Involve CD4....Is there any life in it????

[Quadwreck]

I'm on board.

 

[BigAlt]

I'm still in for one. I now have 2 SMs ( one an original without SQ and an SQ edition which was also an original SM I sent back to Chucky for the SQ chip upgrade ).
BigAlT

 

[All Ears]

I'm still in or count me in if my name never made it to the original list.

Thank you Chucky for keeping this concept alive.

 

[surround.sound.enthusiast]

Hi Chucky,

I'm still in for a CD-4 demodulator too.

 

[Quadro-Action]

During the develope of Lou Dorrens Demodulator around 150 interested Fans has voted to buy one - so far I know. Today it should be possible to collect 100 prospective buyers. But by further longer waiting, less number os interestred Fans are known.
I would buy also a new CD-4 Demodulator, which works by real CD-4 technic.

 

[segacd]

I'm in!

 

[bangsezmax]

Count me in.

 

[Nite1922]

Interesting to see how they do it.
Have 4 Marantz CD-400B's myself, and they are easy to modify to sit in a tape loop to function, so unlikely to buy.
Still interesting though

 

[sukothai]

Still hopeful (and in.)

 

[fredblue]

I'm in :upthumb

 

[bigbillquad]

Missed you fredy....

 

[vinylguy4]

I posted earlier in this thread and still in for the CD-4 unit if it is near $500.

vinylguy4

 

[surroundophile]

Still in.

 

[jwb474]

Put me down as still in!

 

[chucky3042]

Hi All

Thanks for this, gives me some confidence to get Overture off his Lazy arse!

Regards

Chucky

 

[rolvkarsten]

Hi there
How is this project running?
Regarding Lou Dorren's LP and BP filters not much was written, except he mentioned fine-tuning, I think I remember. He published one picture of his main PCB with six daughter-boards. Four small presumably LP-filters, and tow larger, presumably BP-filters.
I downloaded Linear Technology's FilterCAD SW, and fiddled just a little with it and got a response quite similar to one BP-response published by Lou Dorren:
View attachment 28629
The response is with a Switched Capacitor filter LT1068-25 and it is pretty similar to Lou Dorren's. The clock frequency is 825kHz, with all possibilities for clock bleed through.
Filter CAD also gives the choice of "Active RC" like the LT1562
The LP-filter may also be made similar.
The CD-4 system requires a 3kHz deadband between 15khz and 18kHz. Lou Dorren set his LP-filters to 15.667kHz.
The LP-filter shown in the "High Performance 2007 CD-4 Demodulator" Installment II is 60dB down at 18kHz. He stated he used an 8-pole filter. (I got a similar response in FilterCAD.)
Installment III shows the BP-filter down 40dB in the stopband.

I intend to look into this in more detail, and for the time being I believe more in the "Active RC" concept of LT.
However, we do not know if Lou Dorren used Linear Technology devices at all.

Information about the CD-4 specification is appreciated, in the mean time I'll have a look into the AES library.

Regds
Rolv-Karsten

LP-filer = Low Pass filter
BP-filter = Band Pass filter

Chucky, have you been thinking around the analogue filters? What order and type, and 3dB freqency? The sharp filters brings us into the same problems as the first CD players, brickwall filters with horrible phase response. That is a reason for DSP, as Philips did in the 80ties with their digital oversampling filters.
On the other hand, the old analogue CD-4 records are probably recorded via similar horrible analogue filters

Regds
/RK

 

[quattro64]

I'm also in for one of these Hope this works out, be a nice tribute to Lou Dorren. I was on his dmod list a few years back.

 

[kfbkfb]

Regarding LP and BP filters for CD-4 playback:

Why bother with the LP filter for the baseband/sum signals?

Just let the RIAA playback EQ reduce the amplitude of the
20kHz to 45kHz FM carrier (this is exactly what happens when a
CD-4 record in played in Stereo, after the RIAA EQ, the carrier
amplitude is reduced and doesn't damage tweeters).

There are several AES documents that describe the CD-4 system
and could be helpful in determining the BP filter requirements.

Kirk Bayne

 

[lmwallnj]

I'm still in for one.

 

[bangsezmax]

I would like to reiterate my desire for one of the Involve CD-4 units. I love my SQ Surround Master and I love the fact that these crazy guys are even considering making a CD-4 box for us.

I know I said I was in just a few posts back but I'm concerned that this effort is getting lost in some thread shuffling around here.

If the Involve threads aren't going to all be in the same place, can this one at least get a sticky? Obviously Lou Dorren's thing doesn't need the stickies anymore.