FM ACOUSTICS Classic Series F-50B


Etapa de potencia monoaural con entradas balanceadas.

450W @ 8 Ohms.

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  • Superb performance and truly outstanding music reproduction thanks to excellent control of the speaker diaphragm.
  • No dynamic distortion & time-coherent response yield musical accuracy.
    Can drive low impedances without limiting or negative influence on the audio signal.
    Natural sound reproduction resulting from incomparable selection, fine tuning and proprietary circuit technology.
  • Feature totally discrete circuitry using special high-voltage, high-current semiconductors.
  • All amplification stages in pure Class A, output stages use FM ACOUSTICS' proprietary Class A+AB.
  • Resonance damping of vibration-prone components.
  • Multiple fully automatic protection circuits for amplifier and load.
  • Each and every single transistor goes through a multitude of proprietary selections. All are individually hand-selected over the full voltage and current levels. Only perfectly matched components are used throughout the entire circuitry.
  • No need for error correction. Optimal music reproduction is guaranteed.
  • Amplifiers remain absolutely stable even with the most complex loads.
  • Only high-performance parts are used.
  • Rigorous 200h (1000 thermal cycles) burn-in of each amplifier.
  • 50000 cycles vibration testing of each amplifier.

Completely hand-crafted in Switzerland to DIN, IEC and MIL standards.

Products that truly provide lasting value is the philosophy of FM ACOUSTICS. The Classic Series amplifiers emphasize this characteristic and provide excellent value for investment.

The goal of the design of the Classic Series was to achieve natural sonic and optimal technical performance. Described " warm as the best tube amplifiers but with true bass control, dynamics and much better high frequency extension..." the Classic Series provides entirely natural, musically correct reproduction.

Ruggedly constructed, the Classic Series is reliable. It is fully stable with any known speaker load (including electrostatics). It provides unmatched music reproduction without the typical limiting, compression, clamping or other negative influences on the audio signal that are generated by the usual amplifier protection systems. It also protects itself and its load from abuse and fault conditions.

It reproduces music with uncanny naturalness.

The Classic Series is completely hand crafted by experienced craftsmen who work under relaxed (no time pressure) conditions. This eliminates any stress or errors during manufacturing.

Important points to guarantee optimum performance are the fine tuning and calibrating of each individual amplifier stage. All parts of each amplifier are individually pretested and components are pre-selected by hand on testing apparatus specially built for this purpose.
This care results in unmatched reliability and long-term stability.

Contrary to other designs, FM ACOUSTICS precision power amplifiers do not sound harsh when driven into clipping (it must be remembered, however, that in any audio device linearity is only obtained below clipping).

Compared with amplifiers of similar power ratings, the Classic Series amplifiers drive speakers effortlessly to higher levels than the rest. Actual SPL differences of between 2 and 8 dB have been documented. This astounding distortion-free SPL increase is just one of the many factors that clearly demonstrate the remarkable superiority of FM ACOUSTICS' power amplifiers.

The Classic Series contains many unique features:

  • The elaborate balanced input circuitry provides high RFI rejection without the typical compromise of narrow bandwidth.
  • Drawing from technologies used in the Resolution Series power amplifiers, the massive power supplies feature high current capability and ultra low impedance. Therefore, the output stages can supply highest peak currents instantaneously and without limitation or time smear. This guarantees perfect signal transfer and freedom from dynamic compression and distortion.
  • The heart of an amplifier is the transformer and the power supply components. In a decently designed amplifier of high class this will also be a considerably cost of the amplifier. That is the reason why amplifier manufacturers try to skimp at the cost of transformers. Even in expensive power amplifiers one can find cheap toroidial transformers that are OK for refrigerators and the like but not for quality audio applications. While in lower power applications a good toroidial transformer can work well, in demanding high power applications they are not up to the ultimate standard. In the smaller FM ACOUSTICS products one can find carefully designed, specially shielded and carefully made toroidial transformers. In the large power amplifiers (like the F-50B) huge completely hand-assembled, noise-free transformers made out of specially heated, grain oriented high-efficiency steel are used. These transformers cost a small fortune and are heavy, but the result is absolutely unmatched.
  • The overdesigned output stage remains absolutely stable with any known speaker load, even with paralleled drivers and electrostatic speakers.

Proprietary protection systems are used in the Classic Series

  • These continuously monitor important parameters of the amplifier such as:   
  • operating temperature & air flow (at 80 degrees the amplifiers switch off. They cool down and reset automatically. 80oC is a very conservative rating and will perfectly protect the semiconductors without any possibility of thermal runaway or thermal fatigue, a weakness of many amplifier designs).
  • DC+ and DC- offset voltage at the amplifier's output are continuously monitored. The load is protected with an immediate shut-off when the DC offset exceeds 1V. This is done much more quickly and securely than in other amplifiers that boast so-called 'DC-protection' (which often still allows DC voltage of 15V or 20V to pass! Such DC voltages are of course dangerous, as many drivers will already be damaged at such voltages).
  • The amplifier and speakers are also protected from ultra high frequencies, instabilities and oscillation of other electronics .
  • In addition to the above-mentioned protection systems, an input overload protection and an open circuit protection ensure that the Classic Series remains absolutely stable even when no load is connected.
  • In case of any fault condition the output to the load is disconnected immediately. In the protection system there is no possibility of limiting, part-limiting or other negative influences on the audio signal. Either the amplifier works perfectly or its outputs are disconnected due to a fault condition, in which case the error status is indicated.
  • The Classic Series features a mechanically damped chassis and guarantees isolation of sensitive electronic components from induced resonances.
  • The exceptional quality and unique calibration and selection methods contribute strongly to the amplifier's outstanding performance and reliability. Practically all parts in an FM ACOUSTICS amplifier comply with DIN and IEC standards, and a lot of critical parts fulfil MIL (military) standards. Details like high performance wiring, the use of precision dust- and waterproof long-life potentiometers, curve-tracer analysed and hand-selected high-voltage, high-current transistors etc. are indicative of superb quality standards - standards that are only found in FM ACOUSTICS power amplifiers.



Like every product made by FM ACOUSTICS the Classic Series is immaculately hand-crafted. Every part of each amplifier is individually pretested and most components are pre-selected by hand on testing machines specially built for this purpose. All active devices are selected on curve tracers in five different measurements and are used only in perfectly matched sets.
To guarantee outstanding performance and no unit to unit variation, amplifier stages are fine-tuned and hand-calibrated for optimum performance.

This extremely time-consuming procedure is done prior to a heavy-duty, high-power burn-in test. Here the amplifier is run under most demanding conditions for a minimum of 1000 thermal cycles (minimum 200 hours!). After this severe burn-in test, every single amplifier is placed on a shake table where it is subjected to tortuous vibrations for a minimum of 60 minutes (50'000 vibration cycles). Then it is moved back to another test-bench where the amplifier's performance is totally rechecked.

All curves and data are compared to the initial test report. The amplifier is only final tested if the performance has remained exactly the same. If even the slightest deviation is found during the burn-in or vibration test, the amplifier is totally re-analysed, then re-checked and required to again pass the full burn-in and vibration tests.

These procedures result in unmatched reliability and long-term stability.

With decent electronics and speakers, the Classic Series will provide performance far superior to other makes. They drive the most difficult loads without any form of limiting, compression or other negative influences on the audio signal.

Words cannot describe the astonishing improvements achieved when replacing another power amplifier with an FM ACOUSTICS. The more accurate the system, the more dramatic the improvement in reproduction accuracy. Once the difference is experienced, it is difficult to go back to other power amplifiers.

With the Classic Series, FM ACOUSTICS reinforces its commitment to continuous implementation of results from advanced Research and Development and to provide products that serve the client with superb price/performance relation.