Bose 4401 CD-4 Demodulator?

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Asklia said:
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
Click to expand...
I have the 4401 with the stock SQ and CD-4 options. I have had the main unit rebuilt with new caps and 1% resistors and better op amps. But the CD-4 board still has 4558 ICs and the TDM-19 board. Looks like it would be a job to rebuild the TDM-19 board as it is very compact. Did you ever find any info on that board or try to update it? There are lots of pots on it and I don't know about adjusting it? I'd love to have schematic and service info on it.
The CD-4 is working (red pilot lt on) but my motto so far has been "ain't broke, don't fix" I did drill a hole in the lid so I can see if the light on the decoder is on.
My current problem is the main balance controls on the preamp don't seem to be working right? Only thing I can figure is bad pots and I don't know where to get dual concentric replacements.
 
A picture of your modifications would be nice. Which op amps did you choose?

And the serial number of the CD-4 demod would be interesting.

Poties:
You can use any 4 channel poti with suitable value. Here are some examples:
https://www.quadraphonicquad.com/forums/threads/bose-4401-cd-4-demodulator.33861/post-699234

TDM-19 and Adapter board:
Possible changes on the Bose made adapter board and the TDM-19 you can see here:
https://www.quadraphonicquad.com/forums/threads/bose-4401-cd-4-demodulator.33861/post-688289
 
Last edited:
Addendum: Generic Circuit Diagram of the preamp adapter for a JVC TDM-29C. Should correspond more or less with the non-documented Bose adapter board. At least the connector of the TDM board is now documented.


Bose-4401-TDM-29C-Preamp.jpg
 
If anybody has such an TDM-29 or an amplifier with this card, please let me know. I am curious and would like to buy one.

Currently, I do not even know which (JVC?) amp might have this TDM-29 inside.
 
I agree, but this is what I found in the internet. The components itself are visible on the Bose adapterboard. Standard audio opamp like NE5532, and we have now pin description of the TDM boards.
 
This would all be so much simpler if Surround Master would just add a state of the art CD-4 decoder to the unit! With a nice preamp for CD-4 carts built in.
 
audiomaster said:
This would all be so much simpler if Surround Master would just add a state of the art CD-4 decoder to the unit! With a nice preamp for CD-4 carts built in.
Click to expand...
They were talking about doing just that at one time. I suspect that it would be a very complex thing to do develope and a for very niche market indeed. I doubt that they could recoup their development costs for such an endeavour.
 
A CD-4 demodulator needs by design to sit inside the phono preamp audio path. It grabs the high frequency part before it is grabbed by the RIAA network, which lowers the high frequencies of a phono record. So a good CD-4 demodulator needs a phone preamp as well.

A "simple" digital decoding of an high level audio signal with a signal processor only is not sufficient. You have to grab the high frequency FM carrier without losses directly from the pickup. That's why even the Bose 4401 has this special adapter board to connected the TDM demodulator board internally directly to the phono preamp.
 
I think the biggest problem is to record and preserve the old CD-4 recordings resp. LPs. Some of them are available as a new format like SACD (many thanks to Dutton) or BD. But this is valid for a few exceptions.

I know, that a lot, but by far not all, are recorded, decoded on the fly and transfered with a new encoding like DTS. But this procedure has some losses (although I like my DTS encode record of Wakeman's King Arthur very much. It's by far better than my old CD-4 LP).

With "format" I mean something like FLAC for CD extractions. For a future processing with a fully digital CD-4 decoder, it must be recorded without RIAA de-emphasis and frequencies up to 50 kHz.

And this, I guess, will never happen.
 
Asklia said:
With "format" I mean something like FLAC for CD extractions. For a future processing with a fully digital CD-4 decoder, it must be recorded without RIAA de-emphasis and frequencies up to 50 kHz.

And this, I guess, will never happen.
Click to expand...
What could happen is half-speed playing.

Check this for the final step: https://pspatialaudio.com/introduction.htm
 
Asklia said:
I think the biggest problem is to record and preserve the old CD-4 recordings resp. LPs. Some of them are available as a new format like SACD (many thanks to Dutton) or BD. But this is valid for a few exceptions.

I know, that a lot, but by far not all, are recorded, decoded on the fly and transfered with a new encoding like DTS. But this procedure has some losses (although I like my DTS encode record of Wakeman's King Arthur very much. It's by far better than my old CD-4 LP).

With "format" I mean something like FLAC for CD extractions. For a future processing with a fully digital CD-4 decoder, it must be recorded without RIAA de-emphasis and frequencies up to 50 kHz.

And this, I guess, will never happen.
Click to expand...
Needle drops (playing and recording vinyl for re-release) is a last choice for most media companies. It might be the only way to get the performance if the original master tapes have been lost.

It’s better than nothing, though. I made a CD of a record my high school class made for one of our reunions, and nobody had a clue where the tape might have been. Fortunately for that project, I take pretty good care of my records, and nobody said the transfer sucked.
 
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.
 
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