"...I confirmed the KST-150's character: open, airy, transparent, harmonically right... and fast. It deserves to be listed in Class A of "Recommended Components." If the KST-150 sold for $18k instead of 3k, hosannas of praise would be raining down from all sides..." - Sam Tellig, Stereophile May, 2007
"I wanted to let you know how much I have been enjoying using the Luminance KST-150 amplifier. I have had several friends of mine come by who have heard it and were very impressed with it as well. This amplifier is . . . the only game in town, in my opinion, at the $3000 price point." - Michael Wright, Stereotimes.com
Reviews
- Dagogo, August 2006
- Stereo Times, April 2006
Rich harmonics, air, presence and absolutely non-fatiguing detail. This is the amp for those not persuaded by the lure of switching digital amps. This amp has the warmth, life and body that many of those amps do not have. Bottom line: The KST-150 has the speed of digital with the organic richness of analog.
 About Luminance
Luminance Audio was founded by Rick Schultz of Virtual Dynamics, Circuit designer Steve Keiser, known for the legendary B&K ST-140, and Mike Tseng, music lover and proud father of concert pianist Cindy Tseng.
The KST-150
The Luminance
Audio KST-150 is a balanced, cascade-based, 3-stage design with a common mode rejection ratio of
90db+, and a declared objective of being among the top three fastest amplifiers with wide bandwidth and low distortion.
Circuit designer Steve Keiser incorporated an ultra high-current-gain complimentary push-pull cascaded amplification stage to
drive a quadruplet of high-gain power MOSFETS per channel to attain a substantial damping factor of
100. As this damping factor is sustained fully by the driver and output stages from 20Hz to 20kHz, the KST-
100 is able to control a loudspeaker’s woofer movements and tweeter movements with equal
vigor.
Overall negative feedback loop bandwidth is constant from DC to 63kHz and open loop bandwidth and
closed loop bandwidth frequency domain time constants are matched using 1% tolerance polystyrene
capacitors. All resistors on the amplifier circuit board are of 1% tolerance. The input
stage uses a differential amplifier which inputs the signal from the source as well as from the output and
performs the necessary voltage gain, which is 26dB. The driver stage is a fully complimentary push pull
cascaded common emitter amplifier, which in turn drives a complimentary, two parallel push-pull source
follower Hitachi MOSFET output stage. The power supply utilizes a total of 56000 mfd of storage capacity
and is parallel distributed, meaning that total of six 8200 mfd capacitors are used connected in parallel,
instead of the usual two. The input AC is terminated with 3-pole AC line filter to remove power supply line
noise.
The Design Process
Music contains highly complex myriad of constantly changing amplitude, phase, and harmonic information. Designing an amplifier to reproduce accurate sine waves into a resistor makes the design process easy for the designer. Designing an amplifier by ear is farm more relevant, but evolutionary in nateur as the design can always "sound better".
Combining an engineering approach with detailed perceptual listening can produce an amplifier which is essentially obsolescence proof, as is the case with the KST-150.
How the KST-150 works
The main distinguishing characteristic
which puts this amplifier so far ahead of the competition is speed. The faster the amplifier, the better is can keep up with the details in the input signal. Linearity is defined as the ability to retain input waveform accuracy. Luminance Audio employed cascadin and complimentary symmetry in our circuit designed to preserve linearity.
Lightning fast, and measurable too
At 250 Volts per microsecond, the Luminance KST-150 sets a revolutionary industry first when compared to even the fastest of similar solid state designs. Flagship amplifiers offered today of similar design boast slew rates of 100 V/ms, regardless of the fact that many are as much as 27 times the price. The industry standard for this design is 40 V/ms.
Why is this so important? Consider a single string resonating on a guitar: The amplifier needs to control the speaker so that the movements of that single string can be replicated, yet amplified. The advantage of a high slew rate is a cleare reperesentation of complex musical passages, which would include the tonality of the wood behind the acoustic guitar.
The KST-150 achieves high speed, high transient attacks with a not so conventional analog circuit and is revolutionary as it performs as well as even the fastest digital amplifiers in speed. Speed however is not all that this amplifier gets right, in fact it is just the start.
The Analog Advantage
Speed is not the only requirement necessary to outperform other amplifier designs. Switching amplifiers, also known as digital amplifiers, can boast slew rates as high as 220 V/ms. These amplifiers have speed and efficiency, but there is a fullness in detail to an analog solid state amplifier that is unprecedented in accuracy. Analog is a continuous uninterrupted flow that alows all the subtle nuances to be heard, in a switching amplifier, these subtle nuances, are all but eliminated through the process of switching.
| Specifications |
| Power Output: |
150W RMS continuous into 8 Ohms both channels driven over a frequency range of 20 Hz to 20 kHz with less than 0.1% total harmonic distortion. |
| Intermodulation distortion: |
Less than 0.02% using 7000 Hz and 1000 Hz intermixed at a 4 to 1 ratio (This is standard SMPTE method). |
| Power Output into 4 Ohms: |
200W per channel with both channels driven simultaneously with less than 0.1% total harmonic distortion. |
| Power Output into 3 Ohms: |
220W per channel. |
| Minimum load impedance: |
3 Ohms nominally. |
| Slew rate: |
250 volts per microsecond. |
| Damping Factor: |
100 from 20 Hz to 20 kHz. |
| Channel Separation: |
80 dB from 20 Hz to 20 kHz. |
| Signal to noise ratio: |
95 dB below full power output. |
| Frequency Response: |
5 Hz to 630 kHz +0 dB, -3 dB. |
| Output impedance: |
0.1 ohms. |
| Power Consumption: |
140 watts idle,420 watts at full rated output into 8 ohms. |
| Power supply capacity: |
54000 mfd. |
| Resistor type: |
1% metal film. |
| Signal capacitor type: |
polypropylene and polystyrene. |
| DC offset control circuit topology: |
DC servo loop using discrete differential pair. |
| Common Mode rejection ratio of input differential amplifier: |
90 dB. |
| Number of output devices per channel: |
4. |
| Output device type: |
MOSFETS. |
| Power Transformer capacity: |
800W |
Download the Owners Manual (PDF 93kb)
Owner Comments
-
"I must say we love this amp! When we were finally able to hook it up to different pairs of > thoroughly broken-in speakers, we found it to be wonderfully transparent, fast, clear, and dynamically accurate on both small signals and large, even simultaneously. It is very, very musical and a marvelous value at its price. Its tone balance is just right, and the build quality is excellent. We challenged it in some very serious ways, and it stepped up to the plate every time, even to the critical ears of several experienced visitors. We highly commended this amp to anyone!" - Roy Johnson, Green Mountain Audio
- "... I consider it the most remarkable audio purchase I have ever made. Dave Thomas was right in his review. You could easily charge twice the money ..." - KST-150 owner Ken Little
- "... Since I first acquired it, I haven't been able to move from listening chair. Everything in my vocabulary of audiophile jargon has been obsolete by the performance of the KST-150.Terms like musical and detailed just don't cut it, even though the KST-150 is both those things in spades. I cannot describe in words what the KST-150 has done to my system...." - KST-150 owner G. T. Groom
|
