Vali2+ technical measurements

Discussion in 'Headphone Amplifier Measurements' started by atomicbob, Dec 4, 2020.

  1. atomicbob

    atomicbob dScope Yoda

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    Vali2+ technical measurements

    Standard Prologue
    If you are unfamiliar with audio measurements please use a search engine with the query:
    "audio measurements" or "audio measurement handbook"
    Look for publications by Richard C. Cabot and also by Bob Metzler, both from Audio Precision. There are other useful publications as well. These will provide basic knowledge.
    Interpretation of the following measurements is beyond the scope of technical measurements posts.

    The data presented were collected as follows:

    1. PrismSound dScope III, picoscope 5243B, Keysight 34465A, Cal Test CT2593-2 balanced probe
    2. Balanced XLR cables Belden 1800F with Neutrik 110R AES connectors (if used)
    3. Single Ended cables Audioblast HQ-1 3 ft with Rean RCA connectors
    4. 32 and 300 ohm loads used for measurements
    5. dScope analyzer sample rate 48 KHz unless otherwise noted
    6. 0dBu level used for testing unless otherwise noted
    7. Amplifier input to output gain set for 0 dB unless otherwise noted
    8. Audioquest Forest and Schiit Pyst USB cables used with measurement equipment
    9. Vaunix Lab Brick USB hub
    10. Shielded 14AWG and 16AWG power cables
    11. ESD, EMI/RFI controlled lab bench and workspace

    Measurements are made in accordance with AES17:2015

    Sensitivity data for two headphones to keep in mind while viewing these measurements:
    HD 650 impedance 300R, sensitivity 98 dB/mW
    HE-500 impedance 38R, sensitivity 89 dB/mW

    SPL levels for above headphones for reference:
    0 dBu 300R 2.00 mW - 101 dBSPL @ 98dB/mW
    0 dBu 30R 20.00 mW - 102 dBSPL @ 89dB/mW

    All testing performed at 0 dBu unless otherwise noted.
    This level is consistent with listening to headphones (referenced above) at 90 dBSPL average with peaks to 100 dBSPL, if the music has 10 dB Peak to Avg ratio. That is LOUD for long listening sessions.

    Vali2+
    Measurements commenced after 1 hour of warmup.
    Measurements were performed over a period of several days.
    Stock 6BZ7A tube used unless otherwise noted.

    Index
    Post 1 - Measurement setup description, highlights
    Post 2 - 300 ohm load part A
    Post 3 - 32 ohm load part B
    Post 4 - Major differences between Vali2 and Vali2+
    Post 5 - reserved for corrections or additional data

    Notable highlights:

    Hallelujah! Vali2+ offers some major improvements over the Vali2 headamp. For those bothered by residual mains hum and noise (me for instance) this is most welcome.

    Vali2 is longer in production, technical measurements for comparison may be found here.

    I have long had a love / hate releationship with the Schiit Vali2. It has good tonal balance and a pleasing harmonic distortion profile. Conventional wisdom for budding tube headamp listeners was to acquire this inexpensive component, then listen long, gaining insight while saving funds until a significant ascension with more knowledge could be afforded. At headphone meets the Vali2+ has been popular with listeners, myself included. However an important note about can meets is the rather high ambient noise, which may mask low level issues.

    Back in my acoustic lab when listening between 65 and 75 dB SPL on headphones with sensitivity of 95 to 100 dB/mw, mains noise was at the threshold of perception with hum at -75 dBu. I perceived the blackground compromised and a certain sourness to the listening experience that would mostly disappear when listening level was increased to 75 to 85 dB SPL. Mains hum between tracks was still evident. @Changeling sent me an Ultron 7DJ8 which reduced the mains hum and thus improve the situation. But it never was quite enough for me in my very quiet acoustic lab. In normal home environments ambient noise masking is likely sufficient to hide this issue.

    Most listeners will be undisturbed by this issue to which I am so sensitive. Vali2+ addresses power supply noise in a substantial way, offering approximately 27 dB reduction in mains noise and THD+N, 4+HD+N, etc. when operating below -20 dBu; see post 4 below.

    Measurement setup picture:
    DSC_0562_small.jpg

    Listening evaluation picture:
    DSC_0566_small v2.jpg

    Output Impedance with 6BZ7A: 1.54 ohms
     
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    Last edited: Dec 4, 2020
  2. atomicbob

    atomicbob dScope Yoda

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    300 ohm load part A

    Vali2+ A04 THD+N THD nth-HD FFT 300 ohm load
    20201120 Vali2+ 6bz7a A04 THD+N  THD  nth-HD FFT 300R - 4+HD+N with 60Hz 0dBu.png

    Vali2+ 50 + 7000 Hz 300 ohm load - Left Channel
    FFT_2_L1T13_1_A.png

    Vali2+ Gain Linearity 300 ohm load - Left Channel
    G2_L1T3_1_A.png

    Vali2+ THD+N vs Frequency 300 ohm load - Left Channel
    G2_L1T5_1_A.png

    Vali2+ Residual Noise 300 ohm load - Left Channel
    FFT_2_L1T16_1_A.png

    Vali2+ Square Wave 2000mV 10mS/div - Left Channel
    20201124 SigGen Vali2+ 6bz7a 20 Hz square 2000mVpp 0_5uS div 5MHz filter 300R - BW calc.png
    Bandwidth estimation: BW (MHz) = 0.35 / RT (mS)
    Where RT = 10 to 90% Rise Time
    0.35 / 1.028 uS = 340.5 KHz

    Vali2+ Frequency Response 300 ohm load
    20201120 Vali2+ 6bz7a frequency response 5Hz - 96KHz 300R 0dBu.png

    Complete 300 ohm load measurement report pdf attached below.
     

    Attached Files:

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  3. atomicbob

    atomicbob dScope Yoda

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    32 ohm load part B

    Vali2+ A04 THD+N THD nth-HD FFT 32 ohm load
    20201120 Vali2+ 6bz7a A04 THD+N  THD  nth-HD FFT 32R - 4+HD+N with 60Hz 0dBu.png

    Vali2+ 50 + 7000 Hz 32 ohm load - Left Channel
    FFT_2_L1T13_1_A.png

    Vali2+ Gain Linearity 32 ohm load - Left Channel
    G2_L1T3_1_A.png

    Vali2+ THD+N vs Frequency 32 ohm load - Left Channel
    G2_L1T5_1_A.png

    Vali2+ Residual Noise 32 ohm load - Left Channel
    FFT_2_L1T16_1_A.png

    Vali2+ Square Wave 2000mV 10mS/div - Left Channel
    20201124 SigGen Vali2+ 6bz7a 20 Hz square 2000mVpp 0_5uS div 5MHz filter 32R - BW calc.png
    Bandwidth estimation: BW (MHz) = 0.35 / RT (mS)
    Where RT = 10 to 90% Rise Time
    0.35 / 1.144 uS = 305.9 KHz

    Vali2+ Frequency Response 32 ohm load
    20201120 Vali2+ 6bz7a frequency response 5Hz - 96KHz 32R 0dBu.png

    Complete 32 ohm load measurement report pdf attached below.
     

    Attached Files:

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  4. atomicbob

    atomicbob dScope Yoda

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    Major differences between Vali2 (version 1.0) and Vali2+

    Output Impedance
    Vali2 with 6BZ7: 4.93 ohms
    Vali2+ with 6BZ7A: 1.54 ohms

    Vali2 Distortion and mains noise
    20201120 Vali2 6bz7 A04 THD+N  THD  nth-HD FFT 300R - 4+HD+N with 60Hz 0dBu annotated.png
    Mains hum fundamental at 60 Hz is at -74.5 dBu in the right channel. Threshold of perception is at -75 dBu. Note the harmonic series follows a preferred downward slope which is present in numerous tube headamps enjoyed by many listeners. This is good. Now if the power supply noise could be lowered Vali2 would achieve several notches higher blackground. A preferred level of blackground is at least 10 dB lower than threshold of perception, in this case -85 dBu would be a good target.

    Vali2+ Distortion and mains noise
    20201120 Vali2+ 6bz7a A04 THD+N  THD  nth-HD FFT 300R - 4+HD+N with 60Hz 0dBu annotated.png
    Voila! Vali2+ delivers, not just a little improvement but a LOT. Often 3 to 6 dB improvement is highly sought after. But Jason has delivered an astounding 27 to 30 dB reduction in mains noise.

    Vali2 and Vali2+ THD+N vs amplitude comparison
    G2_L1T6_1_A_Vali2_Vali2+6bz7a annotated.png
    Again note the 27 dB reduction of THD+N vs amplitude below -20 dBu. I often listen at between -30 to -20 dBu when using HD6x0 and HD800J-mod headphones. Even lower with Focal Clear and Stellia. For those who prefer lower listening levels this is a great improvement. Blackground is improved and lower level details are not soured with residual mains noise.
     
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  5. atomicbob

    atomicbob dScope Yoda

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    reserved for corrections or additional data.
     
  6. schiit

    schiit SchiitHead

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    Thanks for doing this, and confirming the better performance in terms of noise floor!

    With respect to Vali 2 1.0 vs Vali 2 1.1 vs Vali 2+, here's the deal:

    1. Vali 2 1.0 is the original layout. It had regulated main rails, which is usually sufficient to keep noise down. And, here's the weird thing--some of them were quite a bit quieter than AtomicBob's 1.0 version. I have one on my desk that's a good 10-12dB quieter. However, variability is never a good thing, so...

    2. ...we added more power supply filtering on Vali 2 1.1. This is back before we promised "no more silent revisions." That made them all equally quiet, and quieter than 1.0 by 15-20dB or so. But when I was designing Magni 3+, the performance potential of adding a driver stage and going to matched parts was intriguing, so....

    3. ...I designed Vali 2+, which added a driver stage and matched parts, and tweaked the power supply a bit more. That one came out REALLY quiet, and the additional loop gain from the added driver stage reduced the output impedance. Plus, to me, it sounded better. So we cued up a changeover to Vali 2+.

    And that's pretty much the story.

    One caveat: tubes can vary pretty widely in terms of residual hum, since all Vali 2s and 2+ use AC heaters, and some tubes are better than others. We provide a tube that's pretty solid in terms of noise performance, but you will find better or worse out there...
     
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  7. atomicbob

    atomicbob dScope Yoda

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    Thank-you Jason for filling in the details.

    I am in agreement that Vali2+ sounds much better than the Vali2 v1.0 I have.

    Conventional wisdom remains; budding tube amp listeners would do very well to begin with Vali2+ and hold for a long time. It might turn out that with a synergistic combination of headphones and DAC to be a system valued for many years. Even if ascension is desired later, this still makes a stellar workstation listening amp.
     
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