FM ACOUSTICS FM255
Price unknown (released in 1997)
¥ 2,600,000 (around 2001)
¥ 2,890,000 (around 2002)
¥ 3,000,000 (around 2004)
¥ 3,150,000 (around 2005)
Commentary
A line-stage preamplifier equipped with a unique input and symmetrical output circuit for complete symmetrical signal processing.
The FM255 uses a fully discrete-configuration enhanced Class A circuit with unique precision adjustment without the use of an operational amplifier or IC, and achieves an excellent CMRR (common-mode rejection ratio) of 95 dB over the entire playback band.
The fully balanced super-coupling output has a sensor circuit that automatically compensates for differences between balanced and unbalanced loads, so that all interfaces are 100% compensated and no rewiring or soldering is required to dominate the interface function.
It uses its own fully balanced and enhanced Class A circuit for high stability and high purity signal processing, without any overall feedback or feed-forward.
It uses a specially designed bias circuit to reach operating temperature very quickly without the need for long warm-up, and to minimize the change in tone after warm-up.
The phase of the main output can be inverted by 180 ° with the phase inversion switch on the front panel.
This operation is performed without any additional circuitry, and the signal does not enter the 180 ° phase inversion stage ; the positive and negative signal paths are identical.
A tape monitor circuit using a discrete class A buffer circuit is mounted.
The built-in buffer circuit enables constant sound quality and signal transmission regardless of load or source type.
The built-in high-precision power supply circuit realizes excellent noise characteristics and distortion factor.
The internal power supply is fully shielded and an additional supershield is added inside the transformer housing to eliminate hum, noise, magnetic and electronic interference of all kinds and conduct it to ground.
No internal wiring for signal transmission is used, and variations in performance between units are eliminated.
All output circuits are protected from short circuit.
The chassis structure is mechanically damped to protect sensitive electronic components from inductive resonance. The chassis side panels, covers, bottom and transformer mounting are supported by special rubber and Dellin2 suspension.
Special shielding prevents hum, interference, and noise entering the audio signal path through relays, switches, and potentiometers.
The output level control uses precise and high-resolution spread balance control and is carefully isolated by a unique enhanced class A buffer circuit.
The balance control uses a unique super-wide balance control.
This balance control uses a center positioning system that adjusts the knob within ± 1 dB when the knob is rotated from the center position of ± 45 °. This method provides an excellent resolution of 0.02 dB and allows far more accurate adjustment than a conventional balance control.
It uses a Swiss-made 4-contact ultra-high precision relay with hermetic seal.
The four specially coated contacts can withstand tens of millions of switch-over operations, and the hermetic seal keeps the contacts unaffected by the surrounding environment, preventing degradation of overall performance and sound quality.
The pin arrangement of the balanced input connector is the standard specification of #1 ground, #2 cold and #3 hot, but it can be changed to the configuration of #1 ground, #2 hot and #3 cold by the high-precision switch.
It has a unique control / protection circuit.
Delay type switch-on is adopted. No signal flows to the output when the switch is turned on. The control circuit starts the output after each part is completed by self-diagnosis. It takes about 10 seconds to reach the complete operation state.
It also includes sensors to protect the FM255 and connected devices from excessive voltage drops that can cause malfunction, transient failure, or DC instability.
Equipped with two fully balanced high-level inputs and Route 3 unbalanced high-level inputs, high-precision unbalanced tape monitor loops such as buffers, and fully balanced outputs.
It is a fully modular design.
Model Rating
| Type | Stereo preamplifier | ||||||
| Circuit | Discrete enhanced class A circuits using ultra-high-speed hand-select semiconductors. The circuits are individually analyzed and selected, and carefully selected through listening tests unique to FM Accor Stix. The whole unit consists of an enhanced class A module by hand calibration made by FM Accor Stix. |
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| Input system | Two identical fully balanced, symmetrical and high-level inputs Unbalanced high-level input Route 3 One unbalanced tape / accessory loop |
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| Input Characteristics | Balanced input : fully symmetrical electron balanced discrete Class A circuit for any balanced or unbalanced source (non-polarized floating ground, non-inverted or inverted connection) | ||||||
| Input Stage CMRR (20 Hz to 20 kHz) | 100 dB or more (Typical) 90 dB or more (minimum guarantee) |
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| Input impedance | 100k Ω for both balanced and unbalanced loads. Absolutely linear for the entire playback band. |
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| Input headroom | +21dBv(9VRMS) | ||||||
| Input sensitivity | 100 mV per 100 mV tape output | ||||||
| Maximum gain | 0 dB for all inputs at the tape output 20 dB at main output for all inputs |
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| Frequency characteristic | 20 Hz to 20 kHz ± 0.03 dB | ||||||
| Playback bandwidth | Without RF Filter : 2 Hz to 2 MHz Built-in RF filter : 1 Hz to 100 kHz * The actual frequency characteristics are attenuated above 100 khz by the linear phase anti-RF circuit (bypass is possible depending on the purpose). |
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| Phase accuracy | -0 ゜ / + 1 ゜ (without RF filter, 20 Hz to 20 kHz) | ||||||
| Step characteristic | No overshoot or ringing | ||||||
| Output level and control resolution | 0.02 dB or more | ||||||
| Balance control resolution | 0.02 dB or more (at center setting) | ||||||
| Rise time | 300 nanoseconds = 0.3 μ sec (electronics capability, measured without RF filter) | ||||||
| Drop characteristic | 300 nanoseconds = 0.3 μ sec (electronics capability, measured without RF filter) | ||||||
| Hum and noise | 0 dBv or Less = -95dBV or Less, -120dB or More (20 Hz to 20 kHz, Full Output) | ||||||
| Output | Fully symmetrical, fully balanced, discrete Class A circuit. Drives all unbalanced / balanced loads. Equipped with a sensor that automatically adjusts output regardless of the type of connected device and a circuit short circuit protection circuit. Passed full balance "floating test". |
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| Maximum output level | + 28 dBv at 19.5 V RMS at 4.7k Ω balanced load | ||||||
| Output impedance | 10 Ω | ||||||
| Stereo separation | 85 dB or more | ||||||
| Channel separation | 95 dB or more | ||||||
| Harmonic distortion factor | 0.003% or more (at 3 V output) in all playback bands No higher order harmonics until the clipping level is reached. |
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| Power supply voltage | 115V/230V internal switching, 45 to 66 Hz | ||||||
| Power over voltage | Maximum (short time) : normal 140% V Minimum (short time) : Normal 120% V |
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| Power supply voltage effect | Maximum : Normal 80% (before starting protection circuit) | ||||||
| Voltage range capable of stable operation | 95 V ~ 140 V (115 V Setting) 190 V ~ 280 V (230 V Setting) |
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| Power consumption | Continuous 15W | ||||||
| Operating temperature | -40 ° 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. |
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| Shipping burn-in time | Temperature test 1000 cycles (minimum 200 hours) | ||||||
| Vibration test at time of shipment | Vibration test 50,000 cycles (minimum 60 minutes) | ||||||
| Front panel | Hand polished after brushing 4 mm laser-cut aluminum 9000. No wear as the lettering is treated with oxidation anode. High-precision output level and balance control with hand select, dust-proof treatment and dB scale. Switches have high-precision self-cleaning and long life specifications Power switch, power on indicator |
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| Rear panel | Aluminum 9000 is hand polished after brushing. The lettering is oxidized and anodized so there is no wear. Input / output terminals are high-precision RCA and XLR connectors. Electrical ground is lifted from the chassis to avoid ground loops. Star-ground system is possible depending on the connected equipment. |
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| Connector | Balanced input : female XLR3 pin connector, non-inverted. Pin #1 : Ground, Pin #2 : Cold (Return), Pin #3 : Hot (Signal) (Pin #2 can be hot, Pin #3 can be cold) Unbalanced Input : Female High Precision RCA Connector Output : XLR3-pin connector, balanced Pin #1 : Ground, Pin #2 : Cold (Return), Pin #3 : Hot (Signal) |
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| External dimensions | Width 446x Height 68x Depth 280 mm | ||||||
| Weight | Body : 5 kg Packing : 7 kg |
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| Standard number of parts used |
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