Bose 4401 CD-4 Demodulator?

[Asklia]

Hi friends

Has anybody a (hopefully good) picture of the rare BOSE 4401 CD-4 demodulator? I would like to see this board, if its worth searching or rebuilding. Of course, I would like to buy one, if somebody likes to sell (I offer 1k $ or € ;-)

I am restoring currently my Bose 4401; and have already added in the Involve SQ and QS (compatible) Decoders, made from their evaluation kits. I have added a separate power supply and shielding, since the built in power circuit is not capable to supply these boards with their hungry TI signal processor. The Involve boards are slightly modfied (that means, several parts ripped of) and mounted on two carrier boards with suitable Molex connectors. The Molex are still under manufacturing; even with gold plated springs inside.

Beside the usual replacing of the caps, resistors (the old ones drift over the time), chips sockets, RCA sockets and semiconductors, I changed the gain of the last stage. It is by far to high (in my opinion); with my setup I could barely use the first 90° of the 270° volume poti. And with full volume (at 270°), there is a very noticeable noise and hum in the loudspeakers. So lowering the gain by changing the feedback resistors in the last stage is the first step. Lowering the noise will be another goal. Replacing the volume poti will be the last goal.

The opamps are already replaced with NE5532D - still the best. OPA 2134 work as well, but OPA2604 or exotic Oraclell-02 do not work well. And there is no audible difference between old and new RC4136.

I add some pictures, maybe somebody has fun.

Best regards
KM

 

[proufo]

So beautiful!!

Great work!

 

[Asklia]

Thank you!

Now I wait for somebody with a picture Bose CD-4 demodulator

 

[Asklia]

Here another picture, that might help some other Bose owners. The unusual vertically mounted RCA sockets are still available in Gold and Chrom instead the ugly Nickel plated original sockets at different (professional) electronic suppliers.

 

[quady-de]

Hello,
if you want you can PM me, maybe i can help you.

Greetings from Germany

 

[barfle]

I don’t have a Bose, so I can’t be any help, but that’s really nice work so far!

 

[Asklia]

Thank you!

 

[Asklia]

At least I can confirm that it exists. I got a picture from it. The PCB is shielded by a metal on the top. Shielding underneath would have been better, of course.

 

[Asklia]

I got one of these rare decoders. And its a surprise: Its only a carrier board made by Bose with a Japanese made "TDM-19" CD-4 decoder plugin board.

The white ceramic chips on the Bose PCB are classical CD4066 analog switches. the black are opamps RC4558. Both chips types are still available.

The TDM-19 decoder board is built around the more or less classical "CD-4 392" chips.

The picture shows the (already reworked) Bose Phono Board, the Bose CDM-1 Carrier Board and the TDM-19 decoder board. All together really a lot of sockets and contacts...

Somebody asked me, if it would be possible to rebuild the CDM-1. Radio Eriwan says: In theory, "yes". But you need somebody to re-draw the PCB lines of the single sided boards. AND a set of two CD-4 392 chips from another CD-4 decoder...

If there is somebody willing to re-draw the board lines, I will provide high resolution pictures of the soldering side.

Does anybody know about this TDM-19 decoder board?

 

[Asklia]

I did some research and found an old Elektor article about the CD-4 integrated circuit. Unfortunatly, the 5-pages article it s not free, although they received it 1:1 from JVC. So I give only two interesting citations. At the end of this article, the evolution of the CD-4 decoders is described and a schematic is given:

"The CD4-l is the first generation demodulator used when the CD-4 system was first released, the 4DD-5 is the second generation demodulator using the PLL IC and the TDM-18A is the third generation demodulator which incorporates the CD4-392 IC. Figure 8 is a schematic diagram of the standard TDM-19A. The TDM-18A and the TDM-19A represent a significant step forward in the design and evolution of CD-4 playback hardware with their performance characteristics having been substantially improved."

Text and "Figure 8" from Elektor 1975.

So the Bose CDM-1 is based on the latest CD-4 demodulator TDM-19 developed by JVC. And interesting to know, that the 4DD-5 is the second generation.

 

[Asklia]

Thank you!

All these information are hidden very well or even unavailable. And from what I could see, even here in this forum several people have searched these information during the last 20 years mostly without success. Including me

 

[Owen Smith]

Here another picture, that might help some other Bose owners. The unusual vertically mounted RCA sockets are still available in Gold and Chrom instead the ugly Nickel plated original sockets at different (professional) electronic suppliers.

I don't like upwards facing RCA sockets, they tend to end up full of dust at best and a worst loads of crud that has been dropped.

 

[par4ken]

I don't like upwards facing RCA sockets, they tend to end up full of dust at best and a worst loads of crud that has been dropped.

True, but you would need to have an awfully dusty house to really have a problem.

The S&IC has upward facing jacks as well, I've never noticed them filling up with any crud. It is actually a bit easier to plug in the cables from the top rather than from the back. It is most likely that the jacks are soldered to the main PC board, so no jumper wires are necessary.

There is more room for the jacks when mounted that way! Those gold plated jacks look beautiful!

 

[Asklia]

The main problem of this time was the material used for RCA sockets: They used the metal Nickel instead of Chrome or even Gold for coating. Nickel tends to oxidize heavily, getting grey or green over the time. Giving very bad contact. But it is possible to exchange the sockets; even 50 years later. They are still in production.

Dust: There is a solution for every problem. Either cheap or luxury dust caps for RCA sockets, available from Aliexpress. I use these as a "short circuit noise stopper" for unused, open inputs. Without the inner pin as protective for unused outputs.

 

[Doug G.]

The main problem of this time was the material used for RCA sockets: They used the metal Nickel instead of Chrome or even Gold for coating. Nickel tends to oxidize heavily, getting grey or green over the time. Giving very bad contact. But it is possible to exchange the sockets; even 50 years later. They are still in production.

Dust: There is a solution for every problem. Either cheap or luxury dust caps for RCA sockets, available from Aliexpress. I use these as a "short circuit noise stopper" for unused, open inputs. Without the inner pin as protective for unused outputs.


View attachment 89658

I believe you are thinking of zinc plating that becomes oxidized/corroded over time. It is used on very low cost RCA connectors and is a duller silver color compared to nickel. Nickel plating is shiny, like chrome, and isn't really prone to oxidation/corrosion.

Doug

 

[Owen Smith]

Those gold plated jacks look beautiful!

They do indeed. All of the work shown in the photos in this thread looks great.

 

[Asklia]

Thank you for your compliments!

For those who own a Bose and are not satiesfied with the Phono Stage and want to use an external Phono Pre Amp: It's very easy to make an "passive" Phono Board. Biggest task is to order the Molex connectors from Farnell and a suitable prototype board (pitch 3.96) from Aliexpress.

I tried using a "better" and by far more modern Phono board, but results have not been not satisfactory.

P.S.: The passive phono board might be used for the "needle ripping" without RIAA equalizing of a CD-4 record for later software decoding.

 

[Asklia]

I do no longer have one of these old RCA sockets. But I let the guys in my company make an XRF analysis from the internal connector bars. XRF means scanning the surface with a X-Ray.

Elements found are Copper, Zinc and - Tin. Since the bars itself are made of brass (they shine golden when brushing), the tin is probably the surface coating.

So I think was wrong with Nickel for the RCA sockets, although Nickel itself gets grey over the time (believe me, I am a chemist and have an elemental collection). I think they used tin or a tin alloy for the coating. Which is by far not the better metal for a good long-term coating.

 

[Asklia]

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

If anybody knows more about a receiver with such a board, please let me know

 

[Asklia]

I have replaced the opamps and especially the old CMOS 4066 analog switches with some newer parts: 5532 work nicely. And MAXIM4066A works as well. The ANT4066B from A. Nikitin do not work in both positions, the back channels fail. So I decided to go with the MAXIM ICs.

The electrolytic capacitors on both boards and in addition the transistors on the TDM-19 board are replaced as well. The capacitors in the audio path are replaced with WIMA foil capacitors on both boards. Funnily, all of the nearly 50 years old ELNA caps are still in spec!

By the way, BOSE "forgot" to add two ceramic caps for +/- for every of the three opamps. There are only two instead of six on the board. So I added these capacitors under the board.

The two transistors 2SC458 are well known for degrading and their noise. These are replaced with 2SC1815. For the 2SA628 and 2SC711, I have used BC640 and BC639. Note, that the pinout of the 639 is "ECB" instead of "BCE". These transistors have been mounted mirrored.

To my great surprise, there are no "separation control potis" on the board. The two potis in front of the BOSE carrier board work as volume level control only, not as separation control. Both channels (front and rear) go up or down.

And still working