GM 13.5B Preamplificatore Linea Bilanciato

GM 13.5B IIPreamplifier Line

The project of a line preamplifier is the result of careful research carried out by Mr. Giovanni Mariani during many years of study and experiments in the audio and electronic fields, in order to satisfy the different audio requirements in several electronic contexts.
The GM 1 3.5B II preamplifier combines all these characteristics, and is notable for its rational design and extreme functionality.

The components of the GM 1 3.5B II have been chosen without compromises, using professional oil-paper capacitors and special tubes; there are no time limits in testing and checking the preamplifier. Every circuit detail was studied with great care during the design of the GM 1 3.5B II, a practice which continues during manufacture. The peerless musical reproduction available from the GM 1 3.5B II is the result of high technology married to the traditional virtues of hand-assembly.

The tube preamplifier GM 13.5 B II immediately attracts the attention of the audio enthusiast thanks to the presence on the front panel of two controls never before appearing on GRAAF products. They are two plates which, with a light touch, operate the on/off switch of the preamplifier and permit the choice of overall gain of the unit. The primary function of these commands is the principle of piezoelectricity. These frontal panel controls operate a control board which in turn is responsible for the operation of the relay.

A further notable feature is that it is possible to choose between a gain of O db and one of about 1 4 db through one of the above mentioned controls. The GM13.5B II distinguishes itself from previous GRAAF preamplifiers for its very high versatility having a greater number of useful inputs and outputs. Indeed, provision was made for a pair of stereo outlets, completely balanced, in which each channel is fitted out with its own buffer circuitry.

Technical data :

Gain:	13,5 dB
Input impendance:	300 Kohms
Maximum output voltage:	20 V RMS
Output Impendance:	90 ohms
Total harmonic distortion (THD):	< 0,2%
Signal/Noise ratio:	110 dB A
Frequency response:	da 5 Hz a 500 KHz
CMRR:	> 50 dB
Power requirements:	100 ÷ 125 / 200 ÷ 240 V (50 ÷ 60 Hz)
Assorbimento:	100 W
Dimensioni (L x H x P):	410 x 105 x 420 mm
Peso:	11 Kg

A further two buffers are dedicated exclusively to tape-recorder outlets. Every outlet is characterized by an extremely low impedance which guarantees the assured piloting of whatever power amplifier that one wants to use. These important circuit features over and above their unquestionable technical importance, translate into the dynamics of exceptional listening, and give a natural and clean sound, absent of all distortion. The output signal is released through a very high quality capacitor, of such quality that as a result of the research carried out by the design engineer G. Mariani, results in being the very best capacitor ever used in the field of audio. These, in brief, are the innovations which distinguish the GRAAF preamplifier GM13.5 B II but it should not be forgotten that the common circuit base of all GRAAF amplifiers, like that of the GRAAF GM1 3.5 B II incorporates interstage connections, DC coupled, completely differential circuitry, free from any type of negative feedback.

Via Venturi, 66/68 - 41100 Modena Italy