Theory of huge power amps

Discussion in 'Amps and Cabs [BG]' started by fdeck, Jan 6, 2006.

  1. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I got to thinking about huge power amps, like 1500 W and above. While I hope to never own one, my curiosity is piqued by the following question.

    Say a 1500 W amp is conventional Class-AB, and is optimistically 50% efficient. Then at full power, it is drawing 3000 W from the line cord. The circuit breaker on any standard outlet should pop in a jiffy, if the built-in fuse or circuit breaker doesn't open first.

    If this is true, what is the meaning of a 1500 W power rating? It must be based on very short duration peaks. Are there industry standards for defining the power rating or test conditions for PA amplifiers? Or is it Caveat Emptor?
  2. BbbyBld


    Oct 13, 2005
    Meridian, MS
    In many PA applications, circuit breakers are not an issue. The Peavey Classic 400 has a turn on transient of 200 amps. Circuit breakers are kind of "slow blow." In a music situation, the amp will not always be putting out max power. I don't know if this will tell you anything as far as standards go, but to get a UL listing (if memory serves), a power amplifier must be able to put out 1/8 rated power for 7 hours without thermaling out, blowing a fuse, or reaching 40 degrees above ambient temperature anywhere on the chassis, or 1/3 rated power for 3 hours with the same conditions.

    The efficiency of a class AB amplifier changes dependant upon signal. The power level that UL tests at is the area where efficiency is usually at its worst (which is why they test there). Peavey was just awarded a patent for an amplifier technology that addresses this.
  3. There are a few poweramps out there that are able to project more wattage than they consume - Yamaha have a current model that does it - i'm oblivious tothe tech side of it tho.
  4. Jack


    Sep 6, 2003
    Newcastle, UK
    Id imagine it would be impossible to create more watts than an amp consumes.
  5. But is the power rating given by the producer the power the amp draws or actually outputs? In the SVT manual it is said the amp is capable of outputting 300 Watt, so it must draw a lot more considering the heat it produces. But is it standard to give the output power instead of the 'consuming' power?

    And no, outputting more watts then it draws is impossible.
  6. Delivering more energie than it consumes? *scratch-scratch*
    In the old days (I'm talking about 1970, yip: granddad is talking here :) most amps were about 50 % efficient. If one consumes, lets say, 12 Ampere at 110 Volts then it consumes 12 X 110 = 1320 Watts. Ten to one that the output power of this one was around 700 Watts.
    My Trace delivers 2x300 Watts while it consumes 800. That's an efficiency rate of 75 %. Which means less heat, a smaller fan etc.
    Now my new amp (arrived last week): The Focus from Acoustic Image (no fan): consumes 900 Watts and delivers 1000 Watt at 2 ohm. :eyebrow:
    This would mean that you can built a power station with these. I will ask AI and I'm curious how they will try to knock this one down.
  7. At 07:53 AM 1/7/2006, you wrote:

    Hi Rick,

    I'm extremely pleased with the new Focus. Thanks.

    According to the specifications of the Focus 2R series III the consuming power is 900 Watts while the output power is 1000 Watts at 2 ohm. This would mean that this amp is a kind of power station! Is it possible that this thing delivers more power than it consumes?

    Greetings from Wiro Jacobs

    The answer (within an hour!) from Acoustic Image:

    The rating on the back is somewhat imprecise. It's there to help pick the type of power cord to use. It is very unlikely that the amp would be run at 1000W for very long, probably just for short bursts. In real situations, even playing extremely loud, the average power output (averaged over several minutes) is less than 200 to 300W. The ac power consumed would be about 10% higher than that, so for long term power consumption, the 900W rating is high.

    Like I said, it is imprecise and somewhat arbitrary.

  8. BassikLee

    BassikLee Supporting Member Commercial User

    Feb 13, 2004
    Deltona, FL
    Owner: Brevard Sound Systems
    Most high power amps, as used in PA systems, will have a 30A plug, and require a dedicated 30A line for each amplifier. Case in point, the bigger Crown amps, and even my "lowly" Yorkville AP6040 and AP6020s I use in my PA rigs. Each amp gets a 30A feed. The way my two racks are set up and wired is like this: AP6040 (2000 WPC @4) on subs, AP6020 (2000 WPC @2, about 1300@4 as I use them) on mids, and a QSC PLX 3002 (550/900/1500 WPC @ 8/4/2) on the horns, then a dbx Driverack 260. Each rack is powered by a two pole 30A breaker, feeding 10/4 wire with two 30A circuits, via L14-30 plugs, using a Motion Labs Rackpack, with two 30A and two 20A circuits. Each big amp is rated at 4000W continuous, with peaks in the 7000+ range, and yet they show "average consumtion" on the back at 1800W. How? The same 1/8-1/3 power deal. QSC has/had a page showing the power consumtion of all their amps. On it, they listed the conditions. If I recall, it was 1/8 power with pink noise, which includes a 6dB crest factor. THAT caused "occassional clipping". If you bump up to 1/3 power, pink noise with 6dB crest, that'll produce moderate/severe clipping. Just goes to show what AI said, the AVERAGE actual power put out by these amps is MUCH lower than what we THINK it is, even with some clipping. FWIW, each of my two mains racks powers four Yorkville TX4s and four Yorkville LS1208Blk subs, either stereo or mono, subs fed off the main inputs or separately. Nice little rig, esp when I use all 16 boxes and both racks. THAT will get your attention....

    The above rig is NOT my bass rig, but my PA rig. I wonder how it'd sound as my bass rig..... :)


    look for "rackpacks"
  9. Crockettnj


    Sep 2, 2005
    North NJ
    WOW, wiro!

    AI got back to you super fast, and with a short, honest, realistic, not-needlessly technical answer.

    So, in the end, AI is NOT claiming to break the laws of thermodynamics. <PHEW!>

    (wondering why ALL companies cant be like that)
  10. You know what the funny thing is?
    My Trace RAH600SMX delivers 600 Watt RMS bridged. But this one sounds lots, I mean LOTS LOUDER and more detailed than the 1000 Watt Behringer.
    Now according to AI the Focus doesn't do much more than 200 to 300 Watts. And still this thing blows my Trace out of the room.

    So what good do all these power ratings when they mean so little?

  11. Yup.

    I spent the late 90s as a systems engineer for a big PA hire company. Our power distros had built in digital ammeters on each leg of the 3-Phase and you'd rarely see them read more than 1/10 of the potential amplifier power. I had a 160 box rig out with 250000W of potential amp power out once and with Lynyrd Skynrd on deck and the low end amps flashing clip lights from time to time I measured about 70A per leg. So about 25000W total draw, and that included 6 consoles and FX racks plus stage power.

  12. Part of the answer is that the measurement and rating methods need to be standardized.
  13. SubMonkey


    May 3, 2004
    Denver, CO
    Yah...Mine will make the lights dim for just a sec at some clubs in town :D

    now back to your regularly scheduled posts...

  14. FREE BIRD!!!!!!!
  15. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    Wow, that is an honest answer!!! Kudos to AI.

    AI did not say it could not do more than 200 to 300 Watts, they said the *average* would be 200 to 300 watts. You need the extra watts to handle the peaks. That's basically the "headroom" everybody talks about.

    And be very careful with the ratings from Behringer. I am very, very, suspicious that they are peak to peak, not RMS. Nowhere in the manuals do they state RMS. Whereas your trace did say 600W RMS. 600W RMS = 1,700W peak to peak.
  16. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Good point. I think the Behringer 1400-Watt power amp has a built in 15-A circuit breaker. Thus it could not deliver more than roughly 700 W on a continuous basis (assuming 50% efficient Class-AB design).

    For "home entertainment" amplifiers, the government mandates a test method. In a nutshell, the amp has to run at some fraction of rated power continuously, but must put out full rated power for 15 minutes. And power has to be rated in RMS Watts. There seems to be no way that the aforementioned amp could even be tested to this standard. And remember that this standard was imposed in response to a scandal resulting from manufacturers publishing grossly inflated power ratings.

    I would bet that the power ratings for amps from reputable makers are based on reasonable operating conditions, but when you start getting into the bargain basement, it is probably "buyer beware."
  17. raintalk


    Apr 17, 2002
    I mailed Behringer and they replied!

    They use "unbranded" watts :D

    "Thanks for writing!

    Our instrument amplifiers are stated in RMS. However, our sound
    reinforcement products are stated in a proprietary manner that is best described as "program" power (as opposed to "peak"). These specifications are actually a derivative of an industry standard protocol known as IEC 268-5. Since the spec for our amps is not identical to the IEC spec - the brand of Watt used remains unstated."

    At least they were very responsive and honest in their answer.
    I actually think have a pretty good products overall and have no problem buying them if they fit my needs.

    Many manufacturers stretch the truth - consumers need to keep their eyes open.
  18. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    The facts are that while the amplifier MAY be able to put out the large power, there are limits.

    I'll start by saying some limits don't really matter...... for other reasons....wait a bit....

    First is the mains breaker. Obviously, if you draw more than that is rated for, it will open, sooner or later. It does take a while, for either the one in the unit, or the one in the service panel (breaker box). So 10 or 20 seconds won't generally bother it, and that's a relatively long time, musically.

    Next is heat. Most amplifiers are NOT intended for continuous full power duty, they will overheat something, usually the transformer. That's because the transformer is heavy and expensive, and is pretty good at averaging the power, so it heats slowly. There is a big benefit to keeping it smaller and lighter.

    Why don't those matter? Well they do, but then you have to look at the input and "real world" power needs.

    Let's leave guitar aside..... It's another world....

    For bass, if you can average over 1/3 of max power for any reasonable time over a minute or two, you are one busy player.........

    For PA, count subs as being like bass, about 1/3 power long term average. For full range, likely not over 1/10 power long term.

    Clearly, an amp made for continuous full power would not be needed. It would cost plenty more and be a lot heavier, and you'd not notice the difference in actual use.

    So, if you can pull 12A long term, thats close to 1500W. Assuming modern efficiency, about 70% for Class-G or H and 85% for Class-D, that is about 1000 to 1300 watts available long term.

    Assuming you could ever do 1/3 power playing bass, that's an amplifier as large as 3000 watts, at least.

    For PA, 3000W or up to maybe 6000W , depending if its for subs or not.

    The mains draw rating on the back is usually the mains power drawn at 1/8 of full continuous power output. That is for UL and for CE mark.

    Does that help?

    BTW, if you push that sort of calculation to the limit when powering your stuff, you probably WILL be popping breakers sometimes.
  19. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Yes, very much. Thanks.
  20. chucko58


    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    Typical Class B (or AB) solid state amps are about 65% efficient at max power. Class H amps are even more efficient. So you're really looking at a line cord draw of about 2300 W or so.


    Real musical signals have big transients, but average 10% or less of their peaks. So if you have an amp that is just barely getting to clipping on the highest peaks, your average power out is about 10% of its max rating. This is where big Class H amps are a big win, because they're much more efficient than the equivalent Class AB rig at these lower power levels.

    QSC specifies a typical power input requirement on their amp spec sheets, based on an average of 1/8 rated power out. This is a good ballpark estimate of actual current draw in hard use.

    Also consider that most of us do not run amps of this size into loads that will draw the maximum output power. To use my rig as an example, I have a QSC PLX 2402 driving one 4 ohm Acme Low B-2 per channel. The amp is rated at 1200 W into a 2 ohm load per channel, but only 750 W or so at 4 ohms. So the maximum undistorted output with this load is 1500 W, not the 2400 that the amp is capable of. Most of us will have similar situations.

    Last, how many of us really run a big power amp to clipping at a typical gig? So the original question has little relationship to how we really use our gear.

    Honest amplifier makers rate their amps with continuous power by either the EIA or FTC rating standards. The FTC standard is more stringent because it has a 1/8th power preconditioning phase (used to be 1/3 power), and covers the whole audio band, where EIA is just at 1 KHz. But both EIA and FTC require the amp to crank out full rated power below some specified distortion rating continuously for at least one minute.

    Anything other than EIA or FTC continuous power ratings is PBS (pure bull sweat).