mcth 28V LPS and SMPS technical measurements

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

  1. rtaylor76

    rtaylor76 Can't wipe his tag

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    It's actually black and you can totally tell if it has been sprayed an by how much. I mean I would not grab it, but I feel safer brushing by.

    The best will always be an inline fuse for safety and from current overdraw to protect the transformer and from your house catching on fire.
     
  2. Sanjeev Jain

    Sanjeev Jain Acquaintance

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    @atomicbob ,

    I recently acquired a 3Amp model, A28MT300A to be used with MCTH and being a total electrical novice, could you please help me with the fuse to be used in the inline fuse holder.

    Seems like the Instructions Manual for A28MT300A suggests to use a time-delay UL Listed fuse (250V) in the AC input wiring. So based on the 3 Amp output, would something like (3 Amp Time Delay Glass Tube Fuse 250Vac, UL Listed ) linked below work?
    https://www.amazon.com/Bussmann-BP-MDL-3-250Vac-Listed/dp/B000VWE90O

    Please let me know.
     
    Last edited: May 6, 2018
  3. rtaylor76

    rtaylor76 Can't wipe his tag

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    I think all you need is a 2A fuse.

    For Acopian only, fuse size in amps = (Output Voltage * Output Current * 2.93) / 115 VAC.

    I don't know why this hasn't been shared already on this thread, but there it is.
     
  4. Sanjeev Jain

    Sanjeev Jain Acquaintance

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    Thanks rtaylor.
     
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  5. rtaylor76

    rtaylor76 Can't wipe his tag

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    So my Acopian A28MT300A has decided to start making a slight bit of noise. Not electronic noise, but physical noise.

    It is kind of like transmitter hum, but every now and again, it will get slightly louder and higher pitched. It is kind of random, but also pulsing about once every 4-6 seconds. I think the cage is kind of loose and just amplifiying the vibrations coming from the transformer. I know the cage for mine came slightly dented and I tried to use a small screwdriver to put in there to pop it back out, but it did not stay.

    Anyway, it is not as loud as my hard drive, but enough for me to notice. Also it sits about 4 foot away to my right and it is right at ear level. Just letting others know if they have the same or similar model. Results may vary.

    It kind of makes me want to add a power switch to the LPS. I don't leave my MCTH on all the time as I don't like leaving tube gear on all the time. SS gear I have no issues, but that LPS is constantly putting out 28V no matter what. I know it is only drawing the small amount of mA that the linear circuit needs, but still.
     
  6. Wuthoqquan

    Wuthoqquan Rando

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    Hi! Many thanks for your measurements and for pointing out the availability of this low-cost and more home friendly power supply.

    I got mine from AliExpress a few days ago. Before connecting it to the MCTH I just wanted to take the extra step of confirming the DC Output Voltage. I’ve used a testing equipment available at work and the reading was about 28.2 V, compared to the 27.987 V reading shown in your setup photo.

    It could be possibly due to a poorly calibrated testing equipment that I’ve used. Otherwise, should the reading be spot on, would such an offset from the required 28V still be ok and safe? Could it possibly create unexpected issues to the MCTH in the long run?

    I would have been much happier to read a voltage reading closer to 28V on the lab testing equipment used.

    Many thanks for your valuable opinion on this! I’m far from being an expert on the subject matter... cheers!
     
  7. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

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    Sounds like coil whine. Is the supply switched or regular linear?
     
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  8. dBel84

    dBel84 Friend

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    "would such an offset from the required 28V still be ok andsafe?"

    Yes, there are no risks to these voltage changes.. dB
     
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  9. atomicbob

    atomicbob dScope Yoda

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    Can you cause the noise to cease if by lightly touching either of the covers?
     
  10. rtaylor76

    rtaylor76 Can't wipe his tag

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    It was their linear supply. The Acopian A28MT300. I think it was from the transformer.

    I actually sold it to @zhouharvey and currently lost with USPS.

    I never tried, but I do feel the bottom cage did make it rattle more, but my bottom cage was loose. The hum though was pretty constant, but occasionally would spike. So without the cage issues, there was still a slight low level hum.
     
  11. zhouharvey

    zhouharvey PayPal’s $2 Sensible Enforcer

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    I really wish to hear the hums and spikes by myself!
     
  12. atomicbob

    atomicbob dScope Yoda

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    I've been asked a few times about LPS warmup voltage drift. Here are several measurements that may provide insight.
    Both LPS were set for 28.0V at initial power on.

    Accuracy: how close to target voltage
    Precision: how stable maintaining equilibrated voltage

    BK Precision BK1623A warmup from t=0 (power on) to 60 minutes (y-axis 20 mV / div):
    41 20190217 BK1623A 28V 56R load t=0 to 60min drift - 34465A.png
    It takes the BK1623A about an hour to settle. Thereafter it will wander as shown in the graph below.

    BK Precision BK1623A warmup from t=120 to 130 minutes (y-axis 500 uV / div):
    42 20190217 BK1623A 28V 56R load t=120 to 130min drift - 34465A.png

    Keysight U8001A warmup from t=0 (power on) to 60 minutes (y-axis 500 uV / div):
    43 20190217 U8001A 28V 56R load t=0 to 60min drift - 34465A.png
    Extra cost of the U8001A provides stability within 12 minutes and very little wander thereafter. Lab accuracy and precision. Not necessary for most users.
     
    Last edited: Feb 19, 2019
  13. gixxerwimp

    gixxerwimp Professional tricycle rider

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    I'm curious about the AliExpress LPS if you still have it, even though I leave mine turned on. If and when you have the time and feel like it, of course. Cheers!
     
  14. atomicbob

    atomicbob dScope Yoda

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    Two more 28V LPS warmup times, Zero Zone (aliexpress) and Acopian.

    Accuracy: how close to target voltage
    Precision: how stable maintaining equilibrated voltage

    Zero Zone 28V LPS warmup from t=0 (power on) to 60 minutes (y-axis 5 mV / div):
    44 20190217 ZeroZone 28V 56R load t=0 to 60min drift - 34465A.png
    Zero Zone reached equilibrium after approximately 40 minutes.

    Zero Zone 28V LPS warmup from t=42 to 52 minutes (y-axis 500 uV / div):
    45 20190217 ZeroZone 28V 56R load t=42 to 52min drift - 34465A.png
    While accuracy is a little off compared to U8001A, precision is notably good. Very little drift.

    Acopian A28MT210M 28V LPS warmup from t=0 (power on) to 60 minutes (y-axis 50 mV / div):
    46 20190217 A28MT210M 28V 56R load t=0 to 60min drift - 34465A.png

    Acopian A28MT210M 28V LPS warmup from t=90 to 150 minutes (y-axis 2 mV / div):
    48 20190217 A28MT210M 28V 56R load t=90 to 150min drift - 34465A.png
    After 3 hours the Acopian reach equilibrium. As it was more than 0.25 V high I adjusted the trim back to 28.0 V at 150 minutes.

    Acopian A28MT210M 28V LPS warmup from t=180 to 210 minutes (y-axis 500 uV / div):
    50 20190217 A28MT210M 28V 56R load t=180 to 210min drift - 34465A.png
    Better precision than the BK1623A but not quite as precise as Zero Zone. However accuracy now has been trimmed to match that of U8001A.

    Again, either will work well for intended purpose. This is a microscopic examination of LPS voltage drift.
     
  15. msommers

    msommers High on Epipens

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  16. atomicbob

    atomicbob dScope Yoda

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    The first link is the Zero Zone measured and data presented in the posts above.
    Second link LPS has a different transformer and regulator PCB. Without testing I would not assume equivalent performance to the Zero Zone.
     
  17. msommers

    msommers High on Epipens

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  18. atomicbob

    atomicbob dScope Yoda

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    I may have mentioned it somewhere as being yet another 28V LPS. But I wouldn't want to make any claims that it would produce equivalent data to those presented above for the Zero Zone without measuring.

    All of the above measured LPS produced 28V within some tolerance and after some period of warmup. Noise, drift, accuracy, precision, etc. varied between them. At a non-specific level they are roughly equivalent.
     
  19. msommers

    msommers High on Epipens

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    The ZeroZone R-Core, well all of their products, seem like quality units without the audiophile "tax" as stated here and elsewhere online. Appreciate your work as always, Bob :)
     

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