In today’s times of ubiquitous digitization, electron tubes can be associated as a relic of the previous era. Initially (the second half of the twentieth century) devices using semiconductor technology, and later complex digital circuits dominated the majority of the market and consumer equipment based on tube architecture was thereby almost completely forgotten. Theoretically, the era of domination of electron tubes has ended, but the sound quality limited by the physical properties of audio devices built on silicon components has caused that nowadays electronic tubes are returning to amplification devices for acoustic signals. In terms of sound quality, electron tubes still do not have a qualitative equivalent in the family of semiconductor systems.
In a properly designed device (amplifier / preamplifier) where, apart from the circuit design, special attention is paid to the selection of components to allow the full use of all the advantages of electron tubes. First of all, efficient and stable power supply unit together with the supply transformer is important here. In the case of loudspeakers or headphone amplifiers with high efficiency (for planar / orthodynamic headphones), the majority of loudspeaker transformers are also used. The quality of their performance and the materials from which they are built to a very large extent affect the sound of the amplifier so there is no room for compromise.
Class A – Single Ended
Among the amplifiers for loudspeakers in the White Bird Amplification offer, we propose two basic classes: A and AB. Class A amplifiers are characterized by the least amount of distortion and the highest sound quality (no crossing through zero). However, their disadvantage is low efficiency (up to 30%) and relatively high energy consumption. In addition, the power tubes work on a fixed high current (the current is not controlled by the input signal), so their life is lower than in the AB class. This is also related to the heat emission, which is much larger compared to an AB class amplifier.
Generally speaking, the power loss in the Class A amplifier is the largest. Despite all these disadvantages, the sound quality of a well-configured Class A amplifier is in the foreground compared to other acoustic amplifier circuits. This also applies to semiconductor amplifiers. In our offer, the flagship class A amplifier – Ironbird achieves a power of 40W per channel due to the use of two 100W tubes in each of them (2 x 211 in one channel), which work in a parallel connection. This requires a considerably extended system, in which we taken special attention to the heat dissipation and providing a fully separated power supply for each of the channels including not only the power supply of the power tube and driver tube, but also their heaters. In addition to a separate current source for the right and left channel power tubes, the heater of the control lamps is realized using two DC power supply (separate for each lamp) which allows full separation of channels (highest quality of stereo) and the best conditions in terms of work culture (resistance to interference).
AB Class – Push Pull
The AB class offers the user greater efficiency than class A. Our highest model representing this group offers power up to 70W per channel working with a pair of KT88, KT120 or KT150 tubes. In this class, apart from the relatively high efficiency, we deal with the phenomenon where the lamp’s current is controlled by the input signal. This avoids class A flaws (high loss power, shorter lamp life) while maintaining very high sound dynamics. The quiescent current of the power tubes, i.e. the current with which the lamps operate without providing an input signal, constitutes up to 10% of the maximum tube current achieved during the maximum actuation of the amplifier with this signal. If the amplitude of the control signal (directly from the source or preamplifier) is not large (low volume) and the amplifier will not exceed the quiescent current it will work in Class A.
In practice, for the Thunderbird amplifier, a few watts per channel allows for most moderately effective listening (efficiency determined in dB) speaker set. Thanks to this feature, the user has both a Class B and an A amplifier. Class B is activated automatically at loud listening sessions requiring higher power to be delivered to the speakers. With quiet listening in class A, we have all the advantages.
Headphone Tube Amplifiers
Apart from amplifiers for loudspeakers, WBA’s offer also includes headphone amplifiers and preamplifiers. All preamplifiers and most headphone amplifiers work in class A (SE). Headphone amplifiers in our offer are made with two types of outputs. For dynamic headphones we recommend models working in class A (OTL-SE) without the use of output transformers. The signal from the cathode of tubes, after passing through the capacitor, is fed directly to the headphones. This solution offers low efficiency in terms of output power, but it provides very high sound precision. Our most powerful amplifiers in OTL-SE mode provide power up to 2.5W per channel with a 100W tube. In the case of impedance matching of the headphones to the output impedance of the amplifier, this may be sufficient even for controlling planar headphones, however, we recommend amplifiers strictly designed to cooperate with them. For this application we have designed OTL-PP amplifiers that are working in the Push-Pull (AB) class. Thanks to the use of double triodes with high current, slope of characteristic and relatively low voltage, it was possible to obtain a very high efficiency, which at low impedances (24 Ω) allows obtaining output power up to 15W per channel. The higher the impedance, the lower the output power. For 100Ω headphones it will be about 2 x 7W. P>
The preamplifier in the audio system is a voltage amplifier for signals from sound sources (eg a CD player, turntable, DAC). Its basic task is to provide power amplifiers connected to its output with signals with specific values of currents and voltages, compliant with audio standards. In addition, it is intended to create sound, especially when it comes to tube preamplifiers where a positive effect on color, acoustic bandwidth and dynamics is clearly noticeable. Another function of the preamplifier, which is available in more complex systems, is a control system integrated with the preamplifier for selection of input and output signals. The best solution here is to use good quality switches (so-called relays), which minimize the influence of connectors on the audio signal.
As short as possible signal cables that are used in White Bird Amplification preamps also contribute to the highest work culture of the equipment. The WBA offer includes two lines of preamplifiers: Firebird and Blazebird. Both models are available in both the unbalanced and balanced systems. For all WBA preamplifiers, the use of complete channel separation architecture in terms of right and left channel power supply and the use of separate power supplies for each single lamp of the system ensures the best separation of audio tracks and the dynamics of the system operation. This translates into the highest quality in terms of sound space and stereo. Each of the channels in the Firebird Balanced, Blazebird and Blazebird Balanced models has its own dedicated power transformer, which contributes to even better separation. WBA also offers preamplifiers for cooperation with turntables working with MM type inserts. The customer can choose between Firebird Phono and Blazebird Phono. Both models provide signal amplification according to the RIAA feedback standard. All models of our preamps work without using audio or semiconductor components in audio tracks. This eliminates undesirable distortions or noise (signal transformers, semiconductor circuits). In addition to tubes, our electronic circuits use only discrete components such as resistors or capacitors in their audio circuits.
WBA Technical Solutions
All White Bird Amplification devices are designed according to proprietary studies. We do not do them by cloning ready-made, popular layouts. At each stage of the project, we do everything from scratch, which can be confirmed, for example, by the alternative appearance of our transformer amplifiers, whose casings are made differently than in most models from other manufacturers. We have the ability to place all transformers (power and loudspeakers) inside the amplifier housing, not on the top panel. Such architecture allows only the tubes themselves to be placed above the top panel.
The electronics of White Bird Amplification devices are configured to ensure the shortest possible connections. We use PCB, which contains as many cooperating systems as possible (amplifier, lamp bases, all power supplies), which avoids the need to connect separate modules with wires having an adverse effect on the sound.