Bose 4401 CD-4 Demodulator?

[proufo]

Or you can buy this

Behringer Microphono PP400

for 29 dollars, change a couple of capacitors and have a flat phono pre (see the comments on "How can I further mod this preamp to make it flat (non-RIAA)?").

N-Audio PP400 Phono Preamp Modifications

 

[Asklia]

Thank you very much for your hints!

Nevertheless, I am not impressed. If you look at the Youtube video or at the ratings for this Phono preamp at Amazon, you will quickly learn that this device is more Low-Fi than Hi-Fi. Critics are mostly bad: Several users complain about hum, some of hiss.

The weakest point is obviously the power supply and internal power circuit. To make it cheap, they work with phantom ground and two resistors to divide the external 12 Volt. I do not expect a really stabilized and filtered power supply inside an external China power supply. So hum is no surprise.

The amp is single stage, using a JRC opamp. JRC opamps are cheap, but do not have the best ratings compared to other opamps. The data sheet is not impressive, either. CMMR is 20 dB below of an old NE5532. The guy in the video changes the values of the Low and High RIAA filter only a little bit, but does not change the circuit at all.

I think a linear buffer stage from Ali Express, mounted on a prototype board, replacing the original phono stage inside the Bose, will do better work. It might look like this:
https://cdn2.imagearchive.com/quadraphonicquad/data/attach/85/85199-1679052765821.png
Here at QQ is a lengthy thread about the Spatial Audio software. The software did not get the best ratings either. And there is no easy way for an virtual Apple machine on Windows, since you need still a "legal" copy of the Mac BIOS to install MacOS inside (at least in the old days). And you still need a good external record device with 96 kHz. The software even fails with 192 kHz records.

It needs a good recording lab place for a such a task, converting the old CD-4 records by software to some 4-channel WAV or FLAC files.

That's my opinion. I was impressed when reading the specs of the Spatial Audio software in the beginning (wow, all Q-Formats in one piece of software?), but the drawbacks are huge. I am still wondering how they do the RIAA filtering is software. How many bands they use? There is no continuous "analog" filter in software compared to R-C filtering. I am not surprised that the critics wrote about some bad sound.

A better approach would be to do RIAA filtering with analog compounds, but make a second path before filtering to get the high frequency part (only) without RIAA filtering: Not lowering the high frequency for the FM PLL demodulator circuit. I think Bose did something like this in their phono circuit.

But I appreciate any contributions to the discussion here

 

[kfbkfb]

Mike Green has the Stereo Lab CD-4 (software) decoder working with an Apple emulator/virtual machine (will probably have to join the Old School Quadraphonic FB group to see this info), see his post on October 29, 2022 at 9:37 PM.


Kirk Bayne

 

[Asklia]

I have no doubt that its possible to get a virtual Mac running. But this is a lot of effort. And its still necessary to have a special recording setup to get proper results:

- a record player with a pickup with a Shibata needle, frequency response up to 50 kHz
- a "non-RIAA" phono preamp, frequency response up to 50 kHz without limiting
- a file based 96 kHz recorder
- a computer running MacOS and the Spatial Audio software for offline-decoding
- a suitable multi-channel media player like an Oppo BD

Maybe the results are slightly better than analog demodulating and decoding CD-4 records. For now, I prefer the old analog "real time" way to listen to the old records.

 

[Holger Macheledt]

Hallo Freunde

Hat jemand ein (hoffentlich gutes) Bild des seltenen BOSE 4401 CD-4 Demodulators? Ich würde dieses Board gerne sehen, wenn es sich lohnt, es zu suchen oder neu zu erstellen. Natürlich würde ich gerne eines kaufen, wenn jemand verkaufen möchte (ich biete 1k $ oder € ;-)

Ich restauriere derzeit meinen Bose 4401; und haben bereits die Involve SQ- und QS-Decoder (kompatibel) hinzugefügt, die aus ihren Evaluierungskits hergestellt wurden. Ich habe eine separate Stromversorgung und Abschirmung hinzugefügt, da der eingebaute Stromkreis nicht in der Lage ist, diese Boards mit ihrem hungrigen TI-Signalprozessor zu versorgen. Die Involve-Boards werden leicht modifiziert (d. h. einige Teile herausgerissen) und mit passenden Molex-Steckern auf zwei Trägerboards montiert. Die Molex befinden sich noch in der Herstellung; sogar mit vergoldeten Federn im Inneren.

Neben dem üblichen Austausch der Kappen, Widerstände (die alten driften mit der Zeit), Chip-Buchsen, Cinch-Buchsen und Halbleitern habe ich die Verstärkung der letzten Stufe geändert. Es ist (meiner Meinung nach) viel zu hoch; Mit meinem Setup konnte ich die ersten 90° des 270°-Lautstärkepotis kaum nutzen. Und bei voller Lautstärke (bei 270°) ist ein deutlich spürbares Rauschen und Brummen in den Lautsprechern zu hören. Der erste Schritt besteht also darin, die Verstärkung durch Ändern der Rückkopplungswiderstände in der letzten Stufe zu verringern. Ein weiteres Ziel wird die Reduzierung des Lärms sein. Das Ersetzen des Lautstärkepoti wird das letzte Ziel sein.

Die Operationsverstärker wurden bereits durch NE5532D ersetzt – immer noch die besten. OPA 2134 funktioniert ebenfalls, OPA2604 oder das exotische Oraclell-02 funktionieren jedoch nicht gut. Und es gibt keinen hörbaren Unterschied zwischen altem und neuem RC4136.

Ich füge ein paar Bilder hinzu, vielleicht hat jemand Spaß.

Beste grüße
KM

Hallo KM,
Seid gestern habe ich auch einen 4401. Ich werde ihn mal öffnen und nachsehen, ob ich das gesuchte CD4 Board eingebaut habe. Oder kann ich es von außen erkennen? LG Holger

Hello KM,
Since yesterday I also have a 4401. I'll open it up and see if I've installed the CD4 board I'm looking for. Or can I see it from the outside? LG Holger

 

[Asklia]

Hallo Holger

"Erkennen" kann man das von aussen leider nicht. Aber Öfnen ist ja wirklich harmlos: Das Gerät hat ja einen Deckel und ein Bodenblech. Oben wäre der CD-4 Demodulator; unten könnte ein SQ Decoder sein.

Aber in 99% der Fälle weder noch. Die SQs findet man gelegentlich; der CD-4 war wirklich sehr selten. Der wurde auch erst nach mehr als einem Jahr nach Erscheinen des Gerätes angeboten. Möglicherweise auch nur in den USA. CD-4 war in Europa mindestens Schallplattenmässig ungleich weniger verbreitet.

Hello Holger

Unfortunately, you can't "recognize" it from the outside. But opening it is really harmless: the device has a lid and a base plate. Above would be the CD-4 demodulator; below could be a SQ decoder.

But in 99% of the cases neither nor. The SQs are found occasionally; the CD-4 was really very rare. It was only offered more than a year after the device appeared. Maybe only in the US. CD-4 was disproportionately less widespread in Europe, at least in terms of discs.

 

[Asklia]

Now in its new wooden case, made from real wood instead of cheap plastic foil like the original Bose case.

 

[Holger Macheledt]

Hallo Holger

„Erkennen“ kann man das von außen leider nicht. Aber Öfnen ist ja wirklich harmlos: Das Gerät hat ja einen Deckel und ein Bodenblech. Oben wäre der CD-4-Demodulator; Unten könnte ein SQ-Decoder sein.

Aber in 99% der Fälle weder noch. Die SQs findet man gelegentlich; Die CD-4 war wirklich sehr selten. Der wurde auch erst nach mehr als einem Jahr nach Erscheinen des Gerätes angeboten. Möglicherweise auch nur in den USA. CD-4 war in Europa mindestens Schallplattenmässig ungleich weniger verbreitet.

Ok, ich werde ihn demnächst mal öffnen und nachschauen. Denke es wird am Sonntag werden. Steht CD4 auf der Platine?

Ok, I'll open it up and take a look. Think it will be on Sunday. Is CD4 on the board?

 

[Asklia]

500 currency units. Switzerland is the most expensive country unfortunatly for handcrafted items like this.

 

[Asklia]

Ok, ich werde ihn demnächst mal öffnen und nachschauen. Denke es wird am Sonntag werden. Steht CD4 auf der Platine?

Ja. Am Anfang vom Thread hier sind Bilder. Eine grosses schwarze Abdeckblech ziert den CD-4 Demodulator. Aber zu mehr als 99% wirst du nichts dort finden.

 

[jupp369]

Thank you very much for your hints!

Nevertheless, I am not impressed. If you look at the Youtube video or at the ratings for this Phono preamp at Amazon, you will quickly learn that this device is more Low-Fi than Hi-Fi. Critics are mostly bad: Several users complain about hum, some of hiss.

The weakest point is obviously the power supply and internal power circuit. To make it cheap, they work with phantom ground and two resistors to divide the external 12 Volt. I do not expect a really stabilized and filtered power supply inside an external China power supply. So hum is no surprise.

The amp is single stage, using a JRC opamp. JRC opamps are cheap, but do not have the best ratings compared to other opamps. The data sheet is not impressive, either. CMMR is 20 dB below of an old NE5532. The guy in the video changes the values of the Low and High RIAA filter only a little bit, but does not change the circuit at all.

I think a linear buffer stage from Ali Express, mounted on a prototype board, replacing the original phono stage inside the Bose, will do better work. It might look like this:
https://cdn2.imagearchive.com/quadraphonicquad/data/attach/85/85199-1679052765821.png
Here at QQ is a lengthy thread about the Spatial Audio software. The software did not get the best ratings either. And there is no easy way for an virtual Apple machine on Windows, since you need still a "legal" copy of the Mac BIOS to install MacOS inside (at least in the old days). And you still need a good external record device with 96 kHz. The software even fails with 192 kHz records.

It needs a good recording lab place for a such a task, converting the old CD-4 records by software to some 4-channel WAV or FLAC files.

That's my opinion. I was impressed when reading the specs of the Spatial Audio software in the beginning (wow, all Q-Formats in one piece of software?), but the drawbacks are huge. I am still wondering how they do the RIAA filtering is software. How many bands they use? There is no continuous "analog" filter in software compared to R-C filtering. I am not surprised that the critics wrote about some bad sound.

A better approach would be to do RIAA filtering with analog compounds, but make a second path before filtering to get the high frequency part (only) without RIAA filtering: Not lowering the high frequency for the FM PLL demodulator circuit. I think Bose did something like this in their phono circuit.

But I appreciate any contributions to the discussion here

I was supprised NOT to find a second path / bypass for the 30kHz in the JVC's RIAA.
Just after the RIAA sgnal is devided to the Demod and a LowPassFilter for normal audio and the separation (substract).
Audacity shows triangles with 96kHz and a fine sine at 192kHz (24bit)

 

[Holger Macheledt]

Hallo Holger

"Erkennen" kann man das von aussen leider nicht. Aber Öfnen ist ja wirklich harmlos: Das Gerät hat ja einen Deckel und ein Bodenblech. Oben wäre der CD-4 Demodulator; unten könnte ein SQ Decoder sein.

Aber in 99% der Fälle weder noch. Die SQs findet man gelegentlich; der CD-4 war wirklich sehr selten. Der wurde auch erst nach mehr als einem Jahr nach Erscheinen des Gerätes angeboten. Möglicherweise auch nur in den USA. CD-4 war in Europa mindestens Schallplattenmässig ungleich weniger verbreitet.

Hello Holger

Unfortunately, you can't "recognize" it from the outside. But opening it is really harmless: the device has a lid and a base plate. Above would be the CD-4 demodulator; below could be a SQ decoder.

But in 99% of the cases neither nor. The SQs are found occasionally; the CD-4 was really very rare. It was only offered more than a year after the device appeared. Maybe only in the US. CD-4 was disproportionately less widespread in Europe, at least in terms of discs.

 

[Holger Macheledt]

Da scheine ich wohl gar nichts davon drin zu haben. Sind ja sehr viele Steckplätze frei. Was kann denn da noch alles nachgerüstet werden ? Und wo kann man solch Platinen evtl. Noch bekommen ?

I don't seem to have any of that in there. Are a lot of slots free. What else can be upgraded there? And where can you possibly get such circuit boards?

 

[Old Quad Guy]

Da scheine ich wohl gar nichts davon drin zu haben. Sind ja sehr viele Steckplätze frei. Was kann denn da noch alles nachgerüstet werden ? Und wo kann man solch Platinen evtl. Noch bekommen ?

I translated into English the above using Google translate:

I don't seem to have any of that in there. Are a lot of slots free. What else can be upgraded there? And where can you possibly get such circuit boards?

————————

You may submit a reply in your native languages. But please also use Google Translate or similar thing to communicate in English so we can follow the conversation. Thanks.

Google translate into German:

Sie können eine Antwort in Ihrer Muttersprache einreichen. Bitte nutzen Sie aber auch Google Translate oder ähnliches, um auf Englisch zu kommunizieren, damit wir dem Gespräch folgen können. Danke.

 

[Asklia]

I was supprised NOT to find a second path / bypass for the 30kHz in the JVC's RIAA.
Just after the RIAA sgnal is devided to the Demod and a LowPassFilter for normal audio and the separation (substract).
Audacity shows triangles with 96kHz and a fine sine at 192kHz (24bit)

Triangles and fine Sine: To be expected without filtering of higher order. And the IMHO not that intelligent Spatial Audio software can only use 96 kHz. To what I read her, it even fails at 192 kHz!

 

[Asklia]

I translated into English the above using Google translate:

I don't seem to have any of that in there. Are a lot of slots free. What else can be upgraded there? And where can you possibly get such circuit boards?

Optional decoder places: On top, the CD-4 demodulator. Under the bottom plate, a SQ and an "optional" decoder" could be mounted. Bose only made a SQ decoder. An "optional" QS decoder was not developed. The "Bose" CD-4 demodulator was mainly an adapter board and an original JVC CD-4 module TDM19A.

Where to buy these internal decoders? Nearly nowhere; and at least not for "normal money". That's why I installed the new digital decoders for SQ and QS made by Involve Audio. And they are <by far> better than the old analog version(s). The original SQ decoder gives you only - 3 - decibel channel separation. Only three!!! This is and was even at the old times very disappointing. That's why they "faked" virtual channel separation with this "SQ Logic": Make the slightly louder channel even more loud. The result? Pumping. By the way, same for QS. Yes, there are by far better external SQ and QS decoders from Tate and Sansui. But these are expensive, somewhat rare and external decoders.

As I wrote, I presented probably the only Bose equipped with three decoders for SQ, QS and CD-4. Bose itself delivered only two in the old days: SQ and CD-4. In my Bose project here, the SQ and QS decoders used are "new" digital technology made as evaluation boards by Involveaudio. CD-4 is still the old analog demodulator. Currently, there is no "new" CD-4 decoder available in the world.

And to use these old electronic components, you should replace several of the components, because 50 years later they are not all in "best condition". Even the old carbon resistors drift up to 100% in their value. Capacitors drift or fail very often after 50 years. So there is no easy buying and using.

I tried to show that an old device like the Bose 4401 can be restored and enhanced, even 50 years later. And with amazing results, better than ever before. I shared freely the knowledge and the technical details. Doing this (again) on a commercial basis is by far to expensive. Even all the material added up in the end to more than 5000 (Euro, Dollars of Swiss Frank, does not matter). And a few hundred working hours, not to mention. So commercial rebuild would sum up to 15'000. You must do it yourself...

If you cannot do this, here my recommendation: Use an Involve V3 for really good SQ and QS decoding. Decoding is the same. And a more modern Home cinema amplifier with an 6 channel analog input for this.

Best wishes to all QQ friends here and elsewhere in the world!

 

[Doug G.]

I have no doubt that its possible to get a virtual Mac running. But this is a lot of effort. And its still necessary to have a special recording setup to get proper results:

- a record player with a pickup with a Shibata needle, frequency response up to 50 kHz
- a "non-RIAA" phono preamp, frequency response up to 50 kHz without limiting
- a file based 96 kHz recorder
- a computer running MacOS and the Spatial Audio software for offline-decoding
- a suitable multi-channel media player like an Oppo BD

Maybe the results are slightly better than analog demodulating and decoding CD-4 records. For now, I prefer the old analog "real time" way to listen to the old records.

Boy, you can say THAT again!

And, here goes my pitifully rusty Deutsch - Konnen (umlaut o) Sie wieder das sagen!

 

[Asklia]

You mean, listening analog CD-4?

 

[Doug G.]

You mean, listening analog CD-4?

Jawohl!

Doug

 

[Holger Macheledt]

Hello, I had another good idea to protect open cinch sockets from dust and dirt on the connection side. Very simple 10mm plastic caps. Available in black and also in red. I wanted to see how the seat was and ordered black ones. Sit really well! If you want this cheap way to protect... it's also available on Amazon.

https://www.amazon.de/dp/B07VC4NZQT?ref=ppx_yo2ov_dt_b_product_details&th=1
Hello, I had another good idea to protect open cinch sockets from dust and dirt on the connection side. Very simple 10mm plastic caps. Available in black and also in red. I wanted to see how the seat was and ordered black ones. Sit really well! If you want this cheap way to protect... it's also available on Amazon. Amazon.de

[Translation provided as a courtesy; two requests have been made to use translator on this forum. Please commit to doing this in future posts]
[Übersetzung wird mit freundlicher Genehmigung zur Verfügung gestellt; Es wurden zwei Anfragen zur Verwendung eines Übersetzers in diesem Forum gestellt. Bitte verpflichten Sie sich, dies in zukünftigen Beiträgen zu tun.]