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Few tech questions

Discussion in 'Amps and Cabs [BG]' started by 8_finger, Jun 20, 2003.

  1. 8_finger

    8_finger Supporting Member

    Jun 1, 2002
    Silver Spring, MD
    I'm in teh process of buying a power amp. In local ads paper I came across ad of a guy who builds power amps. He says that his amps use FET PMC technology that uses less eletronic components and therefore ahs less weight, size and less heat generation. Does anybody have more explanations of this FET PMC technology, and how does it sound?
    He states following specs for his amps:
    power: 2X1000W@4Ohm
    THD: 0,001%
    slew rate>1000V/uS
    damping factor>1000
    S/N ratio 130dB

    The guy apperently got few rewards for his inventions in USA, England, Germany, etc.
  2. The best thing to do is call him and ask.

    I can only guess, but I'm thinking he means FET PCM (Field Effect Transistor - Pulse Code Modulated) Which is what is known as a digital amp. They are more efficient, therefor don't require as big a power supply, and if it has what is known as a switching power supply (like the Euphonic Audio and others) It would be even more efficient and probably very light for a 2KW amp. (Did you know that's almost 3 horse power!)

    the signal to noise ratio number sounds outrageously high for an amp. High slew rates are good for transients - My guess is that slapping would really kill on an amp like that.

    Where's all the tech guys? usually they spout off quite a lot with these kind of questions. Maybe PM Mrfunkypants - the guy we all think is Phil Jones. He's a wizard.

    Stay Low,

  3. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    The slew rate mentioned is totally ridiculous.
  4. 8_finger

    8_finger Supporting Member

    Jun 1, 2002
    Silver Spring, MD
    I thought so, maybe it's a typing mistake.
    I guess I have to call the guy for more detailed explanation.
  5. Petebass


    Dec 22, 2002
    QLD Australia
    Maybe you should get a hold of the corresponding specs for a QSC or a Crown and compare. Speaking of QSC, paging Mr. Bob Lee..........
  6. 8_finger

    8_finger Supporting Member

    Jun 1, 2002
    Silver Spring, MD
  7. Those specs are ridiculous. Unless it's a $10,000 amp.

    Next thing he tells you it's a 1 rackspace amp weighing 10 pounds.

    It should be PCM, not PMC, like basstrader said.

    With a signal to noise ratio like that it should sound better than any professional studio could ever do.
  8. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    What you describe functionally sounds like a Class D amp, but the specs sure don't match up with that. The figures are probably either typos, fudged, or measured in non-standard ways.

    The slew rate suggests that it is actually a medium-wave radio broadcast transmitter. ;)

    Slew rate isn't anything to be concerned about in bass amplification.
  9. To sum everything up:

    IT'S A HOAX!!!
  10. 8_finger

    8_finger Supporting Member

    Jun 1, 2002
    Silver Spring, MD
    Thank you all for replying
    I called the guy today and the amp is AB class,he explained that he uses unordinary components (laser toroid transformers, and some other stuf I didn't quite understand) and that's why his amps have that specs.
    I belive he overstated specs a bit
  11. winston


    May 2, 2000
    Berkeley, CA
    Here's an in-depth tech question:

    Last weekend I worked as monitor engineer for a friend's pro-audio company at a large reggae festival. The PA system features about 30K watts of QSC power (PLX 3002/3402 for mains and RMX 1450 for monitors) and an unreal Bag End ELF speaker system with 22-18" subs. FOH board is Spirit digital and monitor board is Allen & Heath, and we used minimal outboard gear.

    We were taking power from a very large, nearly-new generator that I believe provided at least 60 A total to 3 separate lines. We got one 3-phase feed and ran the proper sausage-size cable up to a distribution box onstage and ran all PA equipment from there. The other two feeds were used by vendors at the festival.

    The system sounded incredible, with enough headroom to reproduce even the heaviest dub bass with great depth, punch and fidelity---playing Radioaxiom (Bill Laswell/Jah Wobble)'s "Bass: The Final Frontier" CD over the system was truly remarkable.

    However, we had a recurring problem throughout the festival: at least once every hour we experienced sudden volume increases that overloaded the ELF processor, sent the amps into clipping and threatened to damage the speakers.

    Sometimes the problem would go away after 10-15 seconds but if it continued, a loud, low oscillating "wow" noise developed-truly unsettling. The only way to take care of the problem was by quickly reducing the level on either the FOH board or power amps-not the best solution under the circumstances. It was definitely not acoustic feedback and it happened with both recorded and live music.

    We tried to figure it out. We've never had this problem before, and this is the first time we've run the system on generator power. I kept an eye on the generator display, and it seemed to be providing up to 24 amps of power to our line, with 119-121 volts and very close to 60 hz--even during a loud show at night with the lights on.

    Last month we used the system at a festival that drew power from the grid and it worked fine. All the individual components of the system have been reliable and we removed all but the most essential outboard gear to make troubleshooting easier.

    Has anyone else had a problem like this? I'm not an expert in electrical matters, but my hypotheses were:
    --1)Having to share generator with vendors led to unsteady supply, creating problems in power amps or maybe the digital board, or,
    --2)Placing amp racks and distro box next to really loud, deep subs (response down to 8hz!)can cause weird, audible oscillations in the system.

    Any help with this matter would be greatly appreciated. Thanks!
  12. winston,

    why are you posting this here? Starting a new thread will get you more and better responses.