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Old 15th September 2020, 10:14 PM   #3531
MEPER is offline MEPER  Denmark
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I like to measure everything. I also feel confident when both M2X channels measures equal has has exact same distortion profile.
If you have speakers with sensitivity about 92 - 98 dB and has no audible hum it is quite good I think without shielded Edcor. The trick is to avoid the magnetic field from power transformer to be picked up by Edcor. During measurement I tried to put my finger on the shield on Edcor and 50 Hz raised to astronomic levels. Same applies to the coupling capacitor.
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Old 15th September 2020, 10:46 PM   #3532
thompsontechs is offline thompsontechs  United States
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Nothing wrong with measuring everything as long as you don't tie what looks good to what sounds good. Speakers are Tekton DI, so yes, very sensitive.



I love your meticulousness MEPER, just don't get trapped to into thinking what looks good on a scope translates into what sounds good. Offset of course and yes, both sides should have similar distortion, but it's never going to be perfect and in fact, my 2 ears are quite different and I have found that the optimal for one is not the best for the other. This comes in to play more with phones, but to some degree with speakers as well.



Sometimes I think we would be better of if we just left the analyzers on the bench and let our ears tell us the story... no, that's wrong. I 100% think that;s what we should do. I can hear the hum... yup, fix that. I don't need a meter to read 0.0v. If I can't hear it then what does it matter? Case in point, lots of people do a test, myself included, stick you head in the speaker, can you hear a hum? Who cares? Do you listen with your head stuffed in the speaker? NO, then what's the point other than you can say my **** is dead flat on dc offset.... There's not one thing wrong with wanting it 0.0v, but if I can't hear it at my chair, then it doesn't concern me. Many times to makes things, "exact" you may lose some of the magic.



Just sayn


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Last edited by thompsontechs; 15th September 2020 at 11:04 PM.
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Old 15th September 2020, 11:04 PM   #3533
MEPER is offline MEPER  Denmark
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I put my head into the speakers and if I can hear any hum I want to fix it :-)
I know if I measure something "bad" I need to fix it.....or I will think about it every time I listen. If I know everything measures perfect I listen more relaxed and I concentrate on the music. There is much psychology in music listening. Another aspect of measurements is learning.
About DC offset.....it is very temperature dependent and also depends in some degree on line voltage......so here I am satisfied to be within 50 mV. If you try to get inside 5 mV and get there.....then if you check one week later you may find now it says 20-30 mV.....
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Old 15th September 2020, 11:14 PM   #3534
thompsontechs is offline thompsontechs  United States
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That sounds about perfect...
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Old 16th September 2020, 12:11 AM   #3535
grataku is offline grataku  United States
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@MEPER,
I don't think a multimeter doesn't have the sensitivity to detect a few mV of ripple, maybe an analog scope?
Anyways, I can't really hear any sizable hum with the ear at the woofer or the tweeter.
What I experienced with the transformer case was a completely different high frequency response and sound like going from a regular driver to a compression loaded driver. Quite amazing difference and totally unexpected suggesting that the mains transformer was somehow coupling to the EDCOR and distorting/attenuating it's mid/hi response...but I am talking nonsense..

Having said that, there are changes I want to make to the PS since I am not entirely happy with it.
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Old 16th September 2020, 12:13 AM   #3536
grataku is offline grataku  United States
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Quote:
Originally Posted by MEPER View Post
I put my head into the speakers and if I can hear any hum I want to fix it :-)
I know if I measure something "bad" I need to fix it.....or I will think about it every time I listen. If I know everything measures perfect I listen more relaxed and I concentrate on the music. There is much psychology in music listening. Another aspect of measurements is learning.
About DC offset.....it is very temperature dependent and also depends in some degree on line voltage......so here I am satisfied to be within 50 mV. If you try to get inside 5 mV and get there.....then if you check one week later you may find now it says 20-30 mV.....
Copy that!
Sometimes I break it just to be able to go in and fix it...LOL
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Old 16th September 2020, 08:07 AM   #3537
MEPER is offline MEPER  Denmark
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Quote:
Originally Posted by grataku View Post
@MEPER,
I don't think a multimeter doesn't have the sensitivity to detect a few mV of ripple, maybe an analog scope?
Anyways, I can't really hear any sizable hum with the ear at the woofer or the tweeter.
What I experienced with the transformer case was a completely different high frequency response and sound like going from a regular driver to a compression loaded driver. Quite amazing difference and totally unexpected suggesting that the mains transformer was somehow coupling to the EDCOR and distorting/attenuating it's mid/hi response...but I am talking nonsense..

Having said that, there are changes I want to make to the PS since I am not entirely happy with it.
My DMM has a 0.1 mV resolution in AC mode. So if it shows 0.0 mV I assume that I have less than 50uV of noise. Also my DMM is a true RMS DMM. In your case a distortion measurement will be best like the image attached of one channel of my M2X. Oscilloscopes exists that has 100 uV pr. div. sensitivity but most normal is 1-2 mV / div. if you use a x1 probe. And you should be able to see "something". It is never easy to measure these weak signals and be sure you measure the amp and not something from environment. For my distortion measurement I made an interface box that goes from banana plugs to a 6.8R power resistor and from there to RCA with a divider network so signal fits to the Focusrite sound card input level. Then I can measure amp when it delivers like say 1-4 Watts.
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File Type: jpg m2x_L_channel_test_3.jpg (396.2 KB, 172 views)
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Old 16th September 2020, 08:48 AM   #3538
MEPER is offline MEPER  Denmark
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To show how tricky noise measurements can be I have attached both L and R channel measurements. I have mono blocks and I have tried to make an exact mirror of the mono blocks. But not all components is "mirrored" like IEC and PSU print and also M2X PCB is not an exact mirror of the other. Input board is not mirrored also and Edcor's. So it can't be a 100% mirror. Also the toroid transformers may not have exact same hum field distribution.
So one channel shows more 50 Hz noise and a bit less 100 Hz noise than the other. But levels are still quite low and I am happy with that distortion profile looks about equal on both channels. Also total THD and N is quite equal. So all in all I am happy with my build. The amps outputs 4.7V RMS into 6.8R in these measurements.

What I think I noticed was that with small signal levels the amp is slightly 3rd harmonic and shift to slightly 2nd harmonic when amp delivers more power. But I did not spend time on low level measurements which I should probably do also. Also a check how amp performs at high frequency could be interesting.
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File Type: jpg m2x_R_channel_test_3.jpg (396.6 KB, 166 views)
File Type: jpg m2x_L_channel_test_3.jpg (396.2 KB, 164 views)
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Old 16th September 2020, 01:06 PM   #3539
grataku is offline grataku  United States
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@MEPER
what can I say? Congrats on your choice of instruments! My DMM is 15 bucks good for nothing POS.
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Old 16th September 2020, 02:27 PM   #3540
MEPER is offline MEPER  Denmark
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I also have a couple of those which are good if you need more DMMs for e.g. combined bias/offset adjust. I got my in Lidl. 0.1 mV resolution is quite normal if you pay around 100 - 150 USD :-)
I have considered a bench model which goes lower......but they are more expensive.
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