mcth 28V LPS and SMPS technical measurements

Discussion in 'Headphone Amplifier Measurements' started by atomicbob, Apr 8, 2018.

  1. atomicbob

    atomicbob dScope Yoda

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    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 this post.

    mcth 28V LPS and SMPS technical measurements

    mcth = Massdrop Cavalli Tube Hybrid headphone amplifier
    SMPS = Switch Mode Power Supply
    LPS = Linear Power Supply

    The data presented were acquired using the following equipment

    Power Supply only measurements

    1. picoscope 5243B, Keysight 34461A DMM
    2. 56 ohm 50W load used for power supply measurements
    3. Cable Matters 16 awg cable for 28V connections
    4. Shielded 14AWG and 16AWG power cables
    5. Vaunix Lab Brick USB hub for measurement equipment
    6. Audioquest Forest and Schiit Pyst USB cables used for measurement equipment

    MCTH measurements with LPS and SMPS additional equipment

    1. PrismSound dScope III
    2. Massdrop Cavalli Hybrid Tube headphone amp
    3. Electro Harmonix 6922 driver tube
    4. 30 ohm load used for headphone amp measurements
    5. Unbalanced cables Worlds Best Cable Gotham GAC-2 RCA with mcth
    7. Amplifier gain adjusted to 0 dB gain @ 0.775 Vrms 0 dBu
    8. MCTH gain knob at approximately 1:30 to achieve 0 dB gain

    Power Supplies tested

    1. SMPS 1 mcth XY36S-2801250Q-UW 28Vdc 1.25A 35W max
    2. SMPS 2 Meanwell GST25A28-P1J 28Vdc 0.89A 25W max
    3. LPS 1 Keysight (HP/Agilent) U8001A 0 to 30Vdc variable 3A lab supply
    4. LPS 2 BK Precision 1627A 0 to 30Vdc variable 3A lab supply
    5. LPS 3 Acopian A28MT210 28V 2.1A low noise linear power supply

    Yet to arrive - still in transit
    6. LPS 4 ebay Finished 65VA Ultra Low Noise Linear Power Supply

    Presented is a comparison of 5 power supplies, their noise and respective effect on specific mcth audio
    measurements.

    Notable highlights:
    mcth measurements improve with lower noise linear power supplies. Subjectively my auditory experiences concur, to my ears. Using an RME ADI-2 Pro, Soekris dac1421, Yggdrasil v2, etc. with any of the three LPS enables an extraordinary blackground from which music appears.

    Setup picture:

    20180325 multiple LPS - SMPS noise measurements - small.JPG

    Ripple measurements

    Ripple 28V 56R load 20mV/div 5mS/div 100KHz - mcth SMPS
    20180325 mcth SMPS 28V 56R load 20mV 5mS div 100KHz.png

    Ripple 28V 56R load 20mV/div 20uS/div 100KHz - mcth SMPS
    20180325 mcth SMPS 28V 56R load 20mV 20uS div 100KHz.png


    Ripple 28V 56R load 20mV/div 5mS/div 100KHz - Meanwell SMPS
    20180325 MW GST25A28-P1J 28V 56R load 20mV 5mS div 100KHz.png

    Ripple 28V 56R load 20mV/div 20uS/div 100KHz - Meanwell SMPS
    20180325 MW GST25A28-P1J 28V 56R load 20mV 20uS div 100KHz.png


    Ripple 28V 56R load 20mV/div 5mS/div 100KHz - Keysight U8001A
    20180325 Keysight U8001A 28V 56R load 20mV 5mS div 100KHz.png

    Ripple 28V 56R load 20mV/div 5mS/div 100KHz - BK Precision 1627A
    20180325 BK Precision 1627A 28V 56R load 20mV 5mS div 100KHz.png

    Ripple 28V 56R load 20mV/div 5mS /div 100KHz - Acopian A28MT210
    20180325 Acopian A28MT210 28V 56R load 20mV 5mS div 100KHz.png

    Ripple is considerably lower with all three LPS than either SMPS.
    Data is not presented on the Noise Nuke. While stable with a purely resistive load, neither SMPS was able to stabilize output voltage with the combined Noise Nuke and mcth reactive load. Therefore use of the Noise Nuke is NOT RECOMMENDED.
     
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  2. atomicbob

    atomicbob dScope Yoda

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    FFT measurements

    FFT 28V 56R load 16MHz - mcth SMPS
    20180325 mcth SMPS 28V 56R load FFT 16MHz.png

    FFT 28V 56R load 16MHz - Meanwell SMPS
    20180325 MW GST25A28-P1J 28V 56R load FFT 16MHz.png

    FFT 28V 56R load 16MHz - Keysight U8001A
    20180325 Keysight U8001A 28V 56R load FFT 16MHz.png

    FFT 28V 56R load 16MHz - BK Precision 1627A
    20180325 BK Precision 1627A 28V 56R load FFT 16MHz.png

    FFT 28V 56R load 16MHz - Acopian A28MT210
    20180325 Acopian A28MT210 28V 56R load FFT 16MHz.png

    Clearly SMPS present more high frequency residual noise to the mcth than the LPS.

    mcth SMPS vs LPS Residual Noise measurements

    The Residual Noise measurements below differ from THD+N. Not only is the fundamental removed but also 9 harmonics are removed in the FFT to allow examination of only non-harmonically related noise.

    Residual Noise 1KHz 0dBu sine - mcth SMPS
    20180407 mcth 1 KHz Residual N FFT 0dBu 30R 4XF - SMPS.png

    Residual Noise 1KHz 0dBu sine - BH Precision 1627A
    20180407 mcth 1 KHz Residual N FFT 0dBu 30R 4XF - LPS.png

    An LPS lowers the residual noise by 6 dB from that when using an SMPS. Is it an audible improvement. It depends. See discussion in post 3 below.


    Gain Linearity

    Gain Linearity - mcth SMPS
    20180407 mcth 1 KHz Gain Linearity 0dBu 30R 4XF - SMPS.png

    Gain Linearity - BH Precision 1627A
    20180407 mcth 1 KHz Gain Linearity 0dBu 30R 4XF - LPS.png


    A small but measurable improvement in Gain Linearity occurs with the LPS over an SMPS.
     
    Last edited: Apr 8, 2018
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  3. atomicbob

    atomicbob dScope Yoda

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    Residual Noise measurements were made with absolute dBu reference. When there is no signal, the residual noise will remain relatively constant. This is the noise present during dramatic pauses, pianissimo passages in music. Is it audible? It depends on several conditions. Three immediately come to mind. Sensitivity of the headphone, environmental ambient noise, frequencies of the residual noise.

    Here is a chart depicting the absolute SPL output by a given headphone for an absolute dBu level. This ignores headphone frequency response and unit variance.

    Headphone SPL at -84dBu.
    Headphone Sensitivity -84 dBu to SPL.png

    A listener with Etymotic ER4P in a quiet environment is likely to hear 35 dB SPL of residual noise. Certainly a 6 dB improvement to 29 dB SPL will be welcome. In a typical residential environment a listener with an HD650 will not hear 17 dB SPL residual noise as it is likely to be masked by the ambient noise level.

    Two more charts for consideration in factoring dependencies.


    Iso-Contours of equal loudness
    iso226-2003 Equal Loudness Contours v2.png

    Noise Criteria
    201701001-1040 SSL residual noise 16 dBA 7046-28439.png
    My acoustic lab space is depicted by the green line. Typically below NC-15.
    NC25 to NC45 are more typical for residential spaces.

    Notes on using LPS with mcth.

    mcth creates a split +14 / -14 Vdc supply internally referenced to signal ground at the RCA inputs and headphone outputs.
    mcth floating split supply -14V - small.jpg


    Any external power supply MUST FLOAT with respect to ground. Often a lab supply will be equipped with a shorting bar to connect Power Supply Negative to Ground. REMOVE THIS SHORTING BAR. See pictures below.

    BK 1627A with Gnd to Neg shorting bar - small.jpg
    Shorting bar shown. REMOVE THIS SHORTING BAR.

    BK 1627A without Gnd to Neg shorting bar - small.jpg
    Leave LPS output floating as shown above.

    Disclaimer: all responsibility and risk are assumed by the experimentor.
    Neither myself, @CEE TEE nor Cavalli will be responsible if you blow up your amp experimenting with power supplies. Do not ask for warranty service if you screw up. If the technical details aren't familiar territory, leave well enough alone. MCTH with supplied SMPS provides a great sound experience.

    dac1421 - mcth + 1627A LPS - Focal Clear - small.jpg
     
    Last edited by a moderator: Apr 9, 2018
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  4. Br444m

    Br444m Acquaintance

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    Thanks a lot for doing the comparison - and including the Chinese LPS too. Are you planning to post subjective impressions here as well?

    As a side note: maybe change the title: mcth -> MCTH (sorry, that's my COD).
     
  5. atomicbob

    atomicbob dScope Yoda

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    I'd like to maintain this thread as oriented to measurements. For subjective impressions another thread has mentions of LPS with mcth: Massdrop Cavalli Tube Hybrid Amp.
     
  6. Taverius

    Taverius Smells like sausages

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    How much current overprovisioning is necessary? (If any)

    The Acopian A28NT125 is 35 bucks cheaper, way smaller than your lab unit, and has the same amp rating as the MCTH SMPS, so if I was insane enough to do this I'd be thinking about that one ...
     
  7. Br444m

    Br444m Acquaintance

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    Wouldn’t do that - click on link in previous post (MCTH didn’t power up with it)
     
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  8. atomicbob

    atomicbob dScope Yoda

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    Acopian A28MT210 wiring and orientation pictures

    Acopian A28MT210M no terminal cover - small.jpg
    Highly recommend an inline fuse holder between line (power cable black wire) and line input on Acopian (position on terminal block with red wire from fuse holder.) Very important. Output MUST FLOAT with respect to ground (green wire.) DO NOT CONNECT 28V negative to Ground (green wire.)


    mcth + A28MT210M + ADI2 Pro + Clear - small.JPG
    The orientation here has heat sink on top, plate to which transformer is mounted on the bottom. The LPS is on a mouse pad. This will minimize mechanical noise of the ventilated gold side plates due to magnetic field vibrations from the transformer. Otherwise the gain of lower electrical noise may be offset from ambient noise produced by the LPS.

    My Keysight U8001A came equipped with a rather noisy fan which was replaced with a Noctua low noise fan of appropriate voltage and CFM air movement. Still makes a slight noise that can be heard in my acoustic lab, though probably not noticeable in most listening environments.

    One more LPS picture

    Eitr+Modi_MB+MCTH+LPS+Clear_small.jpg
    Also a very nice sounding system.
     
    Last edited: Apr 9, 2018
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  9. Elnrik

    Elnrik Super Friendly

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    Why do I get the feeling that having open contacts like this would be disastrous in my house?
     
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  10. rtaylor76

    rtaylor76 Can't wipe his tag

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    What value AWG fuse do you recommend?

    I guess you could also use a GFI outlet of your worried about crossing the streams or someone grabbing a live wire. Although some audiophools might not like a GFI on amps.
     
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  11. rtaylor76

    rtaylor76 Can't wipe his tag

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    Industrial power supplies are certainly not residential code.

    I'm going to have to,be creative to keep this away from the kiddos.
     
  12. atomicbob

    atomicbob dScope Yoda

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    Acopian is at least mostly enclosed. Open frame OEM linear power supplies have even more points of potential shock hazard. It would be wise to build a real enclosure for any of these OEM supplies. These are not kid / pet etc. friendly, nor do they meet any residential code when not enclosed. For those situations it would be better to consider one of the lab supplies or have someone build an enclosure.

    I've thought about having someone with great woodworking skills build me an enclosure. Would have a plate for power inlet with fuse and low voltage connector on back, switch, output volt and amp meter on front. Maybe with a steampunk theme.
     
  13. dBel84

    dBel84 Friend

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    Would it be possibly to see how the noise measurements change as you stress the power supplies. ie greater current demand (within safe limits)

    This is great data, thanks for all the effort

    . dB
     
  14. atomicbob

    atomicbob dScope Yoda

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    I would need to acquire several more power resistors. The one I used put a 0.5 amp demand on the supplies. Run time power consumed by the MCTH after initial power on is approximately 0.38 to 0.40 amp.
     
  15. dBel84

    dBel84 Friend

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    I was more curious about the supplies in general with higher current demands.
     
  16. atomicbob

    atomicbob dScope Yoda

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    Maybe I'm not understanding. Let me try this. Suppose we wish to know the FFT and ripple at the following power supply demands at 28Vdc:

    0.5 A
    1.0 A
    1.5 A
    2.0 A

    Then I need the following resistors to provide a steady state load for stable measurements without added noise of an electronic load tester:

    0.5 A - 56 ohm 50W resistor for load
    1.0 A - 28 ohm 50W resistor for load
    1.5 A - 18.7 ohm 75W resistor for load
    2.0 A - 14 ohm 100W resistor for load

    I like to have a good margin on the power ratings. They will get VERY HOT during testing. Each test suite shown above took between 30 and 60 minutes to complete, including setup, data vetting and documentation per power supply. As you can see I need to invest in at least three more large power resistors and a day of time in the lab to obtain the requested information.

    Just a general comment for the large readership of guests that visit this forum:

    An interesting thing about these measurement threads. It can take days to accomplish, sometimes hours to organize and post, yet only minutes to consume by the reader.
     
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  17. Elnrik

    Elnrik Super Friendly

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    Hmmm... I couldn't build the plate, but I could build the box.
     
  18. dBel84

    dBel84 Friend

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    That does sound like a lot of work. My expectation is that we will see increasing noise as the power supplies work harder. This is probably not going to be relevant if the appropriate power supply is chosen for the amp being used.
     
  19. Taverius

    Taverius Smells like sausages

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    They have a snap-on terminal cover for 5 bucks so there that at least.
     
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  20. atomicbob

    atomicbob dScope Yoda

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    I found a second 56 ohm 50 W resistor in the lab. This would allow the 1.0 amp measurement. But I am not expecting any difference over those presented above.

    The LPS supplies have the following for ripple and noise specifications from their respective datasheets:

    U8001: 1 mVrms 20Hz to 20MHz
    1627A: <1 mVrms
    A28MT210: < 0.25 mVrms

    These are specified over the range of operation which includes maximum current draw which is 3A, 3A and 2.1 A respectively.

    Indeed, look at the setup picture in post one and the snap-on terminal cover may be seen along with the inline fuse holder.
     

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