2. amps-preamps
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Watts and power

Can somebody break it down in layman's terms for me? Why is it that sometimes an amp that has a high watt rating (like, say, a lot of class D amps do) don't seem to always have the balls that much lower rated A or AB amps do? I have heard some people say, "It's not the watts, it's the power supply." Are they talking about big honkin' toroidal transformers? I know opinions vary on a speaker like, say, Magnepans - Maggies love power, right? A lot of people caution against using class D amps to drive them and then will turn around and say that a receiver like the Outlaw RR2160 (rated at 110 watts into 8 ohms) drives Maggies really well! I'm not really asking about differences between Class D, A, or AB so much as I am asking about how can you tell the POWER an amp has from the specs? 
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listening99
172 posts
 
The idea is to replace my existing speakers with two speakers that present 4ohms resistance/each. I understand the speakers are efficient, although the manufacture statistic of 98dB is probably overstated. The hope is that the amp functions well at the lower volumes I would listen to, habitually. I mean, if a speaker can produce 90dB with less than a watt of power, I should have very little difficulty, sitting about 8-9' away, and then the amplifier is basically loping along, even with two 4ohm speakers, right? I keep hearing the Moabs are amazing and no one is complaining about the 4ohm load... 
atmasphere's avatar
atmasphere
11,973 posts
 
@listening99  Two 4 ohm speakers in parallel is 2 ohms.

You really want to check with the amp manufacturer to see if its OK with a load like that! But generally speaking, the lower the load impedance, the higher the distortion of the amp- and that will manifest as harshness and brightness. After spending the kind of money that high end equipment costs, this (to me) simply seems like not servicing the speaker or amplifier investment $$$$ very well.
unsound
7,336 posts
 
"2 watts of SS power to equal 1 watt of tube power"

...And it takes 2  inches on a tape measure to equal to 1 inch on a rule.


arcticdeth's avatar
arcticdeth
1,572 posts
 
Repeat:

 I’ve been through a min of 7-8 amplifiers over the years, since about 1990 or so.

 Once I went beyond 300WPC @ 8 OHMs, I NEVER looked back.
during crescendos, and power chords, you will need that headroom to keep up,  o clipping. I have two setups......one is 750W @ 8 OHMS, ........second is 600W @ 8 OHMS. 

NEVER CLIP, always sounds careless, amps rarely get hot.
  I have heated up my upstairs system pretty good, while playing at a constant high volume, always sounds good,
  
 You will thank me later.

 These 2W or 150W maps are,nice for a bookshelf, if u have fullrnage speakers,get a,minimum of 200W at @ 8 ohms
  personally, I’ve had no less than a minimum of 500W/chaannel/rms into 8 ohms.

ive never looked back.

just use caution with your volume knob ;)
listening99
172 posts
 
@atmasphere and others, when I read, for example, the power rating for the parasound A 23+, it states:


  • 160 watts x 2 @ 8 Ω RMS, both channels driven
  • 240 watts x 2 @ 4 Ω RMS, both channels driven


My assumption has always been that the top 8ohm figure is relevant to the use of not one but two 8 ohm speakers, as is stated on the website. Your figuring seems to suggest that playing two 8 ohm speakers would imply the second figure, or 240 watts from the combination of the speakers, or 4 ohms?

The also suggests, following what I think I understand of your claim, that few of the amplifiers on the market should be used for two 4 ohm speakers, as they don’t often state a 2 ohm power rating...
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