Grundig CD-4 Demodulator Service Manual

Hi,
I have the Grundig CD-4 service manual available for download from here

www.grizwald.plus.com/quad

I ended up buying a copy and making a PDF from it, the manual is VERY good quality with large schematics. The setup instructions are in German, but I am working on a translation that will be posted as soon as possible. I know some of you already have this manual, and must have missed my request for one, however this demodulator uses the same "Holy Grail" cd4-392 chip as the Sansui 8001/9001 receiver demodulator.

I wonder if this can be set up in the same way as the Sansui, or even if the setup instructions as given are the same, QB you should be able to answer that one.
Below are filter plots of the Sansui and Grundig filter responses compared, the Grundig has a wider passband, looks nice and sounds good too.

Green trace is Grundig, Blue trace is Sansui.

Enjoy

Malcolm

Malcom, your schematic and component plan is terriffic! I have this manual myself, but only as photocopy. I tried to scan them, but to get all those Voltages and remarks readable I had to increase resolution so much that filesize gets too unhandy...

Anyway, I OCR'd the first two pages and made PDFs of these, file size is under 70kB. When appending your schematics (page 3 and 4) with it I get a file size of roughly 3,5MB instead of 5,1MB.

Unfortunately I couldn't find a way to email it to you over QQ's email system.

-Kristian

Kristian,
The files were scanned at 600DPI and reduced to 300 during the PDF process, I could have reduced the first two pages more, but it was so very clear that I did not. I will look tonight and if they can be reduced without loss of quality, then I will re post the file to my web site. The schematic and component layout should be printed on A3 paper 42cm * 29.7cm (16.5 * 11.7 inches) for best results, but even on A4 it is good.


Malcolm

Danke viemals,I found the schematics very informative.
Sehr gut,
Herr QC

I have reduced the schematic and pcb layout down to 300 DPI, and the text pages to 150 DPI. They still look and print as they should, but now are 2,8Mb so it should be easier for those with slow connections

Malcolm

I had a Akai AS-980 amp that had a thoroughly trashed cabinet.
I used it for awhile but with all he switches problematic I gave
it to a friend.
Before giving it away, I removed the CD-4 board. It seemed to work as good or better than my other demods,my friend had no use for the CD-4 board
so he didn't mind.
When I went to hook it up it up sometime later the left channel
would not work very well.
I shelved it for some time until this 4DD-5 schematic inspired me to
look deeper.
As it turns out,they are the indentical boards,I never noticed theJVC
logo in the printed etching.
It turned out to be a intermittent 100 millihenry coil for ANRS.
If I moved it around, the sound would change fidelity and the
separation setting would screw up.
I Change it to one I happened to have laying around and Viola!

Unfortunately the configuration of the first Ta-7122 chip circuit does not
lend it to injecting a recorded CD-4 file like I can do with
my Panasonic SE-405,thus decoding CD-4 from a 96/24 file,
but I will keep trying.
I thought all circuits would use the emitter-follower design following
the input stage,Too bad.
Thanks for Schematic view.
QC

Is a schematic of the CD-4 board for a Harmon-Kardon 800+ or Pioneer
QX949 available?
QC

I couldn't insert 24/96 signal into H/K 800+ demod.,
the design doesn't make it easy.
However, with the 4DD5.pdf(courtesy Malcolm2010) I not only got
my Akai As980 demod working,but also found one way to playback files.
The resister/cap bridge of C111/C113\R113/R115 appears to be
part of the RIAA eq and gain/feedback for the left input stage;Right input
would be C112/C114\R114/R116 respectively.
If you apply a 1K resister across entire bridge,gain is reduced and
so is the phono EQ.
Now I don't pretend to know exact amounts of db gain,and I would have
thought the 1K input resister and the 1K resister I shunted would have reduced input IC to unity gain but it appears not.
Good news is that I can simply plug the headphone output of my soundcard
(M-Audio Firewire 1814)directly into the phono jacks and set headphone
gain to -10 or so and play back file at -10 to -15db from program.
The outputs have to be adjusted because optimum separation varies
from file to file depending on recording level.
My capture(as previouly posted)is from a Panasonic SE-405,
which by the way still is the easiest demodulator to tweek
for this purpose.
The JVC type demod. is a decent unit and files play back well though
some Riaa eq remains and highs don't sparkle,then again,
noise isn't as noticable either.
My next unit to mod is my Pioneer QX646.
If you have a mind to and have extra units doing nothing,give it
a try.
You will still need to record @24/96 Quadradiscs to computer and play
back 24/96 from compatible soundcard and program.
QC

FYI:
I found the Pioneer cd-4 demod in the Qx646 is also a bit unfriendly
to mod. like the Harmon Kardon.
It is yet again,another completely different design from JVC and other
brands.
Primary Board(not in sheilded metal enclosure):
I cut 2 traces on the board and separated the phono input/Riaa amps
from the demodulator.
I connected computer at that point and demod worked fairly well.
I will try to post picture that shows black spot is where trace needs to
be cut and red lines indicated where RCA jacks would be connected
to play from sound card.
One might need to add controls for level at that point to optimize
levels and separarion.
The secondary board that is the FM/demod circuit requires no
mod.
I'm thinking of wiring phono jacks that switch,therefore I can
use it as a decoder for phonograph or line in CD-4.
It does work;completely playable 24/96 files decode and playback
as good and maybe a tad better than LP plays,although as with
all decoders so far,they only do as good as source file or record.
I forgot to mention,the worst part of this is that Pioneer
used wire wraped posts to wire board in.
You have to remove board for mod so it is a bit tedious.
Although, once wires are cut the first time, it's easy to remove and
insert board should you need to do additional work.
QC

Dear Sirs!

Do you have a copy pdf or something of this Grundig manual?

Could you kindly send it to me or upload somewhere?

Thank you

Sergey

You want to have a look here:

http://www.quadraphonic.info/manuals/

-Kristian