Clearaudio MM -- AT-95E and beyond

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dlaloum

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Re: Clearaudio MM -- AT-95E and beyond
« Reply #720 on: 26 Aug 2014, 11:08 pm »
I really need to spend a few quality hours catching up on that thread...

neobop

Re: Clearaudio MM -- AT-95E and beyond
« Reply #721 on: 26 Aug 2014, 11:51 pm »
The thread has degenerated and J. Carr's posts are about the only thing of interest.  Most of that has been repeated here, and I posted there most of the lab test links I posted here.  I think he and I were the only ones who looked at them, and I also think you could be very affective at getting more info or opinion from J. Carr.  He provided the Accuphase sheets, BTW.

A couple of pages back he was commenting on the stylus mounting of the boron tube cantilevered carts - DL-1000a, EPC 305MC.  I found a photo of a Genesis 1000 tip, but I don't know if the link still works.  After commenting that the 1000a stylus was only mounted to the upper wall of an extremely thin tube, he proceeded to say the 305 was worse because the tip was too long and could rotate.  I thought his assessment was self-serving, especially comments about increasing tip mass.  Where does he get off talking about tip mass on a Technics cart like that, when.....?

Anyway, relations were somewhat strained but civil.  Somehow the conversation got onto phase and I didn't pursue the Ortofon papers.  He insists there's a phase shift at electrical resonance.   I still don't think that's possible based on the measurements.  Maybe I'll look at those MM graphs again.
I took a look at the inner groove thread on Karma.  Maybe I missed it, but it seems like nothing new. 
neo 


*Scotty*

Re: Clearaudio MM -- AT-95E and beyond
« Reply #722 on: 27 Aug 2014, 12:20 am »
The inductance of the MM cart alone with give you electrical phase shift, it's unavoidable unless you cancel the inductance out. The inductance plus the cable capacitance forms a second order filter which results in even more phase shift. One of the advantages of the MC design is the vastly lower inductance figure which results in less phase shift in the audio band.
Scotty

dlaloum

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Re: Clearaudio MM -- AT-95E and beyond
« Reply #723 on: 27 Aug 2014, 12:52 am »
Like Scotty said - it is physics, phase shift is unavoidable in an LCR circuit...

BUT  that phase shift is identical in properties to cantilever resonance phase shift, and if you balance one vs the other, a flat frequency response is an indicator of neutral phase as well.... Hence achieveing flat frequency response using minimum phase methods is critical.

Cantilever resonance can also be modelled as a circuit I believe, at some stage I should add that to my cartridge model...

neobop

Re: Clearaudio MM -- AT-95E and beyond
« Reply #724 on: 27 Aug 2014, 11:29 am »
Like Scotty said - it is physics, phase shift is unavoidable in an LCR circuit...

BUT  that phase shift is identical in properties to cantilever resonance phase shift, and if you balance one vs the other, a flat frequency response is an indicator of neutral phase as well.... Hence achieveing flat frequency response using minimum phase methods is critical.

Cantilever resonance can also be modelled as a circuit I believe, at some stage I should add that to my cartridge model...

The LCR phase shift is NOT separate from the that of the cantilever.  If it was, there would be a shift at electrical resonance in each of the 5 MM plots in the test report.  Even though we don't know what those MMs were, there is only one shift and it coincides with HFR

You can look at it as combining the 2 circuits, mechanical and electrical, because that's exactly what happens.  The LCR circuit has the net effect of lowering HFR.  It's just as CarlosFM (EE) stated on the VE thread.  We can see the physical lowering of HFR in Werner's TNT article Load the Magnets.  Resistance and capacitance are manipulated to augment treble response.  That lowered frequency (16K or whatever) is where the shift occurs.

Gentlemen, we must go with the evidence we have.  The Ortofon tests are the only known measurement of phase vs. amplitude with phono carts.

For years better phase linearity was used as an argument for the superiority of MC.  Why then does Atlas, widely acknowledged as one of the best carts ever, mimic MM phase response?  With HFR @ 20KHz, phase would look more like one of the MMs in the test than the MC200.  Perhaps the strain gauge has better phase characteristics than magnetic carts, at least that's what is claimed.  But I suspect many records don't sound "right" with them.  The mastering is checked with magnetic carts and the imperfections of that playback might be built-in the record.  It's probably sort of the way it is now with some records better served with a forgiving set-up. 
neo 


dlaloum

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Re: Clearaudio MM -- AT-95E and beyond
« Reply #725 on: 27 Aug 2014, 01:16 pm »
Hmmm yes - we do know that where the Frequency/Amplitude (as the sum of LCR and cantilever F/A) goes off from "flat" neutrality there is definitely associated phase variance.

Given that it is a minimum phase system, it should even be calculable...

But if the response in frequency terms is flat, the then associated frequency/phase will also be flat - with the notable exception of anomalies generated as part of hysteresis, eddy currents and other such - all of which tend to be in the very small scale categories (definitely less than 3db, and in the better cartridges less than 1db) - and well below the phase anomalies caused by even relatively "perfect" phase speakers (eg pure electrostatics) - Which is why I tend to ignore these effects... (also none of the test records claim to be accurate to within 1db... so effects on this scale are not measurable with our current tools)

I have to read JCarr's postings on the effects of imperfect coil shapes, etc... and mull on that particular set of parameters...

I definitely have measured substantially reduced upper midrange losses in switching from a high inductance body to a low inductance one - while keeping the same needle (Pickering XLZ7500 & XSP3003) - so I tend to think there is definitely something that is gained in going to lower inductance.

Eddy currents and hysteresis are both heavily driven by signal strength which in turn is the level of change within the magnetic field (ie how motion is turned into electric signal)... fewer turns of the coil seems to improve things - at least in the case of my example - quite measurably.
BUT - in exchange, you have that rising top end, and the associated phase variance.... sigh.... (which can be corrected by adding more damping.... but the damping has known negative impact on the sound too.... )

Later this year I am going to try the XLZ7500 with digital minimum phase filtering to see how it sounds with flat Frequency/Amplitude as well as Phase/Amplitude response.... (one of those "round tuit" exercises I mean to get to!)

bye for now

David

neobop

Re: Clearaudio MM -- AT-95E and beyond
« Reply #726 on: 30 Aug 2014, 01:43 pm »
David,
"we do know that where the Frequency/Amplitude (as the sum of LCR and cantilever F/A) goes off from "flat" neutrality there is definitely associated phase variance."

Looking at the MM plots, there is a small rise in amplitude response at, or just beyond the point of maximum phase shift.  (note: it's difficult to tell exactly, as the phase plot goes off the scale)  Past that bump in amplitude response it either rolls off or continues relatively flat.

"But if the response in frequency terms is flat, the then associated frequency/phase will also be flat"

I don't think this follows.  Just as in the MC plots, phase shift is maxed out at that peak of cantilever resonance (or combined with MM LCR).  On either side of that peak of maximum phase shift there is quite a bit of phase nonlinearity that extends through areas of flat response.  In the case of the MC200 the peak was @ 27K and phase shift didn't reach zero until approx. 7-8K. Some of the MM phase shift extended down to 1-2K.

Another problem - we didn't pay much attention to phase shift on the far side (higher frequency) of the peak.  In the case of the MC200 this is beyond 27K so it's way beyond audibility.  If the peak occurs @ 16K, then phase shift @ 17K will be just as bad as 15K. 

For years phase performance has been used as an argument for MC superiority.  "They" said that LCR determined phase shift frequency and that many MCs had no shift until way into the ultrasonic region based on MC inductance.  This could be way beyond the response of the cart.  MC inductance is measured in uH.  We know this is BS - HFR determines MC phase shift.
What about MMs when LCR can be lower than HFR ?  We don't have enough evidence to prove LCR is meaningless like in the MC case, and we know that increasing capacitance will lower HFR, and because of this the user has another feature to manipulate amplitude response.   Is the downside to this also phase performance beyond HFR ? 

Some of the MMs in the test had HFR or primary shift around 20K.  How is this any different from Lyra Atlas/Kleos ?  It might extend a little lower due to increased MM damping?  So, if we're thinking purely in terms of amplitude/phase, the Atlas is a second rate design.  +6dB @ 20K, where HFR occurs?  It shows how much importance this phase business actually is in the ears of audiofools. 
Lets forget their ears and look at "superior" carts.  How about some Dynavectors or Nakatsuka designs that have far better HF response and resonance in the stratosphere?  They're not perceived as better because of Carr's magic.  Emphasis is on tracing exactitude and excess energy dissipation.  Have you noticed that Anna, Atlas and AT50ANV have titanium or titanium in the bodies?  This is for energy dissipation - send it to the arm instead of messing up the signal in the cart.  Clean up the resonance mess and you have better sound.
neo



 

dlaloum

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Re: Clearaudio MM -- AT-95E and beyond
« Reply #727 on: 31 Aug 2014, 06:12 am »
I was about to go off half cocked as usual without giving this due thought...

had another look at those plots, and indeed the 5 MM's show relatively flat F/R with quite widely varying P/R.

So I took another look at the MC plots....

Look at plot 1 and plot 2

1 is textbook minimum phase resonance - amplitude varies with a gentle bell curve and phase has a sharper bell curve with the peaks coinciding.

2 however is strange... for damping, the curves should both become wider and lower, with the peaks still coinciding.... but they don't.
A shift in overall phase peak should imply the addition of another resonance which is summing - this does not make sense...unless the damping mechanism is introducing something else... presumably it is not a "pure" damper - and may use another mechanism to provide a damping effect on amplitude.
Either something is wrong with the measurement method, or someone played rough and ready with some of the plots (perhaps measurement ended at a lower frequency than shown on the plots?) - or I need to review the physics of this effect..... :?

Maybe I should go ahead with my square wave based phase testing of some cartridges to get some rough experimental results....

neobop

Re: Clearaudio MM -- AT-95E and beyond
« Reply #728 on: 31 Aug 2014, 11:30 am »
Interesting observation.  The MC graphs extend out to 50K and the plots with damping peak somewhere beyond 50K.
The amplitude of the undamped phase peak is +17dB (approx.).   The damped peaks are higher in both amplitude and frequency.  The MC phase curves with damping more closely resemble the MM phase curves, except not as steep.  Remember, an undamped MC is probably a nonentity, so a real world MC actually has phase shift that covers a wider range of frequencies, except most of it is ultrasonic. 

I think the implication is clear.  Damping doesn't just cause the phase curve to extend further in either direction, it also increases the amplitude.  In other words, the curve gets bigger in all directions. 

There's another unknown here and that's the identity of the MM carts.  It looks as if response is falling off beyond 20K in all of them.  I think that's the suspicious factor here.  I suspect a low inductance MM cart with a boron or beryllium cantilever could equal or surpass the MC200 in phase performance.
neo

dlaloum

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Re: Clearaudio MM -- AT-95E and beyond
« Reply #729 on: 31 Aug 2014, 12:22 pm »
I'm gonna have to study some more physics to understand what could cause that rising phase/frequency plot...

Or review some formulae....

J-Pak

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Re: Clearaudio MM -- AT-95E and beyond
« Reply #730 on: Today at 02:09 am »
Followers of this thread may have heard of the AT33PTG II (a favorite amongst some "famous" needle droppers) MC cartridge. One of my friends added one to his system and I heard it over the weekend. Probably the best tracking I have heard/experienced from a moving coil, though may fall slightly shy of the V15. Stunningly clean on known problem records like some MFSL reissues of Bob Dylan which can have headache inducing vocal sibilance (particularly bad on their 45 rpm reissue of The Freewheelin' Bob Dylan). Sound quality was very good, but a touch too dry and clinical for my taste.