GM 100 OTL Power Amplifier

GM 100 OTL Amplificatore di Potenza

Your GM 1OO is the result of many years of study and experience in the audio professional field, carried out by our technical staff directed and supported by Mr. Giovanni Mariani. The GM 1OO differs from conventional tube amplifiers both for its main circuitry, completely balanced from input to output, and for a particular component called a transmission line transformer (TL), which enables the power tubes to drive any type of load. Every circuit detail was studied with great care during the design of the GM 1OO, a practice which continues during manufacture. The peerless musical reproduction available from the GM 1OO is the result of high technology married to the traditional virtues of hand-assembly.

The GM 1OO circuit derives from the OTL configuration and uses a new type of interfacing between the output tubes and the loudspeakers. This system adds to the OTL configuration a transmission line transformer which shifts the tubes impedance from 36 / 72 ohm to 4 / 8 ohm. The two channels are physically separated on the circuit board, as in a dual-mono configuration and there is another separation between the preamplification stage and the power stage. In this way the capacitive coupling effects among the circuit boards are eliminated and the best three-dimensional sound effect is obtained.

In the voltage gain stage, the GM 1OO uses two 6922
double triodes chosen for their linearity and excellent signal-to-noise ratio. In the driver stage, the GM 1OO uses four ECF8O triode/pentode tubes, guaranteeing excellent matching with the power tubes. The power supply is divided into six sections: four are floating in respect to ground and work in the power section, while the others are separately used in the driver and in the input stages.

The power stages use twelve PL5O4 tubes. This particular tube is seldom used in the audio power amplifiers, but the particular circuitry forces us to use it because it's able to supply high currents not obtained with more well-known tubes. The tube circuitry employed in the GM 1OO is optimized by a special stage which provides self-regulation of bias and offset. It's important to point out that the full balanced circuit does not use solid state components.

Technical Data :

Output Power :	100 W + 100 W RMS
Output Impedance :	4 ohms
Input Sensivity :	700 mV
Input Impedance :	100 Kohms
Total Harmonic Distortio(THD):	< 1%
Signal/Noise ratio	lineare 82 dB pesato 94 dB A
CMRR:	50 dB
Frequency Response:	da 16 Hz a 65 KHz (-3 dB
Slew rate:	17 V/µ sec.
Damping Factor :	8
Negative Feedback :	11 dB
Power Requirements:	105 ÷ 120 / 210 ÷ 240 V (50 ÷ 60 Hz)
Power use: :	in riposo 370 W
Dimensions (L x H x P):	400 x 185 x 370 mm
Weight:	25,5 Kg

Via Venturi, 66/68 - 41100 Modena Italy