Yes, but what's in the "empty" 15kHz till 25kHz area? I'm too stupid to read through all that theorethical papers
PANASONIC SE-405 CD-4 DEMODULATOR
- Thread starter J. PUPSTER
- Start date
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Nothing, just noise.
CD4 is up to 15kHz in the two lower frequency channels (Lf+Lb & Rf +Rb if I remember correctly), then the FM modulated difference channels (like FM radio) around the 30kHz carrier.
The phono circuitry of the 405 has inductors which are simple wound cables (yellow), which is strange I guess. Are they prone to pick up hum?
Are those meant to be adjusted by fiddling with the wire loops?
Could the circuitry be improved with the use or a regular inductor?
TIA.
Are those meant to be adjusted by fiddling with the wire loops?
Could the circuitry be improved with the use or a regular inductor?
TIA.
There seems to be more to it (from Lou Dorren's cd-4paper1.pdf, available elsewhere here):
"The input to the preamplifier comes from the phono cartridge control unit. This selects the input network
for the cartridge. For semiconductor strain gauge type, a DC bias voltage is applied to both channels and
one of the channels is phase-inverted 180 degrees. This is done because the DC bias voltage can only be
applied in one polarity, which makes the left and right channels out of phase. For the moving magnet and
moving coil type, the DC bias voltage is removed as is the inversion."
Doug G.
2K Club - QQ Super Nova
Well, the two are two different issues. We were talking about damage to MM cartridges by leaving the SC/MM switch in the wrong position, not the intricacies of what has to happen for correct operation with the two different types.
Doug
I picked up one of those CD4 Panasonic SL-701 turntables in hopes to use it with MM carts (my bad) and have been testing it out with a cheap MM cart that came with another table. I'm researching on if it's possible to tinker with the board to make it more MM friendly and found this thread. It does not have the option to switch out of SC at all but I'm hopeful their other boards are similar enough between other Panasonic units to see if there's a hack. It does have a switch between Stereo / 4CH Auto / 4CH Aux. So far playing a quadradisc on 4CH Auto the radar light comes on, the bass sounds decent and the channels sound to be doing it's thing. However when switching to regular stereo there's little to no bass, reading up just from others opinions on this forum, this is expected with a SC preamp while using a non SC cart. As far as the actual damage it may do, it should shoot photon torpedoes and disrupt the space time continuum from the comfort of your living room, or really nothing I've searched yet says exactly what it could do.
Doug G.
2K Club - QQ Super Nova
What cartridge are you using? I assume it is not a CD-4 cartridge. Almost any regular two channel cartridge will get the radar to light up with a CD-4 record because all it needs is to have a response of sufficient amplitude to 30kHz, to trigger the detector, and a lot of them do. They just don't have enough output above that or good enough separation above that to get CD-4 to work.
I would have to see the schematic for that demodulator to determine why there seems to be good bass in the auto mode but not in stereo. The bass really should be pretty much absent in any mode since, because that demodulator is meant only for SC cartridges, there would normally be no RIAA circuit to undo what RIAA equalization does during record cutting and that is to attenuate the low frequencies to maintain reasonable stylus excursions. The RIAA circuit in the preamp then boosts the low frequencies to restore a flat response, so bass frequencies would decidedly be relatively weak without that circuit.
Any damage to a MM cartridge would just kill its output (no sparks, explosions, or sudden halt to the time continuum or anything like that) as the coils would be opened (burnt out, in common terms) by more current than they can handle. I have stated elsewhere that I have inadvertently left the SC/MM switch in SC mode when installing a MM cartridge and nothing has happened so obviously, those cartridges could handle the DC current. Other cartridges may not be able to. Hence, the warning about having the switch in the correct position.
Doug
I would have to see the schematic for that demodulator to determine why there seems to be good bass in the auto mode but not in stereo. The bass really should be pretty much absent in any mode since, because that demodulator is meant only for SC cartridges, there would normally be no RIAA circuit to undo what RIAA equalization does during record cutting and that is to attenuate the low frequencies to maintain reasonable stylus excursions. The RIAA circuit in the preamp then boosts the low frequencies to restore a flat response, so bass frequencies would decidedly be relatively weak without that circuit.
Any damage to a MM cartridge would just kill its output (no sparks, explosions, or sudden halt to the time continuum or anything like that) as the coils would be opened (burnt out, in common terms) by more current than they can handle. I have stated elsewhere that I have inadvertently left the SC/MM switch in SC mode when installing a MM cartridge and nothing has happened so obviously, those cartridges could handle the DC current. Other cartridges may not be able to. Hence, the warning about having the switch in the correct position.
Doug
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I don't mind sacrificing a VM91r for the cause, as I've been using it for records that are pretty tore up already rather than risk damaging an expensive stylus. My AT15Sa and AT33Sa are not going on this anytime soon! I just found it fascinating and wanted to share the experience. When that CD4 light comes on, all is well, the built in preamp gives good bass, but regular stereo there's no bass as if the preamp shut off with the CD4 not detecting 30khz to fire up. It's a shame really because it's a neat concept to have this all in one. At least the SE 405 you can choose the cartridge type. I'm going to keep looking and researching into this, it's just a bummer if it comes down to a perfectly working vintage turntable turned to a brick without a SC cart.
Attachments
Do you happen to have a photo of where that switch is wired into on the circuit board? I'm trying to see if something like this is even part of another Panasonic board that might be helpful to give me to hack it to play with MM carts.
Doug G.
2K Club - QQ Super Nova
The switch in the SE-405 is mounted right to the board at the rear. Sorry, I don't have a picture but there was a thread about that switch being stuck and there are pictures in it.
https://www.quadraphonicquad.com/forums/threads/panasonic-se-405-cd-4-demodulator.34063/
Doug
https://www.quadraphonicquad.com/forums/threads/panasonic-se-405-cd-4-demodulator.34063/
Doug
@Doug G. 's link gives some good pics. I'll be glad to open it & take something more specific or give you board numbers, whatever.
Doug G.
2K Club - QQ Super Nova
The demodulator in the 701 turntable looks completely different from the one in the SE-405. The SE-405 is undoubtedly a later one with the two large chips. The 701 demodulator looks to have more discrete components with the two smaller chips.
Doug
Doug
I've also seen the SE-405C out in the wild! Wonder what that one was calibrated for?
After a year of searching, I finally managed to pick up a like new 451C and 450C NOS then started looking for one of these units. First I wound up with a Technics SA-8500x for cheap that has a bad amp but still works just you have to turn it up all the way to hear it, however, the CD4 SC capable works so I have it taped out to a Lafayette LA-64 to drive the speakers. Curious to compare what chipset they used for it.
Then today I ordered an SE-405 for my home theater setup. Hope it works well with the 451 and 450.
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