Actual output of 100 watt head

[blazer986]

It is standard practice for amps to be rated for clean headroom and I know they put out more than their rated output when distorted. Given that, does anyone know how much more output this is? Basically I have a dual rectifier and a 4x12 rated at 100 watts. I don't intend to be playing this thing full power ever, but is there a real danger of blowing speakers even at lower settings, half power even? Sounds like a bad high school math problem! Any thoughts?

 

[blazer986]

Another thought - most mesa amps are known for their preamp gain and the power amp stays pretty clean. I would think this would keep them relatively true to their 100watt rating?

 

[94Tremoverb]

There's no rule - it varies depending on the amp. Some 100W amps will put out well over 100W even clean, and over 200W fully distorted. Others might put out less than 100W before they overdrive and not a lot more after. A Dual Rectifier puts out less than 100W in any mode other than Bold/Diode too, down to as low as about 60W in Spongy/Tube.

Speaker ratings are also variable - some companies rate their speakers a lot more conservatively than others - up to about double, or for a cranked-up amp of the speaker's supposedly rated power rather than the electrical power itself. So you really can't tell if a 100W amp will blow a 100W cab when it's fully cranked. In theory if you keep the power amp clean it will be fine, but even then you might need to be careful with some combinations.

As an example I would run a Mesa Dual Rectifier into a cab with four Celestion G12M-25s at any volume and not worry about it. But if you ran a 1970s Marshall JMP Super Lead or 2203 into a cab with four Jensen P12Rs and turned it up loud - not necessarily even right into power stage distortion - expect to blow them.

If you keep the amp turned down fairly low there's no risk at all though. The power curve is very steep, and especially so once you get into power-stage distortion, so 'loud' and 'really loud' are very different in power terms. If you're not overdriving the power stage there's probably very little risk.

 

[phyrexia]

From what I've read, DRs actually put out about 72w "clean"

 

[94Tremoverb]

It totally depends on the power and rectifier mode, because they affect the plate voltage and hence the maximum power (which is related to the square of the voltage, so it changes even more). I can't remember the other two results - they're somewhere in between - but from memory when I tested it my Tremoverb puts out close to a true 100W in Bold/Diode and only about 60W in Spongy/Tube. Power tubes make a difference too, for example if you compare modern Chinese or Russian 6L6s to 1970s/80s Sylvania 7581As (basically top-quality military 6L6s) there is a significant difference in measurable power, with the old tubes producing significantly more.

 

[blazer986]

Very good info! especially with so many factors at play. I'm running my tremoverb through a 4x12 with some new G12M-25s and have been really liking the sounds, but was a little worried about pushing the amp too hard at band volumes. Given all of that, sounds like i should be golden.

 

[94Tremoverb]

I wouldn't worry about that combination at all. Celestions are very tough, and the Tremoverb won't put out enough power to be a risk to them unless it's in Bold/Diode, and probably not even then. A lot of people run older 100W Marshalls cranked up with single G12M 4x12"s and still don't blow them - but it is a risk, and it's why the original Marshall 'Heavy Duty' (model 1982) cabs with G12H-30s that came out in the very late 60s have a '100' badge in the top corner... because they were capable of taking a 100W amp, whereas the standard 1960 cabs weren't, and hence why the stack was invented!

A little while ago I was testing an original Marshall basketweave straight 4x12" with G12M-25s using my Tremoverb, by the way... it sounded incredible.

 

[YellowJacket]

A little while ago I was testing an original Marshall basketweave straight 4x12" with G12M-25s using my Tremoverb, by the way... it sounded incredible.

Ya, I absolutely love any 4 x 12 loaded with Greenbacks.

Measuring wattage is an interesting topic. I think the two big factors are 1) speaker efficiency and 2) the WAY you measure the horsepower of an amp.
As we all know well about how efficient guitar loudspeakers are, especially when compared to HiFi Audio, I think it makes more sense to leave that point alone.

What I DO want to talk about is wattage. HOW do we measure the power of an amp? Are tubes really louder than solid state amps? I don't think they are. I mean tubes are an old and inefficient technology, which is why they have been replaced. And yet, guitar amps can spank home electronics. My brother bought a 50watt NAD home stereo and that thing cooked. I also have Mackie MR5 powered speakers for my computer and they're stinking loud for the wattage they boast. But sadly, these are exceptions. Why is it that our guitar amps can literally destroy a 5,000watt car stereo? I spoke with my engineer brother and he told me that since consumers like big numbers like '150watts', Sony decided to 'fudge' the results in their benchmarks and not long after, the other manufacturers followed suit. Basically, he said they would test the power capabilities of an amp in the best possible situation. So, they pick the one frequency the amp can power the best and they play just that one frequency through one 2 ohm speaker. Basically, it is the equivalent of having a power lifter set records on the moon.
In reality, this sort of a rating system really has no applicability in a real life situation i.e. a stereo running in stereo with two 8 ohm speakers running a full spectrum of sounds instead of one frequency. Do that, and all of a sudden these amps are neutered to being able to push no more than 15watts.

On another topic, people will talk about the feeling of 'punch' or 'horsepower' from a tube amp vs a solid state amp. This is because of the clipping characteristic of each. With a solid state amp, it clips hard so basically there is a very small 'powerband' between where the amp starts to clip and where it saturates. With a tube amp, it 'soft clips' so there is a lot larger of a 'powerband' between where the tube starts to clip and where it saturates. It translates as 'headroom', 'punch', 'sensitivity' and all those things. The result is that the attack, especially when distorted, is louder or more powerful than the decay so you get that bold and percussive feel while playing. The solid state amp, by comparison, sounds mushy because the decay portion is as loud or close to as loud as the attack.

At any rate, I think it is moot to discuss the theory behind all this considering that the end result is that guitar gear is FREAKING LOUD!

 

[greg_moreira]

Let me chime in. I cant give you a technical answer here, but Ill give a little personal experience. I own a triple recto(150 watt head) and more often than not, I use my 2X12 cab loaded with two vintage 30's(60 watts a pop for a total power handling of 120).

I have no idea just how much "wattage" this triple is capable of when distorted....but I can tell you that I havent broke the 120 watt cab yet! This cab sees regular full band rehearsal and plenty of gigs. Reguardless of how loud it can get, any "comfortable" volume level for live playing and rehearsing isnt overkill on these speakers. Unless your getting really crazy with it, Id expect you probably have more wiggle room than you think. As far as the amount of wattage these things produce.....its all about headroom moreso than volume. I dont think there is EVER a situation where I will need to know just how loud this head actually is. its just ridiculous to even contemplate needing to turn it all the way up in any situation, so I dont expect to break my cab any time soon.

im sure mileage could vary a little with say a more sensitive speaker that really starts working hard with less input, but for the most part I think you're safe. I also wouldnt expect it to be a surprise if you blow them. I think you would start to hear them being worked too hard before they blow if you ever pushed them past a safe limit for continuous use

 

[MesaDCLP]

I believe Mesa measures wattage on a proprietary scale. I think they either rate to a specific THD % which would be real low, like less than 5%; or they rate to Peak-RMS. And it could be a combination of both.

For example, the Mark IV is rated at 85 watts and the combo comes with a 90 watt speaker. Well, the speaker is rated at RMS power and peaks at about double that, so the combo speaker can take all the amps wattage. So, I have a 120 watt cab and you could say it is actually safe to roughly 240 watts peak in theory. Ok so the Mark IV is 85 watts, but the manual says that, "When you deleberately push the power section into clip, the wattage continues to rise, peaking out at about double." So 85 watts at 5% THD, 170 watts peak. I can tell you that my 2x12 120 watt cab can take the output to 10, but I did have the channel volume below 2 on the lead channel with the GEQ engaged. Did it just for sh!ts and giggles, and **** that thing was loud. I'll never have to play that loud, unless I'm 100 feet from the amp and 3 feet from the bassist and drummer!! 8)