Benchmark Media AHB2
Der AHB2 ist ein Endverstärker. Sein Klang übertrifft die Qualität von Class A Verstärkern.
Er ist ein echter Benchmark: Kein Verstärker hat geringeres Rauschen oder niedrigere Verzerrungen!
Ein kleines, passiv gekühltes Gehäuse liefert saubere 480 Watt an 6 Ohm im Bridge-Mono-Betrieb!
Mit zusätzlichen Reserven, um auch schwierige Lautsprecher Lasten anzutreiben. Ungleich zu leistungshungrigen Class A-Verstärkern erreicht er eine Leistungseffizienz vergleichbar zu Class D Schaltverstärkern.
Viele Lautsprecher haben ein Impedanzminimum weit unter der nominalen Impedanz.
DerAHB2 treibt locker schwierige Phasenverläufe niedrige Impedanzen.
Stereo Lasten mit bis zu 1,4 Ohms können bis zur Leistungsgrenze sauber betrieben werden.
Die meisten Verstärker erzeugen höhere Verzerrungen , wenn die Impedanz der angeschlossenen Lautsprecher sinkt. Im Gegensatz dazu bleibt der AHB2 auf seinem niedrigen Verzerrungsniveau.auch bei schwierigen Lasten.
Der AHB2 hat einen hohen Dämpfungsfaktor für einen kontrollierte Basswiedergabe.
Der hohe Dämpfungsfaktor sorgt für einen absolut linearen Frequenzgang selbst bei starken Impedanz-Schwankungen.
Der AHB2 kann bis zu 29 A Spitzenstrom liefern, gleichzeiig für beide Kanäle.
Der AHB2 wird unter keinen Umständen hörbare Verzerrzngen erzeugen.
"I very much enjoyed my time evaluating the Benchmark AHB2 amplifier and can heartily recommend it to those seeking one of the lowest distortion and lowest noise amplifiers on the planet—one that is very musically transparent and easy on the ears to boot."
- Frank Alles, Stereo Times
Der AHB2 amplifier ist drastisch anders aufgebaut als herkömliche Verstärker.
Zwei neue THX-patentierte feed-forward error-correction Technologien eliminieren die meisten Verzerrungsquellen.
Eine unkonventionelle Stromversorgung sichert eine feste Regelung und niedrigen ripple zugleich mit niedrigsten magnetischen Feldern.
Hochwertige Abschirmungen und Starquad Signal Kabel veringern die Interferenz.
Das Ergebnis ist ein kühl laufender AHB2 mit einem Signal-Rausch-Abstand von 132 dB, mit Verzerrungswerten unterhalb der Messgrenze der besten Messgeräte.
See John Siau's application note: "A Radical Approach to Power Amplification" for more details.
The AHB2 is the only amplifier that leverages the patented THX-AAA Technology™. This patented system reduces distortion to vanishingly low levels while enabling several power-saving techniques.
"The Benchmark AHB2 is a powerful and efficient amplifier with prodigious low levels of noise and distortion. The fact that it is also very musical and non-fatiguing, courtesy of THX’s patented AAA Technology™, is the icing on the cake. Benchmark Media and THX have a lot to be proud of for the development and implementation of the new technology the AHB2 represents."
- Frank Alles, Stereo Times
The AHB2 has a bipolar class-AB output stage that delivers high output current and low noise. The THX-AAA Technology™ provides accurate cancellation of zero-crossing errors, exceeding the performance of the best class-A amplifier.
Traditional class-AB amplifiers generate crossover distortion every time the push-pull output stage crosses 0 volts. This crossover distortion can be especially problematic at low playback levels.
In contrast, class-A amplifiers eliminate crossover distortion by keeping all output devices turned on at all times. This brute-force class-A approach solves the crossover distortion problem but it consumes lots of power while delivering very little to the speakers. The wasted power produces heat which must be dissipated into the listening space.
Class-A amplifiers eliminate crossover distortion but they suffer from high power consumption, poor damping, and limited output power. The AHB2 is the first amplifier to virtually eliminate crossover distortion without incurring the undesirable side effects of class-A amplification.
In contrast, all conventional class-AB amplifiers have crossover-distortion artifacts.Traditional class-AB designs attempt to control distortion through the use of feedback. Unfortunately, these feedback systems have a limited ability to reduce the abrupt transients that are caused by output device crossover transitions. Feedback networks attempt to correct errors after they occur. In contrast, feed-forward networks can prevent errors before they occur.
THX-AAA Technology™ includes an ultra-clean low-power error-correction amplifier that runs in parallel with the high-power main amplifier. The correction amplifier actively drives the output while the main output devices transition between push and pull states. Like a class-A amplifier, the AHB2 shows no signs of crossover distortion. The feed-forward system virtually eliminates the errors that would have been produced by the output devices in the main amplifier.
The THX-patented feed-forward error correction used in the AHB2 is so effective that biasing of the class-AB bipolar output devices can be reduced to unusually low levels. Benchmark has chosen to maintain a small bias current in the output stage, but this bias current is not critical to the distortion performance of the unit. The benefit of low bias current is that very little power is wasted as heat when the amplifier is idle. The AHB2 only draws 12 W when idle, and less than 1/2 W in standby.
The feed-forward error correction also allows the use of class-H tracking power supply rails without the usual distortion-performance penalty. These tracking rails significantly improve the overall efficiency of the amplifier while the error correction keeps distortion nearly nonexistent. The AHB2 rivals the efficiency of class-D amplifiers while exceeding the sonic performance of power-hungry class-A designs. Green never sounded so good!
Most high-quality power amplifiers have linear power supplies, large toroidal transformers, and large banks of energy-storage capacitors. These linear supplies are usually unregulated and the capacitors help to remove ripple produced by the audio and by the AC line. In contrast, the AHB2 uses a tightly regulated resonant switching power supply that includes a very fast control loop. This control loop responds to audio-frequency load changes and keeps the supply voltage constant without the use of a large bank of capacitors. This active regulation is much more effective than capacitive energy-storage. Consequently, the peak power output of the AHB2 does not vary with line voltage or audio loading. The power supply rails maintain a constant voltage during audio peaks.
The power supply in the AHB2 switches at frequencies that are well above audible frequencies. This eliminates mechanical hum while significantly reducing the strength of stray magnetic fields. For a given amount of power, magnetic field strength decreases as switching frequency increases. The lower field strengths also provide a significant reduction in size. High-frequency transformers and coils are also much smaller than line-frequency components. This size reduction contributes to the small physical size of the AHB2.
The switching power supply used in the AHB2 is a zero-voltage switching, resonant power converter. This means that the power devices in the supply switch near zero voltage and zero current, eliminating the large switching transients produced by conventional switching power supplies. The power supply in the AHB2 is actually much cleaner and quieter than a conventional linear supply.
The power supply In the AHB2 is well over 90% efficient, much more efficient than linear supplies. This means that little power is lost to heat.
The power-efficient AHB2 uses passive heat sinks to maintain cool operation. The AHB2 delivers high power without the need for fans. The unit runs cool, even when playing audio at full output levels. The absence of fan noise is absolutely essential in a high-resolution listening environment.
The precision balanced inputs on the AHB2 are equipped with low-noise input amplifiers. Benchmark considers balanced inputs essential in a true high-resolution system. If balanced sources are not available, Benchmark sells unbalanced to balanced adapter cables that extend a 3-wire balanced connection back to the unbalanced source connectors. These adapter cables provide many of the advantages of fully balanced interconnects while providing full compatibility with all unbalanced sources.
The AHB2 is a low-gain design. Maximum output is not reached until the balanced inputs reach +22 dBu. This is a much higher signal level than is used at the input of most power amplifiers. High interface signal levels are required to achieve the best possible system signal to noise ratio (SNR). Most power amplifiers have far too much gain and consequently they suffer from poor noise performance. The AHB2 is 10 dB to 30 dB quieter than some of the very best power amplifiers on the market. A rear-panel gain switch can be used to set the AHB2 at higher gain settings if necessary. The low-gain setting is designed to interface directly with Benchmark DAC3 converters and other professional audio products.
The AHB2 has a unique protection system that prevents damage from overloads and short circuits. The protection system monitors output voltage, output current, output distortion, output device SOA (safe operating area), power supply current, power supply voltage, AC line voltage, case temperatures, and power device temperatures. Fault conditions silently mute both output channels in order to protect the speakers and amplifier from damage. The amplifier outputs are also muted while the amplifier is turning on or off.
The mute circuits are fully electronic. There are no mechanical relays in the mute circuits. Our tests showed that relays are too slow to protect against certain fault events. Our tests also showed that relay contacts can add significant distortion as they deteriorate with use. The AHB2 is one of very few amplifiers that avoids the use of relays in the output stage. This means that the AHB2 will maintain its rated distortion performance after an unlimited number of power on/off cycles.
Benchmark's unique distortion monitoring system mutes the amplifier if it is excessively driven into clipping. This system protects tweeters from an overdriven amplifier.
Benchmark's short circuit detection system is fast enough to fully protect the amplifier from events occurring at any output voltage or current. This system detects abnormal loads and instantly mutes the outputs.
A status display shows the exact cause of the fault so that the problem can be corrected.
The AHB2 is equipped with high-quality binding posts, and SpeakON output connectors. The high-current SpeakON connectors are designed for heavy-duty commercial sound systems and provide much better electrical connections than binding posts. Benchmark highly recommends the use of the twist-lock SpeakON output connectors. We also highly recommend the use of our top-quality professional-grade speaker cables.
The letters A, H, and B allude to the unique topology of the amplifier's output stage. The AHB2 combines class-AB, and class-H topologies using a feed-forward error correction system.
But there is much more to the story -
The initials A.H.B. can be found on many of the circuit diagrams of Benchmark's early products dating back as far as 1983. These are the initials of Benchmark's founder, Allen H. Burdick. He personally designed many of Benchmark's early products.
Allen had a life-long passion for audio, and he became one of the leading innovators in the pro-audio industry. The AHB2 is named in his memory.