In development of RASA, we devoted to realize the performance of Phantom, Phatlab’s preceding flagship tube amplifier, in a solid-state replicate. Though the component counts of RASA seems multiple times of tube amp, it actually comprises 3-stage structure, first the input buffer and conversion stage to take advantage of fully balanced construction, second the zero negative feedback gain stage for coherent sound quality, and third the powerful output stage to cope with all kinds of loading. The major difference from Phantom might be in the directly-coupled output of RASA instead of transformer coupled output in Phantom. Apart from the similar characteristics like clarity, details, and spaciousness, RASA is more straightforward and Phantom is otherwise implicit by nature.
The precision and match of multi-channel volume control is critical to balanced amplifier’s performance. The imbalance of volume between positive and negative polarities may lead to downgrade in signal integrity. A traditional 2-gang potentiometer has typical 10 to 20% tolerance between gangs, needless to say 4-gang counterpart used in fully balanced construction. The volume control of RASA is a refined and improved version from Phantom. It consists of 4 resistor ladders for positive and negative polarities of individual channel and up to 1024-step resolution. Besides, the volume knob emulates type-A transfer curve that is linear to human hearing. The volume control brings the best linearity and details even in its minimal level. Moreover, L-R volume balance (offset) adjustment is a long forgotten function in Hi-Fi system. The reason is its deterioration to audio quality from multiple interconnection of potentiometers in traditional design. By adopting digitally controlled resistor ladders, we are able to bring back the L-R channel balance adjustment with zero impact to sound quality.
The wide spread of headphones’ sensitivity is always a challenge to modern amplifier design. It demands for both low noise floor and high output power, which usually in conflict with each other. In RASA, the 3-level (-6/0/+9 dB) gain stage brings user both the lowest noise level and highest power output through a simple toggle switch. The unique design of gain stage avoids the side-effect of gain setting through amplifier’s feedback resistor, which usually changes the transient characteristic of amplifier in subjective perception. In RASA, its audio quality is consistent in different gain level and well compatible with IEMs up to planar headphones.
RASA is equipped with a micro controller. It takes programming to fully exploit the potential of integrated devices. We used to avoid digital control in amplifier for its potential switching noise. So we take full precaution to integrate controller in the system. It includes a dedicated power supply starting from transformer, isolated PCB layout, and digital isolator. There is absolute no electricity flowing between digital and analog blocks and no trace of digital noise either through measurement or auditioning.
Except for doing control, we apply the controller for signal generator that can output 1000Hz sine wave and white noise, all based on DDS (direct digital synthesis) technology. It is convenient for users to apply the generated signals through highest quality amplifier for extensive headphones break-in.
As always, we only apply carefully selected components for audio quality and reliability. The Germany made MELF resistors are used through the entire board for their low noise, smoothness, and reliability. SMD film capacitors are located right next to amplifier’s supply for coherent frequency response. Low impedance high capacity electrolytic capacitors are main power reservoirs for supply in highly dynamic music passage. And polymer capacitors are last mile in power supply for extensive high frequency performance. Cost is no object in design and component options. Industry standard Pentaconn® and Neutrik® connectors are used for output connections.
It is well recognized the chassis and enclosure of audio equipment are foundation of superior performance. The enclosure design of RASA is directly derived from flagship Phantom and carefully trimming in dimension and weight. RASA’s enclosure is elegant and compact sitting on desktop and has the most solid construction with aerodynamic aluminum supporting top-notched electronics.
Single gain stage, zero global feedback, high resolution stepping volume system, current mode preamplifier, and high current output stage are unique features behind RASA’s prestigious performance. RASA’s electronics has borrowed the wisdom of tube amplifier. It combines the neat tube-like topology with sophisticated solid-state functionality. There is no artificial details or sharpness that prevails latest solid-state design. RASA presents music coherently and fluently without a trace of obtrusion. The music sounds rich and touching found in tube amp while driving demanding headphone as powerful as a solid-state amplifier.
| Frequency Response |
1 Hz – 100 kHz (+0/-0.1 dB) |
| Output power (4.4φ) |
600mW + 600mW (300 ohm) |
| Headphone impedance |
16 ohm – 600 ohm (recommended) |
| Gain level |
H: +9dB (SE), +15dB (Balanced) |
| Max. S/N Ratio |
>110 dB |
| Power supply |
115/230V (AC) |
| Dimensions (WxHxL) |
330 x 77 x 275 mm |
| Net weight |
5030 g |