Build a Portable SET (Single-Ended Triode) Amp Like Never Before!
PHAntasy is the first member of our Portable Headphone Amplifier (PHA) series. When we kicked off the development of PHAntasy, we determined to achieve two major goals; One is to preserve the true spirit and performance of SET amplifier, pure class-A, transformer coupled output and most important of all, sensational music presentation as we ever experienced on best SET amplifier, and the other is true portability with rechargeable battery via 5V USB port. We examined every detail of SET topology and audition every possible valve candidate and come up with JAN6286, a military grade directly heated triode (DHT). We examined the topology and each element of the amplifier – JAN6286 tubes, boost converter, filament supply, Battery configuration, and Passive Components - to find the best sounding components and combination. As we put them all together we ended up with The PHAntasy, a true fantasy to audiophiles.
The Heart of PHAntasy, JAN6286 Directly Heated Triode (DHT)
At the center of PHAntasy are a pair of JAN6286 valves, each one is soldered on the board and responsible for major amplification of each channel. They are well damped on the PCB and the whole enclosure provides solid chassis to isolate them from external vibration that causes microphonics.
A triode is unique as gain device that tends to generate more even harmonics than odd ones if any. The result is music sounds airy, smooth, and natural than other type of devices. JAN6286, a directly heated triode, instantly enters working condition after power on and provides intimacy and lifelike sound stage more than none filament type triode.
There is only current buffer between JAN6286 and output transformer. The buffer is highly linear and extremely low distortion that adds nothing but driving current. All circuitry are running in pure Class-A mode. JAN6286 designed for military purpose and driven by smart filament bias inherently has ultimately extensive lifespan. There is no obvious degradation of tube performance for 10 years of usage.
Supreme Iron Core
PHAntasy is a masterpiece loyal to the original spirit of SET amplifier. Its output transformer is the last mile in delivering music energy to headphone. The bandwidth, dynamics, distortion, and maximum output power are limited by this iron core. No matter how well active circuitry performs, a worse transformer will choke them all. The output transformer might be the only component that spent more effort than tube in design process. The nickel core and multiple winding transformer is a custom version dedicated for PHAntasy. Unlike home stereo SET dealing with only 16,8,4-ohm loudspeakers, PHAntasy is dealing with headphones’ impedance from 600 down to 30 ohm that complicates things even more. A choice of nickel core is to ensure widest bandwidth and minimal size for portability, otherwise, the transformer will be triple its size and weight. A multiple secondary windings are wisdom to cope with widest impedance range instead of traditional single winding multiple taps.
Simple and Beautiful
PHAntasy is a pure analog and full discrete amplifier. A frequently asked question is why we dare to reverse the trend of integrated DAC. The answer lies in our belief that SET amp is simple and beautiful. We can only make it best instead of adding an average DAC. An amplifier shall explore the full potential of headphone and gives user the freedom to formulate his/her own recipe like what we did in top-notch stereo system. The fact is that even using mobile or tablet as source playing CD-quality music, PHAntasy delivers warm and detailed music on lifelike sound stage you ever experienced.
The filament of directly heated triode is most sensitive to power quality. Any careless treatment or corruption of filament supply easily leads to amplified noise or distortion at output. We separate filament power supply from the rest of system starting from a dedicated battery cell for most pure supply. Though JAN6286 tube is specified for portable device, it still needs high voltage rail to operate similar to all other valves, which is good, especially when we target to drive the notorious high impedance headphone to maximum. It is a painstaking process to create high voltage from a single battery cell. The noise and regulation of boost converter are monsters to deal with in such a tiny space. Our efforts have finally paid off. Combined with smart SET topology and high efficiency booster, you hardly hear any hiss or noise with most sensitive headphones; the driving power and bass slam are realistic and stunning even on the most difficult variation of headphones’ impedance.
Designing a portable version of SET amp is ambitious; designing a portable tube amp with 5V DC rechargeable battery is equally challenging. For the high rail of tubes, designers usually go for battery pack (something like we use in notebook PC) with tens of volt to cope with the supply issue. There is nothing wrong with the decision as battery pack is matured and economical. The real issue is at users’ daily life. When traveling for extensive period of time, a specific high voltage adaptor needs to carry along and true portability is compromised. On the other hand, PHAntasy is rechargeable through mobile phone adaptor, power bank, and notebook PC. An even better scenario is you can listen to music while recharge, of course, with longer charging time.
Inspired by team’s prior background on high-end stereo system, PHAntasy is as solid and delicate as any high-end stereo gear. The enclosure is machined from solid aluminum brick to ensure best rigidity and precision, even the bolts supporting PCB is directly grew from the chassis. The marking is laser trimmed on. There is nothing shaky or loose in PHAntasy. It is designed to last from ground up.
Transformer Coupled Output
Perfect For High-Impedance
Adaptive For Low-Impedance Headphone
Directly Heated Triode & Zero Feedback Topolopy
DC 5V Rechargeable
Frequency Response: 30 Hz – 40 kHz (-3dB); 10 Hz – 60 kHz (-6dB)
Output power: 250 mW + 250 mW (300 ohm); 200 mW + 200 mW (75 ohm)
Headphone impedance: 30 ohm – 600 ohm; 60 ohm – 600 ohm (recommended)
Power supply: 5V/1A via micro B USB port
Operation time (on battery): Approx. 8 hours
Charging time (>1A supply): Approx. 4 hours
Dimensions: 165 mm x 95 mm x 35 mm
Net weight: 750 gram
USB A to Micro USB B Charging Cable