Shortest Way 51+ technical measurements

Discussion in 'Headphone Amplifier Measurements' started by atomicbob, Oct 6, 2019.

  1. mdr30

    mdr30 Rando

    Joined:
    Apr 4, 2016
    Likes Received:
    7
    Dislikes Received:
    0
    Trophy Points:
    3
    Thanks for added measurements and comments, quite illuminating.
     
  2. atomicbob

    atomicbob dScope Yoda

    Friend BWC MZR
    Joined:
    Sep 27, 2015
    Likes Received:
    10,188
    Dislikes Received:
    3
    Trophy Points:
    113
    Location:
    On planet
    And where else on the internet can one find such extensive, detailed information on a relatively obscure headphone amplifier?

    Support your local SBAF!
     
    Soups, Walderstorn, Lasollor and 10 others like this.
  3. atomicbob

    atomicbob dScope Yoda

    Friend BWC MZR
    Joined:
    Sep 27, 2015
    Likes Received:
    10,188
    Dislikes Received:
    3
    Trophy Points:
    113
    Location:
    On planet
    Additional discussion of SW51+ output voltage vs. distortion.

    Maximum output voltage is dependent on load impedance and distortion level tolerated. A much higher Vpp (Voltage peak to peak) may be achieved if greater than 1% distortion is considered.

    Several power measurements are presented in post 20 here Voltage output for a given distortion may be determined by reading the dBu on the x-axis for a given THD on the y-axis.

    Distortion vs. amplitude plots distortion in either percent or dB below the stimulus on the y-axis and amplitude on the x-axis. My power measurements cited above were made with amplitude in dBu which is an absolute: 0 dBu = 0.775 Vrms. Using the formulae below dBu may be converted to Vrms and then Vpp:

    dBu to V conversion formulae - negative.png

    Example conversions:
    20191008-1a SW51+ 6Z51P THD+N vs dBu 1000Hz 300R HiZ 0dB gain - annotated.png
    Example 1:
    For a 1 KHz stimulus the left channel (blue) measures 0.2% THD+N at -10 dBu. Using the formulae above -10 dBu calculates to 0.245 Vrms and 0.693 Vpp.

    Example 2:
    For a 1 KHz stimulus the left channel (blue) measures 2.0% THD+N at +10 dBu. Using the formulae above -10 dBu calculates to 2.45 Vrms and 6.93 Vpp.


    Bifrost-2 + SW51+ system voltage vs distortion oscilloscope measurements at 440 Hz

    Measurement setup

    DAW 440 Hz 0 dBFS sine output to Dante Virtual Soundcard
    Dante RDL spdif output routed to bifrost-2
    bifrost-2 RCA 2Vrms to SW51+
    SW51+ HiZ output with 300R load substituted for HD800-Jmod

    Signal routing diagram:
    20191117-0 RDL SF-ND2 - B2 - SW51+ - HD800.png


    20191117-1 bifrost-2 0dBFS SW51+ 6Z51P max Vpp 1 pct THD 440Hz 300R HiZ small.jpg

    SW51+ volume knob setting (above) for 1% THD when driven by Bifrost-2 440 Hz 0 dBFS 2Vrms - SW51+ output 3Vpp (below):

    20191117-2 SW51+ 6Z51P max Vpp 1 pct THD 440Hz 300R HiZ Vpp.png

    FFT associated with SW51+ 440 Hz 1% THD at 3Vpp:
    20191117-3 SW51+ 6Z51P max Vpp 1 pct THD 440Hz 300R HiZ FFT.png



    20191117-4 bifrost-2 0dBFS SW51+ 6Z51P max Vpp 7_5 pct THD 440Hz 300R HiZ small.jpg

    SW51+ volume knob setting (above) for 7.5% THD when driven by Bifrost-2 440 Hz 0 dBFS 2Vrms - SW51+ output 18.4Vpp (below):

    20191117-5 SW51+ 6Z51P max Vpp 7_5 pct THD 440Hz 300R HiZ Vpp.png

    FFT associated with SW51+ 440 Hz 7.5% THD at 18.4Vpp:
    20191117-6 SW51+ 6Z51P max Vpp 7_5 pct THD 440Hz 300R HiZ FFT.png
     
    Lyander and Vtory like this.
  4. atomicbob

    atomicbob dScope Yoda

    Friend BWC MZR
    Joined:
    Sep 27, 2015
    Likes Received:
    10,188
    Dislikes Received:
    3
    Trophy Points:
    113
    Location:
    On planet
    Explanation of corrections from impressions thread.

    How mistakes happen: complicated manual system setup + multiple serious interruptions.

    In the impressions thread I had incorrectly stated the SW51+ gain was 1.72 as measured on the dScope. However the picoscope measured approximately 3.26 as distortion was rising. There should be a change but typically the gain drops as distortion rises. Here is how the error occurred.

    dScope setup for fully balanced measurements but output derived from unbalanced BNC
    Generator has been set for 2Vrms
    Note the analog output mode set to Balanced normal - this panel is not usually displayed - it is displayed here to make the point
    SW51+ L ch output measures 3.43Vrms
    20191117-21 SW51+ 6Z51P 2V in 3_43V out 440Hz 300R HiZ dScope Bal Norm output amplitude.png

    Gain incorrectly determined as 1.715, which is 4.7 dB
    20191117-23 SW51+ 6Z51P 2V in 6_86V out 440Hz 300R HiZ dScope Bal Norm output gain.png

    Changing analog output mode to unbalanced with the same generator level of 2Vrms
    Now SW51+ L ch amplitude measures 6.6556 Vrms
    20191117-22 SW51+ 6Z51P 2V in 3_43V out 440Hz 300R HiZ dScope unBal output amplitude.png

    Gain correctly determined as 3.32, 10.4 dB
    20191117-24 SW51+ 6Z51P 2V in 6_86V out 440Hz 300R HiZ dScope unBal output gain.png

    Here is the gain linearity sweep for -60 to +20 dBu
    The gain drops as expected, but only significantly so above approximately +10 dBu.
    20191117-25 SW51+ 6Z51P gain linearity 440Hz 300R HiZ dScope unBal output gain.png

    The dScope output mode either derives unbalanced BNC as half of balanced XLR output or corrects by 6 dB depending on the mode setting. I thought I could pull off a quick manual mode measurement. Bad assumption when the day is likely to be filled with interruptions.
     
    Lyander and Vtory like this.

Share This Page