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Hercules II / Stereo Power Amplifier

The horizontal format of the Hercules II amplifier made it practical to create a stereo version—an amplifier in the same chassis as the Hercules II Mono, with the same effortless, extraordinary ...

Brand: Constellation
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The horizontal format of the Hercules II amplifier made it practical to create a stereo version—an amplifier in the same chassis as the Hercules II Mono, with the same effortless, extraordinary sound, but with two 500-watt channels instead of a single 1,000-watt channel.

  • Inputs 4 XLR (2 Constellation Direct), 2 RCA
  • Power output, 8Ω (1 kHz @ 1% THD+N) 550 W
  • Power output, 4Ω (1 kHz @ 1% THD+N) 750 W
  • Power output, 2Ω (1 kHz @ 1% THD+N) 1 kW
  • Outputs metal binding posts
  • Frequency response 10 Hz to 100 kHz, +1/-0.5 dB
  • Gain 32 dB
  • THD+N (1 kHz @ rated power) <0.05%
  • Output impedance 0.05Ω
  • Damping factor (8Ω load) 150
  • Input impedance 10KΩ unbalanced, 20KΩ balanced
  • Output noise <500 µV, -100 dB @ 250 watts
  • Weight 220 lbs / 100 kg
  • Dimensions 19 x 13 x 32 in (whd)

48.26 x 33 x 81.3 cm (whd)

The horizontal format of the Hercules II amplifier made it practical to create a stereo version—an amplifier in the same chassis as the Hercules II Mono, with the same effortless, extraordinary sound, but with two 500-watt channels instead of a single 1,000-watt channel.
The Hercules II Stereo uses exactly the same circuit as the Hercules II Mono and the original Hercules. The same circuit that inspired a leading reviewer to describe our original Hercules amplifier and Altair preamp as “the most transparent, detailed, and cleanest electronics I’ve heard.” The Hercules II Stereo cannot quite match the dynamics of the Hercules II Mono, but the fundamental sound quality is the same.

The Stereo benefits from the same upgrades we made to the Mono. The power supply features substantially larger storage capacitors, to deliver cleaner DC power and more headroom on loud peaks. The pure copper bus bars used for the speaker outputs and power supply rails are twice the size of those in the original Hercules. Both of these improvements allow the Hercules II Stereo to perform even better with low-impedance speakers.

The transformers and digital control circuits are now isolated in their own fully shielded and suspended enclosure, to protect the audio circuits from electromagnetic interference and vibration, and to prevent any vibrations from the transformers from being carried into the listening room.

Despite the reconfiguration from vertical format to horizontal, despite the splitting of the monoblock’s resources into two channels, the Hercules II Stereo maintains exactly the same sonic character, the same unprecedented combination of solid-state power and control with the warmth and musicality of a small, single-ended tube amplifier.

All of our Hercules amplifiers have been based on the same circuit: a single-ended, 125-watt amplifier design tuned purely for musicality. Each of these amplifiers forms a module. Rather than bulking up the Hercules amplifiers with more and more components to make the desired power rating, we simply combine multiple 125-watt modules. This is why the 500-watt-per-channel Hercules II Stereo sounds exactly like that original 125-watt amp.

The revolutionary Balanced Bridged circuit topology used in all Constellation Audio amplifiers gives the Hercules II Stereo exceptionally low noise and outstanding common-mode rejection ratio. But those are just technical terms. What’s more important is that with an essentially perfect balance between the positive and negative halves of an audio signal, the Hercules II Stereo achieves a level of musicality previously heard only in our other amplifiers. The key element in our topology is the use of only N-type output transistors, instead of a mix of N- and P-type transistors as found in other fully-complementary solid-state amplifiers. Because every element of the musical signal passes through exactly the same types of circuit components, all the musicality of the original single-ended module is preserved.
All this would be for naught if the incoming audio signal were not itself perfectly balanced. For that, we equipped the Hercules II Stereo with the same Line Stage Gain Module used in our Altair II and Virgo line stage preamplifiers. The Line Stage Gain Module uses servo circuits and hand-selected field-effect transistors (FETs) to achieve the same perfect signal balancing found throughout the Constellation Audio line. If a Constellation Audio preamp is used, the amplifier’s Constellation Direct input, which bypasses the Line Stage Gain Module, provides the purest possible audio signal path.

For each of Hercules II’s channels, a custom-wound 3,000-watt toroidal transformer, feeding a capacitor bank with even more farads of capacitance per watt than the one found in the original Hercules, provides a consistent, imperturbable source of DC power. Fully regulated, noise-free DC power supplies feed the low-level circuits.

We do recommend the Hercules II Monoblocks for the very largest systems and the most demanding audiophiles. But for music lovers who don’t need the absolute maximum in power and dynamics, or whose listening room cannot easily accommodate two large monoblocks, the Hercules II Stereo can be the path to musical perfection.

500 watts per channel into 8 ohms
Our 500-watt/8-ohm per-channel power rating for the Hercules II Stereo is actually pretty conservative; it’s really more like 550 watts. And 750 watts into 4 ohms, and a full 1 kW into 2 ohms. Thanks to its increased power supply capacitance and ample cooling capacity, the Hercules II Stereo drives low-impedance speakers with ease.
Modular circuit concept
Instead of achieving the Hercules II Stereo’s in the traditional way—just bulking it up with more output devices—we build it from numerous 125-watt single-ended modules. It thus has the musicality of smaller amplifier, and the power and control of a large amplifier.

Balanced drive design for superior musicality
In the Hercules II Stereo, as in all Constellation Audio amplifiers, both the positive and negative halves of the audio signal see exactly the same type of output devices: N-type transistors. In other amps, the transistors are half N-type and half P-type, resulting in an inherent signal imbalance.

Inherently stable circuit design
Our circuit design combines high bandwidth with inherent high stability. Unlike many high-powered amplifiers, the Hercules II Stereo does not need a Zobel network at the output terminals to ensure stability at high frequencies.

Dual-mono design with one 3,000-watt transformer per channel
Each of the Hercules II Stereo’s channels has its own custom-wound, 3,000-watt toroidal transformer. Both transformers contain multiple isolated sets of windings to supply independent power feeds to various circuits within the amplifier. The isolation of the windings assures consistent voltage and current supply to all of the amplifier’s circuits, regardless of the demand placed on those circuits. Because each channel has its own transformer and supply capacitors, it is unaffected by the operation of the other channel.

High-efficiency passive cooling
With more than 1,000 watts total power into 8 ohms, the Hercules II Stereo demands a constant, free-flowing supply of cool air. To achieve this without the use of fans, we incorporate two huge heat sinks and hundreds of large ventilation ports to minimize airflow impedance and maximum cooling.

Perfect balancing through Line Stage Gain Module
The Hercules II Stereo incorporates two Line Stage Gain Modules, one for each channel. This module uses servo circuits and hand-selected FETs to assure that all incoming signals are perfectly balanced by the time they reach the amplifier stages. This is the same exact circuit found in our Altair II and Virgo line stages, and in all of our source components.

Constellation Direct balanced interface
If you are using a Constellation Audio preamplifiers, you can use the Hercules II Stereo’s Constellation Direct input. This input bypasses the amplifier’s Line Gain Stage Module, which simplifies the audio chain for the best possible detail and musicality.

Constellation Audio

Constellation Audio was founded on the premise that one cannot create something extraordinary through slavish adherence to established methods. When tradition is the best path, we embrace it. When new technology is necessary to achieve the performance we want, we invent it. When we find a radical circuit topology that delivers a substantial advance in sound quality, we use it.