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Phatlab Sassy II Portable headphone amplifier

  1. paradisle
    Phatlab Sassy II - a quick review
    Written by paradisle
    Published Oct 13, 2017
    Pros - Oh that warm lovely tube sound; build quality and in-hand feel; portability!
    Cons - Pricey
    This is the first tube based portable headphone amplifier I’ve had the pleasure of reviewing. The Phatlab Sassy II looks somewhat similar to other products in the same class but does seem to be significantly more robust. Parts of the housing are cast and machined and that results in a nice finish, The precise assembly coupled with the rounded off design elements provides a wonderful in-hand feel. At 275 grams it straddles the middle ground of feeling substantial without the notion of carrying around a lead balloon.


    Turn the large and comfortable power-volume knob and you are greeted with some degree of ringing in your headphones as the unit powers on and warms up. In my case, most of my listening was done with Final Audio Sonorous IV ( S IV) headphones. The S IV’s are 8 ohm over the ear headphones and are very easy to drive without an amplifier. Despite this, when plugged into the sassy, the sound reached new levels of high – bass was punchier, the soundstage opened up and warmth and dynamics were tremendous.


    I’ve had the original Sassy on hand to compare and the Sassy II has a different internal layout than the original. Externally, the primary differences include a slightly higher than flush window that gives you a view into those glowing orange tubes and the addition of a ‘Gain’ switch on the outside. The Gain switch allows for a little bit more listening flexibility by making it easier to listen a greater variety of music sources. Internally, Phatlab claims the physical layout and signal paths have been changed from the original – what you will notice is a slightly smoother, sweeter sound. Voices are warmer and more airy compared to the original.


    The Phatlab Sassy II is definitely an amp for those that enjoy the virtues of a Single-Ended Triode (SET) (vacuum tube) amp in a portable form, with a strong emphasis on portable. I say portable because I happily listen to my $60 mini Bravo Audio desktop SET on a daily basis that approximates 90% of the quality of the sound I hear through the Sassy II. Alas, that amp is permanently plugged in and contains no power supply to make it portable enough to keep listening while I grab a cup of coffee from the Kitchen. The batteries on the Sassy II can make it through 3-4 hours of blissful untethered listening. When the on-board batteries diminish the sound starts distorting badly above 40% volume – a recharge fixes the problem. Unfortunately, neither the original nor the Sassy II let you know when you’ve reached that low battery threshold and the music starts distorting – the low batter indicator remained firmly unlit- Hardly what you want to see in this price range. I used the unit primarily while seated at a table or desk. I noticed that any slight contact with a solid surface (during handling) sent waves of ringing through the headphones. While in my pocket, walking around, I did not experience any of that. Ironically it seems more sensitive when placed on a desktop!?!


    I also tried my Echobox Audio Traveler earbuds with the combo of the Phatlab Sassy II and the Dragonfly Red. Once again I was enveloped in that old school tube warmth. The music sounded more spacious, less clinical without being overly bright and tiring. Justin B’s voice on the Despacito remix was remarkably airier and bass bounced like I was listening to sound from giant 70’s speakers powered by a class A amp at my favorite record store. Removing the Sassy II from the line sapped the music of warm dynamism and that old school sexy sound filter.


    I love the warm tube sound that comes out of the amp, and the amp is definitely capable of driving headphones to bring out their full amplified potential. Listening to rock, rap, rock, R&B and alternative tunes, the gain in dynamic punch is palpable. For those wishing for that old school sexy tube sound in a portable package, you will not be disappointed.

  2. crabdog
    Phatlab Sassy II - "My personality is up and down, sassy and cheeky." Katy Perry
    Written by crabdog
    Published Apr 9, 2017
    Pros - Loads of output power. Excellent battery life. Immaculate build quality. Looks great.
    Cons - None I can think of.

    This sample was sent to me for the purpose of an honest review. All opinions and observations here are my own based on my experience with the product. I have no affiliation with the company and do not benefit financially from this review. More of my reviews can be seen from the link in my Head-Fi profile or on my blog.

    The Sassy II has a MSRP of $699 and is available for purchase from Jaben stores. For those in North America you can contact Mr Michael Brown of RSM Comuunications and Final Audio US via email: michael@rsmcomm.com





    Portable HiFi is having a resurgence in popularity of late as can be seen by the current furious competition in the DAP and headphone market. While earphones and IEMs remain the best option for most when they're out and about there are a lot of people using DAPs around the home so as not to be tied to their listening chair or desk. Ones home is also the ideal place for full sized headphones but again people don't always want to be tied to their desktop setups to enjoy music around the house and the majority of DAPs don't have enough grunt to power high impedance or hard to drive headphones. The solution? A portable amplifier to connect to your DAP or even mobile phone so you can lie back on the sofa or watch the sunset from your balcony whilst enjoying your favorite music.

    Phatlab's Sassy II is a single-ended triode/solid-state hybrid portable headphone amplifier. Phew, that's a mouthful! So why tubes and not pure digital amplification? Among all the approaches, single-ended triode tube topology has very unique characteristics of amplification. It produces rich 2nd harmonics, which is not possible in any solid-state amplifier. Since the single-ended triode topology is so simple, it will not introduce IMD (intermodulation distortion), feedback phase shift and all kinds of arguable drawbacks found in solid-state amplifiers. It maintains the clear, purer, and warmer (debatable due to 2nd harmonics) sound.

    I met Mr Lin, the CEO of Phatlab Audio in person at CanJam Singapore 2017. We chatted over some coffee about the Sassy II, portable amplifiers in general and the future of portable audio. It was immediately obvious that he is very well versed and passionate on the subjects of electrical engineering and audio. I was fortunate enough to walk away with a Sassy II which I'll be reviewing today. 

    About Phatlab

    Based in Taiwan, Phatlab was founded in 2015 by a husband and wife team. The company's CEO and lead designer was a previous employee of ENIGMAcoustics and worked on the legendary hybrid dynamic and electrostatic Dharma D1000 headphone. This led him to recognize that the future of the audio industry is in headphones and so he set out on his own to create Phatlab. Right from the beginning Phatlab aimed high at the enthusiast market with the Phantasy, a pure class-A single-ended triode portable headphone amplifier and the original Sassy hybrid amplifier. The Sassy has now been superseded by the Sassy II and Sassy GT (Gold Tuned) amplifiers.

    Like most people on this type of site I'm a lover of music. In my younger days I spent several years as a hip-hop DJ (using real vinyl and turntables) as well as producting a variety of music on computer using a combination of MIDI and live instruments. I did a Home Studio Sound Certificate at the Milton School of Audio Engineering in Brisbane, Queensland which covered the setup of audio for playback and recording in a studio environment along with other basic engineering principles. Nowadays I prefer to simply listen to and enjoy music.
    My taste in music has changed a great deal over the years. For a long time my only interest was in rap and hip-hop music. Now though I listen to all kinds of music including jazz, classical, rock, psytrance, folk and ambient. I listen to music everyday using portable gear consisting of a DAP and mostly IEMs or simple desktop setup consisting of a laptop and DAC at work and my desktop setup at home which is based around my PC or Shinrico D3S with a DAC, often but not always including a tube amp and full-sized headphones or speakers.
    My preferred sound signature is fairly balanced with slightly elevated mid-bass and deep well-extended sub-bass, clear and resolving midrange with a touch of warmth and clean, airy treble. I'm not offended but brighter sounding gear but dislike any sibilance. The majority of my music is 16/44.1 flac files as I stopped using physical media (CD/vinyl) many years ago and prefer the convenience of digital formats. 
    I often list a number of tracks or albums that I have used for testing a specific product in my reviews and they usually relate to things I've been listening to at the time of the review but note that during all my testing there are a number of ADDITIONAL standard tracks that I use for testing various aspects but do not list these in my reviews.



    The Sassy II comes in a plain black box with gold print on the top. On the front side is a magnetic flap that lifts up to open up the box. Inside there is a "Getting started" booklet sitting on a layer of foam with a felt covering. Lifting that out reveals the Sassy II underneath, seated securely in a similar felt covered foam. Under the amplifier is a foam cutout which when pulled out reveals a space under the main foam body where you'll find a USB charging cable. It's a simple yet elegant unboxing experience but I would have liked to see some kind of 3.5 mm to 3.5 mm interconnect cable included so you had everything you need to get started right out of the box.

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    First impressions upon laying eyes on the Sassy II are of a premium product. It's exquisitely crafted aluminum enclosure and machined panels give it a simple yet elegant look which is only exemplified when you hold it in your hand.

    The Sassy II is designed with simplicity and ease of use in mind. On the front panel and surrounded by a protective roll cage (from left to right) are:

    1. 6.35 mm headphone output
    2. 3.5 mm line in
    3. Power (green) and Low battery (red) LED indicators
    4. Volume knob

    The volume knob which also acts as the power switch has a really smooth action and is perfectly weighted with just the right amount of resistance that allows you to make precise volume adjustments. It's the sort of knob that you would expect to find on a premium desktop or rack device, perfectly aligned and silky in its movement.

    Thankfully the LEDs have just the right amount of brightness so they're not distracting and don't clash with the glow from the tubes. Thank you Phatlab for making the power light green because I'm so tired of blue LEDs!

    On the back panel are (from left to right):

    1. Low/High Gain switch (High: 0dB / Low: -10dB)
    2. Charging LED (red)
    3. micro-USB port (for charging)

    Brushed aluminium adorns the topside of the chassis. It's smooth and resistant to fingerprints to boot and surrounds the rear-printed glass viewing window that sports the phatlab logo and emits the warm orange glow of the tubes. On the underside are four rubber feet that keep the Sassy II firmly in place on your desk, table, counter or whatever you decide to place it on.

    If there was one thing I'd change about the design of the Sassy II it would be the addition of a 3.5 mm headphone jack. All of my IEM's and the majority of my headphones have 3.5 mm plugs and it would simplify the experience having the ability to plug directly into the amp without using a 6.35 mm adapter.

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    Frequency Response10 Hz – 100 kHz
    Output power 180 mW + 180 mW (300 ohm)

    1000 mW + 1000 mW (30 ohm)

    Headphone impedance30 ohm – 600 ohm
    Gain SwitchHigh: 0dB / Low: -10dB
    Power supply5V/1A via micro USB port
    Operation time (on battery)Approx. 10 hours (depends on headphone impedance)
    Charging time (>1A supply)Approx. 3 hours
    Dimensions119 mm x 93 mm x 23 mm
    Net weight275 gram

    Let's have a look at the internals. With a full-discrete solid-state output stage the Sassy II is designed to work with any headphones or earphones regardless of impedance or sensitivity. The hand selected military grade JAN6418 tubes are responsible for the major amplification of left and right channels, each one taking care of the left or right side respectively. When it comes to testing each individual tube there are two criteria to meet. The first one is low microphonic effect. Using very low consumption and small size pencil tubes they are more vulnerable to microphonics than bigger size tubes, so they need to see the spectrum of every tube for low microphonics. The second criteria is the Gm ( transconductance) value, or so-called voltage to current gain. For optimal performance they need the tubes with right Gm to fit into right operating point at the circuits.

    The Sassy II has a very low noise floor (generally below -110dB) and I'm told the reason is rooted in the unique circuit topology of Sassy (and all Phatlab products). Sassy has only two gain stages, one for voltage gain based on tubes and another for current gain based on high power transistors, all with discrete devices (meaning no integrated circuit) and without global feedback. This is why selection of the perfect tubes is so important (only 30% pass the criteria for testing). The less gain stage, the lower the noise.

    Phatlab's amplifiers have extreme driving capability beyond the chassis size. Unlike traditional Op Amp circuit topology, they do not count on feedback to make everything right. After screening tubes and making every transistor work at the right operating point, they supply them with higher voltage. It is the high voltage (>20 volt) that provides the extra driving capability on high impedance (>300 ohm) headphones.

    Unlike many tube amplifiers the Sassy's direct heated triode (DHT) is ready to work immediately on powering up without the need to wait until the tubes warm up. That leads me to something I find really unusual (in a good way) about the Sassy II. The unit stays completely cool even after hours of operation. The aluminium enclose doesn't get even slightly warm during use. You might on occasion hear a ringing from the amp after you've switched headphones or just turned the unit on. Don't panic! This is normal and is just microphonics from the tubes within. You're more likely to notice it with low impedance headphones or IEMs. After a few seconds the sound will disappear.


    Sassy II Measurement Report

    Frequency Response (L: yellow and R: red channels)​


    The above graph shows both left (yellow) and right (red) channel frequency response at moderate output level from 20 to 20k Hz.  Counting on the minimum deviation (phase shift) from flat response, the real -3dB bandwidth extends over 10 times both below and above the frequency limits, which is equivalent to 2 to 200k Hz (-3dB) bandwidth meeting Hi-Res requirements.

    Noise Floor ( L and R channels)​


    Just turning on the power of Sassy II and turning the volume to minimum (meaning no input signal), the graph shows the residue noise spectrum generated by Sassy II itself. The inherent noise (low gain) is below -120dB. That is why there is hardly a hiss even working with most sensitive IEMs.

    Signal to Noise Ratio (SNR)​


    The graph shows left SNR (70.3dB). With 1 KHz input signal, Sassy II output 1KHz base frequency and its 2nd (2 KHz) and 3rd (3 KHz) harmonics.


    The graph shows right SNR (72.4dB). It has only obvious 2nd harmonics and barely 3rd harmonics, because of superior characteristics of right channel tube compared with left channel.

    Total harmonic distortion (THD)​


    The input signal is intentionally shifted to 3 KHz and output is lowered to simulate the worst case scenario. It shows about 0.1% THD for left channel.


    It shows 0.125% THD. Again the performance difference between L and R channel is due to variations of tube electrical performance.

    Battery life

    Average battery life is rated at around 10 hours but I found that when using IEMs or lower impedance headphones at lower volume (think evening in a quiet room) then it can be significantly longer. Obviously this will depend on headphones and output levels used and will vary for everyone. There's no need to worry about battery though if you have a power source nearby. The unit can still be used when powered or charging via the USB port.



    Sources used for testing

    1. Samsung Galaxy Note 5
    2. Acoustic Research M20
    3. Mrobo C5 V2.0
    4. PC/MusicBee > Audinst HUD-MX2 > Sassy II

    What I've been listening to lately

    1. Solar Fields - Blue Moon Station
    2. The Gloaming - The Gloaming
    3. Radiohead - Hail to the Thief
    4. Trevor Morris - Vikings OST
    5. Roque Banos - In the Heart of the Sea (Original Motion Picture Soundtrack)
    6. Thundercat - Drunk

    Some readers might find this section a little on the "lite" side after seeing other reviews that wax lyrical about how their amplifier's sound with various headphones and IEMs but in my personal opinion that essentially breaks down into a series of mini reviews of those headphones and IEMs... An amplifier will have a basic signature (hopefully close to flat) that carries across to whatever you connect to it so while I will cover some pairings below, this section will be a very brief description of how I hear the Sassy II.

    As to output impedance of Sassy II, since there is no feedback scheme to reduce its value, it is a very straightforward series resistance at the amplifier output specified at 2.4 ohm. With the added gain select switch the Sassy II is more suitable than the original model for low sensitivity IEMs but has more than enough power to drive high impedance or demanding full sized headphones, including planars. Even on sensitive IEMs at very low volume I haven't been able to detect any channel imbalance whatsoever which is quite remarkable. This is largely due to integrating gain adjustment, when driving higher sensitivity IEMs or headphones and gain setting is low, naturally the user will turn volume higher to potentiometer’s linear region.

    There's little coloration added to music, just some of that tubey goodness that comes across as a bit of extra warmth, the effect of 2nd harmonics taking off the clinical sterility of digital recordings, added airiness to the highs and a slightly increased soundstage. In regards to the extra warmth it doesn't take anything away from the clarity, far from it. The effect is barely noticeable but you can tell it's there, like a little voodoo (the good kind) has been sprinkled over your tunes. You could liken it to a polished vs brushed aluminium: The surface is noticeably changed but it's still smooth, however now it looks and feels even better than before. Okay, I'm digressing there and probably a good amount of people will be left scratching their heads at my analogy. Sometimes I feel like I'm bordering on autistic and things only make sense in my private little world...Overall the Sassy II is a low-distortion tube amp so avoids any drastic splashiness or smearing that you might find in a cheaper or intentionally high-distortion tube amp.


    In use

    In this section I'll be discussing very briefly some pairings that I've tested with the Sassy II. As I have already covered the basic sound signature above this is simply meant to provide the reader with a little insight to the driving capabilities of the amp.

    Full sized

    The first time I heard the Sassy II was at CanJam Singapore 2017 with the Abyss planar headphone. I hadn't heard the Abyss prior to this but had seen people mention its fairly demanding power wise. Well I can state conclusively that the Sassy II took on the challenge like a champ. The sound was full across the spectrum and I was listening at under 50% volume (high gain) so still had plenty of power in reserve.

    With my Beyerdynamic DT990 Pro (250 ohms) I generally sit around 30-40% volume (low gain). This is a nice pairing even though the 990 is pretty weighted in the bass already but there's some added liveliness in the treble that lifts the presentation beautifully.

    The Ultrasone Performance 860 (32 ohms) is a linear headphone with a reference signature. As a result it benefits greatly from the Sassy's touch of warmth and is a more exciting listen with more energy and gusto than with a pure digital amp. In "Opening Set" by The Gloaming the Ultrasone's resolving qualities are perfectly matched resulting in a full-bodied bass, warm inviting midrange. I found myself listening at about 15-25% volume (low gain).

    Sennheiser's HD600 was another great match for the Sassy II at a level of around 40% in low gain, or 25-30% when set to high gain. The HD600's forward vocals sound natural and really engaging along with the Sassy's ability to produce light, shimmering treble.



    In all the IEMs I tested there was no noticeable hiss or background noise. I'm usually not overly sensitive to hissing but in low gain setting I didn't detect any at all.  I tested a few of the IEMs in my current rotation, including LZ A4, Thinksound ms02 and Trinity Phantom Master 4. Although none of those are super sensitive the noise floor was black to my ears. The Phantom Master 4 seemed to benefit the most from the earphones I tested gaining a little more body and fun to their somewhat clinical default signature.


    I've had the Sassy II for almost a month now and although I rarely use portable amps on the go I have definitely become accustomed to using this one at home. In fact because the Sassy makes it so easy to use full sized headphones in any room or around the house I've been using them almost exclusively instead of my IEMs. The battery can get me through a full week on a single charge if I listen to 2-3 hours a day (keeping in mind none of my headphones are especially hard to drive). The Sassy II does everything right for me. Even the green power LED is a refreshing change since nowadays everything seems to have blue ones! 

    The Sassy II has impeccable build quality, great looks, fantastic battery life and is lightweight yet has power output similar to what many desktop units produce. What's more is it gives you a hint of tubey sound whilst retaining a fairly neutral signature and with selectable gain output is versatile enough to drive anything from sensitive IEMs to demanding planar headphones. Try as I might, I simply can't find anything negative to say about it. Granted it's not cheap but neither is what it offers in material or sound quality. If you're looking for a serious portable amp to compliment your kit the Phatlab Sassy II is simply stunning.


    1. View previous replies...
    2. Sound Eq
      great review wonder how it compares to alo v5
      Sound Eq, Apr 11, 2017
    3. gr8soundz
      Are they also making a version 2 of their Phantasy amp?
      gr8soundz, Apr 16, 2017
    4. crabdog
      @gr8soundz I believe there will be but I think the next development will be a balanced portable headphone amp
      crabdog, Apr 16, 2017