MX-1000 "workout"

Discussion in 'Yamaha' started by rottalpha, Nov 26, 2017.

  1. rottalpha

    rottalpha Yamaholic Subscriber

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    I wanted to put a rebuilt MX-1000 through some testing, so last night I had the chance. I figured I shared the findings with the rest of the gang.

    This is no scientific test by any means and it was done on my makeshift test bench, but should give a good idea of the real life abilities of the MX.

    Ya' all know that I am already a big fan of the MX-1000 sound, so bench testing it is just for giggles.:D

    The patient: Fully restored Yamaha MX-1000

    Note: Very important to mention that ALL semis were replaced/upgraded and ALL small resistors were upgraded to metal film.


    Bench test results:

    · Idle current: ~.5A

    · Idle power consumption: ~50W

    · Full power* consumption: ~1020W

    · Clipping @ ~50v @8R or ~312W@ 8R*

    · THD @ full power, @1kHZ: 0.0004%(R), 0.0003%(L)

    Note: THD remains relatively unchanged until ~10kHZ, then it starts creeping up to ~0.004 @20kHZ



    I kept the unit @full power for over 20mins and no fire works. Dialed down to about 30v (output) and let it burn-in for another 3+ hours.


    Here are some snapshots:

    IMG_20171126_033908432.jpg
    IMG_20171126_024034851.jpg


    IMG_20171126_024029424.jpg

    IMG_20171126_033847921.jpg

    I am happy I finally got to use the dummy loads from Bhlaghsorm. I need to get them a better heatsink. It is safe to say that after about 1hr of testing I could have cooked something on those things. Last time I tried testing an MX, I realized I needed some serious dummy loads and abandoned the test. That MX was clipping at well over 50v, but the test lasted for only a few minutes before the crappy dummy loads I was using, started smoking. These bad boys get hot, but it takes them a bit to get there. Resistance staid @8R on the dot and has not drifted a bit, not even a few hours of use.

    Cheers:beerchug:
     

    Attached Files:

    Last edited: Nov 28, 2017
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  2. avionic

    avionic " Black Knights " Subscriber

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    Are those arcols fastened to a heatsink ?
     
  3. rottalpha

    rottalpha Yamaholic Subscriber

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    they are Dales fastened on old car audio amplifier heatsinks, based on what I can make of it. I badly need a proper heatsink. I am using them as I got them, but that needs to change at some point.
     
  4. rottalpha

    rottalpha Yamaholic Subscriber

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  5. Mark B

    Mark B Yamaha Fan Subscriber

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    Good stuff, thanks for sharing!
     
  6. rottalpha

    rottalpha Yamaholic Subscriber

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    One observation is that in order to deliver ~300w of power, it consumes ~1000w of energy. This tells me that it operates at near class A efficiency. ~1200W would have been typical consumption for traditional class A. I guess the sliding bias still offers some efficiencies even at full power. @30% efficiency, The MX operates as a very efficient class A or an inefficient class AB. Maybe an EE could clarify.

    Another aspect I noticed is that THD remains relatively unchanged in refference to power delivery. THD only varies with frequency...barely... as in below human ear discernible levels.

    EDIT: Math above is incorrect. I missed a "minor" variable in my calculations nd that is the amp has two channels drawing current at the same time, albeit I alternated turning the attenuator down, for each channel. So power consumption at full power needs to be retested/verrified.
     
    Last edited: Nov 27, 2017
  7. restorer-john

    restorer-john Addicted Member

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    Check your THD a low power- under 1 watt and sliding up gradually to about 10 watts. That's where any problems will manifest themselves, not at full power.
     
  8. rottalpha

    rottalpha Yamaholic Subscriber

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    Thanks John!
    that's where started...and I found none. I should have stated that the amp is at its 110% :) since it already went through a serious rehab.
    The MX amp had to vacate the bench to make room for a B-1 job, but next time I have one on the bench, I will spend more time testing at low power.
     
    Last edited: Apr 16, 2018 at 1:50 AM
  9. rottalpha

    rottalpha Yamaholic Subscriber

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    I should have added...I am listening to it now at 1-2W of power and to my "perfectly damaged" hearing, it sounds very good:beerchug:
     
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  10. amr2

    amr2 Active Member

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    Nice tests!! Thanks for sharing. Are you testing both channels at the same time (300Wx2)? If so, the efficiency would be about 60%
     
    Last edited: Nov 27, 2017
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  11. rottalpha

    rottalpha Yamaholic Subscriber

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    Thanks!
    I alternated the pots individually in order not to risk messing with the wires too much, but I guess next time I will be more analytical.
     
  12. Beobloke

    Beobloke Super Member

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    Where's the most important picture - namely the power meters showing full output?!! :D
     
  13. rottalpha

    rottalpha Yamaholic Subscriber

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    Lol,
    Meters will be mounted back on at some point
     
  14. Bert 1100

    Bert 1100 Super Member

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    Doesn't it deliver 300 watts per channel ? then it delivers 600 watts using 1000 watts. Your efficiency just doubled :biggrin: ..
     
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  15. rottalpha

    rottalpha Yamaholic Subscriber

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    LOL, that is what I get for testing and doing math at night. Thanks for keeping me honest guys!
     
  16. rottalpha

    rottalpha Yamaholic Subscriber

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    good callout! I edited the post above.
     
  17. Mr. Yamaha

    Mr. Yamaha Not so much Yamaha lately... Subscriber

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    Great workout, thanks for sharing :bigok:
     

     

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  18. 39cross

    39cross AK Subscriber Subscriber

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    Very impressive! What are you using for testing on your bench?
     
  19. rottalpha

    rottalpha Yamaholic Subscriber

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    Audio analyzer, scope and a set of dummy loads. I also used an el cheapo watt-meter
     
    Last edited: Mar 28, 2018
  20. rottalpha

    rottalpha Yamaholic Subscriber

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    sharing some more photos from this old rebuilt

    IMG_20170908_214459207.jpg
    IMG_20171030_113831418.jpg IMG_20171201_192816762.jpg 20171203_171036880_iOS.jpg 20171203_165548668_iOS.jpg
     
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