The diyAudio First Watt M2x

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donhughes111

Member
Joined 2019
Paid Member
pfarrell said:
I want to try this.


I have to put my ear right in the cones to hear anything with M2X monoblocks. BUT there IS as little something. More of a little buzz, than a hum. 92db speaks. Vfet was absolutely SILENT in the same system. I'm not totally convinced that the M2X mini-buzz isn't environmental. It likely is.
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P, by environmental you mean RFI?

Thanks,
Don
 
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airborne11b

Member
Joined 2019
Mark Johnson said:
Grounding the transformer cover helps with electrostatic coupling but not electromagnetic coupling. The external fields surrounding power transformers are electromagnetic, so grounding the transformer surround has little benefit.
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I thought this was only the case with radio frequencies and higher. I am no expert though. I have always grounded my shields.
 
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darrr

Member
Joined 2018
Thank you very much for all your help:)
I pulled out the transformer as far as I could. 50hz is lower but 100hz has increased. I will move it even further tomorrow. Today I am giving myself the time off.
IMG_20210419_210313.jpg IMG_20210419_210734.jpg
 
MEPER

MEPER

Member
Joined 2017
The input board is not Ishikawa when you that much 1000 Hz noise?

If you have a sheet of mu-metal you can try to put it in front of toroid so you screen it. Steel may also work. Also the orientation of the toroid can make a difference. But the 50 Hz noise looks low now with transformer away from Edcor.
 
MEPER

MEPER

Member
Joined 2017
But looking at your Arta measurement you have a generel raise of noise towards the low frequencies. I did not see that on my measurements. It would look nicer if the noise floor was equal all the way from 20 to 20 kHz.....at about -130 dB or so....but it will depend of power level.
 
hayenc

hayenc

Member
Joined 2005
Paid Member
In the process of integrating the parts of the M2x. Power supply has checked out fine on its own. I have connected one channel and turned on with the light bulb in the power line. Bulb turns on briefly, then turns off. Output offset reads very low. After about 10 seconds of being low, it starts to increase slowly. After about 25 seconds the light bulb begins to glow and then when the offset is near a half volt, the light bulb is on. No smoke, nothing getting hot.

I want to get some input before proceeding further. Is still having the light bulb tester in the circuit affecting what it going on, or is there an indication of a problem. I don't want to take the light bulb tester out of the AC line without getting some input on what may be going on. Any suggestions?
 
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dantwomey

Member
Joined 2002
Paid Member
hayenc said:
In the process of integrating the parts of the M2x. Power supply has checked out fine on its own. I have connected one channel and turned on with the light bulb in the power line. Bulb turns on briefly, then turns off. Output offset reads very low. After about 10 seconds of being low, it starts to increase slowly. After about 25 seconds the light bulb begins to glow and then when the offset is near a half volt, the light bulb is on. No smoke, nothing getting hot.

I want to get some input before proceeding further. Is still having the light bulb tester in the circuit affecting what it going on, or is there an indication of a problem. I don't want to take the light bulb tester out of the AC line without getting some input on what may be going on. Any suggestions?
Click to expand...

In my very brief experience with the M2X. Both my channels started up at 500mv and went down to slightly below 80mv after I adjusted the offset using RV1. I'm now waiting on parts for (RV1 and R6) as seen in post #3.

I didn't use a bulb. I rolled the dice at put full power on right away. Risky? Maybe. Other than not getting perfect offset mine warmed up and there was no smoke.

Maybe others will chime in?

Regards,
Dan :)
 
hayenc

hayenc

Member
Joined 2005
Paid Member
I figured out that the charging of the 3300uf caps was the problem. Mixed feedback loops. Pulled the bulb tester and everything is working as expected. And so, I did the blasphemous heresy mod and am cooking one channel at under 10mv offset.

Hopefully music tomorrow.
 
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grataku

Member
Joined 2000
darrr said:
My measuring interface is a notebook soundcard, so not the best. The maximum I can give to input is 0.5Vrms. I didn't even connect the dummy load here. I just wanted to observe the noise.
Input board is still Mountain View.
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Darr,
if I see correctly in the picture (post 5026), you have the speaker gnd blue wires going to the amp board, when I did that my amp exhibited a slight hum as well which I attributed to some type of gnd loop. That goes away completely when I connect the speaker gnd to the star gnd on the PS. I saw this point discussed somewhere around here before. Worth a try to rewire.
 
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cubicincher

Member
Joined 2016
to hayenc #5048

Hello hayenc,


the dimbulbtester - phenomena is well known with the M2X:

If you switch the M2X on the dimbulbtester dims down/ or goes off (then everything is o.k. with your M2X) and after a few seconds the bulb comes back shining. It is the same on my M2X. Also other members reported about this behaviour.


Greets
Dirk ;)
 
thompsontechs

thompsontechs

Member
Joined 2019
hayenc, that behavior you had was normal for the M2.

here's how it goes, light comes in bright as the large caps charge, they reach charge and then dim down, it takes a bit to bias up the circuit.... it comes in slowly and the light will again get brighter. It depends on the wattage of the bulb, just how bright it will get.
 
hayenc

hayenc

Member
Joined 2005
Paid Member
thompsontechs said:
hayenc, that behavior you had was normal for the M2.

here's how it goes, light comes in bright as the large caps charge, they reach charge and then dim down, it takes a bit to bias up the circuit.... it comes in slowly and the light will again get brighter. It depends on the wattage of the bulb, just how bright it will get.
Click to expand...

Thanks much. Did not make it through all of the M2 posts and had limited my search to the M2x thread. After making the blasphemous heresy mods, the amp is settling in with offset.

Hoping for music this afternoon.
 
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grataku

Member
Joined 2000
Are you measurements done with only one channel powered or with both?
I am not sure if I like shorting edcor transformer output and what that tells if anything.
What noise do you pickup with only one channel powered and its input shortened?

I am not familiar with your ps board...is it a dual mono setup PS board? I see you are coming out from two separate opposite points to go to each channel.
 
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