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Thread: Amplifier Recommendation for 2245H's?

  1. #16
    Senior Member DerekTheGreat's Avatar
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    Quote Originally Posted by Ian Mackenzie View Post
    Ah,

    Reading through the above posts it has occurred to me that the actual driver impedance could be a factor.

    I will have to turn on Leap to check but the impedance of the JBL 2245H in a tuned bass reflex enclosure isn’t 8 ohms. It dips down towards the dc resistance of the voice coil and is reactive. Ie not a passive resistance. That means in bridged mode you need to think about how your particular amp will cope in bridged mode.

    In theory @ 600 watts the amp has to deliver 69 volts rms into an 8 ohm load. At the voltage the current is 8.7 amps. However if the load is for example 5 ohm at a frequency region of peak demand the voltage is 54 volts and the current is 11.00 amps. No matter how you look at it ohms law is hard at work here. When semi conductors are pressed reliability becomes a factor.

    Under that condition the amplifier in bridged mode may or may not be adequately rated. The efficiency of the amplifier may possibly be impacted because more current is flowing at a lower voltage.

    My inclination would be to buy a much more powerful power amp than the power your intended to use so the amp is not going to be operating near the worst case scenario.
    A more powerful amp seems to be the take-away. Do you folks have any objections to running one in bridged mode? It's just that way seems like such an easy way for a guy like me with a miniscule budget to get to the goal. However, if a mono block or high power stereo amp is preferred, I will start saving more peanuts.

    Quote Originally Posted by rusty jefferson View Post
    It depends on the amplifier. To be honest I have no idea whether the K-1 is a Class AB with a SMPS, or a Class D, Class H, or something else. It's not that Class D amplifiers (what I was referring to) become unstable into a higher impedance speaker, they just produce less power (typically) into the higher impedance.

    Apologies, the spec sheet I found didn't show a rating for 8 ohms bridged, so it's probably not Class D? But if they can deliver 1100 watts @ 8ohms, a pair should be fine.
    I'm not sure, why don't these companies post what class their amp is under specifications?? I don't understand the technicals and mathematics like I once did. Ever hear of Audio Control? I've got one of their C-101 equalizers from my marantz days. They're still around and making amps. They've got this RS-1000 specifically designed for subwoofer use, mono @ 1000 watts, 2/4/8 ohm or so it says: https://www.audiocontrol.com/downloa...ser-manual.pdf SNR of almost 100dB..
    Too pricy for me at the moment and have fans, but maybe down the road. What really makes this company great are their user manuals, there's tons of humor speckled in them. So not your typical, put you to sleep read.

  2. #17
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    In the above case l think you will find that in bridge mode @ 4 ohms are amplifier is current limited not voltage limited to manage internal power dissipation.

    Looking at the normal stereo power output @4 ohms the amp is rated at 550 watts per channel. In this situation the output voltage is 47.00 volts and the current flow is 11.70 amps.

    Now in theory if we look at bridge mode in an ideal world we should have 47+47 volts = 94 volts available. This would produce 2,200 watts @4 ohms. The current flow would be 23.5 amps.

    However the amplifier is rated at 1550 watts into 4 ohms bridged. This means the maximum voltage available is 78.7 volts and the current flow is 19.7 amps.

    What this means is that the amplifier power output in bridged mode @ 4 ohm is 29% less than what the full bridged voltage available ref 2,200 watts. The current limiting stops the last 3.8 amps flowing into the load.

    While the spec sheet doesn’t list the bridge mode power output into 8 ohms on the basis of the voltage and current available into 4 ohms bridged it should be able to deliver 1400 watts @ 8 ohms where the voltage is 106 volts and a current flow 13.2 amps.

  3. #18
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    See my comments in the other thread on the real driver impedance. Think 5.8 ohms cold. More current flows. That means more current flows through the output stage and the power supply.

    In the above examples l gave you can see even a powerful amp levels off into 4 ohms bridged. I would consider the K2 if you intend to use bridge mode. You really don’t want to be riding on the safe limit with those currents flowing.

  4. #19
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    One thing l should have pointed out in a domestic situation it’s the peak voltage & current into the real load. In other words the driver is not a light bulb. Just how hot it will get is more about the duty cycle of the average current flowing through the driver. At low frequencies it’s going to be demanding. The rms sine wave power is 300 watts. 600 watts program power. Efficiency is 2.1 % A pair of them in parallel will give you 600 watts continuous sine wave and 1200 watts program power. I’d be looking at the K2.

    Have a look at this. They are getting good product review feedback

    https://djcity.com.au/product/behrin...yABEgJ5pfD_BwE

  5. #20
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    Failing all this discussion if you are missing 60 hertz wire them in series and plug them into the power point for comparison purposes.

    The story goes someone who will remain nameless did that with a bunch of LE15’s and stood outside to see how loud it was. Needless to say it changed the way he sees the world..LoL.

  6. #21
    Senior Member BMWCCA's Avatar
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    The "littlest" of the Crown Studio Reference Series amps (Studio Reference-II) is rated at 1,100 watts into an 8-ohm load. I never demand anything like that from mine but I've also never heard the fan come on—ever! It's a pretty stout amp if you like Crown and if you can find one.
    ". . . as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway."—Greg Timbers

  7. #22
    Senior Member DerekTheGreat's Avatar
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    Thank you for the explanation, Ian. I think I follow, mostly. LoL. Are there equations I can use for future reference? Do some folks just wire their audio stuff for 220V in the states vs 120? Seems like a better way to do it, coming from a layman like myself... As it happens, I have a lead on two K2's! I will try my luck with those once again, now that I think I've got my amp failure mode identified and solved.

    That Reference II looks like a nice amp, BMWCCA! There's one for sale on Audiomart right now, but a little too rich for my blood at the moment.

  8. #23
    Senior Member BMWCCA's Avatar
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    Quote Originally Posted by DerekTheGreat View Post
    That Reference II looks like a nice amp, BMWCCA! There's one for sale on Audiomart right now, but a little too rich for my blood at the moment.
    Yikes! $1500 and missing one knob seems a bit excessive . . . but in reality by no more than a few hundred bucks.

    Mine has the incorrect (silver) knobs, is missing the rack-mount covers, and also has a few scratches (touched-up by a car guy with BMW paint) and I got it in a swap with member Sub here. But it sounds better than anything else I've ever heard.

    I'd love another but, in the words of Reb Tevye, "If I were a rich man . . . Ya ba dibba dibba dibba dibba dibba dibba dum".
    ". . . as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway."—Greg Timbers

  9. #24
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    Cool

    When l’ve woken up and had a coffee l will type up the equation.

    Power in watts x the rated impedance

    Therefore:

    500 watts x 8 ohm = 4,000
    500 watts x 4 ohm = 2,000
    1,000 watts x 4 ohm = 4,000

    Take the square root of the above product = volts rms
    2^4,000 = 63.24 volts rms
    2^2,000 = 44.72 volts rms


    Power = volts x current. Power / volts = current

    Therefore 500 watts / 63.24 volts = 7.9 amps
    Therefore 500 watts / 44.72 volts = 11.2 amps
    Therefore 1,000 watts /63.24 volts = 15.8 amps

    In bridge mode both the channels are connected in series and the input signal a inverted on one channel to arrive at 2 x output voltage per channel.

    In the above examples

    63.24 volts x 2 = 126.5 volts squared = 16,002 / 8 ohms = 2,000 watts
    63.24 volts x2. = 126.5 volts squared = 16,002 / 4 ohms = 4,000 watts
    44.72 volts x 2 = 89.4 volts squared = 7,999 / 4 ohms = 2,000 watts

    2,000 watts / 126.5 volts = 15.8 amps
    4,000 watts / 126.6 volts = 31.6 amps

    The above assumes an ideal or perfect power amplifier.

    What you will find is that the bridge mode power is limited by the current available in that mode to drive the load. This is because the twice the current has to flow through each channel of the power amplifier.

    The consequence of this is that the internal heat dissipation of the amplifier has also doubled. The amplifier may not let you do that so it limits the maximum current to the load.

    I will check this after my morning coffee.

  10. #25
    Senior Member DerekTheGreat's Avatar
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    Whoa. Might take me a second to digest all of that, but I can now reference it at will. Thank you.

    So perhaps I shouldn't go with the K2's and just get one amplifier that can do what I need it to do without bridging? Back before they died, the Crowns never felt super hot to the touch. I could place my hand right on the heat sink and leave it there. Warm/hot, but no danger of burning myself..

  11. #26
    Senior Member DerekTheGreat's Avatar
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    Quote Originally Posted by BMWCCA View Post
    Yikes! $1500 and missing one knob seems a bit excessive . . . but in reality by no more than a few hundred bucks.

    Mine has the incorrect (silver) knobs, is missing the rack-mount covers, and also has a few scratches (touched-up by a car guy with BMW paint) and I got it in a swap with member Sub here. But it sounds better than anything else I've ever heard.

    I'd love another but, in the words of Reb Tevye, "If I were a rich man . . . Ya ba dibba dibba dibba dibba dibba dibba dum".
    If I was a rich man I'd certainly try to play ball with it. Buuut I'm going to have to wait. I've got a list going and that got added to it. Someday, perhaps.

  12. #27
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    Here's a link to the data sheet power requirements for the K-series. https://www.google.com/url?sa=t&sour...TmhGGto3LKzdBf

    You can see that running a single K-2 at (probably) 1/3 power @ 8ohms will require 4-6 amps from your electrical outlet. Running a pair of them bridged at 8ohms, 1/3 power will require 13-17 amps from your wall outlet. You mentioned your circuit is 15 amps, so you'd be starving the amplifiers the power they need before even considering the needs of the other equipment on the circuit. They'll turn on and operate, but not properly. A single K-2 would be the way to start, if you have enough electrical headroom for everything.

  13. #28
    Senior Member DerekTheGreat's Avatar
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    Guess I'll just stay where I'm at until I can afford to upgrade my electrical service. What a bummer. What if went to 220V? Aren't most modern audio stuffs configurable for either 110 or 220V? The way I understand it, I'll cut my amperage needs by 1/2 if I double the voltage and that's something a bloke could do right at the electrical box...

  14. #29
    Senior Member HCSGuy's Avatar
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    Quote Originally Posted by DerekTheGreat View Post
    Guess I'll just stay where I'm at until I can afford to upgrade my electrical service. What a bummer. What if went to 220V? Aren't most modern audio stuffs configurable for either 110 or 220V? The way I understand it, I'll cut my amperage needs by 1/2 if I double the voltage and that's something a bloke could do right at the electrical box...
    In general, amplifiers power supplies are switchable to work on 120v U.S. or 220v European. However, 220v European is different than 240V U.S. EU is 220v above ground, while U.S. 240v is two 120v leads in opposite phase, leaving 240v between them. You cannot mix the two. However, there are some really high power amps that will do 240v AC U.S. as well - Crown I-Tech comes to mind…
    That the internet contains a blog documenting your life does not constitute proof that your existence is valid. Sorry.

  15. #30
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    More current flows in the US 120 than 240 overseas. This means thicker gauge mains wire and bigger fuses all for more bass. More expense.

    Are you looking outside the box?

    I imagine that two or conceivable four 2245’s per side is a more efficient way to go. This assumes you have the space for 72 cu ft if bass enclosures. Once bass gets to really loud everything shakes. So how important is an ideal sub woofer?

    A Danly Pro sub is an alternative. If you have the resources a large bass horn which is directional would be effective. Steve Schell demonstrated a large bass horn with a tiny 3 watt amplifier. Very loud.

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