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CD-R and Audio Hardware => Audio Hardware => Topic started by: Levent on 2019-05-16 22:09:37

Title: Two questions about Denon PMA 720AE integrated amplifier
Post by: Levent on 2019-05-16 22:09:37
Hello friends... I have a Denon PMA 720AE integrated amplifier:
(https://www.dukkanhifi.com/images/gallery/1537.jpg)
I have two questions about this unit.

First one is, about speaker systems. As I could understand from the rear panel, if I connect one pair of loudspeakers (to A or B section); speaker impedance is 4 to 16 ohms.

And if I connect two pair of loudspeakers at the same time (to A + B sections); speaker impedance changes to 8 - 16 ohms.

What does it mean? Does the quality reduces when using four speakers?

------------

My second question is about the amplifiers "pre out" section.

I learned from internet, "pre out"  is the unamplified signal.

Can I connect an active subwoofer using Denon's "pre out" section? Is it suitable for this kind of addition?

If "pre out" section is in use, it doesn't turn/cut off the normal speaker, does it?

I mean, can I use this Denon amplifier with four passive speakers and with an active subwoofer at the same time?

Thank you...
Title: Re: Two questions about Denon PMA 720AE integrated amplifier
Post by: StandsOnFeet on 2019-05-16 22:25:56
Here's the manual: https://images-eu.ssl-images-amazon.com/images/I/C1lQpoj83SS.pdf

1). 4 Ohm speakers take more power to drive. The amplifier evidently doesn't have enough power to drive four of them.

2). See page 6 of the manual. It says you can connect a powered sub-woofer to Pre Out.
Title: Re: Two questions about Denon PMA 720AE integrated amplifier
Post by: Levent on 2019-05-16 22:43:51
@StandsOnFeet, I didn't understand. Can't I connect two speakers to "Speaker System A", and two other speakers to "Speaker System B" ?
Title: Re: Two questions about Denon PMA 720AE integrated amplifier
Post by: StandsOnFeet on 2019-05-16 23:41:18
Yes, you can, but they probably ought to be 8-Ohm or 16-Ohm speakers, not 4-Ohm.
Title: Re: Two questions about Denon PMA 720AE integrated amplifier
Post by: antz on 2019-05-17 00:16:44
I think you're getting confused because it's a stereo amp. Each channel is separate, so you're allowed 2 x 8-16 ohm speakers on *each* channel (4 speakers total). Just using one speaker on each channel, you're allowed 4-16 ohms (2 speakers total). Speakers of 4 ohms require more current (not power, actually) and the amp can't supply enough current into less than 4 ohms without overloading it. Two x 8 ohm speakers = 4 ohms overall but 2 x 4 ohm speakers = 2 ohms overall, which is too low. Most domestic amps are rated much the same.

According to the specifications, distortion is slightly higher into a 4 ohm load, so the quality is slighly worse. Doubtful you'll hear a difference though, in reality.
Title: Re: Two questions about Denon PMA 720AE integrated amplifier
Post by: DVDdoug on 2019-05-17 02:33:20
It means 4 Ohms is the minimum total impedance.  The upper limit is nonsense...   More than 16 Ohms wouldn't hurt the amplifier.

If you connect two equal impedance speakers in parallel the impedance is cut in half.   So two pair of 8 Ohm speakers makes 4 Ohms.   If you were to connect two pair of 4 Ohm speakers you'd have 2 Ohms and that's too low...   Too much "load"...

Impedance (or resistance) is the resistance to current flow (Amps).   If the impedance is too low you get too much current and the amp can be damaged.  

You can also consider power (Watts).   If you have 10W going into a speaker, and then you connect another speaker they each get 10W.   (Twice the total power and twice the total current with no change in voltage.)

The pre-out should work with an active (powered) subwoofer, and an active subwoofer usually has a low-pass filter.    But, the full frequency range will go to your main speakers, which is usually not ideal.
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