Please add me to the list as well. Thanks!
Lou Dorren: A new CD-4 Demodulator!!! [ARCHIVE]
- Thread starter loudorren
- Start date
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jefe1
2K Club - QQ Super Nova
Please sign me up too!
You'll have plenty of buyers here
You'll have plenty of buyers here
The Quadfather
1K Club - QQ Shooting Star
Hey Lou:
I have always contended that it might be possible to build a demodulator with improved technology and that had CD-4 suceeded, the modern demodulators would be vastly improved over the old designs. However, I have to look at the reality that while this could improve our current CD-4 performance, it will not spark a return to record companies pressing CD-4 releases. Therefore the design will probably be a limited run. It would be a good thing for us if it is possible to do it with out any proprietary components which will be impossible to find in say 20 years. We currently face this problem with our Tate SQ decoders, Variomatrix QS decoders and our Technics SH400 demodulators. Once the chips die, it's over for that unit. But then, if that is not possible, I would still buy it, for I will always have my backup 4DD5 demods and my SH400.
Incidently, if the transistors in the chips were bad back then, would a chip made to the same design but of modern manufacture improve the legacy demod it is installed in?
The Quadfather
I have always contended that it might be possible to build a demodulator with improved technology and that had CD-4 suceeded, the modern demodulators would be vastly improved over the old designs. However, I have to look at the reality that while this could improve our current CD-4 performance, it will not spark a return to record companies pressing CD-4 releases. Therefore the design will probably be a limited run. It would be a good thing for us if it is possible to do it with out any proprietary components which will be impossible to find in say 20 years. We currently face this problem with our Tate SQ decoders, Variomatrix QS decoders and our Technics SH400 demodulators. Once the chips die, it's over for that unit. But then, if that is not possible, I would still buy it, for I will always have my backup 4DD5 demods and my SH400.
Incidently, if the transistors in the chips were bad back then, would a chip made to the same design but of modern manufacture improve the legacy demod it is installed in?
The Quadfather
loudorren
Well-known Member
Hello Quadfather,
I understand what you mean. The problem of course, is whether the chip manufacturers will continue building legacy components. In the case of the old CD-4 demodulators, some of the original chips that I used in the first modifications that I made are still being produced. Sadly, some custom chips (QSI5022 etc.) are not(this does not mean that they don't exist). In the new design I am using chips that should be around a long while. As far as transistor chip technology, your premise is a good one. Reality is, however, as circuit designers in the 1970's we knew how bad the PNP types were. We simply avoided using them unless it was absolutely required. Most circuits back then were NPN transistor only. To take advantage of the better transistors of today, the circuit designs would also have to change.
Lou Dorren
I understand what you mean. The problem of course, is whether the chip manufacturers will continue building legacy components. In the case of the old CD-4 demodulators, some of the original chips that I used in the first modifications that I made are still being produced. Sadly, some custom chips (QSI5022 etc.) are not(this does not mean that they don't exist). In the new design I am using chips that should be around a long while. As far as transistor chip technology, your premise is a good one. Reality is, however, as circuit designers in the 1970's we knew how bad the PNP types were. We simply avoided using them unless it was absolutely required. Most circuits back then were NPN transistor only. To take advantage of the better transistors of today, the circuit designs would also have to change.
Lou Dorren
Any plans for a DSP based CD-4 Demodulator?
Such a CD-4 Demodulator could possibly include declicking for the
LF+LB and RF+RB signals and a single ended noise reduction system
for the LF-LB and RF-RB demodulated signals.
Kirk Bayne
Such a CD-4 Demodulator could possibly include declicking for the
LF+LB and RF+RB signals and a single ended noise reduction system
for the LF-LB and RF-RB demodulated signals.
Kirk Bayne
Put me down for one too -- and I also think a kit sounds like a great idea.
Mark Z
Mark Z
loudorren
Well-known Member
Hi to the Group,
DSP's when used properly are not bad. However, there are some things that can be better accomplished in analog systems and some things that are better in digital systems. Using this as a mantra, the best system would seem to be a combination of both. This is the design criteria of the new demodulator. If you downloaded the first paper and look at the block diagram, I am using DSP's as precision filters, both low pass and band pass. As far as declicking, have any of you noticed that CD-4 records have far less impulse noise than stereo or matrix records. This is because the 30 KHz carrier in both groove walls acts as an AC bias signal, vibrating the stylus at this rate. This reduces the stylus pickup of imperfections in the disk surface. It also helps the stylus push dirt items out of the way.
Single ended noise reduction unfortunately will affect the front to back separation adversely. This is because of the algebraic sum and differencing that is preformed in the matrix. Sum and difference signals must be in exact time and amplitude to matrix properly. Single ended systems would prevent this. The ANRS system yields equivalent signal to noise and dynamic performance of the subchannel to the main channel without the typical pumping noise of single ended systems.
Proper use and observance of the Nyquist rate(No lossey Data Compression) will not affect the sound quality of analog audio!
Lou Dorren
DSP's when used properly are not bad. However, there are some things that can be better accomplished in analog systems and some things that are better in digital systems. Using this as a mantra, the best system would seem to be a combination of both. This is the design criteria of the new demodulator. If you downloaded the first paper and look at the block diagram, I am using DSP's as precision filters, both low pass and band pass. As far as declicking, have any of you noticed that CD-4 records have far less impulse noise than stereo or matrix records. This is because the 30 KHz carrier in both groove walls acts as an AC bias signal, vibrating the stylus at this rate. This reduces the stylus pickup of imperfections in the disk surface. It also helps the stylus push dirt items out of the way.
Single ended noise reduction unfortunately will affect the front to back separation adversely. This is because of the algebraic sum and differencing that is preformed in the matrix. Sum and difference signals must be in exact time and amplitude to matrix properly. Single ended systems would prevent this. The ANRS system yields equivalent signal to noise and dynamic performance of the subchannel to the main channel without the typical pumping noise of single ended systems.
Proper use and observance of the Nyquist rate(No lossey Data Compression) will not affect the sound quality of analog audio!
Lou Dorren
- Joined
- Mar 2, 2002
- Messages
- 4,242
Any possibility to use such a demod to store our precious cd4 in digital format as stereo file at 192K sample rate?
loudorren
Well-known Member
Hi Winopener,
You would have to have 2 files, one for the left and one for the right, otherwise should work. You would not need a demodulator just a flat preamp. If you could sync the files on playback, you could then feed the D to A output to a demodulator.
Lou Dorren
You would have to have 2 files, one for the left and one for the right, otherwise should work. You would not need a demodulator just a flat preamp. If you could sync the files on playback, you could then feed the D to A output to a demodulator.
Lou Dorren
Winopener,
I have done this, basically my approach was to linearly amplify the phono signal ( no RIAA eq.) then record at line level into my sound card at 96Khz 24 bit sampling. On playback I simply attenuated the signal and fed it back into the demodulator phono input. Someone else, and I forget who, modified a demod and took the signal from a later stage just after the 1/2 eq and recorded that
see the following posts :-
https://www.quadraphonicquad.com/forums/showthread.php?p=39896#post39896
and here
https://www.quadraphonicquad.com/forums/showthread.php?t=5074&highlight=malcolm2010
also see here on a couple of Signetics CD4-392 based demodulator designs and the passband of the filters
https://www.quadraphonicquad.com/forums/showthread.php?t=6170&highlight=malcolm2010
Malcolm
I have done this, basically my approach was to linearly amplify the phono signal ( no RIAA eq.) then record at line level into my sound card at 96Khz 24 bit sampling. On playback I simply attenuated the signal and fed it back into the demodulator phono input. Someone else, and I forget who, modified a demod and took the signal from a later stage just after the 1/2 eq and recorded that
see the following posts :-
https://www.quadraphonicquad.com/forums/showthread.php?p=39896#post39896
and here
https://www.quadraphonicquad.com/forums/showthread.php?t=5074&highlight=malcolm2010
also see here on a couple of Signetics CD4-392 based demodulator designs and the passband of the filters
https://www.quadraphonicquad.com/forums/showthread.php?t=6170&highlight=malcolm2010
Malcolm
The Quadfather
1K Club - QQ Shooting Star
So, what kind of cartridge would be supplied?
The Quadfather
The Quadfather
loudorren
Well-known Member
Hello You All,
Pickup cartridge to be announced. For every ones information. The Signetics CD4-392 and the CD-894 chips are actually a Signetics (NXP) NE565 or a National Semiconductor LM565. Still in production by both!
Lou Dorren
Pickup cartridge to be announced. For every ones information. The Signetics CD4-392 and the CD-894 chips are actually a Signetics (NXP) NE565 or a National Semiconductor LM565. Still in production by both!
Lou Dorren
Last edited:
Lou, part of the reason I am so interested in this is the Technics SH-400 I have which has been repaired twice, worked well for awhile and than failed in the right channel twice. It's still not working. I have hesitated to pay for repairs again.
But it is one of the better demodulators. Will yours favorably compare, and can you repair this one?
Thanks
But it is one of the better demodulators. Will yours favorably compare, and can you repair this one?
Thanks
loudorren
Well-known Member
Hello ress4278,
Your right, it is one of the better ones from the 1970's because it uses a pair of QSI5022 chips. The one I have designed is using technology that is 34 years more advanced. Having designed the QSI5022 and this new one, I expect significant performance improvement.
Can you describe the problem you are having with SH400?
Lou Dorren
Your right, it is one of the better ones from the 1970's because it uses a pair of QSI5022 chips. The one I have designed is using technology that is 34 years more advanced. Having designed the QSI5022 and this new one, I expect significant performance improvement.
Can you describe the problem you are having with SH400?
Lou Dorren
Hi Lou. That was quick.
Well as best I can, the right channel sounds hashy/unclear. Setting up the 400, (using the JVC CD-4 set-up record) the VU meter gives me a steady reading in the left channel, but not the right. The needle either floats or jerks around.
Let me know if you need more. BTW, I am not a technical sort of guy.
Thanks
Well as best I can, the right channel sounds hashy/unclear. Setting up the 400, (using the JVC CD-4 set-up record) the VU meter gives me a steady reading in the left channel, but not the right. The needle either floats or jerks around.
Let me know if you need more. BTW, I am not a technical sort of guy.
Thanks
loudorren
Well-known Member
Ress4278,
What happens if you reverse the left and right phono input leads?
Lou Dorren
What happens if you reverse the left and right phono input leads?
Lou Dorren
Everything is boxed up. Is there anything that reversing the leads will tell me that I can fix here?
This is interesting. I'm having almost the same issue with my SH-400. I'm using - believe it or not - an AudioTechnica eliptical stylus w/ matching cartridge and it gets BETTER CD-4 results than my Ed Saunders Shibata/Cartridge.
Regardless, I get the same odd readings from the dial on my SH-400. I've found that decreasing carrier level on both channels clears up much of the distortion while still giving excellent separation.
I have a funny feeling that the dial on the SH-400 is calibrated more for it's matching cartridge and is pretty much rendered moot (or unreliable) with any other cartridge.
Regardless, I get the same odd readings from the dial on my SH-400. I've found that decreasing carrier level on both channels clears up much of the distortion while still giving excellent separation.
I have a funny feeling that the dial on the SH-400 is calibrated more for it's matching cartridge and is pretty much rendered moot (or unreliable) with any other cartridge.
