Vali2 technical measurements

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

  1. atomicbob

    atomicbob dScope Yoda

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    Vali2 (version 1.0) 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 (version 1.0)
    Measurements commenced after 2 hours of warmup.
    Measurements were performed over a period of several days.
    Stock 6BZ7 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 - reserved for corrections or additional data

    Notable highlights:

    This headamp is no longer in production; this post serves to provide data for comparison to the current production Vali2+. Technical measurements for Vali2+ 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.

    Measurement setup picture:
    DSC_0562_small.jpg

    Listening evaluation picture:
    DSC_0566_small v2.jpg

    Output Impedance with 6BZ7: 4.93 ohms
     
    Last edited: Dec 4, 2020
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  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
    20201125 Vali2 6bz7 A04 THD+N  THD  nth-HD FFT 300R - 4+HD+N with 60Hz 0dBu t2.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 6bz7 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 / 1.118 uS = 313.1 KHz

    Vali2 Frequency Response 300 ohm load
    20201125 Vali2 6bz7 frequency response 5Hz - 96KHz 300R 0dBu.png

    Complete 300 ohm load measurement report pdf attached below.
     

    Attached Files:

    Last edited: Dec 4, 2020
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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
    20201125 Vali2 6bz7 A04 THD+N  THD  nth-HD FFT 32R - 4+HD+N with 60Hz 0dBu t2.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 6bz7 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 / 1.275 uS = 274.5 KHz

    Vali2 Frequency Response 32 ohm load
    20201125 Vali2 6bz7 frequency response 5Hz - 96KHz 32R 0dBu.png

    Complete 32 ohm load measurement report pdf attached below.
     

    Attached Files:

    Last edited: Dec 4, 2020
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  4. atomicbob

    atomicbob dScope Yoda

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    reserved for corrections or additional data
     
  5. Biodegraded

    Biodegraded Friend

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    Is this the original Vali 2, or the 1.1 update with the reconfigured power supply section? Presuming it's the amp on the right of your photo, it looks from the volume knob like an older one. I'm wondering if the 1.1 tweak might have reduced some of the hum.
     
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  6. atomicbob

    atomicbob dScope Yoda

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    It is the original when Vali2 was first introduced.
     
  7. monacelli

    monacelli Friend

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    Anecdotally, I've never heard any mains hum on my unit, which was purchased in November of 2017. I think mine is one of the revised units, because it's also never sounded particularly laid back to me, especially with the stock 6BZ7. It only sounds warm with the GE 5670. I do hear some hiss with iems, even on low gain, and I suspect the Vali 2+ would be a big improvement in that regard. Tempted to pick up the Vali 2+ just to compare. These are such sweet little amps it doesn't make much sense not to keep one around. PS - Great work as always, Bob~
     
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  8. Linkgoron

    Linkgoron Rando

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    If you're really interested - you can see the version number if you look through the holes next to the tube (at least on my Vali 2, it's to the lower left of the tube, when looking from the front).
    upload_2020-12-5_3-8-59.png
     
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  9. atomicbob

    atomicbob dScope Yoda

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    As previously mentioned, most listeners are not likely to hear the hum unless in a very quiet ambient environment. My acoustic lab can get down to 18 ~ 20 dBA at times and is typically less than 25 dBA, which is unusual. Most living environments are more typically 35 to 45 dBA.

    *edit* verified my Vali2 is v1.0.
     
    Last edited: Dec 4, 2020
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