How much power needed.

[Kobus]

Hi,

What size power amp will be optimal for my B&W 803 speakers?. They are rated to 250W.

How does this anyway work, when can an amp be regarded as to small and when will it be regarded as to big?.

[alexs2]

You'll find a few threads here relating to B&W 800 series speakers and their power requirements.

In general,all of the 800 series are a moderately difficult load,and quite demanding in terms of current delivery,especially at low frequencies,which can be a difficult job for many amplifiers.

I use a set of Krells with my 805s,and have found a few other similarly rated amps which struggle with them....my own advice would be to look at not less than 100W per channel,and preferably more,from an amp with very good load tolerance,such as Krell,Bryston,Chord etc,all of which will match your speakers very nicely.

[Kobus]

Thanks,

Is load tolerance just a charactaristic of an amp or is it a spec that one can look for?

[alexs2]

Originally Posted by Kobus

Thanks,

Is load tolerance just a charactaristic of an amp or is it a spec that one can look for?

To an extent it often ends up as an unpublished characteristic,but you can look for things like an amp doubling it's power output as the load impedance halves,ability to drive less than 4 ohm loads(which would be very useful for most of the 800 series),and high current output.

To give an example,my amps are rated at 100W into 8 ohms but will double output as the load halves all the way down to 1 ohm,where they deliver 800+W at approximately 45A.

I'm not suggesting that's what is required,but it illustrates the point reasonably well...all of the amps I've quoted have very good load tolerance and current delivery,and would match the speakers very well sonically also.

[la gran siete]

Can we safely assume Alexs2 that the only amps that do this desirable doubling of power into more difficult loads are expensive ones like Krell, Chord and Bryston and what actually makes them do this? Larger transformer?
I wonder if there are any 70s Jap amps that perform that task? And what make they might be- Sansui perhaps.There is a site that sells a few of these amps/ receivers ie http://www.audiogold.co.uk/catalogue...php?cPath=5_14
http://www.audiogold.co.uk/catalogue....php?cPath=5_9
http://www.audiogold.co.uk/catalogue....php?cPath=5_8
Of course I havent a clue what those products are like but do wonder if they would extricate the last piece of bass from an 8 ohm pair of speakers.

[alexs2]

Originally Posted by la gran siete

Can we safely assume Alexs2 that the only amps that do this desirable doubling of power into more difficult loads are expensive ones like Krell, Chord and Bryston and what actually makes them do this? Larger transformer?
I wonder if there are any 70s Jap amps that perform that task? And what make they might be- Sansui perhaps.There is a site that sells a few of these amps/ receivers ie http://www.audiogold.co.uk/catalogue...php?cPath=5_14
http://www.audiogold.co.uk/catalogue....php?cPath=5_9
http://www.audiogold.co.uk/catalogue....php?cPath=5_8
Of course I havent a clue what those products are like but do wonder if they would extricate the last piece of bass from an 8 ohm pair of speakers.

In general,the ability of an amp to double its power into decreasing loads etc has a lot to do with good power supply design,and in turn,providing the output stages with voltage and current that dont fall dramatically as the load impedance falls,and power demands increase.

In some amps,this is provided by relatively massive transformers,with oversized reservoir caps etc,and in others,massive regulated supplies and so on....Chord adopt a slightly different approach by using switch-mode supplies,but again the answer is a very stable,high current power supply,which equates to a lot of cost,whatever the solution.

A lot of modern amps are capable of either doubling output into 4 ohm loads,or at least going a good way towards this,but very few will do so into 2 ohm loads or less.

Being honest,a lot of those old Japanese receivers and amps were capable of good power into reasonable loads,but really struggled when the going got rough,although many were beautifully made.
One that springs to mind was an Accuphase design rated at 100W with(for the late 70's)amazingly low distortion figures etc,but it sounded awful....very flat and sterile,and really didnt like reactive loads.

My(rather long winded)point is that really good,high powered amps are rarely cheap,and a lot of that cost is in the power supply.

[la gran siete]

Originally Posted by alexs2

In general,the ability of an amp to double its power into decreasing loads etc has a lot to do with good power supply design,and in turn,providing the output stages with voltage and current that dont fall dramatically as the load impedance falls,and power demands increase.

In some amps,this is provided by relatively massive transformers,with oversized reservoir caps etc,and in others,massive regulated supplies and so on....Chord adopt a slightly different approach by using switch-mode supplies,but again the answer is a very stable,high current power supply,which equates to a lot of cost,whatever the solution.

A lot of modern amps are capable of either doubling output into 4 ohm loads,or at least going a good way towards this,but very few will do so into 2 ohm loads or less.

Being honest,a lot of those old Japanese receivers and amps were capable of good power into reasonable loads,but really struggled when the going got rough,although many were beautifully made.
One that springs to mind was an Accuphase design rated at 100W with(for the late 70's)amazingly low distortion figures etc,but it sounded awful....very flat and sterile,and really didnt like reactive loads.

My(rather long winded)point is that really good,high powered amps are rarely cheap,and a lot of that cost is in the power supply.

iIassume by cheap you mean anything less than £1000 .In that site they have an Audio Research D130 power amp and an Inca tech power amp going for less than a grand but they dont give any spec. Do you know anything about those products?

[alexs2]

The Inca's I was never very impressed with personally,but I have always liked Audio Research gear...very well made,reliable and nice sounding....their valve amps are superb.

This little review from the 90's may help...

http://www.audiophilia.com/hardware/d130.htm

BTW,I didnt put a price on performance,but it will be difficult to find amps under the £1k that you've quoted that are capable of that particular trick....it doesnt mean there arent a lot of good sub £1k amps around.

[Kobus]

Interesting, thanks for the informative stuff.

1. Is there an optimal size amp for say a 250 watt speaker?
2. Can an amp get to "big" for a given speaker (I am sure), but at what point?

Thanks

[Steve.EX]

You can never have enough power imho.

[la gran siete]

Originally Posted by alexs2

The Inca's I was never very impressed with personally,but I have always liked Audio Research gear...very well made,reliable and nice sounding....their valve amps are superb.

This little review from the 90's may help...

http://www.audiophilia.com/hardware/d130.htm

BTW,I didnt put a price on performance,but it will be difficult to find amps under the £1k that you've quoted that are capable of that particular trick....it doesnt mean there arent a lot of good sub £1k amps around.

The review doesnt appear to rate it very highly.
If the bulk of budget / mid fi amps are aimed at 8ohm speakers then one is looking at terble and midrange performance but not much bass extension for it is in that area thast a speaker drops to 4 and then 2 ohm which then results in the amp having to ratch up its current delivery which the cheaper amps simply arent capable of. Would that be correct?
Given that dealers want to sell their cheaper amps that would not be information they would willingly give unless they though the punter had the readies to splash out on a plus £2000 amp

[Kobus]

Originally Posted by Steve.EX

You can never have enough power imho.

So more power than the speaker's rated power will can not damage the speaker.

Also is it then fact, in line with what la gran siete (what is that) says, that most receivers (not power amps) will underperform severely with bass, espesially with speakers in the league of B&W 803 etc.

[Steve.EX]

If you are asling for my opinion then the 803's will not be best served on all but the very largest receivers, and then receiver will unlikely thank you for the further additional load other speakers present. I myself would not consider anything other than the sort of amps mentioned above.
It is far easier to harm a speaker via underpowering than simple overdriving, which is almost unheard of in a domestic enviroment. The larger the stable supply the better the transients, and control of will be, amongst other things.
You have some nice speakers it would, in my opinion, be something of a shame to "Yamaha" them up - nothing other than persoanl opinion mind.

Steven

[The Dude]

Hi Kobus,

If you haven't settled on anything in the meantime, one of my Aaron No3 will almost certainly be moving over to Capetown in December... you're more than welcome to a demo with your 803s... I'd be interested to hear the combo myself, whichever way you decide to go...

[Nic Rhodes]

These speakers REALLY need power to drive them, follow Alex or Steve's advice and you won't go far wrong. This is something that you can't compromise on, I have seen MANY examples where B and W owners don't use enough and are not happy. The more the better in my book.