Basic amp questions that I can't find a complete answer to - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 7 Old 04-15-2019, 07:55 AM - Thread Starter
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Basic amp questions that I can't find a complete answer to

These may seem like newbie questions, but dang it if I can't "google" my way to concrete answers to some of my amp questions. These are regarding quality name A/B amps like ATI, Anthem, Outlaw, B&K, etc.

1. If an amp is listed as 200 watts per channel x 7 channels, I know that power is divided among the channels and that you don't get 200 wpc for every single channel simultaneously. So does that mean the amp is capable of 200 total watts at any given time needed, or can it produce that for two channels at once, such as the left and right channels?

2. You can buy a 200 wpc amp for 2, 3, 5, or 7 channels, and I read that "you should get the extra channels in case you need them later" from sources like Audioholics, for instance. However, does that not reduce the output of the amp per channel? Do you not ensure yourself more power to a given 3 channels by only having those in the amp, as opposed to spreading it out to 7 channels? Or is the amp built differently to produce more power for those other channels if you add them.

3. Are the LCR plugs wired any differently to get more power? Would it matter if you switched the inputs (and appropriate output wire) around? If I'm using a 7 channel-amp to drive four surround channels ONLY, should I not use the LCR because they built differently than the one surround output I'd still need to use?

4. If power truly is divided up among 7 channels, then a 200 wpc amp really negligibly more powerful than a 150x7 or even 125x7 amp, correct?

5. If you're using subwoofers that have their own amps (my SVS subs have 800w sledge amps), then the LCR and surrounds are barely using any power at all, correct? An extra amp to drive the front three becomes overkill, as does a 200+ wpc amplifier in general?

Thanks in advance.

Video: JVC RS620/X9500 projector, Stewart ST130 screen, Panasonic ub820 UHD player
Audio: Anthem AVM60 preamp, Anthem MCA525 amp, B&K Reference 125.7 amp
Subs: dual SVS PC-12 cylinders
Speakers: Jamo 626k4 in-wall mains, Jamo 631k4 bi/dipole surrounds, DefTech DI6.5R heights
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post #2 of 7 Old 04-15-2019, 10:59 AM
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1) The makers usually publish power for 2 channels, into 8 ohms. (Sometimes 1 channel, and sometimes different impedances.) That's what you get when only 2 channels are driven. I believe that the amplifiers in most multichannel amps are identical. However, the 2 channel rated power is usually not available when more are driven; it's probably a power supply limitation. Cooling is also a consideration. Sound And Vision magazine (https://www.soundandvision.com/) does multichannel testing, but they only test a fraction of the AVRs/amplifiers that are on the market. A few manufacturers (NAD, Emotiva) specify the multichannel output. For home theater, it would be unusual to drive all channels to high levels simultaneously. For multichannel stereo, the story could be different.

2) No. Not much power is wasted in the unused channels. Most amplifiers are designed to consume little power when they are providing no output.

3) Not usually. There may be exceptions. Example: an Emotiva XPA-11 Gen3. It's a modular amp. Three of the modules are high-powered mono amps (typically used for LCR). Four are 2 channel amps that produce less power per channel, nad would be used for surround and Atmos channels.

4) It's not divided. However, 200W is 1.25 dB above 150W, and 2 dB above 125W. You can get a larger volume change due to the sensitivity of the speakers.

5) Barely any power? That's an exaggeration. Depending on your speakers and the distance you listen from, you may need lots of Watts to achieve head banger volume levels. (And the power would go up as your hearing is progressively destroyed.) Or, if you're an audiophile, and worship at the altar of "headroom".

I presume that others will jump in if I've misrepresented reality.
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post #3 of 7 Old 04-15-2019, 02:20 PM - Thread Starter
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Quote:
Originally Posted by bobknavs View Post
1) The makers usually publish power for 2 channels, into 8 ohms. (Sometimes 1 channel, and sometimes different impedances.) That's what you get when only 2 channels are driven. I believe that the amplifiers in most multichannel amps are identical. However, the 2 channel rated power is usually not available when more are driven; it's probably a power supply limitation. Cooling is also a consideration. Sound And Vision magazine (https://www.soundandvision.com/) does multichannel testing, but they only test a fraction of the AVRs/amplifiers that are on the market. A few manufacturers (NAD, Emotiva) specify the multichannel output. For home theater, it would be unusual to drive all channels to high levels simultaneously. For multichannel stereo, the story could be different.

2) No. Not much power is wasted in the unused channels. Most amplifiers are designed to consume little power when they are providing no output.

3) Not usually. There may be exceptions. Example: an Emotiva XPA-11 Gen3. It's a modular amp. Three of the modules are high-powered mono amps (typically used for LCR). Four are 2 channel amps that produce less power per channel, nad would be used for surround and Atmos channels.

4) It's not divided. However, 200W is 1.25 dB above 150W, and 2 dB above 125W. You can get a larger volume change due to the sensitivity of the speakers.

5) Barely any power? That's an exaggeration. Depending on your speakers and the distance you listen from, you may need lots of Watts to achieve head banger volume levels. (And the power would go up as your hearing is progressively destroyed.) Or, if you're an audiophile, and worship at the altar of "headroom".

I presume that others will jump in if I've misrepresented reality.
Thanks.

Regarding #1 , you're saying that if it's published for two channels into 8 ohms, both the left and right channels are getting 200wpc each from a 200w amp? There are two taroidal transformers typically. Then it would lessen if more surrounds were involved. Correct?

Video: JVC RS620/X9500 projector, Stewart ST130 screen, Panasonic ub820 UHD player
Audio: Anthem AVM60 preamp, Anthem MCA525 amp, B&K Reference 125.7 amp
Subs: dual SVS PC-12 cylinders
Speakers: Jamo 626k4 in-wall mains, Jamo 631k4 bi/dipole surrounds, DefTech DI6.5R heights
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post #4 of 7 Old 04-15-2019, 03:41 PM
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FTC ratings were for 2 channels only. Google FTC speaker ratings.
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post #5 of 7 Old 04-15-2019, 03:44 PM
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I would not worry about watts per channel unless you are a head banger. If you could get it to play 200 watts per channel you would not want to be in the room with it.
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post #6 of 7 Old 04-15-2019, 07:59 PM
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Quote:
Originally Posted by Erod View Post
Thanks.

Regarding #1 , you're saying that if it's published for two channels into 8 ohms, both the left and right channels are getting 200wpc each from a 200w amp? There are two taroidal transformers typically. Then it would lessen if more surrounds were involved. Correct?
Correct.

I neglected to mention the FTC ratings, which may be more honest than ones that don't conform. (I'm skeptical, though. As far as I know, there are no regulatory bodies that check audio gear for whether it meets the claimed power specs.)
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post #7 of 7 Old 04-15-2019, 08:31 PM
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Here's a Polish website that measures receivers/amps (more units and more detail than S&V): https://audio.com.pl/testy

Might not have everything you're looking for since the model selection sometimes differs in Europe and they don't review everything, and obviously you'll need to use Chrome or another method for translation, but there's a good chance you could find something to extrapolate from.

Setup:
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