Does the PE 250W plate amp have "soft clipping"? Rythmik?

Discussion in 'Home Theater Projects' started by Jeff Meininger, Nov 29, 2003.

  1. Jeff Meininger

    Jeff Meininger Second Unit

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    A while back, I built two AV15 subs using identical alignments. One is powered with a PE 250W plate amp, and the other with a rythmik 350W (380W?) plate amp with the TL072 upgrade.

    I've noticed that the two amps produce very different results when they clip. Playing the PE amp at levels that absolutely MUST be clipping only produces moderate distortion that makes things sound "funny" or "somewhat wrong". Clipping the Rythmik creates a loud POP or CLACK sound. It's scary... makes you JUMP.

    Does the PE have "soft clipping" or something? Why would these two amps behave so differently when they clip?

    If "soft clipping" is the answer, can it be added to the rythmik amp? If so, are there drawbacks to doing so? Perhaps losing some dynamics?

    Thanks!
     
  2. Rob Formica

    Rob Formica Stunt Coordinator

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    Unfortunately I'm unaware of those amps designs, but "soft clip" is definitely not the answer.

    Ideally neither amp should be pushed into clipping for a substantial amount of time, as clipping is dangerous for the driver.

    I think your AV15 are underpowered... but you should be able to find a pro amplifier for slightly more than the value of your existing amps. This would be "answer" which would help both dynamics and eliminate clipping entirely. [​IMG]

    Later...
    Rob
     
  3. Jeff Meininger

    Jeff Meininger Second Unit

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    I don't push the rythmik into clipping for substantial amounts of time. In fact, it's only ever happened once (one of the rocks falling after the deeping wall is breached in LOTR:TTT). Well, actually it's happened 3 times, but the second 2 times I was doing it on purpose to try to figure out what was going on. It's not something that has happened in any other movie I've watched, including some other serious bass monsters.
     
  4. Brian Bunge

    Brian Bunge Producer

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    Jeff,

    What alignments are your AV15's?
     
  5. Jeff Meininger

    Jeff Meininger Second Unit

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    250 liters tuned to just a smidge under 20 Hz. I've set the rumble filter to 20 Hz.
     
  6. Brian Bunge

    Brian Bunge Producer

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    Hummm...have you considered the possibility that you're bottoming out the sub using the Rythmik amp? I know according to the sims you shouldn't be, but from what you say you're hearing it sounds more like bottoming than clipping.
     
  7. Jeff Meininger

    Jeff Meininger Second Unit

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    My previous sub was an EBS Shiva, and I bottomed that out quite a few times.

    This is a very different kind of noise. It's a much sharper, more "metallic" sort of noise. Louder, too. Quite scary sounding.

    When it first happened, I thought for sure it was the coil hitting the back plate. A very loud, fast, metal-on-metal type of noise. I called John Janowitz thinking I had a faulty driver or something, but he walked me through a test and it turns out my driver is fine. He had me push the cone all the way in to see if it makes contact with anything, and it does not. He told me that's just what it sounds like when you clip the amp with an aluminum-cone driver.
     
  8. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    Jeff, your description of the sound is exactly what a voice coil bottoming out sounds like.
     
  9. Matt Dolejsi

    Matt Dolejsi Agent

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    I use the rhythmic amp, I got it before they started giving the option for the 24 db/oct crossover....I worked with the guy and he talked me through what bridges to joint with what capacitance values and I did the soldering at home.... Hence they offer it now cuzz he thought it would be a good idea to have that offered. I've never had a problem clipping the amp (and yes that scene in LOTR is great, but i had no problems) I'm running a tempest though so maybe you have your gain up highter than me. maybe, but i too see something else as the culprit. bottoming out??? i dunno the AV15s have a lot of room back there...
     

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