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Discussion Starter #1
Hi everyone,

I hope you can help me understand my Marantz MM500 amplifier -- there is very little information online about this amp so I am posting some details here, including a block diagram.

I would like to know if I can use this as a 4-channel amp -- hooking the 4th speaker to the rear speaker outputs at the L CH and R gnd?

Its a multichannel amp from the ProLogic days. It has 4 RCA inputs (Front L, Front R, Center and Rear), and it has 5 speaker outputs (Front L+R, center, and rear L+R). The rear L+R run off one channel.

Here are its specs:
front ..... 75W/ch rms into 8 ohm
center ... 80W rms into 8 ohm
rear ...... 40W/ch rms into 4 ohm

I'm guessing that the front L+R channels are better quality. They use an AN7062 chip while the center and rear use STK401 chips. I'm also guessing they used the STK401 chips so the rear was 4ohm stable -- then they ran 2x 8-ohm speakers in parallel to present a 4 ohm load. I don't know why the output of the rear channel doesn't increase compared to the center channel at 8 ohms.

Thanks for your help!
Dave
 

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Rear L & R are in series not parrallel. Practically your receiver send a mono signal to rear and that's whay they say 4 Ohm, the final load is 4+4=8 Ohm.
You can connect your forth speaker as (+) to L rear and (-) to Rgnd as you said. It must be 8 Ohm.
Regards,
tba
 

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Rear L & R are in series not parrallel. Practically your receiver send a mono signal to rear and that's whay they say 4 Ohm, the final load is 4+4=8 Ohm.
You can connect your forth speaker as (+) to L rear and (-) to Rgnd as you said. It must be 8 Ohm.
Regards,
tba
I'm not disputing the above, but wishing to learn. wouldn't two 4ohm speakers give you a 2ohm load rather than 8 ohms ? I don't understand how a second speaker could increase rather than decrease the resistance.:scratch:
 

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I'm not disputing the above, but wishing to learn. wouldn't two 4ohm speakers give you a 2ohm load rather than 8 ohms ? I don't understand how a second speaker could increase rather than decrease the resistance.:scratch:
If you connect the "normal" way yes it would be 2 Ohm however as said above if you connect the speakers in series it will go up to 8ohm see below:

Amp (+)-------(+ speaker -)------(+ speaker -)------(-) amp
 

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Discussion Starter #5 (Edited)
Thanks for the replies! I will try it as a 4-channel amp tonight.

Now that I look closer at the diagram I see the rear speakers in series.

For the rear channel running two speakers, I thought I was hooking up two 8-ohm speakers in parallel to present a 4 ohm load to the amp. Then the amp's 80 watts are divided equally into the two "channels" for reporting on the spec sheet (40W/ch at 4 ohm).

...in series those two 8-ohm speakers present a 16 ohm load and the output of the rear channel drops to 40 watts (divided into 2 speakers). Yes?

Shouldn't Marantz have rated the rear channel as 20W/ch into 16 ohms (assuming 2 8-ohm speakers are connected)?

Thanks,
Dave
 

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Yes, connecting 2 8ohm speakers in series will give you 16ohm and drop the watts to 20 however thats not going to be very much to power them.
 

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Discussion Starter #7
Yes, connecting 2 8ohm speakers in series will give you 16ohm and drop the watts to 20 however thats not going to be very much to power them.
No kidding. I guess that shows low emphasis on the rear channel in Pro Logic.

I don't have the owner's manual any more and I would like to know if it recommends 8 ohm or 4 ohm speakers for the rear channel.
 

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For sure it would be 8ohm its very uncommon to have 4ohm speakers on the surround channels. 4ohm would probably damage the amp.
 
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