Bose 4401 CD-4 Demodulator?

[audiomaster]

My Marantz SR7013 has inputs for multi-channel analog, including sub. That's one reason I bought it. My 4401 with the CD-4 and SQ cards feeds it fine. But it's older technology. I had it updated with new caps, 1% resistors and better ICs. And it doesn't do QS which is not really a problem as I don't have many of them. I am trying to figure out how to transfer my quad discs to digital. I bought a Zoom L12 mixer as it has multi channel digital recording but also 5 independent analog monitor outs which I think I can use to feed the 4ch discreet tape loop on the Bose for playback. I don't have any computer equipment in my theater, my computer is 50ft away at the office at the other end of the house.

I know you have probably spent $$$ to "hot rod" your 4401 and your work is impressive, but I don't have the ability to do that, or really can justify it.

At 77 and with tinnitus and known progressive hearing loss above 8KHz, I think the days of enjoying my LP collection may be numbered. For someone who depended on his ears for his livelihood for 50+ years, this is somewhat disconcerting! Visiting the audiologist at the VA hospital next month. I'm told they deal with hearing loss regularly, and can get the best aids much cheaper than I could get elsewhere. We will see.

 

[Asklia]

My congratulations for your Bose 4401 and its CD-4 decoder. The SQ Board itself is really weak, it is as you say old technology. I have one for myself, but a Surround Master from Involve ist by far the better solution. It can be easily connected to a Bose using the Equalizer In and Out port.

My best wishes for your health!

If you find a chance to look inside your Bose, some pictures and the serial number of the CD-4 would be nice.

 

[audiomaster]

My CDM-1 #1-1005 and is serial J-00843

Several questions;
Did you replace the 4558s on the CDM with something else and was it a direct swap/ Same questions on the whiteRCAs?
Also it appears there are a number of adjustments. You said R1 and R2 where just level pots. Where did you set them?
And it looks like there are several pots on the phenolic sub-board. Do you know what they are and how to adjust?
Did you change out any components on that board?
I'll try to get pictures, but it's a stock board.

I am having trouble with the front and rear and left right balance controls not working right. I took readings at the end of R112 thru R412 that connects to the ends of the pots. .
With both controls centered, ICs pulled, internal EQ out and external EQ button IN to disconnect that, I am getting readings as follows to chassis/ground
R112 67K
R212 104K
R312 89K
R412 94K
Since these pots are identical values and wipers are grounded, it seems the values should be identical or near so???
Thank you or anyone else for any help. I am reluctant to disassemble the boards as this is a bit above my skill set.

 

[audiomaster]

4401 Photos

 

[audiomaster]

I don't think the market for SQ or QS decoders is bigger than the market for CD-demodulators.
A SQ or QS is by far easier to handle: A decoder can be put anywhere "in the line" between your devices. A matrix decoder runs at line level, so it might use any matrix encoded line level source.

I admit, in the past the sources have been LP records only. But today, we have (or can get) them on CD and as digital files as well, feeding the preamp from different sources. And somewhere between pre- and main amp is the decoder "in line".

CD-4 is bound to LP records only. So a new demodulator has to integrate a suitable phono stage and the demodulator itself. We would have to connect our turntable player to this integrated phono demodulator, feeding a "free" multi channel line input !

All modern cinema amp do no longer have a 6 channel analog line input. A digital HDMI output would be a possible and especially losless solution after decoding/demodulating with a signal processor.

Such a new "universal three format" decoder would need a phono input, a stereo line input, and HDMI output as a minimum.

HDMI makes it more complicated, but a DA processing and volume control would not be necessary.

A device like this is technically possible, but who would be willing to buy? For 1200 currencies? Or even 1600?

In pure fiction, an additional software for a Yamaha Aventage 5x00 or Denon cinema amp would be possible. But did you ever see a big company listening to customer wishes?

All the former ultra proud recording companies decided that its easier to die than to give customers what they want. Sellung our archive contents at lower prices? Selling multi channel recordings in whatever format? Producing vinyl records? God beware.

Only small companies do this nowadays again with success. The managers of the old companies were "big money addicted". And cared never for their customers.

I had a discussion with a former EMI manager in the 90's about digital media. All he could think was "it must be protected" and "it must be expensive". Offering for downlaod for low money? Impossible in his brain.

Apple offered music download for 1 currency, and EMI and all the others collapsed faster than an earth quake could destroy a city.

Big companies driven by big money addicted managers will never listen to customers.

So we will not get any cinema amp or preamp with a SQ or QS decoder.

I wonder who owns the rights to the TDM-29C circuit? Since it is no longer made or sold. I would think one might be able to get the rights to it fairly cheaply? It would be "found money" for the original owner! If you had that, I would think laying out a more modern board with a phono preamp wouldn't be too hard. Don't know how many Surround masters have been sold, but guess that most of the people into vintage quad will have CD-4 records as well as SQ and QS? So maybe a decent market for those within the Surround Master circle of buyers?

 

[barfle]

I wonder who owns the rights to the TDM-29C circuit? Since it is no longer made or sold. I would think one might be able to get the rights to it fairly cheaply? It would be "found money" for the original owner! If you had that, I would think laying out a more modern board with a phono preamp wouldn't be too hard. Don't know how many Surround masters have been sold, but guess that most of the people into vintage quad will have CD-4 records as well as SQ and QS? So maybe a decent market for those within the Surround Master circle of buyers?

I don’t have statistics, but if memory servies, CD-4 suffered from requiring more hardware outlay than the matrix decoders did. Likely that your turntable’s cartridge and stylus would not be up to the task, so sales would have naturally been less. I know it turned me away for many years.

That’s not to say a CD-4 demodulator would be a bad idea. I would be early in line if one became available.

 

[Asklia]

A lot of questions

I try to answer one after the other. First the hardware changes: As described in my answers above, I did the following:

I have replaced the opamps (4558) and especially the old CMOS 4066 analog switches with some newer parts: NE 5532 work nicely (as replacmement for the older 4558). And MAXIM4066A works as well (for the white 4066). The famous ANT4066B from A. Nikitin does 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.

You can recognise the WIMA foil capacitors quite easily in my pictures: They are red

Up to now, I did not exchange the resistors on the TDM 19 board, but all of the carbon resistors on the green Bose adapter board. The old carbon resistors used by Bose are known to drift heavily with their values.

 

[Asklia]

The image again:

 

[Asklia]

Replica of the TDM Board:

It is a single sided PCB only. So the PCB itself is not the problem. But there are two very big obstacles:

You need the nowadays unobtainable ICs Signetics CD4-392. They are out of production now for half a century. For every "new" CD-4 decoder board, you would have to kill an old existing CD-4 decoder with these circuits. Not a good yield, I guess.

Second obstacle is the adjusting of the circuits with the poties. I do not posses an operating procedure for this; and I doubt you will find this in the internet nowadays. I did a lot of research; and shared all of this here in my thread. Circuit diagram is available, but nothing else.

Not to mention the special Panasonic coils "224" or "102", but this could be obtained or manufactured in a small series. On the obviously simplified TDM-20 board, there are only two poties, by the way.

I cannot imagine that there is any "simple" way to reproduce the old analog board. And in the end, you would need all the components visible in the picture above: Phono preamp, switching board, CD-4 decoder.


By the way: CD-4 was by far more widespread in the U.S. than in Europe. Most used CD-4 records come nowadays either from Japan or the U.S. In the old days, CD-4 LPs were really rarities in the European record shops. As well as today. SQ and some QS are still available in the used markets here in Germany and Switzerland, for example.


CD-4 capable phono pick up:

These are still available. For example, I am using an MM Audio Technica VM750SH with Shibata needle for a very reasonable price.

 

[Asklia]

...I would be early in line if one became available.

Me as well, for sure!

 

[Asklia]

Poti measurement:

The balance poties are 1 MegOhm nominal, from right (1) to left (3) pin. The middle pin is connected to ground, giving more and more "load" onto the output of the stage before.

But at R112 to 412 you are measuring the input resistors of the next stage R113 to 412, not the balance poti setting. The value of R113 to 413 is around 100 kOhm.

But you can measure the balance poties: From the middle pin (2) to the outer pins. There you should find 500 kOhm. They are not logarithmic.

 

[Asklia]

By the way, the search term for the balance poties would be "Dual Concentric Stacked Potentiometer 1M linear". For example, Vishay seems to have suitable linear poties, even with 1 M. You might have a look at the data sheet. Some soldering will be neccessary, of course.

https://www.mouser.ch/ProductDetail...WnJQ-c_EZ8kSsWV_jMXEU_pTvSXErj5hoCQIMQAvD_BwE

 

[Asklia]

4401 Photos

As I can see, some, but not all of the capacitors on the TDM19 board have already been exchanged. I would recommend to exchange the noisy transistors on this board. These old japan transistors get noisy over the time.

In addition, I would recommend to exchange especially the old carbon resistors on the Bose adapter board. And this horrible old chip sockets please.

And thanks for the serial number: From this I would say, Bose has made not more than a series of 1000 CD-4 boards. They are really hard to see or find: Yours is the second one I have seen over the years (with a picture); and one other Bose owner with this demodulator here in the forum is known (but without picture).

 

[Asklia]

There is currently a Bose 4401 with the rare CD-4 demodulator on sale. Unfortunatly, the price is by far to high:


https://www.audioscope.net/bose-440....html?osCsid=f2f11984ae050f3d6e3305491221b9a7

 

[audiomaster]

I just looked at my receipts. I bought my 4401 (with SQ board) in July of 1975 for $450.00.
And my CDM-1 in May of 1977 for $119.95.
At the time I thought that was outrageously expensive! But in hindsight I guess it was a pretty good investment! Considering it's still mostly working 49 years later! Of course then there is the Apple stock I didn't buy?

 

[Asklia]

The Bose was in Europe at his time 2500 DM = German Mark, equivalent to 2300 Swiss Frank. The U$D was calculated with 1:4.

And yes, we all missed to buy Apple and M$ shares...

 

[audiomaster]

Question on the 4401. If I play a regular stereo record and put the selector in CD-4 position, I still get sound from the rear channels almost like if I put it in Stereo or Stereo X position. Only if I put it in "Discreet" are the rear channels silent? Is this normal? Why is the adapter outputting rear channels if it doesn't get the carrier?

 

[par4ken]

Question on the 4401. If I play a regular stereo record and put the selector in CD-4 position, I still get sound from the rear channels almost like if I put it in Stereo or Stereo X position. Only if I put it in "Discreet" are the rear channels silent? Is this normal? Why is the adapter outputting rear channels if it doesn't get the carrier?

Both CD-4 demodulators and Q8 decks output double stereo, when not outputting discrete quad. The exact same as an FM stereo radio outputting sound from both channels on a mono station. That is the way it should be IMHO!

In the case of FM stereo and CD-4 the same signal is fed to both output channels, ie L&R for FM radio and the front and back stereo pairs for CD4. When the difference signal is detected it is added and subtracted from the main audio signal, giving a discrete output.

In the case of Q8's they were used heavily in automobiles, there you normally wouldn't want stereo to play only through the front speakers!