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.

Pure Power

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.

Smart Power

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.

Specifications

A portable Single-Ended Triode for Everyone Everyday

Sassy is designed for every enthusiast and audiophile who enjoy sound of SET amp while demands more portability and practicality. Sassy as 2nd member of portable headphone amplifier (PHA) series has inherits many technologies and advantages developed for PHAntasy, the bigger sibling. One may immediately notice Sassy’s extremely compact and light-weighted ever seen for a tube amplifier. The secret is elimination of output transformer and choice of high efficiency subminiature tube. A newly developed full-discrete solid-state output stage replaces costly output transformers, which is capable of delivering precise and powerful energy into headphones no matter what impedance and sensitivity.

The Heart of Sassy, JAN6418

At the center of Sassy are a pair of JAN6418 tubes, each one responsible for major amplification of left and right channels. JAN6418 is a triode-connected filament type pentode in Sassy. The main amplifier topology is Single-Ended Triode (SET) from input up to voltage gain stage to preserve sound signature of Directed Heated Triode (DHT) followed by solid-state output buffer. A triode is unique as gain device that tends to generate more even harmonics than odd ones if any. The result is music sounds airier, smoother, and richer than other type of devices. JAN6418, a directly heated tube, instantly enters working condition after power on and provides intimacy and lifelike sound stage more than none filament type tubes. Hand selected JAN6418 driven by smart filament bias has extensive lifespan. There is no obvious degradation of tube performance for 5 years.

High-fidelity solid-state output stage

The biggest difference sets Sassy apart from traditional SET amp is solid-state output stage. The effort is beyond imagination and takes much longer time to come up a viable solution with satisfactory performance. The challenge is to make it stable and consume extremely low power, while faithfully delivering SET signature of sound and plenty of energy on demand. The efforts have finally paid off. Sassy is capable of up to 20V and 1A output that is something never been done in such a small form factor. Sassy meets the balance of both worlds with sweetness of Single-Ended Triode and precise slam of power transistor. Sassy’s overall tonal balance and driving capability are comparable to best amplifiers either desktop or portable formats.

Simple and Elegant

Sassy is a pure analog and full-discrete design. We make Sassy as pure as possible by doing the best in analog domain and leave the freedom to users for choice of front end as concept in hi-end stereo. Disregard the simple connectivity and control, Sassy can handle plenty energy dynamically for any types of headphone. Users can choose whatever they prefer without concern of impedance and sensitivity, A small form factor forges Sassy’s simple and elegant look in aluminum enclosure and machined panels, yet the inside complexity and technology.

Pure and Smart Power

Sassy is capable of playing music over 10 hours on battery (*1). This is unprecedented achievement for a tube amplifier. Instead of using two batteries like PHAntasy, there is only one cell in Sassy to supply both filament bias and amplifier. A filter in front of filament supply ensures the purity of power. Careful ground planning and layout topology guarantee minimum interference between blocks. And, as always, we adopt USB port as DC 5V charging supply for best convenience and true portability.

(*1) the actual time depends on type of headphone and sound level of playback

Minimal Design

From the beginning of project, we intend to design a simple yet high performance amplifier for daily life without concern of control manipulation, trouble of carrying adaptor, choice of suitable headphones, etc. We are proud to say the goal has achieved. By leveraging the sweetness of tube and power of solid-state devices, Sassy is able to deliver touching and powerful music anytime anywhere. Following the adaptive nature of smart design, Sassy eliminates all the unnecessary switch and control. It is so much more comfortable to use Sassy without hassle, just plug and play.

Specifications