SOUND ON SOUND

[ef37a]

I wonder if Dave meant that or, maybe, touching the tip of the guitar lead and the resultant loud buzz we are all familiar with?

Indeed so Sir but yes, Speakons at these power levels to be sure.

Dave.

[MOF]

I wonder if Dave meant that or, maybe, touching the tip of the guitar lead and the resultant loud buzz we are all familiar with?

Yes, I hadn’t thought of that. A loud buzz or a temporary short wouldn’t be good either way. :lol:

I’m still interested to hear from an electronics expert how 80 watts power input can sustain (pun not originally intended, but now I see what I’ve done there I’ll say it was - visions of ‘prog rock’ lead bass guitarist doing Hendrix style feedback impressions) 500 watts of output.

[Wonks]

It can't, is what I think everyone is saying. It can produce a brief peak 500W level whilst playing back a 'music program', but the 'music power' rating will be closer to 250W and an equivalent 'RMS value' would be more in the 125W rating. Assuming you leave a couple of dB of headroom, then the average output power will be nearer 60W, which I can see tying in with an overall 80W power draw.

So the figures used are heavily manipulated and used to show the biggest output figure and smallest consumption possible.

[The Red Bladder]

So the figures used are heavily manipulated and used to show the biggest output figure and smallest consumption possible.

Nothing is so dishonest as amp output ratings in the UK and the US.

Take your amp, feed a sine wave into the damn thing and feed the output into a Watt meter and an oscilloscope. Now crank-up the volume and be amazed at how much BS you are being fed.

The sine wave will clip (get a flat top) and the Watt meter will show you a tiny fraction of the so-called 'peak' or 'music' power. (What happens over a few milliseconds is pure fugazi!)

I sometimes joke that you could take a piece of cheese and stuff a few wires into the damn thing and call that a 1000-Watt amplifier. I wouldn't be too far wrong!

[Agharta]

I sometimes joke that you could take a piece of cheese and stuff a few wires into the damn thing and call that a 1000-Watt amplifier. I wouldn't be too far wrong!

Wasn't that tried in the recording of Gong's Camembert Electrique album? :bouncy:

[CS70]

Here’s hoping Hugh, or someone else well versed in electronics, will explain how this amplifier gets more power out than its input.
Even the RMS figure of a 500watt peak doesn’t work for me.

It's more about physics than electronics imho. Power is energy over time. So 500Watts means that the amp is capable at most to produce 500 joules of energy per second without melting. It doesn't say that for how many seconds it can do that - not even if it can do it for an entire second. Technically it doesn't even say that the speaker won't explode when the amp does briefly produces 500 joules, but of course there's an expectation that all the component in a device can handle the peak power made available by the energy-producing unit..

So 500W means that the amp circuitry is rated not to melt or explode when it occasionally has to pass all that energy, and the speaker and speaker actuation mechanism can sustain that energy for just a little longer time than the amp is capable to produce it.. but that's about all that it means.

Peak power (i.e. maximum instantaneous power) is always a questionable measure to compare devices, if it's not accompanied by data on how a device develops and can sustain it over time. There are always better ways. Not just in amps, but in everything. If you take a car analogy, a Tesla Model S 100D "has" 605HP (451KW) of power. A Bugatti Veryon has 987HP (763KW) of power. Yet the Tesla is quicker (on a straight line) because of the way it develops and sustains that power (till it goes out of juice, that is :D). The trick is that "has power" means "has maximum power" and tells you nothing on how it develops. Hence the Tesla wins drag races. If you looked at the integration of power over time (the max energy that can be made available over time) then you get a far better picture. You will see that in the same 10 seconds a Tesla produces much more energy than the Veyron, even if its peak power is lower. That's why it wins races.

Same with a person.. a power lifter athlete can lift say 150Kg, and so can a small forklift. They "have" the same power. But the athlete cannot do it for more than a second, the forklift can do it indefinitely. Real-world performance is not about peak power.

Peak power is useful - you need to know it when you design a device, so that you can ensure that all the parts of the device can withstand it when it happens. And in power lifitng. But not so useful to compare stuff.

[Hugh Robjohns]

There are situations in the engineering world where an amplifier is required to amplify a full amplitude signal continuously -- motor control being one such application.

But an amplifier designed to provide 50W of continuous power with a sinewave signal will appear to be a heck of a lot more powerful than that when handling live music which has a massively larger ratio of peak-to average levels, simply because it can draw on energy reserves stored in the power supply to handle brief transient peaks.

Consequently, the marketing departments of most amp manufacturers prefer to quote a 'music power' rating or some other non-specific peak-power description to give a better idea of how powerful the amp is its intended application.

It is all marketing BS... but it's also arguably more relevant in the real world than giving a largely pointless continuous power rating.

One thing to be aware of though: the peak-to-average ratio of a live band performance is a lot bigger than that of commercial music played in a 'disco' (or club for the young 'uns) style. So an amp that works great for a band's PA may struggle to sustain as loud a perceived output for a dance rig!

[CS70]

That's why drag races exist! :D

[Sam Spoons]

So the figures used are heavily manipulated and used to show the biggest output figure and smallest consumption possible.

Nothing is so dishonest as amp output ratings in the UK and the US.

Take your amp, feed a sine wave into the damn thing and feed the output into a Watt meter and an oscilloscope. Now crank-up the volume and be amazed at how much BS you are being fed.

The sine wave will clip (get a flat top) and the Watt meter will show you a tiny fraction of the so-called 'peak' or 'music' power. (What happens over a few milliseconds is pure fugazi!)

I sometimes joke that you could take a piece of cheese and stuff a few wires into the damn thing and call that a 1000-Watt amplifier. I wouldn't be too far wrong!

I did exactly that with my MusicMan combo (a 112RP65 modified to 100 watt spec, 2 x EL34s and 500VDC HT) and measured it into a dummy load with a 1kHz sine wave. The scope showed a clean (reasonably, i.e. not clipping) 100 watts (can't remember the exact numbers but it was slightly more than 100 watts). We (my engineer mate and I) didn't believe it was possible to get 100 watts out of just two EL34s, we were proved wrong. TBF we measured the voltage peak to peak...

[The Red Bladder]

I know little about valve designs but that does not sound right to me. Did you monitor on a Wattmeter, or was that calculated?

In push-pull, the most you are supposed to be able to get out of a pair of EL34s is about 80 Watts with a plate voltage of 800V.

[Sam Spoons]

Measured on the oscilloscope screen, peak to peak. MusicMan made the claim, the 65 watt version (which mine started out as, I should never have sold it BTW :headbang: ) was identical apart from the mains and output transformers and the speaker. IIRC the 65 had 350V HT and the 100 was 450 05 500 V HT. Either way, while my electronics chops are modest my buddy was a qualified and competent tech so I have no problem taking what he said at face value.

[Wonks]

Well, with a sine wave, times your peak voltage power reading by 0.707 (or divide by root 2 - it's the same thing) to get the RMS value.

So that would be around 70W RMS.

[jjlonbass]

The EL34 was originally specified by Philips / Mullard to give 100W in pentode connected push-pull with 800V on the anodes and fixed bias. Some excerpts from the original data are here http://www.r-type.org/articles/art-016.htm

John

[Sam Spoons]

Well, with a sine wave, times your peak voltage power reading by 0.707 (or divide by root 2 - it's the same thing) to get the RMS value.

So that would be around 70W RMS.

Unless you talk to Dave and he'll telly that RMS Watts is a nonsense :D

FWIW I had thought about that but can't remember whether we did it or not (it's a long time ago) so didn't claim 141.4 (or more) watts peak :D

If we kept notes (highly unlikely) I definitely have no clue where to find them and said buddy left us just over a year ago.

[Wonks]

RMS watts obviously isn't nonsense, it is a known electrical quantity/measurement (and Dave will tell you that). And you were testing the amp with a single frequency sine wave, which is exactly what RMS watts is all about.

What is dubious is trying to apply RMS wattage to a guitar amp that isn't going to output a single continuous frequency wave, but a very dynamic, non-continuous, mixed-frequency signal as an indication of how loud it goes.