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New Lepai amps?

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  • AMC
    replied
    Re: New Lepai amps?

    Originally posted by jsr View Post
    The numbers aren't matching up. With the supplied 12v 4A supply, that gives the unit a total of 48w. At 4ohm load, if the unit provides 12w into 4ch, thats 48w of output power, so the unit is 100% efficient...doesn't add up.
    I would guess, as with the other Lepai amps, the power supply that they come with is under what the unit is intended to use. With the first amp, it wants a 4 amp supply, and came with a 2 amp. Point is...

    1. Lies, Dam lies, and ratings.

    2. It could benefit from a better power supply then what comes with it, and in fact would need it to come near it's ratings.

    Leave a comment:


  • jsr
    replied
    Re: New Lepai amps?

    Originally posted by Whitneyville1 View Post
    I asked about the 8 ohm out of the 2.1 amp and Mikevv said his was about 8 watts per channel with the 4 amp power supply that comes with it. 12 watts per channel @ 4 ohms. At 4 ohms that makes this amp about 75% efficient. Sooo, it's rated at 40 watts per channel (we'll assume @2 ohms) and 68 watts for the sub. I'll derate it 50% @ 4 ohms so the output is about 78 watts @ 4 ohms. That means the amp needs at least 25% more power input than audio out~120 watts. At 12 VDC that's 10 amps. Now the "specs" make sense. I know of a computer salvager who sells working ATX supplies for $5. 12 amp 12 VDC and up, you supply the IEC cord. To me, they're still worth playing with. You don't have to worry about feeding them too much amperage. They're like a light bulb, they only consume as much power as the chip can dissipate heat. If you have a ammeter that will go to 30 amps ($7-8 at O'Reilly's) you can use your car battery and test the amp draw in the real world (my plan). They just can't deliver 148 watts (peak) even @ 2ohms with 5 amps @ 14.4 volts (78 watts).
    The numbers aren't matching up. With the supplied 12v 4A supply, that gives the unit a total of 48w. At 4ohm load, if the unit provides 12w into 4ch, thats 48w of output power, so the unit is 100% efficient...doesn't add up. If the supply is pretty robust, it might be able to hold a higher voltage under full load, and typically decent 12v supplies output close to 13.8v. Assuming the supplied PS can hold 13.8v @ 4A draw, thats 55w, so efficiency with 4 ohm loads would be about 87%. still seems too high. That figure looks more realistic under 8 ohm load conditions. Unless he was using a 5A PS instead of the supplied 4A one.

    These amps still look really interesting. It'd just be nice if someone could provide real performance numbers. Channel separation is poor, but thats expected with such small size. I still wish the 2.1 had FM tuner and inboard mp3 playback capabilities. I'm turn between the 2.1 version for the sub output and the 4ch version for the radio and mp3 features, though I'd only use 2 of the channels.

    Does the 4ch have separate LPFs for the 2 channel pairs? I'm assuming these can't be bridged, though each channels load handling suggest it's possible if the channels were designed to allow bridging.

    Leave a comment:


  • djkest
    replied
    Re: New Lepai amps?

    Originally posted by fbov View Post
    Understanding is great, as long as it's in line with reality.

    Have fun,
    Frank
    It's really not that simple.

    Wall: ~115V AC- 1-2 amps
    Power supply: 12V, 10 amp
    To speaker: varies

    There's a circuit in the amp power supply, and there is a circuit in the amplifier itself. It's not as simple as ohms law.

    Leave a comment:


  • AMC
    replied
    Re: New Lepai amps?

    Originally posted by fbov View Post
    This makes sense to you????

    Ques: How do you draw 10 amps at 12v???
    Ans: V=IR at all times; use a 1.2 ohm load

    Ohm's Law isn't legislated; you can't break it. The only way to increase power at a constant load is to up the voltage. V=IR, so 12V will pull 3A into a 4 ohm load, nothing more, nothing less. While simplistic, first-order results set the boundary. Actual output will be less, based on amp efficiency.

    Understanding is great, as long as it's in line with reality.

    Have fun,
    Frank
    Load of the speakers has nothing to do with the draw from the amp. By that theory, car audio amps would peak at about 36 watts for a single 4 ohm speaker.

    Leave a comment:


  • fbov
    replied
    Re: New Lepai amps?

    Originally posted by Whitneyville1 View Post
    I asked about the 8 ohm out of the 2.1 amp and Mikevv said his was about 8 watts per channel with the 4 amp power supply that comes with it. 12 watts per channel @ 4 ohms. At 4 ohms that makes this amp about 75% efficient. Sooo, it's rated at 40 watts per channel (we'll assume @2 ohms) and 68 watts for the sub. I'll derate it 50% @ 4 ohms so the output is about 78 watts @ 4 ohms. That means the amp needs at least 25% more power input than audio out~120 watts. At 12 VDC that's 10 amps. Now the "specs" make sense....
    This makes sense to you????

    Ques: How do you draw 10 amps at 12v???
    Ans: V=IR at all times; use a 1.2 ohm load

    Ohm's Law isn't legislated; you can't break it. The only way to increase power at a constant load is to up the voltage. V=IR, so 12V will pull 3A into a 4 ohm load, nothing more, nothing less. While simplistic, first-order results set the boundary. Actual output will be less, based on amp efficiency.

    Understanding is great, as long as it's in line with reality.

    Have fun,
    Frank

    Leave a comment:


  • Whitneyville1
    replied
    Re: New Lepai amps?

    I asked about the 8 ohm out of the 2.1 amp and Mikevv said his was about 8 watts per channel with the 4 amp power supply that comes with it. 12 watts per channel @ 4 ohms. At 4 ohms that makes this amp about 75% efficient. Sooo, it's rated at 40 watts per channel (we'll assume @2 ohms) and 68 watts for the sub. I'll derate it 50% @ 4 ohms so the output is about 78 watts @ 4 ohms. That means the amp needs at least 25% more power input than audio out~120 watts. At 12 VDC that's 10 amps. Now the "specs" make sense. I know of a computer salvager who sells working ATX supplies for $5. 12 amp 12 VDC and up, you supply the IEC cord. To me, they're still worth playing with. You don't have to worry about feeding them too much amperage. They're like a light bulb, they only consume as much power as the chip can dissipate heat. If you have a ammeter that will go to 30 amps ($7-8 at O'Reilly's) you can use your car battery and test the amp draw in the real world (my plan). They just can't deliver 148 watts (peak) even @ 2ohms with 5 amps @ 14.4 volts (78 watts).

    Leave a comment:


  • Whitneyville1
    replied
    Re: New Lepai amps?

    Even my cheap lap-top has a 4 channel soundcard in it, and "Frank" my desktop is 5.1, so the 4 channel amp makes sense to me for most any 'puter-thingey made in the last decade. I think this is a much newer 2 ohm stable chipset much better than the now "old" Tripath. I've seen the chips advertised for a couple of years on the DIY sites, like the DIY 9.2 AVR chipsets for $29.99 that give you 55 watts per channel. I'd bet money these chipsets are sourced from automotive applications from the micro-cars sold in Asia. (They make a SMART look big, like the TaTa Nu two seater that you sit on the engine!)

    Leave a comment:


  • Bart Oetken
    replied
    Re: New Lepai amps?

    I think Jonny said it best. Its a the truth and sweet. I will leave it at that. lol

    Bart

    Leave a comment:


  • Bart Oetken
    replied
    Re: New Lepai amps?

    Well they look pretty cool. Either way t amp or no t amp. Im going to get my hand on the two new ones.

    I have the silver lepai amp inside and out and always caught myself saying " man, I wish lepai came out with something with alittle more power."

    Well looky looky here. Would love to hook them up and do some comparing.

    Its funny you see these amps all over ebay. And, its nice pe is caring these amps now. So I dont have to wait on HK to deliever.

    Leave a comment:


  • jsr
    replied
    Re: New Lepai amps?

    Darn, I had assumed they were Tripath amps. I wonder if theyre even class T or D topology.

    I wish the 2.1 amp had all the features of the 4ch. I really like the FM tuner & mp3 capability via usb and sd, but I want the ability to drive a sub also.
    I still dint think these will do anywhere near claimed power at rms...maybe peak, but still should have enough power for my small bookshelves and maybe even my small sub.

    If anyone is willing to use a separate power supply for a nice class D amp, look into the Rockford Fosgate PBR300x4. Tiny little amp pushing out a clean 75 real rms watts into 4 channels, and has gain adjustments per channel pair and a LPF.

    Leave a comment:


  • AMC
    replied
    Re: New Lepai amps?

    I think I want to put the 4X45 in my boat!

    Leave a comment:


  • fbov
    replied
    Re: New Lepai amps?

    Originally posted by XtremeRevolution View Post
    ...I wonder what that USB port is for though. Says its for charging. Huh?
    Originally posted by AMC View Post
    Interesting features, 2ohm stable, and of course the 2.1 ability.
    If you weren't aware, the front USB port on the 4-channel is an MP3 input. It "plays" thumbdrives. The rear USB port on the 2.1 may well be for charging a source player, as that unit's missing an MP3 decoder.

    In truth, 2 ohms is the only way to get anything close to the rated power. 14.4v across 2 ohms dissipates a little over 100W, so perhaps the 2.1's rating is acheivable... without the sub. 4x45W isn't happening in any multi-channel RMS sense.

    I have a small Lepai LP-V9, and it's a tolerably good amp, but I've never tried to make it sound bad, per se, as my application is battery powered, and that works well.

    Have fun,
    Frank

    Leave a comment:


  • AMC
    replied
    Re: New Lepai amps?

    Interesting features, 2ohm stable, and of course the 2.1 ability.

    Leave a comment:


  • XtremeRevolution
    replied
    Re: New Lepai amps?

    Tempted to throw one of these in the cart. At that price, you could very easily power one of those 6.5" buyout subs and a pair of stereo speakers. Incredible.

    I wonder what that USB port is for though. Says its for charging. Huh?

    Leave a comment:


  • Paul Carmody
    replied
    Re: New Lepai amps?

    Where's Neil when you need him to clear this up?

    Leave a comment:

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