How much power do you need ?

Matt Horne

Well-known Member
In my continuing quest to buy into a power amp for my system.. I have to ask.. how much power do you really need...

I have a average front room.. and some of the amps I have been looking at (marantz monoblocks / 5 Channel) are rated at 125W per channel.

At the other end of the spectrum if I wanted to go a Arcam route then using P75+ amps gives out about 50W per channel.. a huge difference.

Would I find that the Arcams are overworked? My current Yamaha Amp outputs about 85W a channel.. and I have never run it above half on the dial..

My goals for this upgrade are improved sound quality and musical ability without breaking the bank. (stage 2 will then be a processor which probably will break the bank :) )

Currently I am running Mission M73/M74 floorstanders along with a Mission Centre...

Any advice ppl?




Distinguished Member
u can never have too much power.

gmt steve

Active Member
Half way on the dial is all the useful power an amp has, everything above 1.00 on the dial is distortion.
Plus, the above post says it all.


Absolute power of an amp is irrelevant, it's the actual way the power is delivered, and the amount of distortion. The reason an amp like the arcam p75 has "only" 50W is that you *can* turn the dial past half way without distortion, which might not be the case on an amp with double the numbers. Basically a good quality amp will be able to provide the required current to keep the signal clean across a larger range than a high power-high distortion one.

Ian J

This is another instance where manufacturers massage the figures. Many amps quoting 100w will only be delivering 40w maximum when all channels are being driven. Amp reviews in Hifi Choice quote quite startling real world figures in their reviews.


Active Member
Besides, 50W to 125W isn't actually a "huge" difference. Remember that sound volume only goes up 3dB for double the wattage. To double the volume you have to multiply the power by 10. So 50 to 125 is only about 5dB.



Lots of power is nice and makes the reproduction of dynamic extremes more realistic..... but it isnt everything



One of the problems you'll find is that different manufacturers power figures often don't mean the same thing.
Hence you get some 40W/ch rated amps which are in reality more powerful than some rated at 100W/ch.

All things being equal, a true 100W/ch amp will offer about an extra 3dB SPL in headroom over a true 50W/ch amp - ie, it's really not that much in real terms.

The problem is deciding what is and isn't a true 50W or 100W amplifier.
I think some of the more specialist hifi manufacturers tend to be a bit more honest and open with their specs.
Looking at the electrical label on the rear can give you a rough idea - a budget AV amp rated at 260W, won't be able to deliver 6x100W simultaneously, unless it's the magical "dynamic power" watts :)

Looking at the Arcam P75+, it's rated at 2x50W, with a total max power consumption of 400VA (which is "usually" around about 280W).
Some manufacturers can get 6x100W output, drive a preamp, display and full DSP engine with the same power.
Are Arcam just wasteful ?

I'll leave the conclusion to you :)

EDIT - see what happens when there are no replies, you open a reply window, and then get distracted with some work :)


Originally posted by bob007
Quality over power anyday. :)

but quality power does rule over!

of course there is no need for power if you are using hugely sensitive speakers........



Distinguished Member
actually its a tyre manufacturer


Matt Horne

Well-known Member
So would someone care to comment on the selection below :

These are the sort of amps I am looking at.. this is only the first stage of the upgrade.. my Yamaha AV Amp will be acting as the pre-amp for the time being.. and price is the factor as to whether I can immediately power all channels or only the front 3.

Current Sources :

Arcam DV88 +
Yamaha RV695 DD/DTS Receiver

These are the contenders below :

Marantz MM9000 (5 channel THX Amp) approx £600

Marantz M6100 ( Monoblock THX) x 3 approx £600

Arcam P75+ (Stereo Power Amp) x 2 approx £640

Cyrus XPA (Stereo Power Amp) x2 approx £700




my preference is using stereo amps....... i'd probably put the arcam as my favorite..... but you might as well demo first to find out.



Distinguished Member
Like just about everyone else has said,as much good clean power as you can afford,remembering that some amps deliver much better power despite lower ratings.
I'm lucky enough to have a group of (old) Krells in my system....only 100W per channel,but able to deliver up to 100amps and 800W into a 1ohm load.

Samsung DVD
Linn CD
TagMclaren AV32R
Krell KMA 100 monoblocs
B&W Nautilus 805 speakers
REL Q201 sub

General Skanky

Well-known Member
This has got to be one of my favourite topics.

All that has been said is all true, accurate and well advised.

The reviews in HCC 'only' show power output with 2 channels driven! About a year ago, I asked for the reviews to show true output with 'all' channels driven, but that never came to be. Odd that, as it is an AV mag with 5 or more channel amps.

I think the simple fact you are looking at separate power amps will eventually prove itself to you in the quality stakes. If you can get a demo, I think you'll find the sound really will open right up with a lot more of everything.

The first thought that comes to mind about the monoblocks vrs the Arcam is that 'maybe', the monoblocks will just be more capable on short term peaks in their delivery. More in reseve. However, that'd be on an insensitive speaker load, at higher than normal volumes at a certain impedance dip.

Basically, if you're pile driving a set of insensitive speakers at high volumes, then the more power the better.

The Arcam will be no slouch itself I'd say, but unless it has good reserves, I'd say they'd sound great at more normal levels, ie, not being deafened.

The latest video from AVForums

Movies Podcast: Star Trek in 4K. Is the new boxset worth it?
Subscribe to our YouTube channel

Full fat HDMI teeshirts

Support AVForums with Patreon

Top Bottom