iAmp 800 Power Measurements

Discussion in 'Amps and Cabs [BG]' started by EAGary, Oct 25, 2003.

  1. EAGary

    EAGary Registered User

    May 27, 2002
    It takes more than a Fluke meter and a load resistor to properly measure the power of the iAmp800. The technique that was tried works OK for the most basic measurements; however, the 800 is a little more sophisticated. I can't blame anyone for trying as this is how people learn, and I'm the last one to discourage learning. Everyone at EA encourages all players to learn as much as possible about the equipment they own or intend to own.

    The 800 will deliver 1000 watts RMS into a 2 ohm load, and 800 watts into a 4 ohm load. What complicates matters is that the internal limiter engages once the amp goes into clipping. Once the limiter engages, the power is scaled back. The time constant of the limiter is a few hundred milliseconds and is something you can't see with a digital meter. To look at what is actually going on, you need a storage oscilloscope that is connected differentially to the load resistor and is set to trigger at the point just before the limiter engages. Getting this set up correctly is tricky as the limiter is somewhat frequency dependant (for that matter, any power measurement made without visual examination of the output waveform is marginal at best). And, signals from bass guitars are usually not symmetrical and have huge peaks, and this lack of symmetry also interacts with the limiter circuitry. Also, the original power measurements were made with the limiter out of the circuit, something the end user cannot duplicate.

    One other variable that is usually overlooked is that as you crank up the power (from any amplifier) using a sine wave input signal, the AC line voltage will sag. The 800 will draw 10 amps at full power from the AC line, and it is not uncommon for the line voltage to sag 5-10% under these circumstances. The lower line voltage means lower output power. When a sring instrument (excluding keyboards and such) is played through an amplifier, the AC line current is extracted in pulses, and the current available to the power amp stage is averaged out due to the storage capacitors in the power supply. We pick the capacitor values to help compensate for the sag in the line voltage.

    Everyone at EA is available for technical discussion on any of our products. Mike Dimin is also a good resource. So is Dave Freeman at Club Bass.

    Gary Gibilisco, Euphonic Audio, Inc.
  2. A true RMS voltmeter is inadequate to measure the output power of any amp as far as I'm concerned. You really need a scope at the least. I would have commented on that in the original thread, but it was closed before I got to it. Testing sinusoidal test tones into a static load resistor is also not a great barometer to judge real world performance by.... ;)

    Anyway, I mainly wanted to say that I appreciate representatives of gear manufacturers taking the time to post on TB. It's indicative that they care about their products and customers. It's great to have you guys (EA) aboard as well as Bob Lee from QSC, and all the luthiers (and anyone else I may have forgotten).
  3. notanaggie

    notanaggie Guest

    Sep 30, 2003
    Vell, Vell, das ist goot.....

    Back to english....

    Naturally I used a scope, I have repaired probably a few thousand pieces of gear....I do know something....

    I looked for a limiter , but didn't see the usual burst and decay that most limiters show. Must be too fast.....

    What surprised me as well, was that the Mosfet devices were 100V rated, and the power supply was also right at 100V. looked very close, I am used to seeing a much greater margin.

    But, no doubt the EA folks did their homework...

    Ah joost vanted a question to ask.....maybe it vas ansvered goot....
  4. Nightbass


    May 1, 2001
    Seattle, WA
    Is this a full bandwidth figure, or at a single midband frequency such as 1kHz?
  5. Mike Dimin

    Mike Dimin Inactive

    Dec 11, 1999
    Gary - thanks for your clarification!
  6. notanaggie

    notanaggie Guest

    Sep 30, 2003
    We didn't measure the "power bandwidth", but EA put in a ton of power supply capacitors.

    That means the ratings will probably be pretty similar at the low end, which is where most amps fall off.

    The tone was a little more muted at the high end with 2 ohms, but with the class-D that's not uncommon. They have an output filter that can't be perfect for all loads.

    It did get mighty loud though, didn't sound bad....
  7. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    This doesn't relate to measuring power (at least not objectively), but it does pertain to the iAMP 800, so here goes.

    I recently picked up a used iAMP 800, which was one of the earlier models. Well, the day after I received it, I shipped it down to Gary to have the updates performed (remount the tuner chip and a few other tweaks) as well as to add the newer black knobs. My iAMP returned to me last week, and even though I have only had a chance to play through my "practice cabs" (Mesa Boogie Diesel Powerhouse, Jr. and modified Peavey 1820), I have been very impressed. Those cabs don't sound too bad (the 1820 has a Madison Executioner 18" and two Selenium 10"'s), but they have never had much speed to their attack. Well, the iAMP 800 changed that! I was blown away by how deep, fast, and articulate those cabs sounded with the iAMP. I can't wait to try it with my EA and Epi cabs!

    With regard to the "Deep" switch, I really didn't contemplate using it much, because I figured that it would result in an overwhelming boomy tone with little definition. Boy, was I wrong! It certainly increased the low end punch (that 18" could cause heart failure, if pushed hard with the Deep switch engaged!), and added significant low end weight, but the clarity and articulation remained constant. I was very impressed. I definitely agree with Vanselus' early posts about how the iAMP 800 can really thicken up your low end, but retain clarity. I'll have to try it with my two Epi T-112's and mimic his experiment more closely. ;)

    As usual, Gary and John were the epitome of customer service. And once again, they have produced a product that meets and exceeds my needs.

    Thanks again, guys!

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