N11 Preamplifier

The MBL Noble Line preamplifier N11 incorporate a new technology developed by MBL called “UNITY GAIN” which provides a clearly audible and measurable sound enhancement. In a typical music system, the preamplifier has the task of receiving the music signal originating from the source device, preparing it, and forwarding it to the power amplifiers. The power amplifiers expect the preamplifier to relay the signal to them with a maximum of 2 volts RMS. They are designed to deliver their full rated output at 2 volts input level (this value varies within limits, depending on line voltage and rated load, and applies to all output stages of MBL’s and most manufacturers’ amplifiers). Analogue source devices, such as turntables, with the associated equalizer pre-amplifier, or tape decks, provide a voltage of 0.5 volt maximum (tuners and turntables) to 0.75 volts (tape decks). Nevertheless, in order to achieve a maximum voltage of 2 volts at the amplifier input, the signal must be “pre-amplified” before being passed on to the output stage. This is the responsibility of the preamplifier, hence its namesake. Today’s preamplifiers typically amplify the input signal by 12 dB before delivering it to the amplifier’s input. This corresponds to gain by a factor of 4, making it possible to achieve the required 2 volts at the output even at input levels of only 0.5 volts. In a source device with a voltage of 0.75 volts, for example, a voltage of 3 volts would already be reached at the power amp input and the volume potentiometer would have to be reduced to about 67% in order to not exceed the maximum level. In the majority of cases, today’s source devices are digital sources and the music signal supplied to the preamplifier comes from a D/A converter. These are standardized to the extent that they deliver a maximum output voltage of 2 volts RMS (+/- 5%) and all D/A converters from MBL strictly adhere to this requirement (although other manufacturers sometimes exceed this value to sound “louder”). Pre-amplification of this signal is not necessary, since the output voltage of the D/A converter corresponds exactly to what the output stage expects from input voltage. Nevertheless, manufacturers of preamplifiers have adhered to the system of amplifying a signal originating from a D/A converter. In this situation, with the volume turned up fully, a voltage of up to 8 volts (!) would appear at the output stage’s input, and in order not to exceed the 2 volts, the potentiometer would need to be turned down to a maximum of 25%.