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

This. If I got it right it was related to other projects\business he then dropped.
Of course, if a new generation of devices is going to see the light, things are due to change.

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INTRODUCTION
K-Power amp's technology, analogic but not banal, studied but not expensive, is the result of years of research in the field. The design is free of any kind of compromise on materials; solid-state technology has been chosen in order to offer the best results in terms of linearity and reliability. The quality of components, from the transformer to each single component is aimed at offering the musician a great quality.

Circuits use carbon-film resistors for the least thermal noise; ceramic, multi-layer and electrolytic capacitors; an oversized transformer, a 2-mm aluminium frame for the ultimate lightness and other peculiarities.
This monolithic, class A\B amp has been conceived in order to linearly amplify (i.e. with no distortion) the monophonic input signal. Designed around the National LM3886 integrated circuit, it exhibits a number of protection mechanisms such as the Under Voltage Protection, which serves the purpose of preventing the "bump" on the loudspeakers when switching the unit on\off. The output is protected against both short-circuits and overloads. Two stages safeguard the chip against overheating: the SPIKe (Self Peak Instantaneous Temperature °Ke) chimes in in case of the final transistors' temperature raising; the second protection circuit operates on the whole chip interdicting its operation when the temperature goes over 165° C. The K-Power amp also hosts two 2-A T fuses on the power supply line.

DATA SHEET
230 V AC / 50-60 Hz
Power chip: IC National LM3886, thermal convection cooling.
Minimum\Maximum power absorption 23 / 100 VA
Power absorption in stand-by 21 VA
Voltage gain: 27 dB
Maximum power: 68 W\4 ohm, 38 W\8 ohm, 22 W\16 ohm
Efficiency: from 113 dB to 121 dB, with 1-2 1x12", 100 dB\1 W\1 m cabs. Add 3 dB for 2x12" cabs and 6 dB for 4x12" cabs (more details in the Connections chapter).

Instantaneous peak output power: 135 W
Frequency range: 27 Hz - 105 kHz +0.5 / -3.0 dB
Damping factor: 200
Distortion factor THD+N: 0.1% 20-20,000 Hz
Signal-to-noise: > 92 dB
Noise voltage: 2.0 uV rms unweighted
Input sensitivity @ 4 ohm: -0,6 dBV / 0.72 V

Solid-state bridge rectifier stage
Dual power supply 28 V per branch with 2 x 2 AT, 250V, 5x20 mm fuses
0.5 A T, 250V, 5x20 mm fuse
Protection circuits: Over-Voltage, Under-Voltage, Short To Ground, Overloads, SPiKE Protection, Over-temperature

INPUT: 1/4" unbalanced, 10 kohm impedance
Maximum input level 2.0 Vpp @ 4 ohm. Settable through an on-board trimmer

OUTPUTS: Monitor Out 1/4" unbalanced for a line-level connection (external power amp, recording device, mixing desk and the like). 2 x 1/4" for connecting loudspeakers in the 4-16 ohm range (minimum load: 1 cabinet @ 4 ohm or 2 cabinets @ 8 ohm).

MUTE/ACTIVE switch. POWER switch.

Main frame: 2-mm aluminium.
Size: 360 x 117 x 88 mm (14,2” x 4,6” x 3,5”). Internal depth 76 mm (3,0”)
Weight: 2,0 kg (4,4 lbs).

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Quote from DADA

Great to see this development is actual maturing!
Make a 1U stereo version in an aluminium casing and I see a bright future

Do you mean an external case, as for the Matrix?

Quote from mDan

Looks good... I'm just wondering why the transformer is soooo huge

This is the size and the form factor of a classic, non-switching, 100 W transformer. Andrea Ambrosi thinks they sound better

Quote from mDan

There are also some nice small toroidal core transformers... smaller/lighter/cheaper, maybe your amp builder can have a look on them

Do you really think an amp builder has never heard about toroidal transformers?

The K-Power amp has been conceived in order to multidimensionally optimize a vast array of parameters

The first video should be online tomorrow

No, they are more expensive here in Italy. And are not smaller in all the dimensions, which would require a diagonal mounting in this case. Basically, this would make the project more complex, less solid and more expensive overall.

LOL

This was actually my hope when I started my quest for an amp... and an amp builder

Sure, if the amp actually ends up hitting the market, each customer would receive a unit with the proper transformer

HTH

The short introductory video (the first of the series) is out

No music example yet, but the explanation of the system and the procedure we used.

The next videos should follow more or less daily as long as Andrea cuts them.

For the whole series we kept the video quality low in order to save bandwidth, but the audio quality high.