Ambrosi Amps' K-Power Amps - Retrofit poweramp solutions for the Lunchbox - With pictures & videos

    The design and price is very attractive, but I dont like the idea of having a amp without any cooler generating heat inside of a digital device like kemper. Its better and inexpensive to put a passive cooling rack to power transistor to put the heat outside the chassis.

    Hi all, some answers to your questions and observations :)


    The amp, in its current "on-paper" incarnation is mono.
    Andrea Ambrosi has chosen the class A/B for sonic reasons, he thinks it's more musical than the digital class.


    The price is not optimistic, and it should be between 120 and 150 € for this configuration.
    As for SPL, using a 2x12" with 102 dB sensitivity per cone we get the following:


    68 watt = 123 dB
    38 watt = 121 dB
    22 watt = 118 dB


    Add 3 more dB for a 4x12".


    If your cones have a different sensitivity use this formula:


    SPL = SPL1watt + 10 * log (PotMax)


    where SPL1watt is the cone's sensitivity.


    Add 3 dB for a 2x12" and 3 more for a 4x12".


    Note the nominal power values are undistorted, so this is "clean" SPL.


    The plate is made of aluminium, and it should be enough to dissipate the heat. We had though of a passive cooling rack for the integrated circuit, or of cooling slots cut straight on the plate itself.
    Class A/B dissipates less than class A (but more than class D indeed).

    Quote from viabcroce


    Andrea Ambrosi has chosen the class A/B for sonic reasons, he thinks it's more musical than the digital class.


    This 'superiority' of class A/B vs. class D comes up regularly, and personally I think it's a myth.
    The powered Kemper makes use of a class D amp.


    Any thoughts concerning this common perception?

    Well, if €150 is indeed realistic, then I'm with DangeRuss and mDan - will there be a US-friendly (110V) version, and how soon can I send a check? :)


    Also, is Ambrosi considering a stereo build, or would the thermals be problematic? I notice that while Ritter's pricing is expensive across the board, there isn't a huge jump from mono to stereo. (In my opinion, their most powerful stereo option is the best value; the "cost of entry" seems to be high.) If Ambrosi's mono design can be realized at €150, I have to wonder where he would price a stereo option.

    as I said earlier, I was told by a close friend ( Hifi specialist and long time tube amp builder ) that the tests he did proved the lack of a good bass response (muddy ) towards other types of amps. It's sad since class D has a fantastic efficiency. I wonder How Kemper did solve this issue with the powered version.

    I've inquired him about the stereo option(s), let's see what he comes up with.


    As for the class struggle (LOL), in his words
    class D works at two different (low and high) powers depending on the power demand. This implies switching between the two power levels, which implies a small distortive anomaly. In class A/B the power efficiency is lesser but the sound is more natural.


    Now, clearly any difference has to be weighted depending on the application. In my 35+ years of experience in the hi-fi world, there may be even big differences between two amps based on the same project but differently engineered, and I have never met two amps which sounded the same. Pretty sure a different working class makes an amp sound differently. Whether or not a specific user is able to tell a difference depends on a lot of parameters, including his experience and skills, the application and the measurement tool.
    For example, the Profiler is not certainly the proper tool to check a cab's linearity :)


    As for the costs, exporting, a stereo version etc... everything is in the
    brainstorming phase at this stage. I'm not even sure what kind of
    involvement I'll have in all this, if any. But for sure, and apart my personal use, I will not advice about this amp until I've tested it in different situations and for a long time, and I get confident I know it inside out.


    @ waraba: an amp is of course much ore than just its working class. The complexity of the elements built around a simple op amp are meant to model the sound according to the engineer's taste and aim.
    There are certainly class D amps that sound better than some class A/B amp, and the other way around.
    It would be like saying that a 12-cylinder engine is always superior to an 8-cylinder one, hence a car based on the former will always outperform one based on the latter... You know, overall performance is much more complex than just an engine.


    :)

    Great work!


    I always love it when people take the initiative to create something for their own needs and share this under a normal and realistic price tag.
    This is exactly how Matrix amplification entered de modeling world back in 2010.


    Cheers

    Thanks for the appreciations :)


    I have to say tho that I've never seen any price as a hardwall or as not realistic: a seller is entitled to ask for any amount of money for anything they sell. A price will never be more or less ethic, unless it's related to essential goods: it's the market that will determine whether it's "right" or not. They're not pushed to sell, you're not pushed to buy... but if you meet and agree on a price, that will be the right price for the moment (and the market).


    :)


    I'd also note that a high price represents a value under certain circumstances, that is a reason to actually buy the good.

    I'm in too, 240V in Aus so the only issue is postage. I'll still use an active setup most of the time, but it would be cool to have the flexibility of driving any cab I come across.

    @ tyler: See here for details. In its current development state this amp would output 22 W @ 16 ohm. To determine how much volume (SPL) you'd get from this you can apply the simple formulas I put there. With cones exhibiting 102 dB 1 W/1 m you'd get 121 dB, which is loud. Check you cones :)


    @ jpm: my thoughts exactly. Plus, I've a wonderful 14-kg 2x12" currently collecting dust, and it would make for an extremely light setup: guitar on my back, Profiler cables etc on one shoulder, cab held with one hand. Around 20 kg total, and I'd still have one free hand for scratching my head LOL
    For the heavyweight lifting there are always the CLRs.

    Quote from tylerhb

    If this thing has enough headroom to drive crisp clean sounds on my 16 Ohm cabs at loud rehearsal volumes, count me in.


    I'm not sure a high SPL automatically means something can deliver a big loud clean headroom without any sign of distortion.
    The SPL value doesn't measure "or care" if the sound is clean or distorted. Clean sounds are much less compressed and more dynamic so they often require a lot of W.
    22 W @ 16 ohm might or might not have enough clean headroom to deliver crisp clean sound for you at loud rehearsal volumes.

    I'd disagree with this, HK :)


    Of course the notion of SPL per se doesn't carry any information about the distortion % at which it is expressed, but the wattage figures I supplied relate to clean, undistorted power. The SPL you get from the formula is hence clean.