300 watts at 2 ohms means....

Discussion in 'Amps and Cabs [BG]' started by Quadzilla, Mar 3, 2002.

  1. Quadzilla

    Quadzilla Supporting Member

    Hey there. I am looking at an amp that says on the back (under the 2 jacks for the cabs) "300 watts at 2 ohms). I have 1 - 4x10 8 ohm cab. How many watts will that be with that one cab at 8 ohms? Also, if I hook up an aditional 8 ohm cab (to make the load 4 ohm) how many watts will that be at 4 ohms?
  2. 300 watts at 2 ohms =
    250 watts at 4 ohms &
    150 watts at 8 ohms

    Fergetaboutit kid.
  3. Quadzilla

    Quadzilla Supporting Member

    Thumbs up and thanks!
  4. Speedbird


    Jul 10, 2000
    If you add a 8 ohm extention cab to the combo it will have a load of ~2.6 ohms (extracting a little less than the 300w max) no big deal.
    The big catch is that you are mixing the 4ohm internal speaker and the 8 ohm external cab. The internal speaker, it beeing the path of least resistance, will draw twice the power as the 8 ohm ext. cab. Your ext. cab may seem underpowered, but you are still extracting more power from your amp, feeding more power to your internal speaker, but you may just never power the 8 ohm external speaker to its potential with this config.
  5. monkeyfinger

    monkeyfinger Moderator Staff Member

    Actually, that is not necessarily true. The change in output for different loads varies from amp to amp. For instance some of the SWR combos only gain 20 watts when using an external cab. It mostly has to do with the capacity of the output transformer. In fact, amps that have bigger increases in gain for lower loads are usually the ones with the most headroom. (The Crown Amp site has some good info on this.)

    What make and model of amp is it?
  6. Quadzilla

    Quadzilla Supporting Member

    Well when I first posted this I was going to buy a Randall RB1000 and it said 300 watts at 2 Ohms on the back. I did not end up buying it. Instead I bought a Dean Markley Link for what I bought . This one is rated at 400 watts at 4 ohms. So I wonder what this will put out at 8 ohms (prob over 200 watts I guess).

  7. monkeyfinger

    monkeyfinger Moderator Staff Member

    Yeah that sounds about right in many cases. The whole thing about watts is very wierd anyway. I have played through a 500 watt Ashdown head that was unbelievably loud. Much louder than the 1600 watt QSC I was using. I also hear that the new Aguilar DB750, 750Watts @ 4 Ohms, is incredibly loud too. My DB728 tube power amp is rated at 400 watts and obliverates the QSC 1602PLX is replaced. It think it has to do with the extra headroom these amps have. They are designed with a huge amount of instantaneous peak power, not something that your average PA amp has. (Crown VLZ's excepted.)
  8. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio!

    Jul 3, 2001
    Chester, Connecticut
    Former Technical Communications Developer, QSC Audio
    No, it has to do with gain. If you match the gains of two amps, they'll be just as loud as one another up to a point, but the higher-power one will be able to go louder if you push it that far.

    If you have a weak preamp, you might not be able to push the amp hard enough to make it louder than what you're comparing it to.

    However, if you understand how gain works and how to set it, you can get plenty of volume. I can pretty much guarantee that the PLX 1602 has a lot more power--continuous, even-- than a 400-watt tube amp has in peak power, and if you drive it properly, you'll get noticeably more loudness. If you don't understand gain, you could easily come to incorrect conclusions that end up costing you lots of money.
  9. Gabu


    Jan 2, 2001
    Lake Elsinore, CA
    I usually assume that most distortion appears in the preamp gain, so I try to leave that around 50%, and then control the volume with the master volume. I am unsure of how people get more volume from tube amps, assuming similar ratings. I can only guess that a 300w tube amp distorts slowly, so perhaps you get 600w or maybe even more ... worth of "clean enough" power. And of course some people really like that slightly overdriven sound, so that's a plus too.

    Here's another thing that's weird to me. I have a 100 watt tube amp, lets say it's apparent volume is equal to a 300 watt ss amp. (For this example we will say that both amps are turned to 10 to use the full power available) I put the tube amp on a 100 watt speaker cab. It probably sounds cool. Now, I take that exact same speaker cabinet, and use the 300w ss amp to get about the same apparent volume and what happens? Does it blow the speaker because the actual power is upped by 3x?
  10. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio!

    Jul 3, 2001
    Chester, Connecticut
    Former Technical Communications Developer, QSC Audio
    Maybe, but don't assume that "50%" is the best setting. Try different settings. Turn down the master volume a ways and turn up the preamp gain and see where you get distortion when you're playing as hard is you normally do, then back off a little.

    Then set the master volume.

    Probably not that much. ;)

    That's true, and possible.

    First, if the two amps have the same apparent volume when they are both turned up all the way, then they probably both have the same maximum gain, or close to the same. But don't assume that any two amps do unless they're the same model.

    BUT, turning an amp up all the way does NOT "use the full power available." It's a common misconception. Turning an amp down reduces the voltage, and therefore the amount of power, it puts out with a given input signal, but it does not reduce the amount of full power it is capable of.

    Assuming the 100-watt amp wasn't clipping, no, you won't blow the speaker, because the new amp is still putting out the same amount of power as the one before. But you could go a few dB louder with the 300-watt amp than you could with the 100-watt amp.

    Let's say you have a 50-watt amp with a gain of 100 and a 1000-watt amp (both @ 8 ohms) with a gain of 40.

    In your living room or garage, the 50-watt amp will seem really loud, and you might be amazed at how it "blows away" the kilowatter even with the volume knob just cranked up maybe a quarter or halfway. But if you go out to play a good-sized club or other venue, you're not going to get the sound level you need, and you'll get lots of distortion, but the 1000-watt amp probably will work perfectly well.

    Why? The smaller amp's max gain means if you put 0.1 volt into it, cranked all the way up, you'll get 10 volts out, which is 12.5 watts into 8 ohms. The bigger amp, though, will put out 4 volts when turned up full, which is 2 watts into 8 ohms.

    But if you put 0.2 volts into it, the small amp will reach its max of 20 volts, or 50 watts into 8 ohms. The bigger amp will be up to 8 watts. If you go up to 0.5 volts, the little amp's going to be clipping like a fuzzbox, but the bigger amp's going to be up to a clean 50 watts. Let's go up to 1 volt. The little amp might've shut down by now, but the bigger amp's up to 40 volts, or 200 watts @ 8 ohms.

    The smaller amp started out with 8 dB more maximum gain than the bigger amp. If you want to make them both the same loudness, turn the smaller amp down 8 dB and keep them under 50 watts. Don't confuse gain with power output capability. Gain is just a voltage multiplication factor and doesn't really cost anything in manufacturing--it's usually just a choice of one resistor value over another; power, on the other hand, costs money.

    That's why there are knobs on preamps and power amps--so you can get a good match from one stage to the next. Some basses put out a hotter signal than others--and you've got a knob on the preamp to compensate. Some preamps put out hotter signals than others--and you've got a knob on the power amp to compensate also.
  11. Gabu


    Jan 2, 2001
    Lake Elsinore, CA
    Thanks! That makes much better sense to me now!
  12. monkeyfinger

    monkeyfinger Moderator Staff Member

    In both cases I used a Kern IP-777 with +24dB max gain on the output stage. Usually I have this about 1/3 to 1/2 max. In reality I probably used a little over +4dB gain, (maybe +6?) from the pre.

    Anyway, the Ashdown and my Aguilar DB728 have, to me, significantly more percieved volume than the QSC. I know the spec-hounds will argue, but I am going by my experience.
  13. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio!

    Jul 3, 2001
    Chester, Connecticut
    Former Technical Communications Developer, QSC Audio
    Is that "+24 dB max gain," or do you mean +24 dBu max output level"?

    The way you had it set up, I'm sure it did have more volume because it just has more gain, although you could've easily boosted the preamp gain to drive the QSC harder and gotten a lot more volume.

    If you drive a Ferrari light-footedly at only 20 mph, it's still a Ferrari going only 20 mph, and you might well get passed by Mazdas, Chevys, Lincolns, Volvos, etc., that happen to have more perceived speed because their drivers push the gas pedal a little more.
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    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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