catrafter
Marantz Specialist
I was reluctant to post this as I have not checked to make sure the FM multiplex circuit in the 4400 is exactly like the 2325. Use at your own risk, or better yet, correct as required to match the 4400 and repost it.
Tom
This applies to the 2275, 2325 and probably the 2250B as well although some of the component designators are different.
Note: An 'ON' NPN transistor has a base voltage about 0.6V more positive than the emitter. This will cause the collector to become very near the emitter voltage.
Wire-anded: the junction of two or more components where either one can pull that point to or near ground potential.
FM Stereo MPX operation:
Intermediate Frequency (IF) signal strength is monitored by H308. If signal strength is above muting level, H308 is ON, H309 is OFF.
If there is excessive noise, then H311 is ON which is wire-anded to H309 keeping H301 (FET) OFF.
If the discriminator is outputting DC due to the tuning being off station, either H314 or H315 is ON which are wire-anded to H309 as well. This also turns H303 ON grounding Pin 8 of the decoder forcing MONO operation.
If the station is properly tuned, not noisy and the signal strength is high enough,
H308 is ON, Signal Strength OK
H309 is OFF, Signal Strength OK
H311 is OFF, Noise is OK
H314 is OFF Tuning centered
H315 is OFF Tuning centered
H317 is OFF, SS, Noise and center tuning OK then:
H301 is ON allowing audio and MPX signal to pass into the decoder.
H303 is OFF If SS sufficient for Stereo operation and MONO button is not pressed
H302 is OFF VCO runs (AM not selected)
Tom
This applies to the 2275, 2325 and probably the 2250B as well although some of the component designators are different.
Note: An 'ON' NPN transistor has a base voltage about 0.6V more positive than the emitter. This will cause the collector to become very near the emitter voltage.
Wire-anded: the junction of two or more components where either one can pull that point to or near ground potential.
FM Stereo MPX operation:
Intermediate Frequency (IF) signal strength is monitored by H308. If signal strength is above muting level, H308 is ON, H309 is OFF.
If there is excessive noise, then H311 is ON which is wire-anded to H309 keeping H301 (FET) OFF.
If the discriminator is outputting DC due to the tuning being off station, either H314 or H315 is ON which are wire-anded to H309 as well. This also turns H303 ON grounding Pin 8 of the decoder forcing MONO operation.
If the station is properly tuned, not noisy and the signal strength is high enough,
H308 is ON, Signal Strength OK
H309 is OFF, Signal Strength OK
H311 is OFF, Noise is OK
H314 is OFF Tuning centered
H315 is OFF Tuning centered
H317 is OFF, SS, Noise and center tuning OK then:
H301 is ON allowing audio and MPX signal to pass into the decoder.
H303 is OFF If SS sufficient for Stereo operation and MONO button is not pressed
H302 is OFF VCO runs (AM not selected)
. Love that thing!
