too many watts into a speaker?

[rabies]

I ran my EL34 dual monobloc Marshall power amp into my Genz Benz gflex 212 cab the other nite.

Each gflex speaker is rated 75watts RMS. Each Marshall monobloc puts out 100 watts via 4xEL34 tubes (200 watts stereo).

So I ran the amp in stereo into both speakers @ 8 ohms simultaneously and had the output turned up to 3 out of 10 on my JMP-1 preamp.

Apparently there was no damage to the speakers (didn't blow anyways) and I have continued to use the cab at home at lower volumes.

Is it ok to continue to do this? How would I know when I am outputting up to 50-75 watts RMS per side from the power amp? (if I turn the output level to noon, what wattage is it outputting?)

[txstrat]

Calculating the output of an amp is very complex matter.
See this thread: http://music-electronics-forum.com/s...ead.php?t=8577

If the speakers get driven too much they start to flutter and eventually blow.
It depends on the speakers and how much they are driven over their wattage.
When you hear the fluttering it can already be too late and the speakers are damaged.

Better use a proper cab.

[rabies]

interesting thread. seems like there was no definitive answer to how many watts a pair of P/P EL34's put out. But I am betting it's not much more than 50 watts on avg.

anyways, I did it as an experiment b/c my 412 cab only has one 8ohm jack...

I'm not sure what you mean by fluttering or if I have ever heard that but it seems to be ok for now...

I will call the vendor to verify...

[rabies]

Can I calculate the wattage if I use my weber bias rite? It display plate voltage and current draw in mA...

Seems there should be a simple formula to get the watts based on those two variables...

maybe this: Calculate Plate Dissipation Based On Plate Voltage And Cathode Current Readings.

http://www.webervst.com/tubes/calcbias.htm

so hypothetically (and I haven't actually used the bias rite on this power amp yet), for 450 V and 36 mA, the wattage per tube is 16 watts. that's 64 watts per 4xEL34.

now if the output on the JMP1 is only turned up to 3, would that mean 30% of 64 watts? or is that not a valid assumption...

when you measure bias, there is supposed to be no signal in the circuit, correct? so you can't measure the plate voltage and current draw, etc. when the output on the JMP1 is turned up...

[rabies]

talked to Mr. Genzler himself @ Genz Benz and he said I should be ok if I don't fully crank the power amp. He said that it's not easy to determine how many watts are coming out of the amp unless you put it on the bench b/c it depends on other factors such as active or passive pups, for example.

he said that the fluttering is like a farting out sound where the speakers can't handle the bass and you'd definitely be able to hear it. I didn't hear it. he said the spkrs in the cab handle 75-100 watts.

[txstrat]

The weber bias rite gives the value for tube dissipation in watts. The power output is something else (I learned it the hard way ) Not easy to manage without the proper tools.

now if the output on the JMP1 is only turned up to 3, would that mean 30% of 64 watts? or is that not a valid assumption...

No, the way a pot works is different all over it's way. There are pots increasing the volume much more on the first third of the whole way, others don't.
Therefore the 30% thing won't work, cause you don't know the value of the pot at "3", unless you open the amp and measure (don't open the amp).
I think I know what you're aiming at. You don't wanna spend more money on other speakers, right?
Speakers have a rated wattage and a peak wattage. Usually the given wattage means the power it can handle with a peak much higher than that (often the double value).
If you don't turn the amp up more than half I would tend to say it's save for the speakers. BUT don't take me at my word.

Biasing means you set the idle current for the amp. No signal applied.

[rabies]

The weber bias rite gives the value for tube dissipation in watts. The power output is something else (I learned it the hard way ) Not easy to manage without the proper tools.


No, the way a pot works is different all over it's way. There are pots increasing the volume much more on the first third of the whole way, others don't.
Therefore the 30% thing won't work, cause you don't know the value of the pot at "3", unless you open the amp and measure (don't open the amp).
I think I know what you're aiming at. You don't wanna spend more money on other speakers, right?
Speakers have a rated wattage and a peak wattage. Usually the given wattage means the power it can handle with a peak much higher than that (often the double value).
If you don't turn the amp up more than half I would tend to say it's save for the speakers. BUT don't take me at my word.

Biasing means you set the idle current for the amp. No signal applied.

I like the cab the way it is in terms of bass response, tightness and overall sound for rock and metal. It's ported and baffled. pretty sick in my opinion for a 212.

I have noticed w/ the JMP1 (b/c I actually have maxed out the volume/output knobs in the past) that most amps don't really get "louder" after noon on the output. After that point, it seems to be just add'l power tube distortion that gets generated. so it sounds/behaves differently at max than noon but not necessarily louder. mesa amps (the mark iv anyways) are like this as well.

My gut feeling is with the JMP1 output pot, 9 o'clock = 50% output in reality and not 25% (expected).

So if that's true, that means I was running approx. 50 watts into a 75 watt spkr. But who really knows...

[MWJB]

"But who really knows... " If you have a RMS AC voltmeter you will really know. Hook up the meter accross the speaker load, play through the amp at the volume you are going to use and watch the meter...readings will fly about some but if you can determine an average, take this voltage, square it, then divide by speaker load in ohms. What do you get?

Rule of thumb is to use speakers rated at twice the RMS wattage of the amp.

[defaced]

Rule of thumb is to use speakers rated at twice the RMS wattage of the amp.

Not that this is particularly relevant to the discussion, but an important back-pocket item to have, is that is for a tube amp. For a solid state amp, you want the opposite, the amp to be 2x the power of the speaker. This is because you do not want the amp to clip and send square waves to the speaker. At high power levels, that will shred it. This is how the pro audio guys setup their racks for live sound.

http://www.prosoundweb.com/article/danger_low_power/
BTW, that's a very good site to dig through. Those guys know their stuff.

----

To simplify the measurement process, I'd run a signal generator through the amp with a dummy load and measure power at a couple of different frequencies, like 60 hz, 1 khz, and maybe at 5k. From there do the RMS calculations and get an idea of where your volume knob range is.

[stokes]

Not that this is particularly relevant to the discussion, but an important back-pocket item to have, is that is for a tube amp. For a solid state amp, you want the opposite, the amp to be 2x the power of the speaker. This is because you do not want the amp to clip and send square waves to the speaker. At high power levels, that will shred it. This is how the pro audio guys setup their racks for live sound.

http://www.prosoundweb.com/article/danger_low_power/
BTW, that's a very good site to dig through. Those guys know their stuff.

----

To simplify the measurement process, I'd run a signal generator through the amp with a dummy load and measure power at a couple of different frequencies, like 60 hz, 1 khz, and maybe at 5k. From there do the RMS calculations and get an idea of where your volume knob range is.

You gotta be kidding me!I didnt even bother to read that article,but before you put a 200watt amp into a 100watt speaker,I suggest you read it again.There is no way someone is telling you it is okay to put 2X the wattage into a speaker,tube or solid state.Like I said,I didnt read the article,but there has to be something more to what he is saying.You put 200watts into a 100watt speaker it blows...period.

[stokes]

"But who really knows... " If you have a RMS AC voltmeter you will really know. Hook up the meter accross the speaker load, play through the amp at the volume you are going to use and watch the meter...readings will fly about some but if you can determine an average, take this voltage, square it, then divide by speaker load in ohms. What do you get?

Rule of thumb is to use speakers rated at twice the RMS wattage of the amp.

That is the best way to determine what you are getting.Some DMM's have a feature that will lock at the highest AC volts it reads,that will tell you the max watts you are putting out.Using a signal generator will get you an approximate,but different frequencies will react differently,so it is best to use the guitar you are using.

[Enzo]

I'd be more concerned with average powr than peak. The max reading meter will tell you peak, but that occurs only now and then.

The volume controls are not power controls anyway. Setting the knob at 3 is no more guarantee of 30% power than only playing soft rock. If you turn the amp down to 3, you can turn the guitar or effect pedal UP some amount and be right back as loud as ever. VOlume controls set sensitivity, not power output.

The AC voltmeter across the speaker will tell you how much power is being produced. At least close enough. But if you play into the amp and measure this way and get 40 watts - for example - that doesnt tell you the amp is limited to 40 watts at the current "settings." What it tells you is when it is "this loud" the amp is making 40 watts.

[black_labb]

how accurate is using the ac voltmeter across the output for judgeing power? im curious how much power my builds are putting out, but dont have a signal generator/scope/dummy load. will it pick up the harmonics and such well enough to be accurate?

sorry to be off topic, was curious.

[MWJB]

It's accurate enough for "real world" output, e.g. how much power actually hits your speaker at the settings you actually play at. Trickiest part is interpreting the average voltage.

Quoted W RMS are generally accepted as maximum clean watts, with a 100mV signal (or refer to manufacturers specs). Some instruments/pickups might put out ten times 100mV. Usual instruction is to turn tone controls fully clockwise, you might not play like that?

[defaced]

You gotta be kidding me!I didnt even bother to read that article,but before you put a 200watt amp into a 100watt speaker,I suggest you read it again.

No one said anything about running the amp at full power. Because it's a solid state amp you need head room, that's the reason for the higher power. Think about the system and the ways it can fail vs a tube amp and I think you'll see the logic.