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What can drive 2 pairs of MRX518's 2 ohm stable

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  • #16
    Why would turning down the 2450 create more heat? That seems counter-intuitive....not being smart here, looking to learn! "2-tier Class H" - this is basically a pair of linear amplifiers in series, right? Wouldn't turning it down prevent the output from swinging all the way rail-to-rail and generate less heat?

    Wes
    <div class="signaturecontainer">--<br><br>Hammond: BC, M3, Split L111, L122 / Leslie: 51, 760 / Yamaha: DGX-620, PF-85<br><br>Follow my new band, <a href="http://DrBombay.ca/connect.html" target="_blank">Dr. Bombay</a>! We're going to be organasmic!</div>

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    • #17
      I'm also confused about how turning down generates more heat. And I understood that the 1850HD was just a derated 2450. There might be more to derating than I know. I never run loads that low and have never had an power amp thermal. (I have had a powered speaker thermal once.) I also generally don't push my equipment.

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      • #18
        An old PLX 1802 works well on a pair of MRX 518's when run 2 channel. A 2 ohm load is tough on most of the amps available. The RMX 1850 was always advertised as 2 ohm stable where the 2450's didn't make that claim. The heat thing also has piqued my interest. Would you explain please Andy?

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        • #19
          Turning a 2450 down to match an 1850's power will still dissipate greater power because the dissipation is a function of rail voltage which is higher on the 2450. Class H doesn't matter since both amps are class H. Look up the dissipation curves for class h amps and plot for 2 different sets of rail voltages and you will see what I mean. Since the hi-low rail ratio is about the same between amps, the heat ratios track as well. Class d does not suffer the same way, as it's non-linear and does not scale proportionally.

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          • #20
            Or buy another 2450 and run 4ohm loads instead of 2. Running subs at 2ohms seems like an invitation for issues.

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            • #21
              Originally posted by Tomm Williams View Post
              Or buy another 2450 and run 4ohm loads instead of 2. Running subs at 2ohms seems like an invitation for issues.
              I respect your opinion, BUT why put it in the manual if it can't meet the exepctations of the customer?

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              • #22
                If you're running 2ohm on both channels I'd recommend the 1850hd for sure. How about 2 smaller lighter amps with 1 box per channel? I have only 1 pair of mrx518s. Most often they are powered off 1 channel of a yamaha P5000 with the other channel powering tops (ev sx300 or jbl 4725). I didn't know how this was going to work long term but the amp has been rock solid through 100+ gigs! same with the amp too, and this is using the crossover built into the amp. Another amp rack I use has yamaha P7000s and with 2 dual 15/2" over dual 18 per side the mid channels are at 2 ohms. Also rock solid. I used to have one amp at 2 ohms stereo driving mids and I could get it to shut off by sweeping the mids with the channel strip eq at +9 or so. It would just turn off, I'd have to turn it back on again. But with one channel driving 2 ohms and the other at 4 it has never had any issues. The point is... Run top boxes off the second channel of the 2450 and get a another 2450 and do the same. Or sell it and buy 2 lighter amps (p5000 or p7000)
                <div class="signaturecontainer"><a href="http://www.rock-bot.com" target="_blank">www.rock-bot.com</a><br />
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                • #23
                  Unalaska: Thank you for the post, I see what you mean, love the yamaha stuff I already own. Unfortunately I am running Stereo (those damn DJ's!!). I don't want to do it, but probably for this weekend I will put the yamaha cp 2000 on sub duty, it has never went down running 2 ohm loads, BUT to the ear it just doesn't seem to sound as good as the 2450 (probably just me), so not all is lost, there is a solution, your post has helped to turn me to that solution.

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                  • #24
                    Stereo subs?
                    <div class="signaturecontainer">--<br><br>Hammond: BC, M3, Split L111, L122 / Leslie: 51, 760 / Yamaha: DGX-620, PF-85<br><br>Follow my new band, <a href="http://DrBombay.ca/connect.html" target="_blank">Dr. Bombay</a>! We're going to be organasmic!</div>

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                    • #25
                      Originally posted by wesg View Post
                      Stereo subs?
                      No but the tops are.

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                      • #26
                        Originally posted by nchangin View Post

                        I respect your opinion, BUT why put it in the manual if it can't meet the exepctations of the customer?
                        Wouldn't be the first time a product didn't meet promises made by a manufacterer. I suggested a second 2450 as I owned about 4-5 of them at one time and thought they were pretty good amps, except for 2ohm sub loads in spite of what the manual states. With 4 ohm loads, never had a problem. And as stated, ohm load can deviate to where you could actually be under 2ohms. Give youself some room to spare.

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                        • #27
                          Thank you Tomm I see your point now. Gosh another 40 lbs to haul around, I know now why I have 2 u rack space left, maybe it's a sign. heh

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                          • #28
                            Originally posted by nchangin View Post
                            Thank you Tomm I see your point now. Gosh another 40 lbs to haul around, I know now why I have 2 u rack space left, maybe it's a sign. heh

                            Yep I had two per case and they were no fun to haul around, went to PLX and IPR's instead. I believe it was Andy who I first recall making a statement about 2ohm sub loads being a little risky. I've stuck with that approach ever since................zero amp issues.

                            I thought the 2450 made a great main or monitor amp, wouldn't hesitate to use one on an install.

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                            • #29
                              Originally posted by Tomm Williams View Post
                              I believe it was Andy who I first recall making a statement about 2ohm sub loads being a little risky.
                              Risky with the 2450 but not so much with the 1850HD.

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                              • #30
                                Used RMX2450's are dirt cheap ($300?), just buy another and keep the loads to 4 ohms or above.

                                "We Have Met the Enemy and He is Us" - Walt Kelly​

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