FM ACOUSTICS FM711

Commentary

This is a stereo power amplifier of the Resolution Series that has been developed over 10 years.

The power supply is equipped with a toroidal transformer made of steel with excellent properties and manufactured by a special method.
In general, using multiple transformers has advantages such as reducing crosstalk. However, in FM711, only one excellent transformer is installed to improve the performance by the circuit, physical layout and power supply design.
By installing only one powerful transformer, it is possible to play back with a margin even from a source that requires more power than a single channel such as timpani.

In the FM711, a custom-made high-precision capacitor can be supplied with extremely low impedance by driving the transformer into an optimum shape.
The FM acoustic capacitor reflects a technique that greatly reduces the ESR (Electrical Series Resistance), with a very high ripple current capacity resulting in linearity across the frequency band.
In addition, the Resolution Series has a special surge protection circuit with a soft start function to limit the rush current, which reduces the deterioration of the capacitor due to the rush current and extends its life.

The Resolution Series uses a star-ground system to reduce impedance.
In the star ground method, each amplification stage is connected to the ground point at the center, and ground modulation and power supply impedance are suppressed to prevent interference between stages caused by the ground connection.

If the chassis is connected to an electrical ground and XLR cable is connected to a preamp connected to ground, a ground loop will be formed, causing distortion, oscillation, hum, etc.
In FM711, the chassis is only connected to the power ground, not the audio ground, eliminating this problem.

The amplifier circuit features a unique full discrete Class A design, no overall feedback, and a discrete Class A balanced input stage for a superior common-mode rejection of 90 dB or more.
The balance input stage consists of three voltage gain stages with precisely adjusted steps, followed by a pre-driver stage, a driver stage, and an output stage. This allows each stage to operate within the optimum operating range without excessive load and enables high stability over a long period of time.

The transistors are selected not only under static conditions but also under dynamic conditions.
In the FM Accor Stix, a single transistor is measured over a wide range up to a voltage of 250 v and a current of 20A or more, and transistors with absolutely identical transmission characteristics are used as a pair.
In addition, the transistor chip is encased in a hermetically sealed ceramic housing with an average output semiconductor of approximately 10-20 mm to allow for temperature variations.²46 mm vs.²It is a large one with surface area.
FM Acoustic semiconductors are about 10 times faster than ordinary high-quality output devices, and bipolar devices are used instead of MOSFETs in consideration of sound quality.

In FM711, pure class A operation is guaranteed over all stages before the driver stage, and the output stage is specially enhanced class AB operation. This circuit configuration and the use of carefully selected parts reduces dynamic and static distortion.

It is equipped with a protective circuit, and in the event of an error such as transient in the power line, high-frequency oscillation of the connected equipment, strong RF signal, short circuit, DC offset voltage, or incomplete earth / ground, the load is immediately disconnected and turned off.
The FM711 protection circuit allows the computer to sample various parameters such as peak and average output current, rail voltage, output voltage, temperature and bias at a rate of 20 times per second and compare the data with the actual values. Therefore, the circuit path, audio output line, and DC supply rail can be configured without fuses or other non-linear components. Current limitation and compression are not used to reduce the negative impact on the audio signal.
In FM711, when DC of 1 v or more appears, the output is cut off and DC Error is displayed. If the DC is removed after the measurement is continued, the amplifier automatically returns. In addition, it is equipped with a sensor that measures all frequencies of 20 khz or more. When there is a continuous high-frequency signal, the output is cut off instantly and the power lamp blinks to display HFError. When the high-frequency signal is removed, the amplifier returns.
In addition, it is equipped with protection mechanisms such as multi-sensor / multi-area overheat protection circuit and protection circuit for protection circuit to improve reliability.

Special low-loss FORCELINES cables are used for the internal wiring and are carefully soldered to the contacts. In addition, in order to use materials suitable for the application, gold is not used for the contacts of the high-current wiring materials.
Internal connections, ground connections and screws are tightened with a torque variable screwdriver so that each screw is tightened to the correct torque.
Moreover, the connection of rail voltage (supply voltage) and connection of output are made with high precision soldering.

High-precision anodized machined aluminum 900 is used for the front panel.
We also analyze all parts such as manually rounded edges, special processing to prevent objects from falling inside the amplifier, and isolated output terminals to thoroughly eliminate resonance.
Parts where resonance is likely to occur are damped with special foam, rubber such as Delrin / 2, and other materials.

Model Rating

Type	Stereo power amplifier
Minimum rated output (Each channel)	When both channels are driven by music or tone burst 500W peak (8 Ω) 900W peak (4 Ω) 1400W peak (2 Ω) 250 WRMS (8 Ω) 450 WRMS (4 Ω) 700 WRMS (2 Ω) 100-hour operation using sine wave at minimum distortion rate in playback band 220 WRMS (8 Ω) 330 WRMS (4 Ω) 460 WRMS (2 ohm
Maximum output voltage	140Vpp
Maximum output current	The peak output current can be repeated infinitely. Continuous 35A or more for each channel No Output, DC Fuse, No Power Supply, No Current or Other Restrictions
Distortion factor	Average Distortion Factor 0.006% (THD)
Playback bandwidth	3 Hz or Less ~ 60 kHz (Input Filter Included) Can be switched from 1 kHz to 60 kHz (low pass) and from 1 Hz to 1 kHz (high pass) as needed
Gain	29dB
Rise time (at full output)	3 μ s
Hum and noise	Full Output or Less, Normal -115dB (20 Hz to 20 kHz) Minimum UNWTD-100dB or less
Input	Unique electronic balanced discrete enhanced class A circuit Floating ground with no polarity, inverted and non-inverted mode. Ideal for either balanced or unbalanced (single-end) sources Unbalanced source is automatically balanced at FM711 input
Input sensitivity	1.6 VRMS (for full power)
Input impedance	40k Ω (balanced / unbalanced, at all levels)
Input stage CMRR	90 dB or more (Typical) 80 dB or more (at 50 Hz, or more at other frequencies)
Maximum input level	+20dBm(7.75VRMS)
Load impedance	No minimum impedance. Can operate for 1 Ω ~ 10.000 Ω devices. Dynamic (music) signals can drive any speaker impedance (1 Ω or less) without affecting the audio signal, such as limiting, compression, etc. Unique on-board computer that constantly monitors key parameters protects the FM711 from short circuits, open circuits and other adverse conditions
Protection circuit	FM Accor Stix's own protection mechanism. Protects the FM711 from short-circuit, high-frequency oscillation, RF interference, + DC/-DC offset, overheating, and damage to the protection mechanism itself. With an open-circuit stabilizing protection circuit, the FM711 operates perfectly stably even when there is no connected load.
Housing resonance damping	The special chassis design isolates electronic components from adverse effects such as inductive resonance. In addition, the mechanical resonance of the panel is damped. The entire housing including the cover, plate, transformer mounting part, side plate, etc. is supported by FM Accor Stix's unique non-resonance technology.
Pwer	100 VAC, 50Hz/60Hz
Maximum power overvoltage	Short-term (excluding switch-on) : 180% nominal Long-Term (including switch on) : 120% nominal
Power consumption	150W RMS (idle) 1,000W RMS at 30% output 2,300W RMS at full power
Power supply condition	No voltage drop when the following power supplies are supplied Continuous 12.5A at 100 V, peak 50A
Operating temperature	-20 ° C to + 40 ° C
Operating humidity	Long-term : 0 to 85% Short time : 0 to 95% * If high humidity continues for a long time, the life of some parts will shorten.
Shipping burn-in time	Minimum 100 hours (500 cycles of temperature test)
Vibration test at time of shipment	Vibration test 50,000 cycles (minimum 60 minutes)
Rear Panel Functions	Input connector : Female XLR3 pin balanced connector Non-inverted : Pin #1 : Ground, Pin #2 : Cold (return), Pin #3 : Hot (signal) Inverted : Pin #1 : Ground, Pin #2 : Hot (Signal), Pin #3 : Cold (Return) Output connector : Female XLR3 pin balanced connector Uses ultra-low loss and high precision connector "Four Plug 200".
External dimensions	Width 430x Height 200x Depth 450 mm
Weight	Body : 25 kg Packed : 28 kg