Stupid Power amp question

[Lerxst]

Hi,

I have an 80 watt power amp. The household name varieties start at 500 watt. Ish.

Power (watts), in this context, is not linear as I understand it, so a 100 watt system with be 2x as loud as a 10 watt system - outside.

Indoors, there are other factors, like resonance and reflections which will, I assume highten the difference in volume.

500 watt would at first sight seem like overkill for me. I am told a higher power amp will be able to deliver dynamic music faster (ie it can draw on more reserves quickly). That sounds logical and desireable.

I have never owned a 500 watt power amp but I suspect some of you may have. So, if I were to buy a 500 watt amp and hook it up to the same pre-amp I am interested to hear from members what happens in practice.

With the 80 watt amp a nice listening level is at about 10 o'clock on the volume dial on my preamp. 75dB ish. No audible distortion.

What happens with the 500 watt amp? Is the 10 o'clock setting still the same volume level?

It is louder? Or is it the "reserves" that are important? If were much louder the volume control would become less adjustable/useable. That sounds like a rubbish idea

I guess it would be able to drive higher resistance speakers, or more speakers.

And why isn't 80 watt enough anymore? Mine is fine.

So, any experience on that front? I haven't got a few grand lying around to test it, so it will not happen in practice. Just interested. I feel I should know the answer, but I don't.

Over to you. Thanks in advance.

[walpurgis]

You do realise that 500 watts will only give something like 8db increase in maximum loudness over 80 watts?

[Lerxst]

Hi Geoff,

Yes, I get that. Let's say for argument's sake that it is twice as loud (+10dB). Would my volume control be half as sensitive?

[jandl100]

The volume knob will stay in the same position (assuming amp sensitivity is the same, which is totally unrelated to power).
As you say, it's all in the reserves which are available for peaks.

I've had 300 - 500wpc amps - some of which I liked and some of which I didn't, just on sound quality grounds.

So if you love your 80wpc job, then it's a sound quality lottery as to whether you would prefer a 500wpc amp. It will sound different, but that will not be very strongly related to the power available.

Some speakers, though, present difficult loads and would welcome the extra power (or, more likely, would welcome extra current delivery) and you would hear that as an improvement in sq, but by the sound of it you have a good amp/speaker match already.
As ever, it all depends ...

[Jazid]

The volume knob will stay in the same position (assuming amp sensitivity is the same, which is totally unrelated to power).
As you say, it's all in the reserves which are available for peaks.

I've had 300 - 500wpc amps - some of which I liked and some of which I didn't, just on sound quality grounds.

So if you love your 80wpc job, then it's a sound quality lottery as to whether you would prefer a 500wpc amp. It will sound different, but that will not be very strongly related to the power available.

Some speakers present difficult loads and would welcome the extra power (or, more likely, would welcome extra current delivery) and you would hear that as an improvement in sq, but by the sound of it you have a good amp/speaker match already.
As ever, it all depends ...

Assuming like for like amps (of course they won't be but...) along with the 10dB increase in power output you will get a 10dB increase in noise floor which may make a more significant difference as this is independent of listening level so may be audible when listening at low levels.
I do not see the need for extra power, although I had a 250wpc amp once and liked it very much. I have a 25wpc amp in the home system and occasionally the 5w LED flickers if the music is very very loud. Speakers are average efficiency. 6wpc amp in the main system with the AN-Es and its more than I need.

Sent from my GT-I9195 using Tapatalk

[Haselsh1]

I currently (geddit) use a 40 Watt valve amplifier but have in the past used a 300 Watt per channel studio power amp. The difference was quite simple really. The valve amp has a more explicit treble whereas the transistor amp had an effortless bass which never seemed to run out of sheer grunt. The valve amp is, I guess, a whole lot more refined though. Do I prefer it ? No. I liked both of them.

[walpurgis]

I used to drive my low 84db sensitivity Celestion SL600Si speakers with a pair of 15 watt valve monoblocks with no difficulty and I've driven 102db sensitivity horns with a 220 watt mosfet power amp, so really, anything can work, but of course common sense applies.

50 watts will be more than enough in most situations. Buy active speakers and then the power of the amp is already decided for you!

[Haselsh1]

I used to drive my low 84db sensitivity Celestion SL600Si speakers with a pair of 15 watt valve monoblocks with no difficulty and I've driven 102db sensitivity horns with a 220 watt mosfet power amp, so really, anything can work, but of course common sense applies.

Of course Geoff and your experience here proves it. Common sense always. I seriously loved the first Celestion SL6's though but not with valve amps. I didn't discover valves myself until many years later but I remember hearing a track by Joan Armatrading at a dealers place on SL6's and it sounded sublime. That would've been around 1981/82. Those vocal sounds were stunning.

[Pharos]

My take.

Firstly are you happy with your current speakers? Speakers are the most variable component IMO, and they should be chosen after careful auditioning.

Then choose an amp which will best suit the speakers, the speaker variables being; sensitivity, ease of drive, some speakers end up presenting negative impedances at some frequencies, and this demands very high current capability from an amp. (Current capability was a much discussed issue in the late 90s, and is needed for difficult loads), and how loud you want the system to be, (IME we can listen too loudly when we actually want is clarity).

Of course you may have a preference for valves over SS, or vice versa, my personal view is that SS have it nailed, and that the lack of maintenance is a real bonus, but I am not decrying the love of valves.

The position of a volume pot is not really much of an indicator of anything because sensitivities are not standardised, but a useful range of sweep is of course desirable.

I would not recommend listening at more than 80dB for extended periods, and even that can do ear damage, and the range of speaker sensitivities is from about 83 to 105dB/W. Even at the low end of 83dB sensitivity, your 80W will give you about 100dB.

[RothwellAudio]

Let's say for argument's sake that it is twice as loud (+10dB). Would my volume control be half as sensitive?

No, not necessarily.

The volume knob will stay in the same position (assuming amp sensitivity is the same, which is totally unrelated to power).

Amp sensitivity is usually/often specified as the input voltage required to deliver full power. In that case, a 100W amp with the same sensitivity rating as a 10W amp will actually have more voltage gain and be more sensitive, ie louder for a given position of the volume control.
But yes, sensitivity doesn't have to have any relation to total power.

Assuming like for like amps (of course they won't be but...) along with the 10dB increase in power output you will get a 10dB increase in noise floor which may make a more significant difference as this is independent of listening level so may be audible when listening at low levels.

Yes, maybe. Or maybe not.


It's actually more useful to consider power amps as voltage amplifiers - in fact, that's what they are. The power rating is really only a measure of the maximum voltage swing they're capable of into a specified load. The gain of a voltage amplifier could be anything, and power amps have gains covering quite a range. About 30dB is typical, but it could be more or it could be less, and it has nothing to do with the maximum power available. It's quite common for valve amps with only a few watts available to have a higher than average voltage gain and be very sensitive. But that isn't always the case.

It's also unwise to assume that more power equals a better amp. It's quite possible to design a low power amp that performs beautifully, and equally possible to design a high power amp that sound horrible.
50W should be enough in a domestic setting - unless you like it really loud - and if it sounds good there's no need to worry. I suspect the trend towards higher powers is driven by the idea that customers are more likely to buy a 100W amp than a 50W amp, and modern semiconductor technology has introduced more transistors that will cope with higher powers.