2. home-theater
  3. 140257-119892

Power supply VA rating and how much is really needed

I have a general question. Two actually.

How much capacity of a power supply is needed to allow for each channel in a multi channel amplifier feeding demanding speakers preferred? 

Is 300VA-400VA per channel enough?  Will less be detrimental to performance and SQ? Is more always better?

What are ideal specs for a multichannel ( or stereo amplifier ) that will provide a pleasant experience.  Not looking for the 'best' of the best... but for a decent amp... what are specs that I should be focused upon?

I realize SQ is important, but specs play a role in narrowing down the list I have put together.
--

Second question:

How much output current capacity is need/required/preferred to drive speakers adequately?  And how to calculate the output if the spec isn't given.  I tried google, sadly I didn't find the formula I was looking for.

Is for example 40A enough? Is 30A?  

What factors need I consider in figuring out what spec matters most?

--

My speakers consist of B&W CDM 9NTs with matching center channel.  

Contenders:

Emotiva XPS 5ch
Monoprice 5-7ch 
Rotel RMB1585
Odyssey Stratos 2ch and adding emotiva basX 5-7ch or something like it ... possibly used market parasound, rotel, acurus, etc for surround duties.


Not sure which of these actually have the best specs that translates in to best bang for the buck purchase to provide sweet midrange, tight punchy controlled bass, and nice sweet highs but not to bright.

I know the Rotel is highly recommended based on blending well with my speakers - but when do specs trump sound? Or does it?

I am removing power cords, fuses etc from the equation for a moment.

lightfighter2018
erik_squires
5,268 posts
 
Is 300VA-400VA per channel enough? Will less be detrimental to performance and SQ? Is more always better?

That's about 300-400 Watts per channel. Simultaneously. That's quite a bit.

What are ideal specs for a multichannel ( or stereo amplifier ) that will provide a pleasant experience. Not looking for the 'best' of the best... but for a decent amp... what are specs that I should be focused upon?

This is really dependent on the size of the room, the efficiency of your speakers and how close you sit to them. The efficiency of the speakers can vary by huge amounts. Get theater grade horns and 10-20 watts will be too much.

I think it's also important to note that 300-400 watts / channel is 1,500 - 1,600 simultaneously.

Specs never trump personal preference, but they do ensure that manufacturers don't try to cheat you too badly.

Best,
E
lightfighter2018 OP
75 posts
 
@erik_squires 

Just to clarify. And maybe I worded it unclear.  

I was asking about capacity of power supply. Ex: A 2 ch amp with a Tor PS of 1100VA ... you are saying it translates into 550w per ch? That doesn't makes sense if amp is rated at 8Ohms at 200wpc... 

If it was unclear - I want to know how much power a PS should have to drive difficult speakers... and how much output in current is suggested... 45A etc?

Sorry if there was confusion.

erik_squires
5,268 posts
 
VA = AC watts.

This is really the upper limit of what the power supply can deliver.

However, the actual wattage spent is the power consumed by the speaker divided by some efficiency factor. So
200 Watts at the speaker / .6 = 266 VA continuous required. Probably more. LOTS more if class A. Class D, use about 0.8

Also, watts at the speaker are impedance dependent. Half the impedance = 2x the power required. 
A stiff 200 Watt amp at 8 Ohms may do 400 Watts at 4. If very stiff, 800 Watts at 2 Ohms.

Still, the power supply limits all, so if you have 550 VA available per channel,  you'll be lucky to see 330 max at the speakers.
Further, this is all compounded by the fact that music is dynamic. Short term power delivery may be more important for music than steady state.

Fun stuff, right? :)
E
More to discover