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4270 in Stereo Mode: What happens to the rear channel signals?

mcsew2k

mcsew2k

Active Member
On a Marantz 4270, which we know is a Stereophonic 2 / Quadradial 4 model, what happens to the rear channel signals when the amp is set to stereophonic mode? Are they still available at the rear preout terminals? Can one add an additional power amp to drive the rear channels from the preouts to boost the total output power?
I own a 2270, so I was thinking if I pickup a 4270 I could set it to stereo amp mode and run the rear preouts of it to the main ins of the 2270 and get a full 70 watts per channel in all 4 channels.
If I actually owned any 2/4 model I would try it myself, but I don't and just wanted to know if that is possible.
 
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The preamp outputs are still there dependent on the mode switch on the front....

Yes on adding an amp via the rear preamp out even with the rear switch set to stereo.

Jk
 
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Great... it looks like a 4140 would be a better choice than a 4270 so that the tuner is not duplicated. I will be looking for one of those soon; they seem to be in short supply right now.
 
I now have a 4140 on the way. By looking at the schematic it appears that the level meters are connected to the output stages of the main amps after the power mode switch. When the 4140 is in 2 channel mode the rear level meters are disconnected from the power amps but still connected to the rear speaker terminals. So, it looks like I could connect the outputs of my 2270 to the 4140 rear outputs essentially making them inputs to the meters. I could remove the knob from the power mode switch as a reminder to disconnect the 2270 before switching the 4140 back to 4 channel mode.

Since I am a little rusty at reading schematics could someone please verify that this would work?

I am looking at this schematic (a hifiengine user account is needed):

http://www.hifiengine.com/hfe_downloads/index.php?marantz/marantz_4140_service.pdf
 
I did the attached trace from a 4140 schematic and by golly I think this is going to work. On the 4140, the output of the 2270 can be connected to the remote rear speaker connections and the rear speakers to the main rear speaker connections. With the 4140 in 70 x 2 power mode the rear meters and speaker terminals are left open but still connected to each other. Connected this way the main speaker on/off switch will work for all four speakers. In addition, the remote speaker on/off switch can connect and disconnect the 2270 from the 4140 meters. Connecting the 4140 rear PRE OUTs to the 2270 MAIN INs completes the amp setup. On the front end I can connect the 2270 TAPE 1 RECORDs to the TUNER input of the 4140.

Edit: Note that the rear headphones jack will also be fully functional.
 

Attachments

  • Tracing 4140 Rear Meter Input while in 70x2 Power Mode.jpg
    Tracing 4140 Rear Meter Input while in 70x2 Power Mode.jpg
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I received the 4140 a couple of days ago and have checked it out; it needs work as does the 2270. I would like to end this thread and start anew with separate threads as I work on each unit, then a third additional thread, with an appropriate title, dedicated to combining the two into a working system of systems.
 
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