PS Audio BHK Signature Series 250
by PS Audio
- Product Code:
- PS Audio
- BHK 250
- Power Amplifier - Black or Silver
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The BHK Signature 250 and 300 power amplifiers are the culmination of one manís half-century search for perfection in musicís reproduction. Bascom H. King has designed amplifiers for many companies, some selling in excess of $100,000, including: Constellation Audio, Marantz, Infinity, and Conrad Johnson. This is the first amplifier Bascom felt was good enough to lend his name to. It is his finest achievement in a lifetime of work.
Available in both stereo and mono models, the BHK Signature series is unparalleled in its ability to render details formerly lost in the music. The BHK Signature is a hybrid design enjoying performance benefits from multiple design techniques including, a balanced differential vacuum tube input, balanced differential MOSFET power outputs, and separate, isolated, analog power supplies feeding each.
When it comes to musically controlling and powering loudspeakers, the BHK Signature has no peer. The stereo Signature 250 produces 250 watts/per channel into an eight-Ohm loudspeaker, 500 watts/channel into four-Ohms, and stable into 2-Ohms; enough power to satisfy even the hungriest of loads.
The Mono Signature 300 doubles the output current with half the impedance of the stereo model. Each Mono Signature produces 300 watts into an eight-Ohm loudspeaker, 600 watts into four-Ohms, and 1000 watts into 2-Ohms. But more than just doubling the current, the BHK Signature 300 also doubles every internal component of the 250 into one: double tubes, double power supplies, transistors, capacitors and resistors. The results are hard to put into words. The BHK Signature 300 is a clear step above the stereo 250, on the order of 20% better, though both have the same character of sound. Both the Stereo 250 and Mono 300 are one of the best performing, musical sounding amplifiers ever made. Imagine your delight listening to either.
Unit Weight: 83 lbs
Unit Dimensions: 17.1Ē x 8.7Ē x 14Ē Chassis only. 15" deep including connectors.
The power amplifier is technology always present in stereo systems. Yet, despite the fact everyone uses them, few appreciate the power ampís critical role in preserving musicís nuanced details, because most amplifiers fail to preserve them. Overtones from plucked instruments, subtle cues defining placement, depth, soundstage width, and transient decays are often lost in the power amplifier.
The BHK Signature power amplifiers are unique in their ability to faithfully pass even the tiniest of details. The first listen to the BHK is like pulling a blanket off the loudspeakers. Suddenly revealed are the tiniest of details that now ring clear through the BHK, perfectly preserved through its extraordinary bandwidth, low feedback, vacuum tube and MOSFET design.
The input stage is a critical interface:
The connection between preamplifier and power amplifier is critical, for it is at this junction where most essential musical details are easily lost. Nothing in the design of a power amplifier is more important than its input stage when preserving musicís finest nuances. In the BHK Signature a vacuum tube serves as the perfect interface between the preamplifier and the massive power output stage inside the BHK Signature. The input stageís seemingly impossible task of passing both delicate and powerful musical information without loss is made possible by massive numbers of free flowing electrons traveling within the BHKís vacuum tube; electrons quantities that are not to be found in transistors.
Used as the interface between the preamplifier and the input stage of a power amplifier, tubes have no peer. Invented by Fleming in 1904, and refined by deForest in 1906, the vacuum tube is unique amongst amplification devices: it boils an abundance of free electrons in empty space while modern devices pull fixed numbers through solids. A tubeís high voltage, empty space, rich numbers of electrons and connection through unattached fields preserves details lost in the solidity of silicon. Tubes are the perfect interface between sources and power stages.
The BHK Signature input features a classic triode vacuum tube in a modern configuration. Hand matched pairs of Russian Gold Lion 6922s are self-biased with constant current and high voltage, free of timing and phase distortion without the use of negative feedback. They provide the perfect interface between the delicate musical transitions output by the DAC or preamplifier, and are electrically isolated from the BHK power output stage which is connected to the loudspeaker.
The hybrid approach used in the BHK Signature takes advantage of the best traits technology has to offer, unavailable in traditional solid state or tube designs. While vacuum tubes are the perfect input stage, they cannot make the same claim on a power amplifierís output. Conversely, solid state designs are correct for output stages, but suffer when used as inputs. Only a hybrid approach takes advantage of the best in both disciplines.
A power amplifier connects its reservoir of energy to the loudspeaker through a type of valve (solid state or vacuum tube) controlled by the input stage. If the input stage has done a good job of preserving musicís subtle details, textures, timing and phase information, transferring it without loss to the power stage and eventually the loudspeakers is best handled by a tube-like solid state device known as a MOSFET.
MOSFETs handle power without the additional circuitry needed by tube power amplifiers, and they sound better than tubes or their solid state alternatives, bipolar transistors. Field effect transistors were first invented by Julius Edgar Lilienfeld in 1925 and because they require very little current and operate with an invisible field, their sound is more closely related to vacuum tubes than transistors, without suffering any of the issues driving loudspeakers typical of vacuum tube power amplifiers.
Not all MOSFETs are the same, their differences characterized by their relationship with the input signal and the power supply driving them: N-types for the positive going signals, P-types for negative. It turns out that N-types have lower distortion and perform better than P-types. Despite this anomaly most power amplifier designs use both types of transistor in a configuration known as complementary symmetry. The BHK takes a different approach, one that avoids the problem of uneven performance between N and P devices altogether. Using only N Channel MOSFETS in its output stage, the BHK Signature produces a near-perfect balanced waveform without the degradation inherent in a complimentary design.
Voltage Options (Factory set only): Japan 100V, North America 120V, Europe/Asia/Australia/New Zealand 230V
Mains Power Inputs: IEC C14
Fuse Compliment all Countries: 4 - 10 amp fast blow H-Rated 5x20mm Rail Fuses
Fuse Compliment Mains:
1 - 2 amp slow blow H-rated 5x20mm
1 - 12 amp slow blow H-rated 5x20mm
1 - 1.6 amp slow blow H-rated 5x20mm
1 - 10 amp slow blow H-rated 5x20mm
1 - 1 amp slow blow H-rated 5x20mm
1 - 5 amp slow blow H-rated 5x20mm
US (NEMA 5-15P) (all versions)
Schuko (CEE7/7) (230V version)
UK (BS 1363) (230V version)
Speaker Outputs Signature 250: Gold plated copper binding posts (2 pair per channel)
Speaker Outputs Signature 300: Gold plated copper binding posts (2 pair)
Other: DC Trigger Input 3.5mm 5-15VDC
3 years parts and labor on unit
1 year on vacuum tube
@Ready: 75 Watts
@Idle: 175 Watts
@Rated power 8Ω: 850 Watts
@Rated power 4Ω: 1600 Watts
Gain: 30.5dB +/-0.5dB
Sensitivity for rated output power of 250 watts into 8Ω: 1.3V
Noise: 100-20KHz <-85dBV
Input impedance Signature 250 stereo: Unbalanced 100KΩ , Balanced 200KΩ
Input impedance Signature 300 mono: Unbalanced 50KΩ, Balanced 100KΩ
Output Impedance: 50Hz, 2.8VRMS <0.1Ω
10Hz Ė 20KHz +/- 0.1dB
10Hz Ė 200KHz +0.1/-3.0dB
1KHz, 1W/8Ω: <0.01%
20-20KHz, 1W/8Ω: <0.1%
1KHz, 200W/8Ω: < 0.1% (120VAC Mains input)
1KHz, 400W/4Ω: < 0.1% (120VAC Mains input)
Both channels driven 120vac mains, 1kHz, 1% THD
8Ω: 250W minimum
4Ω: 500W minimum
2Ω: Stable for musical transients
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