Schiit Audio Vali 2+ headphone amplifier Measurements

Sidebar 3: Measurements

After installing the single GE 6BZ7 dual-triode tube, I measured the Schiit Vali 2+ with my Audio Precision SYS2722 system (see the January 2008 "As We See It"), repeating some tests with the magazine's sample of Audio Precision's current top-line APx555. I took a full set of measurements from both the front-panel headphone jack and the single-ended preamplifier outputs on the rear panel in both the High and Low gain settings.

The Schiit's input impedance is specified as 50k ohms. I measured 45k ohms at 20Hz and 1Hz, and an inconsequential drop to 40k ohms at 20kHz. The maximum gain from both the preamplifier and headphone outputs was very close to the specification at 14.1dB, High gain, and 0.9dB, Low gain. The Vali 2+ preserved absolute polarity (ie, was noninverting) from both outputs and with both gain settings. Its output impedance from the headphone output, with gain set to High, was extremely low, at 2.6 ohms at 20Hz and 1.7 ohms at 1kHz and 20kHz. Setting it to Low reduced the output impedance slightly. Though these values are a little higher than specified, they include the series resistance of an adaptor cable and 2m of interconnect. The preamplifier output impedance was 101 ohms from 20Hz to 20kHz.

The Schiit's frequency response was flat in the audioband and down by 1.3dB at 200kHz. With the very low output impedance, the response into 300 ohms (fig.1, cyan and magenta traces) was identical to that into the high 100k ohm load (blue, red traces). Fig.1 was taken from the headphone output with the Vali 2+'s volume control set to its maximum. The response from the preamplifier output was identical. However, a channel imbalance appeared at lower settings of the volume control. With the control set to 12:00, for example, the right channel was 0.6dB higher in level than the left.


Fig.1 Schiit Vali 2+, headphone output, frequency response with volume control set to maximum at 1V into: 100k ohms (left channel blue, right red), 300 ohms (left cyan, right magenta) (0.5dB/vertical div.).

Even though the tube is shared between the channels, channel separation was very good, at 80dB in both directions between 300Hz and 1kHz, though it decreased to 60dB at 20kHz (not shown). The wideband, unweighted signal/noise ratio, measured with the input shorted to ground but the volume control set to its maximum, was 86.75dB in the High gain condition and 99dB in the Low gain condition. (Both ratios are ref. 1V output and the average of both channels.) Restricting the measurement bandwidth to the audioband increased the S/N ratios to 95.6dB and 109dB, respectively, while switching an A-weighting filter into circuit further improved the ratios, to 102dB and 116.5dB. The drop in the Schiit's noise floor when the gain was switched from High to Low can be seen in fig.2, which shows the low-frequency spectrum as the Vali 2+ drove a 1kHz tone at 1V into 100k ohms. AC supply spuriae at 60Hz and 120Hz can be seen in this graph, but these are very low in level, even with High gain (blue and red traces).


Fig.2 Schiit Vali 2+, headphone output, spectrum of 1kHz sinewave, DC–1kHz, at 1V into 100k ohms with High gain (left channel blue, right red) and Low Gain (left cyan, right magenta) (linear frequency scale).

Fig.3 plots the percentage of THD+noise in the Vali 2+'s headphone output as the level was increased into 300 ohms. Gain was set to Low. The THD+N gently rises above 200mV but remains well below 0.1% until the waveform starts to clip at 9V. Fig.4 repeats the test into 30 ohms, an impedance that is typical of many headphones. The THD+N is still low up to 5V, but now the Vali 2+ reaches 1% at 8.3V. This is well above the level necessary to drive low-impedance headphones to unbearably high sound levels. However, the picture changed dramatically when I switched the gain to High. Fig.5 shows that the THD+N is around 20 times higher at low output levels than it was with Low gain and that it rises in a linear fashion, reaching 1% at 3.1V. Repeating these tests from the preamplifier outputs gave identical results.


Fig.3 Schiit Vali 2+, headphone output, Low gain, distortion (%) vs 1kHz output voltage into 300 ohms.


Fig.4 Schiit Vali 2+, headphone output, Low gain, distortion (%) vs 1kHz output voltage into 30 ohms.


Fig.5 Schiit Vali 2+, headphone output, High gain, distortion (%) vs 1kHz output voltage into 300 ohms.

I measured how the Vali 2+'s distortion changed with frequency at 1V. The THD+N percentage was consistent across the audioband into both 100k ohms and 300 ohms and didn't increase into the lower impedance (fig.6). However, it was very much higher with High gain (blue, cyan, red, and magenta traces) than with Low gain (gray, yellow traces).


Fig.6 Schiit Vali 2+, headphone output, distortion (%) vs frequency at 1V: Low gain into 300 ohms (left yellow, right gray); High gain into 100k ohms (left blue, right red) and 300 ohms (left cyan, right magenta).

It is appropriate to note that Schiit's Jason Stoddard explains on the company's website that the Vali 2+ "is not a low-distortion design. It is designed to reflect the distortion of its tube gain stage, so total distortion is high, but it also falls off sharply for higher orders."

The distortion's harmonic signature was indeed almost entirely second harmonic with the gain set to both Low (fig.7) and High (fig.8), though the harmonic's level is very much lower with Low gain, –80dB (0.01%), than with High gain, –50dB (0.3%). Again, this performance was identical from the preamplifier outputs. I tested the Vali 2+ for intermodulation distortion with an equal mix of 19 and 20kHz tones at a peak level of 1V. With the gain set to Low (fig.9), the second-order difference product at 1kHz lay just below –90dB (0.003%), and the higher-order products all lay close to –120dB (0.0001%). While the intermodulation products were higher in level with the gain set to High (fig.10), they were not as high as I was expecting.


Fig.7 Schiit Vali 2+, headphone output, Low gain, spectrum of 50Hz sinewave, DC–1kHz, at 1V into 300 ohms (left channel blue, right red; linear frequency scale).


Fig.8 Schiit Vali 2+, headphone output, High gain, spectrum of 50Hz sinewave, DC–1kHz, at 1V into 100k ohms (left channel blue, right red; linear frequency scale).


Fig.9 Schiit Vali 2+, headphone output, Low gain, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 1V into 100k ohms (left channel blue, right red; linear frequency scale).


Fig.10 Schiit Vali 2+, headphone output, High gain, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 1V into 100k ohms (left channel blue, right red; linear frequency scale).

Even without taking its very affordable price into account, the Schiit Vali 2+ in its Low gain mode offers excellent measured performance. As the higher level of second-harmonic distortion in the High gain mode is not accompanied by high levels of intermodulation distortion, I would expect a "fatter" sound in this mode.—John Atkinson

Schiit Audio
22508 Market St.
Newhall, CA 91321
(323) 230-0079

thatguy's picture

It seems like using it as a preamp could be fun. I'd love to hear some impressions of that.

thethanimal's picture

My mother-in-law gifted me a subscription to that other audio mag after my wife suggested it for Christmas. After reading their latest issue last night, coming across your article this morning was like a breath of cool morning air — right in line with our unusually frosty morning in Atlanta. I look forward to each of your articles for the excellent prose, artistic references, and eclectic music. My Tidal library is getting hard to manage these days after adding so many of the recordings you’ve referenced!

Which brings me to a recommendation: Areni Agbabian’s album “Bloom” on ECM (Tidal MQA). Gorgeously atmospheric vocals and piano from this Armenian American woman, with Nicolas Stocker on various hand drums, chimes, bells, gongs, etc. Air, space, reverb tails, timbre, tactile drum skins, nuance, and emotion for days. Seems right up your ally.

Herb Reichert's picture

I am glad to be some 'cool morning air' and I am grateful for your time spent reading.

And thank you forever for the album recommendation.

I am listening to Areni Agbabian’s “Bloom” right now, and you definitely nailed my taste. It is a beautiful recording that is seducing me completely. Look for it in one of my next stories.

Got another album tip?

peace and tulips,


thethanimal's picture

I can’t claim any special credit for finding that album. I’ve added several albums from the ECM label over the last few years thanks to you and other Stereophile recommendations, and then I found a Tidal-curated playlist titled “Label Focus: ECM - Tidal Masters.” I hit play and the first track from Bloom — “Patience” — graced my ears a few minutes later. I’d recommend the whole playlist.

For other album recommendations I’ll start with something completely different: Kendrick Lamar’s “DAMN.” Not the best sonics, but as a cultural landmark and an eye-opening view of a life so different from mine as a upper-middle class white guy I consider it required listening. It won a Pulitzer for a reason.

Beyond that, Sturgill Simpson’s “Cuttin’ Grass - Vol. 1” and The Avett Brothers’ “Emotionalism” for newer (and perhaps pop-ier) bluegrass or Americana. But don’t miss Avett Brothers’ “Murder in the City” off “The Second Gleam” album. Any of the versions of Steve Reich’s “Music for 18 Musicians” or “Eight Lines” (all on ECM I think) to close your eyes and take a hallucinatory trip through your subconscious. For contemporary choral work, I love Eric Whitacre, with my favorite album being “Cloudburst” performed by Polyphony led by Stephen Layton, but it’s not on Tidal. He might be more mainstream than Erik Esenvalds’ works (thanks again to Stereophile and John Atkinson for the albums with Portland State Choir!) but I hear similarities in their work.

I may have to find one of those Japanese input tubes you mentioned for my Decware SE84UFO. I have NOS rectifiers — an RCA from the 1950s and a military surplus (JAN) that might have been made by Sylvania in the 1960s — but I didn’t get those until the stock rectifier blew on me so never got an A/B comparison.

thethanimal's picture

The Atlanta sun scorched my potted tulips, but the baptisias and coreopsis are in full glory, with the rudbeckias coming soon. Cardinals and finches and nuthatches battle for the sunflower seeds at the feeder. Thank God for spring!


Jack L's picture


Potted Tulips should NOT be put under direct sunshine.

Last month I got 2 potted Tulips (still bulbing), one red & one yellow, from Home Depot. I put them indoor with mild sunhshine thru the patio door vertical blinds. Now booming with beautiful large flowers !!!

Every spring/summer, I spend soo many hours outdoor gardening. I dare say I am a lawn turf repair 'expert' using seeds & black soils. NO no need costly sod.

Jack L

Herb Reichert's picture

are not as exotic as yours and my poor knowledge of flower names is comedic. But we must share a lot of interests as my writing desk sits arm's length from a window that looks over my plot in a community garden which currently features hoards of exploding tulips. When they pass, the Zinnenias and honeysuckle take over. (I bet you got mad good honeysuckle!) Also, right at my writing window are several bird feeders that mostly service sparrows and doves but sometimes I get 'visitations' from mocking birds, woodpeckers, blue jays, robins, and starlings - which are always exciting. Yesterday, a GIANT crow appeared on the ground in the garden. I had not seen a crow in years and this one was the size of a small dog!!!

And then, and then, me and my brother Jeffrey Jackson (The Salt Cellar horns) are also into Kendrick Lamar’s “DAMN.” Thank you again, I will check out your other recommendations.

peace and verdant gardens,


thethanimal's picture

Indeed. Gardening has become a passion and I’m playing catch-up on bird identification.

I remember reading the reference to Lamar in your Salt Cellar horn article and wondered if it was DAMN. I’m loving my SET amp and full-range drivers, but ever since reading that article I’ve been longing to experience some horns like that system, or WE 15a’s, or even an Altec VOTT A-7. I’d like to hear some Devore Orangutans too, but there isn’t a dealer in Atlanta. Not that I could afford any of that, though. I did listen to a ~$50k KEF Blade rig at Hifi Buys (which is a great store with some great guys) but I liked my system better. My crossover-less SET rig has an immediacy that $50k can’t buy, it seems.

Jack L's picture


I wish gardening is a "passion" for me as well like my vinyl music.

It is now my job instead due to my fully-fenced backyard is converted to somewhat like Saint-Saens' "The Carnival of the Animals" in spring/summer.

Besides birds, intruders coming from nowhere include squirrels, rabbits, wild cats, & raccoons etc. These animals manage to squeeze through gaps between the wooden fence boards to enjoy the sunshine on the lawn.

My most hated is the rabbits, some big like a medium raccoon, eat away the lawn turf. So I got to patch it up.

So besides a lawn guy, I've become a fence mender as well, No choice !

Just last week, I spotted a huge dirty grey raccoon, sized like a small pig, walked across my lawn. It may look bulky & clumsy, but its long sharp claws can climb it up to any house rooftop. No kidding. By the law here, we have to leave these animals alone.

Jack L

Jack L's picture


Yes, tube SET is my passion like vinyl music.

For years, I've been playing vinyl & digital music with my design/built
SET. It's a very simple 2-stage all-triode class A SET power amp 5W+5W.

I'm now building a larger 2-stage 10W+10W SET power amp using the same zero-global/LOCAL-feedback class-A grounded cathode topology & triodes of the same models. For best sounding, IMO. Let's see.

Yes, "full-range drivers" are excellent sounding to those music lovers not too fancy for hi-low frequency extremes.

For for yours truly, I want to enjoy full range music with glass-shattering high pitch of soprano singing as well as floor shaking cathedral pipe organs deep bass music.

"Full-range drivers" can't deliver it. This is physics.

To achieve such frequency extremes, I've added a pair of Motorola direct radiating piezo (no-horn) tweeters (up to 40KHZ) to my fully-upgraded KEF 2-way bi-wired standspeakers. For deep bass, added 3 powered subwoofers (L, R & L+R) hooked direct to my design/built all-triode tube phono-linestage. It works like a chime, IMO.

For good music, don't bank on luck. Nothing comes easy.

Jack L

My Fi's picture

Any tips on where one can pick up an Electric Industry Co. Ltd. 7DJ8 that served as the capstone to this excellent review? Thanks!

Currawong's picture

...then these little amps do remarkably well. The key thing is that they run out of power much faster than the larger Asgard and Jotunheim.