I don't really want to change too many variables at once. The Norwood is already a proven design, so I'd prefer to leave it as-is. Additionally, I see improved distortion values when I keep the output impedance low. That focuses my attention on the Zobel.
Given the variation between PH104's measurements and the Spice sim, perhaps the best course of action would be to build a 21 dB gain version with the normal Zobel and check the frequency response. If it looks flat enough - no need to solve problems that don't exist.
Which preamp for the M2X?
I built the B1 Mesmerize TYA, Being unity gain, there was not enough drive when my TT was used as the source.
So I built the Elekit TU-8500 valve pre and the B1 Korg.
Which is technically better suited?
I have been running the TU-8500 for about a month and am thinking I should try the B1k for a month.
I built the B1 Mesmerize TYA, Being unity gain, there was not enough drive when my TT was used as the source.
So I built the Elekit TU-8500 valve pre and the B1 Korg.
Which is technically better suited?
I have been running the TU-8500 for about a month and am thinking I should try the B1k for a month.
Hi,
It was indeed something silly.... something wrong with my speaker binding posts
Anyway, my M2X seems to working now. Some measurement graphs attached. 10kHz square wave: ringing at transitions. Normal?
1kHz 1W 8ohm spectrum: seems 3rd harmonic @ -73dB is higher than 2nd harmonic. How can I get the "nicer" 2nd harmonic?
Attachments
Have a chat with member xrk971, who measures lots and lots of 2nd harmonic on his M2x. Nelson Pass, on the other hand, saw "a fairly pure third harmonic signature", as he stated in the M2 owner's manual (figure copied below)
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I about drove myself crazy in early 2000"s when most dacs sported a phase flipping switch, and thought I had divested myself of that rabbit hole. But many here, and If I remember correctly I think I have heard Mr Pass comment in that this can make a difference with these amps.
Once I put my Aleph J or M2 in a system I always check that out, and I think I hear a difference. One way image is a little more compressed and seems not to project forward. The other way, it seems to expand and come forward.
I may be hypnotizing myself about all this, but your description of before and after sort of reminded me of the differences I thought I heard...I really think I did notice!
Easy enough to flip speaker wires and listen anyway.
Russellc
Once I put my Aleph J or M2 in a system I always check that out, and I think I hear a difference. One way image is a little more compressed and seems not to project forward. The other way, it seems to expand and come forward.
I may be hypnotizing myself about all this, but your description of before and after sort of reminded me of the differences I thought I heard...I really think I did notice!
Easy enough to flip speaker wires and listen anyway.
Russellc
Some people can hear a difference between non-inverted polarity and inverted polarity. Why assume that ALL people can hear a difference?
In crass commercial terms, only 1% of the preamps ever sold, included a "polarity invert" switch. Yet 100% of them sold anyway, even the {vast majority} units that cannot invert polarity. What does this tell you?
In crass commercial terms, only 1% of the preamps ever sold, included a "polarity invert" switch. Yet 100% of them sold anyway, even the {vast majority} units that cannot invert polarity. What does this tell you?
That many hifi and preamps and audio practice was not done as well as it could have been done. What does out tell you?
Thanks for your comment. If a listening test is done as the original post mentioned, then the absolute polarity should be taken into account so that the test is valid.
Did I say that ALL people can hear a difference? No... I said I and others hear it. Nevertheless, proof of absolute polarity audibility is attached, perhaps not perfect but pretty damn good, and more recognised than I expected...
Just found another paper about absolute polarity, by non other than Richard Greiner from 1994, a little dated now but I expect still relevant.
A quote from the conclusion, "While polarity inversion is not easily heard with normal complex musical program material, as our large-scale listening tests showed, it is audible in many select and simplified musical settings. Thus it would seem sensible to keep track of polarity and to play the signal back with the correct polarity to ensure the most accurate reproduction of the original acoustic waveform."
A quote from the conclusion, "While polarity inversion is not easily heard with normal complex musical program material, as our large-scale listening tests showed, it is audible in many select and simplified musical settings. Thus it would seem sensible to keep track of polarity and to play the signal back with the correct polarity to ensure the most accurate reproduction of the original acoustic waveform."
It tells me that 99% of the population of preamp buyers simply didn't care whether or not their preamp had the ability to invert phase. Whether audible or not, it just wasn't important. Today's preamps appear to continue the trend of not offering phase inversion, and today's preamp buyers appear to continue the trend of not caring whether phase inversion is offered or not.
Uh ha... So are you advocating a lowest common denominator approach to audio?
What about if people don't know if better sound is possible? Should we have stuck with mono because not enough people cared about stereo when there was little program material?
Given that preamps are largely obsolete now, at least a number of digital players get this right and invert the polarity if the flag is set in the file. Maybe we can even get this right for punters and improve their sound without them even having to know about it.
Birthing of another M2X—So far—wow what an amp! LOVE.I haven't put it into the main system—but I did grab a pair of cheap test speaks to use on the bench—and it sounds awesome (thanks 6L6! ...again...). I was most excited to try some particular boards—and am VERY reluctant at the moment to remove them to at least make sure the others work.—Well Mountain Views light up—they were my bulb test subjects with the LEDs. Also, haven't built Austin yet—have all the parts though.
AMP sounds freaking fantastic. BIGTIME.
Still have to finish the fronts. Making these cases was pretty time consuming. I'm definitely approaching tap-master status though. And making them from absolute nothingness was pretty rewarding.
Had a little drama which 6L6 (again... What would we do without him???) noticed where I had 37R instead of 37K for R6—well we kinda noticed at the same time really.... That was some nice DC offset! Easy fix and they biased right up. Er zeroed.
So with this build I decided to try something I read in the bonsai article and attached some crappy earphones directly to the speaker outs (input shorted, used an RCA Y to mini jack). If you try this, don't have them on ears when turning amp on and off. Ask me how I know!—and it was an accident—because I knew not to do that. WOW this was a serious learning experience... Three things that were/are? facts for this build:
1. Rotating toroid 100% affects hum/noise—there's a sweet spot with minimum noise—actually I learned this while building Aleph J.
2. Shielding the autoformer is absolutely worth it. HALF the noise when covered. Used mu metal.
3. Ferrite core around primaries did something—but not as much as 1 and 2. But it was an audible difference.
I would suspect that having the donut in a can would also be a no-brainer—but I was risking it trying to keep the boxes as small as possible. I did pass copper, aluminum, and mu metal sheets in front of the toroid and couldn't hear any differences... perhaps total encasement is the secret? Or perhaps my tuning of the transfo position was 90% of the cure?
Also was able to hear differences between input boards. With the only 2 I tried so far one was twice the "noise" as the other.
I have no idea if "silence" is an attainable goal under these listening conditions—first time I've tried it. What I can say is that I can't hear anything at all in between tracks when playing music or volume maxed. Speaks are 89db. Main system speakers are 98db... so we shall see.
Definitely a fan of the ceramic pads for the mosfets. Sinks get warm, not hot.... Bias is perfect—(6L6 again—OMG
)B1K is also totally not ringing. And usually it rings a tad... but only when touched. Not sure what that is about. I have it pretty well maxed and it could still go louder for dance parties. I'll try Noir tomorrow! Per something I just read that MJ is using that combo. And I LOVE Noir.
Will also be trying with Waynes BA18 and ZM Iron pre. Iron+Iron! Hmmmmmm.....
Anyone building this amp needs to head over here too:
A Noob's First First Watt - M2x
EXCELLENT info in there thanks P. Anderson.
More later—and beauty pics.
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Spectacular build! The monobloc chassis look gefrigginge awesome with a heatsink on only one side and with asymmetric vent holes. I'm sure the "antique white wood" faceplates will be killer gorgeous too. Give some thought to pairing them with a blue LED that rhythmically "breathes" -- drop dead awesome.