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Speaker Power Amp Requirements and Suggestion

M

metaturtle

Member
Hi, I've got a pair of Missions SX2s and I am in the market for a new power amp. Based on the specs (see below) I have worked out that a suitable amount of power would be 150W into 6 Ohms. However, the specs say that the peak load handling is 103W.

Can you advise on a suitable amount of power I would need for these? Should I not exceed 100W?

Additionally, do you have any recommendations for a sub £500 power amp? Either new or old is fine, preferably solid state with a toroidal transformer. For reference, I've got a Croft Super Micro Valve Pre.

I have been considering one of the below:
  • Arcam Alpha 10P
  • Cambridge Audio P500
  • Audiolab 8000P
  • Emotiva BasX2 (this one is 160W into 8Ohms so feeling it's too powerful)
Thanks!

Specs
Sensitivity85dB (1w @ 1m)
Reccomended amp power20-100W
Peak power output100W
Peak SPL102dB
Impedance6-8 Ohms nominal impedance

3.9 Ohms minimum impedance
Frequency Response58Hz-42kHz
 
these would be superb

www.maverick-hifi.com

FOR SALE.. Acoustic Reality 1001-Ref 500wpc. Now inc delivery.

As I have sold on the two pairs of speakers that I used with these amps, I cannot demo them at home. So delivery included, insured in the price. 500wpc into 8 ohms. I was using these with my Maggies 1.7 and Kef ref 104/2. Both sounded wonderful. Both of which I have since sold. All the power...
www.maverick-hifi.com www.maverick-hifi.com

no toroidal though
 
metaturtle said:
Hi, I've got a pair of Missions SX2s and I am in the market for a new power amp. Based on the specs (see below) I have worked out that a suitable amount of power would be 150W into 6 Ohms. However, the specs say that the peak load handling is 103W.

Can you advise on a suitable amount of power I would need for these? Should I not exceed 100W?

Additionally, do you have any recommendations for a sub £500 power amp? Either new or old is fine, preferably solid state with a toroidal transformer. For reference, I've got a Croft Super Micro Valve Pre.
Click to expand...

Why do you value a toroidal power traffo over, say an old-style 'EI' one?

And I suggest your "power requirement into 6 ohms" calculation is a bit simplistic. It is more important what the minimum spkr impedance is; if it is low then the amps which @hifinutt recommended ... would undoubtedly be superb.
 
You can exceed 100W in your amp, but just don't use it all. You won't anyway, unless you have a teenage party and leave them to their own devices to "see wot it will do". 100Wpc is deafening in any domestic situation. As others have said a 200W amp is safer for speakers than a 50W amp because at 50W it is strolling in the park, with no distortion, no clipping, etc.
 
andyr said:
Why do you value a toroidal power traffo over, say an old-style 'EI' one?

And I suggest your "power requirement into 6 ohms" calculation is a bit simplistic. It is more important what the minimum spkr impedance is; if it is low then the amps which @hifinutt recommended ... would undoubtedly be superb.
Click to expand...
I'm haven't read enough literature on the merits of different types of transformers. It's just that I have a vague notion that toroidal transformers tend to deliver warm and punchy bass though I suspect there might be a deal of sneak oil in that. Would you say that the transformer technology is not that important?

Fair point regarding my power calculations. Would you say 3.9 Ohms minimal impedance is low enough for the @hifinutt's recommendation?
 
hifinutt said:
these would be superb

www.maverick-hifi.com

FOR SALE.. Acoustic Reality 1001-Ref 500wpc. Now inc delivery.

As I have sold on the two pairs of speakers that I used with these amps, I cannot demo them at home. So delivery included, insured in the price. 500wpc into 8 ohms. I was using these with my Maggies 1.7 and Kef ref 104/2. Both sounded wonderful. Both of which I have since sold. All the power...
www.maverick-hifi.com www.maverick-hifi.com

no toroidal though
Click to expand...
Amazing, thanks! Will check these out.
 
stevec67 said:
You can exceed 100W in your amp, but just don't use it all. You won't anyway, unless you have a teenage party and leave them to their own devices to "see wot it will do". 100Wpc is deafening in any domestic situation. As others have said a 200W amp is safer for speakers than a 50W amp because at 50W it is strolling in the park, with no distortion, no clipping, etc.
Click to expand...
That's fair. I suppose I was concerned about potentially overloading the speakers. No pesky teenagers here so shouldn't be a problem.
 
I run my LS3/5As (power handling 15w "speech and music") with a NAIM NAP250 - 80wpc. Never had an issue if you're sensible.
 
metaturtle said:
That's fair. I suppose I was concerned about potentially overloading the speakers. No pesky teenagers here so shouldn't be a problem.
Click to expand...
It's not the fault of the equipment but who's operating it! Now of course you *can* overload a pair of speakers rated to 100W RMS but you would need to be in the next street in order not to be deafened. 100W is nightclub stuff.
 
awkwardbydesign said:
Too much power is better than too little, as driving a lower power amp into clipping can destroy tweeters.
Click to expand...
This.

There's really no such thing as "too much power" when it comes to speaker matching in the sense of being a danger to the speakers. Theres is of course a point where all the extra power of the amplifier is pointless though. But that does depend a lot on the speakers themselves (as said above in relation to speaker impedance etc).

As an aside. Two speaker measurements that are probably a more useful guide than the "power handling" of the speaker, are the max SPL they're capable of, (though a lot of manufacturers don't tell you that number) combined with their sensitivity. Using both you can work out what power of amplifer would be required to theoretically push the speakers to their maximum ouput.

For example: If you have a pair of speakers with a sensitivity of 87dBA for 1W and a maximum ouput of 108dBA (from a pair)*, then you can calculate the following:

1 pair @
1W = 90dBA
2W = 93
4W = 96
8W = 99
16W = 102
32W = 105
64 W = 108

So a 64W amp would be sufficient to already drive such speakers to their maximum power handling. For such speakers I'd probably be looking to use a minimum of an 80W per channel amplifier, to allow for the fact speaker sensitivity is taken with a single 1khz tone and to also allow for extra power to deal with the fluctuations of speaker impedence at other frequencies than 1khz. Most speakers have their lowest impedences somewhere below 1khz.

*Both figures being at 1 metre.

NB: This is why there is too much emphasis placed on differences in wattage between amps with high power outputs IMO. Especially once you get over 128W. 256 W will only gain you 3dBA in volume, and 512W will again only gain another 3dBA.. So the difference between say a 250W and a 300W amp is (all things being equal) totally inconsequential, it amounts to a fraction of a dBA of extra output. The only reason to use such amps is if the speakers are dipping down significantly below 4ohms (particularly with large phase angles at the same point).
 
metaturtle said:
I'm haven't read enough literature on the merits of different types of transformers. It's just that I have a vague notion that toroidal transformers tend to deliver warm and punchy bass though I suspect there might be a deal of sneak oil in that. Would you say that the transformer technology is not that important?
Click to expand...

My understanding is that EI traffos filter power supply nasties better than toroids do. In spite of this ... toroids are more popular these days.

I've never come across the idea that toroids deliver better bass than EIs.

metaturtle said:
Would you say 3.9 Ohms minimal impedance is low enough for the @hifinutt's recommendation?
Click to expand...

3.9 ohms is low - but not drastic. 3 - or even 2 - ohms is a problem.

To drive these sorts of loads well, the power amp spec needs to show it is able to "double down" into 4 ohms - and be stable into 2 ohms.
 
Of the amps listed in the OP, dump the Cambridge A500, it is nowhere near the SQ of the Audiolab or Arcam amps.
Instead replace it with either a Rotel 800 or 900 series.
In the past I've had and used an Arcam 8P & Rotel 9xx as a summer amp in my main rig. Both stonking amps for their modest used price, the Rotel being tight and punchy whilst the Arcam was a tad smoother and warmer.
 
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