Power amp selection

Roust_m

New Member
Feb 24, 2022
18
7
3
49
Hi,

I am looking at upgrading my front channels and getting a power amplifier.

I currently have a dedicated cinema room with 7.2.4 Monitor Audio Silver range speakers and Yamaha A8A AVR:
2 x RX6 (front)
1 x RXLCR (centre)
2 x RXW12 (sub)
2 x RXFX (side)
2 x RX1 (back)
4 x Monitor Audio CP-CT380 8" In Ceiling Speaker

I am looking to replace the 2 front and the center speakers with Monitor Audio Silver 500 7G floor standing speakers and Monitor Audio Silver C250 7g Centre speaker.

I use my cinema room mostly for movies. I was recommended Rotel RMB-1555 5-Channel Power Amplifier. But wondering will it be sufficient?

The front speakers are 250W. But the amplifier is 120W all channels driven. The seller said something about that at 4 Ohms it delivers nearly double of that. I am a bit confused. The speakers specs say:
Nominal Impedance: 8 Ohms
Minimum Impedance: 4.1 Ohms @ 150 Hz

So are they 4 Ohms or 8 Ohms? Will this amp be enough?

The seller also mentioned that front and center speakers are the most important. Do I need a 5 channel amplifier or just 3 channel, perhaps more powerful?

Thanks.
 
Last edited:

AMR / iFi audio

Industry Expert
Aug 21, 2019
2,636
1,153
260
43
UK
ifi-audio.com
Hi,

I am looking at upgrading my front channels and getting a power amplifier.

I currently have a dedicated cinema room with 7.2.4 Monitor Audio Silver range speakers and Yamaha A8A AVR:
2 x RX6 (front)
1 x RXLCR (centre)
2 x RXW12 (sub)
2 x RXFX (side)
2 x RX1 (back)
4 x Monitor Audio CP-CT380 8" In Ceiling Speaker

I am looking to replace the 2 front and the center speakers with Monitor Audio Silver 500 7G floor standing speakers and Monitor Audio Silver C250 7g Centre speaker.

I use my cinema room mostly for movies. I was recommended Rotel RMB-1555 5-Channel Power Amplifier. But wondering will it be sufficient?

The front speakers are 250W. But the amplifier is 120W all channels driven. The seller said something about that at 4 Ohms it delivers nearly double of that. I am a bit confused. The speakers specs say:
Nominal Impedance: 8 Ohms
Minimum Impedance: 4.1 Ohms @ 150 Hz

So are they 4 Ohms or 8 Ohms? Will this amp be enough?

The seller also mentioned that front and center speakers are the most important. Do I need a 5 channel amplifier or just 3 channel, perhaps more powerful?

Thanks.
Let us start with the speakers. Speakers impedance is a parameter that changes with frequency. This is why manufacturers provide a nominal impedance that dominates. Looking at your speakers, they are usually 8 Ohm, but at 150 Hz, they drop to 4.1 Ohm. So you need an amplifier that can handle that.

Regarding amplifiers, think about the potential problem you want to resolve. We want to have a better sound by providing better amplification. Usually, the most power-hungry are the front speakers. If we separate them with an external power amplifier, you have a win-win situation. Front speakers are powered better, and the rest of the speakers don't have to fight with them for power. So regarding your question, even a stereo power amplifier will be a reasonable upgrade. Of course, 3 channel amplifier will allow the centre channel to sound nicer, too, so that is some food for thought.
 

Roust_m

New Member
Feb 24, 2022
18
7
3
49
Let us start with the speakers. Speakers impedance is a parameter that changes with frequency. This is why manufacturers provide a nominal impedance that dominates. Looking at your speakers, they are usually 8 Ohm, but at 150 Hz, they drop to 4.1 Ohm. So you need an amplifier that can handle that.

Regarding amplifiers, think about the potential problem you want to resolve. We want to have a better sound by providing better amplification. Usually, the most power-hungry are the front speakers. If we separate them with an external power amplifier, you have a win-win situation. Front speakers are powered better, and the rest of the speakers don't have to fight with them for power. So regarding your question, even a stereo power amplifier will be a reasonable upgrade. Of course, 3 channel amplifier will allow the centre channel to sound nicer, too, so that is some food for thought.
But what about 5 channel? Does it provide any benefits? This particular amplifier can do 120W with all channels driven. Two front speakers are 250W, the centre one is going to be 200W and all of them 8 Ohms, side speakers (RXFX) I could hook up to the remaining 2 channels are 80W and 6 Ohms. How does it all add up together? If the amp is doing 120W with all channels driven and the front speakers are 250W and the side speakers are only 80W and 6 Ohms, will the amp redistribute some extra power to the front speakers because the side ones don't need 120W?

The front speakers amplifier requirement is 80W to 250W, meaning the amp I am looking at is within the range, but is there any benefit of going closer to the upper range around 250W?

Also, my Yamaha A8A is 150W with 2 channels driven. The back Monitor Audio Silver RX1 are 80W and 6 Ohms. My Atmos Monitor Audio CP-CT380 8" In Ceiling Speakers are 120W and 6 Ohms. Would it be a good balance?

Would putting my side speakers on power amp make them sound different from back surround speakers?
 

AMR / iFi audio

Industry Expert
Aug 21, 2019
2,636
1,153
260
43
UK
ifi-audio.com
But what about 5 channel? Does it provide any benefits? This particular amplifier can do 120W with all channels driven. Two front speakers are 250W, the centre one is going to be 200W and all of them 8 Ohms, side speakers (RXFX) I could hook up to the remaining 2 channels are 80W and 6 Ohms. How does it all add up together? If the amp is doing 120W with all channels driven and the front speakers are 250W and the side speakers are only 80W and 6 Ohms, will the amp redistribute some extra power to the front speakers because the side ones don't need 120W?

The front speakers amplifier requirement is 80W to 250W, meaning the amp I am looking at is within the range, but is there any benefit of going closer to the upper range around 250W?

Also, my Yamaha A8A is 150W with 2 channels driven. The back Monitor Audio Silver RX1 are 80W and 6 Ohms. My Atmos Monitor Audio CP-CT380 8" In Ceiling Speakers are 120W and 6 Ohms. Would it be a good balance?

Would putting my side speakers on power amp make them sound different from back surround speakers?
It can be very confusing, but the power is not helpful information in this case. It doesn't mean too much for us because, at most listening levels, we won't even get close to the maximum power of the speakers. Also, you have a calibration inside the AVR that matches all speakers' volumes. No need to worry about matching their volumes :)

5 channel is the best solution because all your speakers use identical amplifiers (but with surround channels, the difference between amplifiers will be minuscule, as they don't play a lot of sounds.

If you are looking for a price-to-improvement ratio, then a 2, or 3-channel amp will bring better value for the money you spend.
 

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