched to colour production in anticipation that it would be more accepted in the future.
NBC pushed colour hyped by the peacock, the CBC copied them with a butterfly!
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Owen Smith
2K Club - QQ Super Nova
SECAM was a total pain, video faders were much more complex because just fading the entire composite signal as you could with NTSC or PAL screwed up the colour with SECAM.
NTSC was also known as "Never Twice the Same Colour".
https://www.videokarma.org/showthread.php?t=273079
(sliding OT...)
Color TVs I used/owned:
1969 Sears (no auto color)
1975 Sylvania (auto color - tint error minimizing type)
1983 Zenith (auto color - tint error minimizing type)
1984 Emerson (no auto color)
(all TVs I bought after 1984 had no auto color)
Kirk Bayne
(sliding OT...)
Color TVs I used/owned:
1969 Sears (no auto color)
1975 Sylvania (auto color - tint error minimizing type)
1983 Zenith (auto color - tint error minimizing type)
1984 Emerson (no auto color)
(all TVs I bought after 1984 had no auto color)
Kirk Bayne
SECAM was often referred to as ‘Something Essentially Contrary to the American Method.”
Then there was PAL-M, which used NTSC timing and PAL encoding, only used in Brazil, but a really good system. Because it was used in somfew sets and didn’t have the economies of scale, it meant “Pay A Little More,”
