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MX-1000 "workout"

rottalpha

rottalpha

Yamaholic
Subscriber
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:

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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:
 

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avionic said:
Are those arcols fastened to a heatsink ?
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they are Dales fastened to an 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.
 
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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.
 
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restorer-john said:
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.
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Thanks John!
that's where I 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.
 
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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:
 
rottalpha said:
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
Click to expand...

Nice tests!! Thanks for sharing. Are you testing both channels at the same time (300Wx2)? If so, the efficiency would be about 60%
 
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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.
 
Audio analyzer, scope and a set of dummy loads. I also used an el cheapo watt-meter
 
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