anyone else using these?

[Roly]

I understand the 100-watt rating is the rms rating and not peak.

This requires some clarification, so I'll take a shot at it.

Firstly, 100 watts (RMS*) of audio is a LOT of power.  With speakers of respectable efficiency this will result in a Sound Pressure Level (SPL) one metre in front of the speakers well in excess of 120dB (e.g. 135dB).

When listening to a personal music system with stock earphones at a maximum volume, the sound generated can reach a level of over 100 dBA, loud enough to begin causing permanent damage after just 15 minutes per day!

    A clap of thunder from a nearby storm (120 dB) or a gunshot (140-190 dB, depending on weapon), can both cause immediate damage.

Quoted permissible exposure times for various levels differ depending on a few things such as the frequency of the sound and local OH&S laws, but there is no doubt that exposure to levels in excess of 120dB_SPL for more than a few minutes can lead to permanent loss of hearing (not to mention tinnitus or ringing in the ears, which is incurable)


* Strictly speaking the term "Watts RMS" (Root Mean Squared) applied to a power level is not correct, but it has a well defined meaning to guitarists (and techs) which I would state as - "the power level at the onset of clipping which can be sustained by the amplifier for at least 30 minutes".  These are sometimes called "thermal watts" because they will produce real heating in a water load, that is it takes real watts sustained to boil a jug.

It is significant that watts RMS for an AC circuit (your amp output) are exactly equivalent to watts in a DC circuit such as a resistor connected to a battery - the heating effect is identical.

The reason for this definition arose when Hi-Fi marketing people started inventing some silly power ratings to make their amplifier appear to be more powerful than the competition, "peak power", "music power", "peak music power output - PMPO", "peak-to-peak music power", and so on.  This is where we see puny computer speakers that actually produce only a watt or two with absurd ratings such as "400 watts PMPO".

The "logic" behind this is that domestic sound gear is often built with an economised power supply (transformers being relatively expensive items), and while it may be able to make, say 50 watts for an isolated sudden cymbal crash, when presented with some solid wall-to-wall death metal it will buckle at the knees and produce maybe a sustained 10 watts (which also explains why a "50 watt" home stereo makes a truly hopeless guitar amp).

The underlying justification for this is that most recorded music has a duty cycle of 30% or less.  This is also the reason why you sometimes see reference to "tone burst" testing where an amp is subject to say 100 cycles of 1kHz on a 10% duty cycle - driven to full power for 100mS then allowed to recover for the rest of the second, and naturally produces some rather inflated power figures.

This marketing crud does not apply to stage amps, guitar, PA, etc., where the duty cycle may be a full 100% for many minutes at a time, and which are therefore rated on a much more conservative basis of the ability to deliver continuous power for a whole gig (without producing smoke) so such amps normally have real deal power supplies with hunky transformers that can hold up their end of the plank.

Tone bust testing applied to a typical guitar amp will produce some pretty unimpressive figures, say 10% more power, simply because the supply is very stiff and capable and doesn't sag much worth talking about.  There is always some supply sag, so the burst power will be a little bit higher than sustained, but not by much.

This is not to say that there isn't occasionally some number inflation, particularly with smaller amps from unknown manufacturers, but these days the stage world has thankfully adopted "Watts RMS" as the most conservative and dependable benchmark for comparing amp output.

So, if you applied a tone burst measurement to a name amp such as your Yamaha I would expect it to return a peak power figure of perhaps only 110 watts.  This low ratio of impulse to continuous is not bad, it's good; it means that the power supply is very solid, not sloppy and under-designed.


Now at the risk of confusing matters we need to take a closer look at what is happening with the amp output driving the speaker load.

Say this is a signal coming out of the amplifier;


This shows the relationship between Volts_RMS and the peak voltage of the signal Volts_peak (and also Volts_peak-to-peak which we can ignore here).

V_RMS is the equivalent of the DC voltage that would have the same heating effect (watts) and is 0.707 (1/root(2)) of the peak voltage.  It is inviting to think that the ratio between watts_RMS and the peak wattage would be the same ratio, but it isn't.

The power in a circuit is given by;

P = E²/R
  Where:
  P is the power in watts
  E is the voltage, and
  R is the resistance (or in our case the speaker impedance or "ohmage", which is assumed to be constant).

So power is proportional to the voltage squared, E * E.

The upshot of this is that the power at the peak of the wave is double the RMS power.

In practical terms this is about the same as saying that 100mph is the same as 160km/h; it does not mean that you are going 60% faster, just a different way of expressing the same thing.

Now when an amp is driven hard into overdrive and produces square waves the effective power is considerably more than the power just at the onset of output stage clipping, but since this applies equally to any well designed amp we are again effectively comparing speed in MPH to speed in KPH, and all well designed amps will perform (roughly) equally in this respect.

tl,dr; the only power that really matters is "watts_RMS" at the onset of clipping.


The reason it stays clean (until your ears bleed) is because it's basically a V-8 with a huge amount of stoke, raw power - your ears will overload before it does, and has nothing to do with any small difference between momentary power (1/10th of a second) and sustained power output (3 min 50 sec of a song).

As an aside, these Yamaha amps are the only one I've ever seen that quote actual power in the air, 1.5 watts for the 100 watt unit, and gives you some idea just how inefficient loudspeakers are in converting watts electrical into watts acoustic, and why speaker efficiency is an important "sleeper" detail to most guitarists; why only a few extra dB_SPL per Watt can make a really significant difference to the apparent loudness of a given amp, and why one amp of a given power may sound louder than another of the same power.

{I'm ready to take delivery of my beautiful Air Hostess now...  <3) }

[Enzo]

what he said^^^


Those "RMS watts" are the only real comparison of amps.   All that peak watts is nonsense.

Allow me:
Imagine a 900 pound piano sitting there.  Can you lift it?  Probably not.  How much can you lift?  200 pounds?  250?  maybe 300?   Now imagine that 900 pound piano is on top of your foot, you are trapped.  (OK, it is a steel toed boot, so you are stuck but not injured)  You grasp the piano and yank it upwards with all your might.   It moves just enough for just long enough that you could pull your toe out from under there.

That 200/250/300 pounds is your RMS lifting ability.  The 900 pound momentary jerk is your peak lifting ability.   The peak reading is not really a very useful or practical thing, but it sounds more impressive to say you can lift 900 pounds instead of 200.

[J M Fahey]

{I'm ready to take delivery of my beautiful Air Hostess now...  <3) }

Ok, you earned it , but why travel all the way to Argentina?

I suggest you fly (almost local) NZ Air and take your pick.

http://youtu.be/DZRmcKX85so

Only problem is, they seem to be cutting costs to remain competitive so, among other things, their uniforms are not what they used to be

[ChewyNasalPrize]

Man! Great explanations!

So do some amp companies market their "peak" rating as if it were an "RMS" rating? I hear guys talk about an amp's rating and and say something like "true RMS" meaning (I guess) that it can produce that level all night long no sweat. But then what is "not-true RMS" ? ? Peak- but marketed slyly to give the impression of RMS?

I totally agree with speaker efficiency too. I replaced several speakers in some older otherwise stock combos with either new Eminence or WGS speakers and was amazed at not only the volume boost but the overall improvements in brilliance, fullness and clarity.

I really thought I struck a gold mine by finding a way to make these old amps that other people are practically giving away sound SO much better with a simple speaker swap! But people still look at it and say, "Oh, it's an old Peavey- I'll give you ten bucks for it." 

[Roly]

why travel all the way to Argentina?

Why not?  It's only "just over there", and you could take me to one of your famous BBQ's and I could try a side order of pickled armadildo.   

Man! Great explanations!

Phew, not bamboozeld then.  Good.

Yep, "true RMS" simply emphasises that point, but just "W_RMS" should be sufficient.  Normally these days you can safely assume that "Watts" means "W_RMS", but with cheap no-name amps, and particularly with eBay YMMV.  One thing you do find on eBay, and it's often an honest mistake, is to take the amp power consumption printed on the rear as the amp power.

All you need to know is that a typical amp power stage is no more than 50% efficient, so this figure will typically be about double the actual output power (maybe plus a fudge factor, particularly for heaters in a valve/tube amp).  Normally if it says on the front panel something like "Golden Chook 50" then it's generally safe to assume that 50 watts RMS output is in the ball park.

I used to have a party trick where I would hook up a pocket transistor radio (or these days it might be an MP3 player) to a guitar speaker stack, and astound everyone with how different and full it sounded.  Half a watt is never going to be ear-shattering, but the increased bandwidth and speaker efficiency is normally enough to impress - "Wow!  Bass!".

Cheapo amps are normally fitted with even cheaper speakers, and cheap speakers are normally pretty inefficient, so a speaker upgrade can transform an "ordinary" amp.  With anyone who doesn't get it, just smile inwardly and move on.

[ChewyNasalPrize]

Yeah- I've been confused before about the "power consumption" number. Thanks for the clarification.

[Enzo]

I think "true RMS" is a term someone saw elsewhere, then applied it to amps.  RMS is RMS, nothing cosmic.   SOme lesser voltmeters will measure AC voltage as an average, or maybe just 0.707 of peak, which is fine for a sine wave, but if you have a triangle wave or a sawtooth wave or some other non-sinusoidal wave form, that simple average will not accurately reflect the voltage being measured.  So better meters are designed to read "true" RMS, meaning they really do measure the RMS voltage instead of approximating it.


Now people are familiar with the term true RMS even if they don;t know where it came from, so they apply it to amplifiers and speakers, where the "true" part is either redundant or meaningless.

SO ignore the true part on these specs, or go to the restaurant and look for True hamburgers instead of some other kind.