The diyAudio First Watt M2x

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Russellc

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Joined 2003
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batty said:
Is there a "run in" period? because if there is this amp is going to be monster, it is awesome at only 5 or 6 hours run time.
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When I first used mine, it sounded a little murky and bass a bit squooshy. That quickly subsided and it got better and better. While it may be psycho-acoustic, like others here I have noted that this amp sounds better after prolonged "warmup"....may be imaginary, but I dont think so?:confused:

That said, I imagine the repairman of your amp listened to it some....

Russellc
 
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Russellc

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Joined 2003
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gary s said:
Hi batty, then on top of that you have the 5 or six different daughter boards to try with the M2X - all are different, but you probably need to listen to each one for a month or so, before swapping to the next. All part of the fun.

Then there are a lot of good preamps to mate with it as well around here. BA3, Korg Nu Tube, Wayne's BA2018 linestage to name a few. Then their sound is influenced by how good a regulated PSU you can choose.

So many combinations to arrive at your ultimate sound choice.
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Agreed. I didnt care for B1 so much with it, not fault of B1, I just wanted more beans/gain even with high efficiency speakers. BA3 and Wayne's 2018 LS are great paired with it. Really liking this linestage of Wayne's.

Russellc
 
dBel84

dBel84

Member
Joined 2006
I love the sound of the M2X too. SissySIT has taken backstage despite being the more revered. Might have to do with the suitability with the Maggies, sissy sounds great but M2X has better bass and overall better synergy. Am planning to switch out the Maggies for the Moth Cicadas sometime soon to see how that pairing works.

.. dB
 
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Russellc

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Joined 2003
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dBel84 said:
I love the sound of the M2X too. SissySIT has taken backstage despite being the more revered. Might have to do with the suitability with the Maggies, sissy sounds great but M2X has better bass and overall better synergy. Am planning to switch out the Maggies for the Moth Cicadas sometime soon to see how that pairing works.

.. dB
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Agreed again! Neither of these amps are as Maggie killers. Maybe you should do BBA3 mono blocks? I keep coming back to my "regular" 30 volt rail BA3 amp. That will drive the Maggie speaks...

Maybe Zenmod's M25? Keeping closer to the M2, and much more drive into less efficient loads?

Russellc
 
JSA1971

JSA1971

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Joined 2016
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cubicincher said:
I fully agree with gary s,


I am listening a lot to my M2X and the NUTUBE - Preamp at the moment.
In the M2X switching between the inputboards, at the Nutube playing with
the adjustment of positive/negative 2nd harmonic, changing preamps,....


I don't have that much time at the moment!


But it's all about beautiful music coming out of this soundmachines.
I don't care that much about measurements.


Greets
Dirk
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Hi Dirk,
I am considering building the B1 with the NuTube preamp as well. As per the M2x thread build notes #5

"Capacitor “C0” is not present in the original M2 amplifier by Nelson Pass. The M2 owner’s manual explains that this makes it easier for tube preamps to drive an M2. However C0 does perform a useful function: together with input resistor R1, it filters (removes) unwanted radio frequency interference. The transformer’s HF rolloff helps too. I suggest that if you’re absolutely certain you’ll never drive M2X with a tube preamp, never ever ever, consider soldering C0 into the amplifier board. C0 is a NP0/C0G ceramic capacitor, 50 volts, 220 pF. Of course you can cut it out later if you change your mind."


Did you install C0 in your build? I didn't when I built my M2x and am wondering if its absolutely necessary, and what others have done when they've used a tube preamp with the M2x. I'm considering installing C0 and wiring up a shorting switch to remove it from the circuit when not needed.
 
JSA1971

JSA1971

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Joined 2016
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Mark Johnson said:
Make sure you don't accidentally short together the pins of C0. That would prevent any signal from reaching the amplifier! It's okay to replace C0 by an open circuit (perhaps by cutting it off the board entirely, using diagonal cutting pliers) but don't replace it by a short circuit.
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Thank you so much for pointing that out Mark. In my mind I was “seeing” what you’ve said, but would have implemented it wrongly. What I meant was to solder the cap in-line with the switch creating an electrical loop to tie it in or out of the circuit.
 
C

cubicincher

Member
Joined 2016
to JSA1971

Hello JSA1971,


I didn't use C0 in my M2X. I have a tubepreamp but thought to never use it with the M2X.
The NUTUBE and the M2X made no problems together (till now). But I try to be
careful. I try to avoid switching during operation.
Adjusting the Nutube (the two 10kohm pots) is no problem.


Greets
Dirk
 
JSA1971

JSA1971

Member
Joined 2016
Paid Member
. Capacitor “C0” is not present in the original M2 amplifier by Nelson Pass. The M2 owner’s manual explains that this makes it easier for tube preamps to drive an M2. However C0 does perform a useful function: together with input resistor R1, it filters (removes) unwanted radio frequency interference. The transformer’s HF rolloff helps too. I suggest that if you’re absolutely certain you’ll never drive M2X with a tube preamp, never ever ever, consider soldering C0 into the amplifier board. C0 is a NP0/C0G ceramic capacitor, 50 volts, 220 pF. Of course you can cut it out later if you change your mind.

Can someone please explain the consequences of installing or not installing C0 with regard to using a tube amp with the M2x? I don’t believe it has been explained.

Thanks!
 
M

meanie

Member
Joined 2018
CRCRC.jpg

hum.jpg


Freshly built, but still trying to rid off the elusive humming on both channels.
I decide to move the left channel away from the PS unit, true enough the hum reduced, then i experiment by placing a iron chassis in between, and trial by turning the heatsink at an angle to the PS unit. And the hum went completely away, dead silent on left channel. So i can conclude there was no ground looping in my case, except radiation from the tranny.

I may consider caging both channels like a Faraday cage when i house it into a proper chassis then, or follow the MuMetal tape method.

Just sharing...
 
chede

chede

Member
Joined 2016
Paid Member
I have one channel below 100 uV, the other 100-200 uV on my M2 (not X), built on JPS64's boards. Measured with two of my DMMs set to mV AC.

Needed a copper belly band (https://www.diyaudio.com/forums/pass-labs/321925-diyaudio-watt-m2x-69.html#post5562870), a sheet metal case for the Edcor (Teko 3710, https://www.diyaudio.com/forums/pass-labs/321925-diyaudio-watt-m2x-68.html#post5560562), and some magnetic steel partition between transformer and PSU / amp boards. I also have a CLC PSU with a Hammond 159ZL choke (2.5 mH, 10A, 44 mOhm).
https://www.diyaudio.com/forums/pass-labs/321925-diyaudio-watt-m2x-68.html#post5561134

So ... yes, it is possible :D

Best regards, Claas
 
chede

chede

Member
Joined 2016
Paid Member
One addition:

My SissySIT, which uses Cinemag CMOQ-4HPCs, is totally silent over my 100dB/W sensitive widebander speakers.
In that build, I also have used chokes in a CLC PSU, but the smaller Hammond 156B.
There is only a belly band on the Cinemags; no steel or mu-metal cover. On the other hand, according to Zen Mod and others, high-nickel transfomers are less sensitive to hum pickup than those with ordinary steel laminations.

https://www.diyaudio.com/forums/pas...ysit-building-tips-tricks-73.html#post5739449


Best regards,
Claas
 
Mark Johnson

Mark Johnson

Member
Joined 2011
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CLC, CRC, Capacitance Multiplier are delightful ideas which reduce supply voltage ripple nicely. But they do not reduce hum in an M2 or M2x. Hum in these amplifiers arises from electromagnetic coupling between the AC mains power transformer on the chassis floor, and the two Edcor transformers on the two amplifier PCBs. Hum reduction in these amplifiers comes from screening the mains transformer, shielding the mains transformer, boxing the mains transformer, moving (e.g. rotating) the mains transformer, screening the Edcor transformers, and boxing the Edcor transformers. Not from ripple reduction.
 
chede

chede

Member
Joined 2016
Paid Member
Thanks Mark, and I'm with you on that :). Might not have been very clear as to my intentions.

That the mains transfomer is the primary agent in induced hum has been exactly my experience in experimenting with rotating or shielding the mains transformer, or shielding the signal transfomers on the amp boards.

I did mention the chokes not because I think they have been reasons for less hum, but because I had been suspecting that they might add to the hum because of their own radiated magnetic fields ... but in fact, as written in the referenced post, I could detect little difference when holding a magnetic steel sheet between choke and Edcor in my M2 ;)

Best regards,
Claas
 
G

garyalex

Member
Joined 2019
cubicincher said:
O.K.! Sounds good.


Have a good week and hopefully your M2X will give you the same listening pleasure as my one!


Greets
Dirk
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Thanks to Jim's stellar help I now have a working M2X. My only previous experience with Nelson's First Watt amps was the ACA. As amazed as I was with the sound quality of that amp, the M2X is in another league. I've had amps that cost a lot more, but I've never had one that sounds as good as the M2X. I'm using the Tucson board and will also try, at minimum, the Mountain View. I'm using it with a preamp I've had forever, the Cary SLP-98P.

Jim, Mark - thanks again for your help, and for making this remarkable amplifier available.
 
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