Unity Gain Technology
In a conventional music system, the sole function of a preamplifier is to receive the music signal coming from a source device, process it, then pass it on to a power amplifier. The power amplifier, in turn, expects the signal from the preamp to arrive at a maximum of 2 volts RMS as the amplifier is designed to deliver its full rated power at an input level of 2 volts.
Analogue source devices, such as turntables or cassette decks, only supply a maximum voltage of 0.5 volts (tuners and turntables) to 0.75 volts (tape decks). In order to be able to pass on a maximum voltage of 2 volts to the power amplifiers, the signal must be "pre-amplified" before it is routed to the power amplifier. This is the sole purpose of the pre-amplifier, and explains the origin of its name.
Today's preamplifiers typically amplify the input signal by 12 dB before delivering it to the power amplifier. This corresponds to an amplification factor of 4, and makes it possible to achieve the required 2 volts at the preamp output, even with source input levels as low as 0.5 volts.
With a source device producing a voltage of 0.75 volts, as an example, a voltage of 3 volts would already be achievable at the power amplifier input, and the volume control would have to be reduced to approximately 67% in order not to exceed the maximum level.
Thankfully, most of today's source devices are digital in nature, and the music signal fed to the preamplifier typically comes from a D/A converter. These are standardised to deliver a maximum output voltage of 2 volts RMS (+/- 5%), and all D/A converters from MBL strictly adhere to this specification. Other manufacturers sometimes exceed this value in order to sound louder.
Under these circumstances it seems obvious that pre-amplification of the signal coming from a D/A converter would actually not be necessary at all, since the output voltage of the D/A converter already corresponds to what the output stage expects in terms of input voltage. Nevertheless, virtually all manufacturers of preamplifiers have stuck to amplifying a signal coming from a D/A converter.
In the situation where the potentiometer (volume control) is fully turned up, a voltage of up to 8 volts would be generated at the power amp input. In order not to exceed 2 volts, the volume control would have to be turned down to a maximum of 25%.
The music listener does not notice this dichotomy, since he or she controls the desired volume via the preamplifier's volume control, and compensates for excess gain by setting the volume low. A listener might even be inclined to believe that he still has plenty of reserve, since he already reaches a high volume at a low volume setting and there is still "room for improvement". To all appearances there is no problem making any adjustments.
But is that really the case? Is it really without side effects if the signal is turned down by the volume control, then amplified again by the same factor by the preamplifier? The answer is a clear “No.” Unnecessarily reducing the signal level and then amplifying it causes dynamics and resolution to be lost. At the same time, noise and distortion increase – factors one seriously wants to avoid in a high-quality audio system.
For this reason, MBL has developed a one-of-a-kind process in its pre-amplifiers and integrated amplifiers where the input signal is regulated precisely to the point where exactly the maximum 2 volts is passed on to the power amplifier. As a result, the entire dynamic range of the D/A converter is completely preserved and no dB in the signal-to-noise ratio is wasted. The results are noticeably audible, measurable and proven. This proprietary technology is called MBL Unity Gain, and is the standard setting for the Noble Line pre-amplifiers and integrated amplifiers.
If required or preferred, the Unity Gain setting of the Noble Line can be switched to a Regular Gain setting. The signal is then pre-amplified by 8 dB. This can be useful if, for example, significantly higher volumes are desired at parties and the accompanying distortions are accepted. The music listener has generous reserves and does not have to worry about not being able to dial up sufficient volume.
Even better, it is not necessary for the listener to adjust the volume when switching between Unity Gain and Regular Gain, as this is done by the unit itself via stepper motors on the volume dial. As a result, there is no audible change in volume when switching. There is also no difference in tonal balance if Unity Gain is switched on or off. This is ensured by two separate signal paths, each with different components and individual tuning.
MBL’s Unity Gain technology allows for maximum dynamics and resolution with minimal noise and extremely low distortion. In short, superior and clear sound advantages compared to conventional pre- and integrated amplifiers.
It’s the discerning choice of audio connoisseurs.