KRELL Model250M

Commentary

FPB (fpB (full power balance) series monaural power amplifier with a completely symmetrical separate configuration for left and right channels.

All stages of direct coupling and full complimentary service, fully balanced differential circuit is adopted.
The first stage employs a unique current-mode amplification method that operates by current between inverting and non-inverting amplifiers with perfect symmetry characteristics. In addition, the gain between each amplification stage is strictly controlled by the microcontroller to improve operation accuracy.

Our carefully selected employment includes specially designed metal can-type, bipolar, and power devices jointly developed with Motorola.

The サスティーンド and Plateau Bias II circuit is adopted to realize the full range class A operation.
In this circuit, the operating condition is constantly monitored by the built-in microcontroller, and each parameter is automatically calibrated (auto-calibration function) when the power supply is turned on, so that the optimum bias current is always supplied. This greatly reduces the burden on the components due to heat generation, etc., and realizes ideal class A operation over a long period of time.

The microcontroller centrally manages all parameters related to the operation of the amplifier, such as regulator voltage and DC offset. It also functions as a protector that quickly detects problems such as output shorting, DC leakage and oscillation and shuts down the operation.
This circuit realizes a direct connection between the speaker and output stage without using a common protective circuit such as a relay or fuse.

A fully regulated power supply is used as the power circuit.
A large-scale constant voltage circuit using eight Pc250W class large-capacity power transistors and a microcontroller fully regulate the drive current and voltage to each part of the amplifier, eliminating adverse effects caused by input signals and load fluctuations.
Unlike conventional capacitor types, this method can almost completely compensate not only current but also voltage fluctuations.

The Model250M was sold as a pair, but it was sold as a unit.

Model Rating

Type	Monaural power amplifier
Rated Output (20 Hz to 20 kHz, Continuous)	250W (8 Ω) 500W (4 Ω) 1000W (2 Ω)
Output voltage	138Vp-p, 49 Vrms
Input Sensitivity / Impedance	2.14Vrms/100k Ω
Distortion factor	0.03% or Less (1 kHz) 0.28% or Less (20 kHz)
Frequency characteristic	20 Hz ~ 20 kHz + 0 -0.1 dB 0.1 Hz ~ 240 kHz + 0 -3.0 dB
Gain	26dB
Input terminal	Balance 1 system Single-end one system
Power consumption	175W (idle) 1700W maximum
External dimensions	Width 323x Height 260x Depth 430 mm
Weight	31kg