Bose 4401 CD-4 Demodulator?

[jupp369]

Same with JVC's, measure points, but no hint what should be there ...

 

[audiomaster]

And I only see one pot on that schematic. Looks like it is connected across two pins on the IC and wiper to ground. Maybe a balance control? So that schematic is not complete as manufactured!

 

[Asklia]

This is unfortunatly a generic schematic only around the 392 circuit. I would be lucky to find more.

 

[Asklia]

We have a small chance. The former German company Grundig has made a CD-4 Demodulator based on the 392 chip. In the service manual is a procedure for some adjustments: 30 kHz oscillator (R138, between Pin 2 and 3 of the 392); channel separation; ANRS noise suppression (R168).

I am surprised that the chip uses its own 30 kHz oscillator instead of using a PLL following the carrier frequency from the record. Its a free analog oscillator without a crystal of course, therefore the adjustment.

For this adjustment, an Oscilloscope or sensitive frequency counter is necessary. A normal signal generator and a FM modulated signal generator are necessary.

I guess that the FM modulated signal generation might exist in software, if the sound card output goes up to 48 or 96 kHz output. Maybe someone likes to search for this.

 

[Owen Smith]

I am surprised that the chip uses its own 30 kHz oscillator instead of using a PLL following the carrier frequency from the record. Its a free analog oscillator without a crystal of course, therefore the adjustment.

PLLs in consumer grade chips continue to be problematic today, I've wrestled with some of them. I can't imagine how awful PLLs were in the 1970s, especially since they were probably discrete analogue circuits.

 

[Asklia]

The generation of CD-4 demodulators before the CD392 used an integrated PLL circuit.

The benefit of using the PLL ist the correct frequency, delivered by the record itself. So any deviation from cutting, LP or TT is not relevant.

Using a fixed frequency inside the demodulator is always slightly wrong.

 

[Owen Smith]

The predecessor CD-4 circuit before the CD392 used a PLL circuit.

And maybe it was unreliable and/or expensive.

 

[Asklia]

More expensive for sure. The amount of circuits was higher, if you look at the older CD-4 demodulator boards; i.e.the Marantz demodulator.

 

[Doug G.]

I always love to see original quad hardware posts pop up on here in the midst of never-ending soft/firmware posts.

Doug