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[heymjm]

Originally Posted by heymjm

Can I second this request. You can never have enough power

The above comment was written in haste and a bit tongue in cheek ..... but it got me thinking - can you have too much power? To take a specific case, if you have a pair of WD25As in a medium/large room, say 20 sq metres, what is the ideal amplifier size to get realistic volume levels? Is 40 'valve watts' OK or do you need to hook up something like a Musical Fidelity A5 packing 250 watts, or even more from one of the new Class D amps which are starting to appear?

regards

Malcolm

[NickG]

Well the classic problem is if having a amplifier that can produce 40w means that the first watt, or 0.1w is naff, then yes you can have too much power.

[petercom]

Originally Posted by Will Cowen

Peter, more info needed, nice to know how thick damping materials etc. are but need more dimentions.
Will.

Sorry about that, paste didn't work properly, now corrected!

[petercom]

Originally Posted by heymjm

The above comment was written in haste and a bit tongue in cheek ..... but it got me thinking - can you have too much power? To take a specific case, if you have a pair of WD25As in a medium/large room, say 20 sq metres, what is the ideal amplifier size to get realistic volume levels? Is 40 'valve watts' OK or do you need to hook up something like a Musical Fidelity A5 packing 250 watts, or even more from one of the new Class D amps which are starting to appear?

regards

Malcolm

Like everything it is a question of balance. For transistor amps you really need 75W or more for a typical loudspeaker of 87dB/W efficiency because transistor amps use feedback and this 'holds back' the dynamics subjectively. They also sound very nasty when run into overload, as well as doing unspeakable things to speaker voice coils, so the more power the better.

However in order to get high power you usually need to run in Class B. This elicits crossover distortion which is pretty horrible subjectively, so most amps run in Class AB where the output devices are biased partly switched on. This means that small signal outputs will be handled in Class A too, which is a bonus.

It doesn't hold a candle to true class A, though, where each device is permanently switched on. This is inefficient in terms of power consumption and heat, though, as the output devices consume at least half the available power even when there is no signal. Class A transistor amps get very, very hot and need huge heatsinks to cope.

Don't get me started on Class D. It may be OK for subwoofers but for full range music? I don't think so (and before you ask I have tried them, even the TACT range).

So, in my view, it makes sense to use valves where you want Class A. Valves also have the advantage that they don't need anything more than local feedback for subjectively low levels of distortion. They also clip more gradually and generally don't sound horrid when they do.

So if you consider that, with a pair of 90dB/W speakers like the WD25s, you will be operating normally in the 1 - 2 Watt region with occasional dynamic excursions into higher powers, the clipping behaviour of valve amps allows you to get away with less maximum power for subjectively the same results.

We could have designed our amps to run in Class AB enabling us to get 80W out of a KT88 design. But there is little to be gained. Remember that doubling the power gives you only 3dB extra dynamic range. Far better to get that from sensitive speakers and lessen the work done by the amplifier. 40 W of nice KT88 Class A amplification runs very nicely into WD25s even in large rooms.

[Gerry]

Peter

I accept what you say and agree.....but:p ...the 40watt Class As just cannot control or drive a planar speaker in the way they require.
I am a convert and will never go back to boxes...hence my question and the quandry.
In AB most of the sound is produced using A ......only the odd foray into B.
I have used EL34 32watt, 5661/KT88 40watt and finally settled on a EL34 85watt amp just b/c the sound was so much better due to the control.

Regards
Gerry

[NickG]

I am not sure just how a amplifier of higher power will produce more "control". Maybe its a question of the damping factor, and the higher power amp happens to have a lower output impedance.

[vitalstates]

I think I might have lost the plot here.....surely maggies need the speed rather than the 'hard to describe - control'...theres nothing in them to control, except maybe a couple of square feet of air...its not like you're trying to move ounces of paper, plastic and coil all over the place.

Could I be a bit controvertial and suggest that the circuit in the el34 amp might have been slightly different, and its that difference that you've identified as being nice, not necessarily the power?

regarding control, perhaps you do need a tad more during anticyclonic conditions...tee hee just kidding

Ed

[Gerry]

Nick/Ed

I don't know how else to describe it other than control....but it is true...try some.
Bit like Quads which have been known to "crowbar" amps (HFW term).
They are very ineffient...83/84db at 4ohmms.
Once tried a 18w amp,loaned to me by Nick at the Emporium...I took it back not impressed....he understood why when he realised what the speakers were.

Regards

[funk hunter]

Peter,

Great news about WAD supplies. Having thought about taking the plunge into the world of valves & kits for some time, I finally ordered my first kit last November.....hopefully you can end my wait.
Will you be selling the PHONO-ll,PSU-ll & PRE-ll, if so, when do you think, if not, are you going to develop your own WD design.
It seems to me these simpler kits are a great "in" to kit building, as all going well with the PHONO/PSU I hoped to tackle a power amp kit (blimey, look out for the "unfinished project" on ebay).

Cheers, Francis.

[vitalstates]

Hi Gerry

this is a bit OT here so I'm embarrassed to continue, but check out my 211 thread under amps.....my diy electrostats are a pig to drive since I ditched my meridian MPA but the WAD 6550(at half the power of the meridian) makes a thoroughly decent job of it(much better in all but one respect). I can guarantee that my stats are a much wilder demand than your maggies......but I wont get controversial and start discussing sonic comparisons..

regards

Ed