Stupid Power amp question

[Yomanze]

Just to make things a bit more complicated, watts for amps are measured as a continuous sine wave rating, which does not reflect the dynamic nature of music and what happens during musical peaks.

For example, there might be a 250W amp that measures well for THD in the traditional way, but has low instantaneous current delivery. A lower wattage amp, say 90W, could be able to deliver short peaks of 900W or more. A lot of people seem to mention how Colin Wonfor's amps, whilst only 10W or 20W, seem to have extreme grip of the speakers, more so than 100W+ on paper amps. This will be due to the amp having high instantaneous current delivery i.e. the amp can quickly dump current into the speakers during musical peaks.

[Haselsh1]

Just to make things a bit more complicated, watts for amps are measured as a continuous sine wave rating, which does not reflect the dynamic nature of music and what happens during musical peaks.

For example, there might be a 250W amp that measures well for THD in the traditional way, but has low instantaneous current delivery. A lower wattage amp, say 90W, could be able to deliver short peaks of 900W or more. A lot of people seem to mention how Colin Wonfor's amps, whilst only 10W or 20W, seem to have extreme grip of the speakers, more so than 100W+ on paper amps. This will be due to the amp having high instantaneous current delivery i.e. the amp can quickly dump current into the speakers during musical peaks.

Yep, I have found the same from experience over the decades but surely this ability has a lot to do with the amplifiers power supply ? I am certainly no expert but the power supply must be able to deliver huge chunks of power in an instant ?
I don't understand it but I sure as hell love the sound it gives.

[Yomanze]

Yep, I have found the same from experience over the decades but surely this ability has a lot to do with the amplifiers power supply ? I am certainly no expert but the power supply must be able to deliver huge chunks of power in an instant ?
I don't understand it but I sure as hell love the sound it gives.

I’m not expert either but yes it is pretty much all down to how quickly current can get delivered, and how stiff the power supply is I.e. doesn’t drop voltage or clip during peaks.

[bobvfr]

Another non expert here.

Firstly 500w is meaningless by itself, for a start off a lot of amps are now shown as 500w, if that is into 4 ohm and that would be pretty dammed close to another amp for sale at 250w into 8 ohm.

If my understanding is correct, if everything is about equal (Same input and same speakers etc) to double the volume you would need to go from say a 100w amp to a 200w amp and this would give you about a 3db increase in sound intensity, to double it again you would need a 400w amp to get to about a 6db gain over the 100w amp but I would guess there is a lot more to this especially the way a lot of "Hi-Fi" is both measured and marketed.


Someone mentioned "Only gaining 10db", again not claiming to be an expert but a 10db gain on a logarithmic scale is massive increase in sound levels as, at the higher end of the scale it would be the difference between putting your hands over your ears in pain or "too late you have burst eardrums", by going up 3db you have doubled the sound intensity, so by going up 10db you have doubled, doubled again, and then doubled again with a bit more thrown in for good measure.

I have an 80w Pioneer receiver (I only use stereo) that 80w is into 6 ohm so probably only about 55/60w into 8 ohm speakers, but even then you have speakers with massive differences in sensitivity, I have a pair of Tannoy Cheviots, these were considered a reasonably sensitive speaker, and they can easily take the full power of the Pioneer, given I live in a flat, I would be asked to move out pretty quickly if I ever put it on full blast.

I also have a 40w Aiwa and Quad 33 pre amp with a Quad 405 power amp that is 100w into 8ohm and is a lot more powerful than the Pioneer but luckily it has a volume control dial on the pre amp so I can turn it down, but given the sensitivity of the Tannoy's all three amps could get me thrown out of my flat with ease, but the Quad's are capable of causing long term hearing loss.

As someone else mentioned if the sound you get from your gear is fine then don't get hung up on the figures and only worry about the power of you amp if you are needing the volume dial up at 9 or 10 (Out of 10) to get it to sound normal, if your speakers need a bit more poke then buy a bigger amp so you can produce the same sound with a lower volume setting as most amps would be designed to work somewhere in the middle ranges of volume.

[Haselsh1]

If my understanding is correct, if everything is about equal (Same input and same speakers etc) to double the volume you would need to go from say a 100w amp to a 200w amp and this would give you about a 3db increase in sound intensity, to double it again you would need a 400w amp to get to about a 6db gain over the 100w amp but I would guess there is a lot more to this especially the way a lot of "Hi-Fi" is both measured and marketed.

Yep, inverse square law methinks the same as light.

[paulf-2007]

Doesn't make much sense and it doesn't seem that anyone has explained it. A 500w amp in a hifi set up can only mean the speakers are dogs, too much old crap between the binding posts and drivers. I know scanspeak drivers are very inefficient.
Not completely off topic, I used to play in bands and in pubs I used a 20w valve Marshall with plenty of spare power on tap, obviously no crossover as all drivers, whether one, two or four were ran full range of whatever came from the amp. In my home set up I have used 4w PX25 into Zu omen but now use a Sony receiver, solid state of course and more horses, controls the bass much better. I would have to say of the set ups I've heard with huge bel canto and other big ss amps they sounded very ordinary, probably due to the inefficient speakers.

[RothwellAudio]

I used to play in bands and in pubs I used a 20w valve Marshall with plenty of spare power on tap...

Guitar amps are a different kettle of fish because they're hardly ever played clean - at least not by people looking for the classic rock sound. A hi-fi played with the same amount of distortion as a typical guitar amp would sound awful.
But I agree, if you want it loud it makes sense to go for efficient speakers rather than trying to push ever more power into inefficient speakers.

[paulf-2007]

Guitar amps are a different kettle of fish because they're hardly ever played clean - at least not by people looking for the classic rock sound. A hi-fi played with the same amount of distortion as a typical guitar amp would sound awful.
But I agree, if you want it loud it makes sense to go for efficient speakers rather than trying to push ever more power into inefficient speakers.

yes Andrew, I was aware of the distortion from guitar amps and it being what was wanted, strangely, the solid state guitar amps in the '70s sounded dreadful and I avoided them for decades.

[Colin Wonfor]

The problem has and always has been how manufacture specifies Watts.

I rate my designs in RMS or if you like the equivalent to DC power.

Others spec there's in Peak Music Power or even Peak - Peak music power. This type of spec IMO is crap and meaning less, so beware of the Techno Babble ask for real Watts in RMS.

Also some will spec in RMS but it is for a short time I spec mine at RMS all day not just 10 or even 20mS, dissipation is the problem and over heating can occur.

Also the PSU design is normally the last thought in a standard audio designer head, and in my designs I design them to be big enough plus a horrid load bit added and using my favourite saying give us a KISS.

I also allow for 0.5V2C = J or W/S energy stored in my Bulk Caps and to have reserves available. For horrid loads.

Sorry about the grammer and spelling but I am not a writer. Thank god.

[Yomanze]

I couldn’t give a monkeys about your grammar, some of the brightest people I have met are dyslexic, and some of the least bright people I have met spend time correcting grammatical errors. You’d think such clever people would be able to read posts regardless.