saga preamp technical measurements

Discussion in 'Portable and Other Gear Measurements' started by atomicbob, Jan 23, 2017.

  1. atomicbob

    atomicbob dScope Yoda

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    saga preamp technical measurements

    The data presented were collected as follows:

    1. PrismSound dScope III, picoscope 5243B
    2. 100 Kohm load used for measurements
    3. Unbalanced connections used Sescom with Canare L-4E6S RCA cables
    4. Preamp gain set to minimum attenuation (full clockwise)
    5. Active path used OTK 6H8C provided with Saga
    6. Vaunix Lab Brick USB hub for dScope and picoscope USB connections

    Highlights:
    Ultralow distortion for a tube preamp
    Fast rise and fall times on square wave response
    Relay stepped attenuator
    Small footprint
    Unbelievable price considering exemplary performance, both auditory and measured

    These are impressive results - well done Schiit!


    Notes:
    Industry standard is A-weighted measurements, which can hide noise at low frequencies. These are unweighted measurements unless otherwise noted. Schiit publishes A-weighted specs to remain comparable to other manufacturers specifications. I would note that Saga's unweighted measurements are better than many other vendors A-weighted specifications.

    Picture of the Audio Lab setup for Saga
    20170123 Saga dScope picoscope seteup.jpg

    Active path measurements 6H8C OTK tube part 1 of 3

    Saga square wave 20 Hz 1 Vpp 10 mS / div
    20170123 SigGen Saga 20 Hz square 1000mVpp 10mS div 100KHz filter 100K load 6H8C.PNG

    Saga square wave 20 Hz 1 Vpp 1 uS / div
    20170123 SigGen Saga 20 Hz square 1000mVpp 1uS div 5MHz filter 100K load 6H8C.PNG

    Saga amplitude - phase - gain (A01)
    20170123 Saga A01 amplitude - phase - gain 100K load 6H8C.png

    Saga signal to noise (A07)
    20170123 Saga A07 SNR 100K load 6H8C.png

    Saga THD+N THD nth harmonic distortion (A04)
    20170123 Saga A04 THD+N  THD  nth-HD 100K load 6H8C.png

    Saga 1000Hz THD+N THD nth-HD 0dBu
    20170123 Saga 1000Hz THD+N THD nth-HD 0dBu 100K load 6H8C.png

    Saga Crosstalk (A08 A09)
    20170123 Saga A08 A09 Crosstalk 100K load 6H8C.png
     
    Last edited: Jan 23, 2017
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  2. atomicbob

    atomicbob dScope Yoda

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    Saga active path measurements 6H8C OTK tube part 2 of 3

    editorial - I believe there is a tendency to focus too much on numbers such as THD attempting to reduce a complex topic to a single number representing a sort of goodness rating. Graphs can present far more data conveying a better understanding of the measurement over a range of frequency, levels, etc.

    Saga Frequency Response and Interchannel Phase pg 1/2
    G2_L1T2_1_A.png

    Saga Frequency Response and Interchannel Phase pg 2/2
    G2_L1T2_1_B.png

    Saga Gain vs Amplitude Left
    G2_L1T3_1_A.png

    Saga Gain vs Amplitude Right
    G2_L1T3_1_B.png

    Saga THD+N vs Frequency Left
    G2_L1T5_1_A.png

    Saga THD+N vs Frequency Right
    G2_L1T5_1_B.png

    Saga THD+N vs Amplitude Left
    G2_L1T6_1_A.png

    Saga THD+N vs Amplitude Right
    G2_L1T6_1_B.png

    Saga Crosstalk Left to Right vs Frequency
    G1_L1T10_1.png

    Saga Crosstalk Right to Left vs Frequency
    G0_L1T11_1.png
     
    Last edited: Jan 23, 2017
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  3. atomicbob

    atomicbob dScope Yoda

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    Saga active path measurements 6H8C OTK tube part 3 of 3

    Saga 50 Hz + 7000 Hz spectrum Left and Right
    20170123 Saga 50+7000Hz dual tone 0dBu 100K load 6H8C.png

    Saga 600 Hz + 1700 Hz spectrum Left and Right
    20170123 Saga 600+1700Hz dual tone 0dBu 100K load 6H8C.png

    Saga IMD spectrum Left and Right
    20170123 Saga IMD 0dBu 100K load 6H8C.png


    for basic information on interpreting the data presented, please visit:
    https://en.wikipedia.org/wiki/Audio_system_measurements

    and also use google to find additional resources.
     
    Last edited: Jan 23, 2017
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  4. atomicbob

    atomicbob dScope Yoda

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    Passive path measurements part 1 of 3

    Saga square wave 20 Hz 1 Vpp 10 mS / div
    20170123 SigGen Saga 20 Hz square 1000mVpp 10mS div 100KHz filter 100K load passive.PNG

    Saga square wave 20 Hz 1 Vpp 1 uS / div
    20170123 SigGen Saga 20 Hz square 1000mVpp 1uS div 5MHz filter 100K load passive.PNG

    Saga amplitude - phase - gain (A01)
    20170123 Saga A01 amplitude - phase - gain 100K load passive.png

    Saga signal to noise (A07)
    20170123 Saga A07 SNR 100K load passive.png

    Saga THD+N THD nth harmonic distortion (A04)
    20170123 Saga A04 THD+N  THD  nth-HD 100K load passive.png

    Saga 1000Hz THD+N THD nth-HD 0dBu
    20170123 Saga 1000Hz THD+N THD nth-HD 0dBu 100K load passive.png

    Saga Crosstalk (A08 A09)
    20170123 Saga A08 A09 Crosstalk 100K load passive.png
     
    Last edited: Jan 23, 2017
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  5. atomicbob

    atomicbob dScope Yoda

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    Saga passive path measurements part 2 of 3

    Saga Frequency Response and Interchannel Phase pg 1/2
    G2_L1T2_1_A.png

    Saga Frequency Response and Interchannel Phase pg 2/2
    G2_L1T2_1_B.png

    Saga Gain vs Amplitude Left
    G2_L1T3_1_A.png

    Saga Gain vs Amplitude Right
    G2_L1T3_1_B.png

    Saga THD+N vs Frequency Left
    G2_L1T5_1_A.png

    Saga THD+N vs Frequency Right
    G2_L1T5_1_B.png

    Saga THD+N vs Amplitude Left
    G2_L1T6_1_A.png

    Saga THD+N vs Amplitude Right
    G2_L1T6_1_B.png

    Saga Crosstalk Left to Right vs Frequency
    G1_L1T10_1.png

    Saga Crosstalk Right to Left vs Frequency

    G0_L1T11_1.png
     
    Last edited: Jan 23, 2017
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  6. atomicbob

    atomicbob dScope Yoda

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    Saga passive path measurements part 3 of 3

    Saga 50 Hz + 7000 Hz spectrum Left and Right
    20170123 Saga 50+7000Hz dual tone 0dBu 100K load passive.png

    Saga 600 Hz + 1700 Hz spectrum Left and Right
    20170123 Saga 600+1700Hz dual tone 0dBu 100K load passive.png

    Saga IMD spectrum Left and Right
    20170123 Saga IMD 0dBu 100K load passive.png


    for basic information on interpreting the data presented, please visit:
    https://en.wikipedia.org/wiki/Audio_system_measurements

    and also use google to find additional resources.
     
    Last edited: Jan 23, 2017
  7. atomicbob

    atomicbob dScope Yoda

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    reserved for future.
     
    Last edited: Jan 23, 2017
  8. jexby

    jexby Posole Prince

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    gawd damn. I (try to) learn so much from SBAF members here such as @atomicbob .
    @Marvey Can we please anoint his SBAF status/label to Leto God Emperor, or some similar Shai-Hulud Oracle of Wisdom ?
     
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  9. Cspirou

    Cspirou They call me Sparky

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    While I wouldn't expect anything else in passive mode, I am still really impressed by the 20hz square wave.

    I am a little surprised that the S/N ratio is 'only' 116dB in passive mode though since the signal is only going through two resistors. Not that this is audible but why wouldn't it be lower? Would the power supply need to be housed separately? Are you reaching the limits of the equipment?

    Curious what something like a Goldpoint stepped attenuator would look like. Or just two resistors.
     
  10. Grahad

    Grahad Friend

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    Probably dominated by Johnson noise.
     
  11. Cspirou

    Cspirou They call me Sparky

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    Reading over the settings it says the gain is at 0.000dB. Which to me would imply that the volume is set to MAX and should essentially be just a wire. Johnson noise shouldn't be a factor unless I am interpreting it wrong.
     
  12. OJneg

    OJneg The Most Insufferable

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    The signal is going through more than 2 physical resistors, strictly speaking, in an R-2R attenuator.

    Otherwise given that only the best D/A A/D converters achieve 120dB SNR it's about as good as you can expect. Probably some hum induced in the single-ended wiring either in the box, in the cables, or in the test gear.
     
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  13. atomicbob

    atomicbob dScope Yoda

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    Look at the second to last graph for the passive measurements, 600 Hz + 1700 Hz spectrum. Note the bump at 60 Hz. Power supply. Now consider that 116 dB below 1 volt is approximately 1.6 uV. It doesn't take much to induce that amount of noise into a circuit. So better separation of the passive from the active circuits could possibly lower the residual noise. But at what expense. Larger enclosure, larger footprint, more money, I like the tradeoffs Jason made and voted for it with my wallet.

    @jexby - thank-you for the feedback :D
    If these measurements are enlightening then the effort has been worthwhile.
     
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  14. atomicbob

    atomicbob dScope Yoda

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    Look at the setup picture. Great care is taken to separate AC for the unit under test from the AC to the test equipment. SMPS for the laptop and Vaunux lab hub are powered via a shielded extension cord on a separate run from the mains. And with all that effort a small amount of residual noise is probably still present as you mention. One of these days I may install a metal bench to make a better ground plane. But that won't be representative of a real world situation. I'm tempted to rerun some of the tests with a more typical distribution of power and jumbling of cables together. Experiment for another day.
     
  15. schiit

    schiit SchiitHead

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    It's actually not an R2R attenuator, it's a log attenuator. But yep, it's passing through more than 2 resistors, typically, depending on volume setting.

    Thanks again, AtomicBob, for a great set of measurements. The guys at Audio Precision were smirking when we went up to their booth with Saga (to check out an intermittent problem with a prototype at RMAF). They were clearly looking forward to showing us just how bad a tube preamp would measure.

    The smirks quickly left their faces after they hooked it up, though.
     
  16. atomicbob

    atomicbob dScope Yoda

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    The 0.000 dB is a self-relative reference for that measurement.
    When the gain is set to maximum this particular Saga exhibits the following insertion loss:
    -0.49 dB Active
    -0.17 dB Passive
    There are components in the path creating a slight attenuation. Nothing to worry about.
     
  17. atomicbob

    atomicbob dScope Yoda

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    I wish I could have seen the looks on their faces personally. My ears told me this is special preamp. But when I measured yesterday, I probably exhibited a similar facial expression. Well done Jason!!
     
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  18. ultrabike

    ultrabike Measurbator - Admin

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    I think Johnston noise is depedent on room temperature and the amount of resistance. So maybe there will be a resitance dependent noise floor even if there is no signal going through.
     
  19. ultrabike

    ultrabike Measurbator - Admin

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    BTW, Awesome preformance.
     
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  20. Grahad

    Grahad Friend

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    "Total" Johnson noise is dependent on the room temperature, resistance, and bandwidth.
     
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