One thing to watch for when comparing power ratings for amplifiers is the load impedance for which the power rating is specified. It is common for amplifiers intended for automotive use to be rated at 4 ohms and some “pro” amps may be rated at conditions other than 8 ohms. I believe consumer amplifiers are actually required to be rated a 8 ohms so their power outputs are more directly comparable. Read the “fine print”. Even then there is “wiggle” room since the test conditions required for measurement may not accurately reflect the real operating conditions. There are many subtle differences in things such as the character of the distortion at clipping which can affect how loudly you can play which does not show up in the specs. Guitar amplifiers are typically operated in distortion so the maximum undistorted output does not have the same significance it does for PA amplifiers.
For a self-powered speaker impedance is a design issue only and watts are watts. The question then becomes one of the efficieny of the speaker/enclosure design chosen. With more efficieny the watts are used more effectively and you may be able to get a bit more sound pressure for a give wattage with a high-efficiency design. Horns are significantly more efficient than direct radiators and vented designs are more efficient than acoustic suspension (sealed box) designs. Larger cabinets also tend to be more efficient. Obviously efficiency is not the only consideration, achieving improved frequency response and low distortion may lead to efficiency compromises. It is important to realize that most loudspeakers are very inefficient with efficiencies of less than 2% being common.
The current trend toward using much smaller guitar amplifiers which are driven into distortion to get the desired tone then mic’ed and mixed into the PA is a great thing for musical balance and hearing protection, both for the players and the audience. That said, I have heard 15-watt guitar amps that play as loud as I would ever want to listen to, even outdoors. Sometimes amps provide electronic loads to suck up some of the power so you can drive them further into distortion while maintaining reasonable output levels.
Jim
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| I know guys who get 15 watt amps so they can absolutely saturate the snot out of the power tubes. |
One of the reasons I yanked two EL84’s outta my BelAire to reduce the power section to 25 watts. I can get to the “grit” quicker that way. And the thing is still WAY FREAKIN’ LOUD!!!
D
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| one can speak of peak power (instantaneous max power) or RMS power (continuous power, the only value that matters) |
I’m not sure I’d say instantaneous max power rating doesn’t matter. If you’re running flat out at max continuous power, it’s nice to know that the amp can still handle the transients without clipping or squashing.
But what is RMS power?
An interesting article…
wikipedia
and another one…
Why there is no such thing as ‘RMS watts’ or ‘watts RMS’ and never has been
Eyup!
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| I yanked two EL84’s outta my BelAire |
I know a lad who did that. The amp worked fine for a couple of days and then blew up (literally) in a very spectacular fashion.
Trouble was that valve power supplies are very simple things, usually unstabilised, and the removal of two of the output valves allowed the voltage to rise above the rated level of the mains smoothing cans.
We recovered one of the cans later, it was stuck in the ceiling
Steve
| Quote (Gizmo @ April 20 2006,15:07) | ||
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I’m not sure I’d say instantaneous max power rating doesn’t matter. If you’re running flat out at max continuous power, it’s nice to know that the amp can still handle the transients without clipping or squashing. But what is RMS power? An interesting article… wikipedia and another one… Why there is no such thing as ‘RMS watts’ or ‘watts RMS’ and never has been |
Fine… continuous power versus peak.
But you know what I am referring to… amps with stupid high peaks specs and they are just hyped junk.
| Quote (Beefy Steve @ April 20 2006,15:08) |
| Eyup! I yanked two EL84's outta my BelAire |
I know a lad who did that. The amp worked fine for a couple of days and then blew up (literally) in a very spectacular fashion.
Trouble was that valve power supplies are very simple things, usually unstabilised, and the removal of two of the output valves allowed the voltage to rise above the rated level of the mains smoothing cans.
We recovered one of the cans later, it was stuck in the ceiling
Steve
Oooohh... fireworks!
Yeah Steve. You must first make sure the power section of the amp is designed to allow this "mod" safely. The only thing I had to do was change the speaker impedance selector to match the load change when I pulled the two tubes so I would not endanger the ol' transformerator. Then I checked/adjusted the bias. Which on this amp is easily accomplished.
I've been running her this way for three years now. No problems.
D
Eyup!
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Try doing something like that with a transistor amp. Lifespan measured in milliseconds
I wouldn’t mind having a go at a low voltage valve amp. It might be interesting to build something like that and see how it compared to the “traditional” method.
It wouldn’t sting the fingers quite so much either
Steve
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There speaks the voice of experience!
But hey Beefy, at least we can say we were hit by a full 240v, not that light-weight 110v stuff.
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| But hey Beefy, at least we can say we were hit by a full 240v, not that light-weight 110v stuff. |
I’m in industrial maintenance. You don’t know what being electrocuted REALLY feels like until you get into 480 volts… I did NOT enjoy the time that happened to me.
D
Eyup!
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| Quote But hey Beefy, at least we can say we were hit by a full 240v, not that light-weight 110v stuff. I’m in industrial maintenance. You don’t know what being electrocuted REALLY feels like until you get into 480 volts… I did NOT enjoy the time that happened to me. |
Huh! a mere bagatelle!
I used to be in TV repair, so I got 240, and 27kV (yes twenty seven thousand) from the crt final anode.
That kinda turns your fingers black for a while
I moved into industrial stuff about 11 years ago, so I’m “experienced” with 440 too.
I used to know a guy who could brush the dust off a PL509 line output valve whilst it was still working, drawing an arc to his fingers (around 7kV) I tried it and it burned a hole right through my fingernail.
I should have been a lumberjack
Steve
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But then you’d have to cut down trees, wear high heels, suspenders and a bra, and on wednesdays you’d go shopping and have buttered scones for tea.
Hey Beefy,
Yep. My dad has been in TV repair since '52. I grew up in the shop. Dem flyback transformers can BITE!
D – lumberjack does indeed sound safer… eh… don’t need the bra though… yet…
Geez… how did we go from watts, ohms and PA speakers to High Voltage Lumberjacks???
D
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| Geez… how did we go from watts, ohms and PA speakers to High Voltage Lumberjacks??? |
Probably something to do with testosterone…
…and anyway, don’t you think it would be easier if amplifier output was measured in Horse Power. We can all relate to that…
Hi Guys:
Any of us who has been around AC and DC currents and made a living with maintenance and service of Power and Electronics, has stories to tell…
I find myself unable to tell you all how fortunate I’ve been over the years to be able to sit here and type this post… With all the tight spots I’ve found myself, in…
I once saw a guitar player burn the strings off his guitar when the neck of his guitar touched the mic stand… The strings went up in a shower of fireworks… Everyone in the audience thought IT was part of a “Stage Effect”…
For anyone who knows… there is always one stage amp that causes AC Polarity HUM in the Audio system… Who knows why that is…
Anyway, in order to FIX IT you have to lift the Ground of that amp, and what-do-ya-know… NO HUM…
IT has to do with the lighting circuit and the Audio circuit inter-action… Who Knows…
I remember sticking to an amp rack one night… I wasn’t able to let go… Someone wrapped their jack cable around my shoulders and wrestled me to the floor…
I survived IT… I think…
Bill…
| Quote (Mark A @ April 20 2006,19:27) |
| ..and anyway, don't you think it would be easier if amplifier output was measured in Horse Power. We can all relate to that..... |
A one horsepower geetar amp would be a d@#n MONSTER!
My kid would love it! "Dude! I gots me a 764 watt amp brah."
D -- watts is easier...
| Quote (Bubbagump @ April 20 2006,10:56) |
| The Originals are the PAK, or P1, or G1. Depending on what site you look at (Musiciansfriend, American Musical, etc.) they all call the same thing something slightly different depending on if they bundle a speaker stand with it etc… but it is the same speaker and it is plenty for a rock band in reasonable sized clubs. |
The specifications between Pak and P1 are different. I know by now that it doesn’t really matter (watts and the link with power) but for example the watts are different. PAK has 130+50 and P1 has 300+100. Didn’t compare the rest of the specifications but I think they are not the same. Or are the aaaaallmost the same?
Specs for both types of EONs:
http://www.jblpro.com/eong2/eon15g2/assets1/specs.pdf
http://www.jblpro.com/pub/mi/EON15P-1.pdf
The interesting part is the specification for the power supply: It is exactly the same for both types (175W) .
Which proves the “higher” specs for the G2 are dramatically hyped to impress the customer.
There is no way you can get 300+100W true RMS power out of a 175W power supply.
| Quote (hansje @ April 21 2006,05:05) |
| Specs for both types of EONs: The interesting part is the specification for the power supply: It is exactly the same for both types (175W) . Which proves the "higher" specs for the G2 are dramatically hyped to impress the customer. There is no way you can get 300+100W true RMS power out of a 175W power supply. |
You compare the 15P G1 en 15P G2. I thought I had the P1 G1 but I found out that i have the 15PAK. I'm afraid there are more differences between 15P en 15PAK.
The 15PAK has a power supply from I think (I hope I understand it well) 140 Watt. Will the difference be only 3 Db??