288 Power Amplifier Monoblock Pair
60W Class-AB
Ultralinear Push Pull Tube Power Amplifier
The 288 Monoblock Power Amplifier is an audio powerhouse with explosive dynamic capabilities and effortless audio presentation thanks to 60 watts RMS output power at only 1.0% Total Harmonic Distortion + Noise. It has plenty of power to drive most loudspeakers to appreciable sound levels with ease.
$8,199.99 / Pair
Not only is this amplifier quick and accurate, it is also very musical. Its extremely wide full power bandwidth means that the ultra low and high frequency content is accurate and free from unwanted artifacts.
During extended listening sessions, the amplifier never becomes overbearing and fatiguing like some. The 288 also has built-in features, including ammeters for tube biasing and testing, making operation a breeze.
The Circuit
A matched pair of KT88 tubes operating in a Class AB Ultralinear output stage offers 60 Watts of power with extremely low distortion all the way up to clipping. At the heart of the 288 is the custom wound Ultralinear output transformer, weighing in at a colossal 13.5 lbs. This transformer reduces losses and improves bass weight and sound stage. The frequency response is extended well beyond the audible range with -3dB rolloff points at a full 60 Watts well below 15Hz and well above 100KHz. This wide bandwidth ensures that the audible frequency response is not only flat, but also very low distortion and free of phase shift. Any of these unwanted artifacts are well outside of the audible band.
A preamp consisting of a pair of 6SN7 dual triode tubes offers extremely low preamp noise as well as superb detail and nuance. The 6SN7 is considered to be one of the best Hi-Fi preamp tubes ever made due to its great sound and high linearity. In this preamp, the 6SN7 is a perfect fit.
Tube rectified for component longevity...
A 5AR4 / GZ34 tube rectifier provides AC to DC rectification for the high voltage supply and provides a slow and controlled startup with low voltage drop at full power.
A CLC filtering topology uses a large 10 Henry 200mA filter choke inductor to reduce ripple early in the filter chain with minimal supply sag to the KT88 power stage. Additional stages of filtering are added in before the high voltage supply feeds the preamp tubes. The helps keep overall noise to a minimum for 110dB Signal to Noise Ratio (SNR) at the speaker.
Premium components are used throughout for the utmost performance, sound quality and longevity.
Features
The 288 Power Amplifier offers features that make owning and operating a pair of mono amplifiers easy. A 24 position stepped attenuator volume control allows precise matching of the individual left and right audio channels. Unlike a standard rotational potentiometer, the stepped attenuator clicks into position setting the volume precisely and accurately through a fixed resistor network while eliminating the annoying background noise associated with conventional volume controls. Perfect matching is made by setting each amplifier into the same "click" of the volume control.
A VU or Volume Unit meter on the front illuminates when the amplifier is powered on and indicates the relative power output to the speaker. It offers compression and controlled movement to display the average power. Each meter is calibrated to display 0dB at 60 Watts of output power. No longer do you have to worry about overpowering and damaging sensitive loudspeakers.
Never visit a technician, adjust bias at home...
With the 288, biasing the output tubes is hassle-free. No external metering is required, so you never have to visit a technician. Analog milliammeters monitor the current through the KT88 output tubes. To bias, simply set the meters to the indicated level in the User's Manual via the adjustment point in the back.
The cathode current meters also serve as an in-circuit tube tester. If there is a discrepancy in the current of each meter, the output tubes are no longer matched.
Construction
An 1/8 inch thick aluminum alloy chassis rigidly supports all of the components and heavy transformers while acting as a heat sink for the tubes. The chassis pulls away heat and dissipates it effectively from the tubes, helping them run cooler and increase their lifespan over cheaper steel chassis. An aluminum transformer cover and back panel, as well as stainless steel hardware, ensure good shielding as well as minimal 60 cycle noise induction into the ground path from stray transformer magnetic fields. The ends of the amplifiers are solid walnut end caps with curly maple inlays with an oil-rubbed finish.
Point to Point hand-wired...
The circuit is all hand-wired using point-to-point method for the amplifying stages. This keeps signal wires extremely short, reducing noise and increasing stability. Tube sockets are mounted directly to the chassis to remove the risk of cracking a circuit board as often the case on cheaply constructed amplifiers caused by changing tubes and heat stress.
The power supply is kept to the back of the chassis with the large capacitors mounted on 1/8 inch thick electrical grade fiberglass eyelet board for easy service and rugged construction. Independent voltage rails run from the supply board to each amplifying stage, helping to keep the coupling of the stages to a minimum. Special attention is made to the grounding and power supply return paths to reduce crosstalk between stages and maintain signal-to-noise integrity. A multiple star ground configuration is used to control ground currents.
288 Features
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PSEUDO INTEGRATED DESIGN WITH VOLUME CONTROL ACCEPTS MOST LINE LEVEL SOURCES
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24 POSITION STEPPED ATTENUATOR VOLUME CONTROL WITH DALE RESISTORS
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ILLUMINATED VU METER WITH LOGARITHMIC COMPRESSION FOR POWER MONITORING
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ANALOG AMMETERS FOR OUTPUT TUBE MATCHING AND BIAS MONITORING
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CUSTOM MASSIVE US MADE 13.5LBS CUSTOM WOUND ULTRALINEAR OUTPUT TRANSFORMER
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10 HENRY 200MA US MADE FILTER CHOKE CLC POWER SUPPLY
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ETFE HIGH TEMP MIL-SPEC AEROSPACE GRADE WIRE
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MOGAMI W2330 COAXIAL SHIELDED INPUT WIRE
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PRP PR9372 US MADE METAL FILM NON-MAGNETIC AUDIO GRADE RESISTORS
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1/8" ALUMINUM CHASSIS AND NONMAGNETIC STAINLESS HARDWARE
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INSULATED 5-WAY GOLD PLATED BINDING POSTS
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ISOLATED GOLD PLATED RCA INPUTS
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SHIPS WITH ELECTRO-HARMONIX KT88 TUBES AS STANDARD
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IN HOUSE CURVE TRACED MATCHING OF PREAMP TUBES
Maximum Output Power
60-Watts RMS
THD+N at 60-Watts 1KHz
1.0%
Full Power Bandwidth (60-Watts)
20Hz - 35KHz at -0.5dB
THD+N at 1-Watt 1KHz
0.035%
Maximum 1W THD + N
<0.45% 20Hz - 200KHz
1-Watt Bandwidth
<13Hz - 50KHz at -0.5dB
Input Voltage for Rated Output
1.7V RMS
SNR 1-Watt into 8ohms
-93dB A-Weighted
SNR 60-Watts into 8ohms
-110dB A-Weighted
Gain
22dB
Negative Feedback (Closed loop only)
15dB
Input Impedance
250K ohms
Speaker Taps
4, 8 & 16 ohms
Power Tubes
2x KT88
Preamp Tubes
2x 6SN7
Rectifier Tube
GZ34
Power Consumption
150 Watts
Dimensions
20" x 13" x 9.5"
Actual performance will vary depending on vacuum tube quality. Specifications subject to change.
288 Typical Specifications