[neobop]

I'm happy to report the plastic reduction surgery went well.  I removed the stylus guard and used 2 different size wire cutters to trim about 1mm off the sides.  I was thinking of a plastic-ectomy CA style, but this plastic seems a little thicker and I was a little tired and didn't want to get near the magnets and cantilever.

I only played 1 album with the 440/MR-ML, but the difference seems substantial.  Output is louder, more dynamic and more like the 440/ATN152ML.
I'm a happy camper, but I wonder about the old Signet body that's supposed to be the same.  Maybe it suffered some sort of trauma?  For some reason it didn't age well.  I suspect it was fine when new?

It makes me wonder about differing results with the "same" cart.  One person gets a good one and another gets a dud.  Maybe age has more to do with it.
neo 

[dlaloum]

I doubt it is age... JCarr may have it right in pointing out the difficulties of getting perfect evenly laid coils in a high inductance design..... Hence the hand picked at20 bodies, and the "reject" 13/14/15?

[neobop]

It could have been trauma - cores and coil misalignment.  Here's what Carr said:

Regarding coil impedance, my general experience is that the fewer the components comprising the coil bobbin, and the fewer the number of coil layers, the more consistent the coil shape and impedance will be. Using more components for the coil bobbin (as in a laminated coil) increases the likelihood of bobbin mis-shaping and non-flat surfaces, while each coil layer added results in a less flat surface for the next coil layer to be wound onto.

So it's conjecture on our part, but the resistance measures a larger than normal discrepancy between channels.  I know Signet division had a facility in the US, but I don't know if carts were assembled there.  If so, that could explain it, or maybe part of the internal design is different, but I doubt that. 
Signet was the high end line and QC should have been at least as good. 

Hence the hand picked at20 bodies, and the "reject" 13/14/15?

The 13 is a higher inductance cart (1200 ohms, 4.2mV) - not one of those.  The DC of my 15 measures within an ohm or 2, not only ch to ch, also the spec.
Who knows, the hand picked 20 could have been BS like Grado Gold/Silver.  Maybe there were only so many they matched up with a stylus and "calibrated".   More likely they weren't calibrated at all.  The bodies were probably measured and the stylus was checked for alignment. 

You know those little amplitude response graphs that come with some high end carts - why are they all identical?  "They" run them off on a copy machine and throw them in with the paperwork.  Maybe not every company, but remember Kiddman's Agon post? 

I don't know about the Signet 5.0ML, but my experience is that AT is one of the better brands for QC.
neo

http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1200430667&openflup&11348&4#11348

[dlaloum]

This may explain Technics' choice of HPF for the core of the EPC100 & EPC205 - fewer components, more consistent and precise forming?

The EPC100 adds to this by being lower inductance and therefore having fewer coils.... interesting...

The AT25/TK10 family might have similar advantages...

This may also explain some of the variability in very well regarded designs like the Shure V15 family...

Here is some data for the AT25 / TK10 family (my own measurements of several samples)

Ind Bal    Imp Bal     Ind L     Ind R     Imp L     Imp R
4.8%   5.0%    81     85     235     247
2.4%   7.7%    84     86     249     231
0.1%   0.2%    88     88     228     228
0.6%   2.1%    87     88     241     236
1.1%   4.7%    88     87     251     239

and the AT20/15/14/TK7 family

1.1%   5.5%    453     448     489     463    AT20
0.0%   0.6%    453     453     474     477    AT20
4.7%   2.7%    437     458     493     480    TK7
0.9%   0.3%    456     460     455     453    AT14

A few Shure groupings (sticking to the top end):

V15V               
1.6%   1.1%    312     317     855     846
2.5%   1.9%    328     320     796     811
4.5%   0.7%    349     334     817     811
               
ML120/140/Ultra300/400               
1.3%   1.3%    380     375     1,073     1,059
2.6%   0.1%    394     384     1,012     1,011
4.4%   1.2%    379     396     1,009     1,021
4.5%   1.3%    382     399     1,016     1,029
               
V15Vx/M35/SC35/V15RS               
2.3%   1.4%    401     410     989     975
0.2%   0.6%    424     425     993     999
1.0%   1.1%    434     429     967     978
               
V15III/IV               
0.4%   0.2%    499     497     1,394     1,397
2.1%   3.1%    496     506     1,349     1,392
0.4%   1.1%    531     529     1,398     1,413
3.3%   3.5%    548     530     1,412     1,363


My sole TK7 does not fare so well - one AT20 is really excellent, and the other is just OK

The V15V's are in the OK territory but not really in the same league as the best matched bodies...

Keeping in mind that I have limited sampling (all my samples in each category are quoted here..) - this appears to be quite a problem area in manufacturing.

It may be one of the few (quantifiable) justifications for megabuck cartridges.... To get a TOTL body you may need to manufacture 10 cartridges for each 1 that makes the grade....

My best AT215/Tk10 family body is a lower end TK9, and my best V15Vx body is a low end M35 ....

I would have assumed AT to have better QC than Shure.. but then there is that TK7 sitting among the very tightly specced AT20's and AT14.... is an outlier? or was Signet a marketing brand rather than a TOTL attempt?

bye for now

David

[neobop]

My sole TK7 does not fare so well - one AT20 is really excellent, and the other is just OK

The V15V's are in the OK territory but not really in the same league as the best matched bodies...

Keeping in mind that I have limited sampling (all my samples in each category are quoted here..) - this appears to be quite a problem area in manufacturing.

It may be one of the few (quantifiable) justifications for megabuck cartridges.... To get a TOTL body you may need to manufacture 10 cartridges for each 1 that makes the grade....

My best AT215/Tk10 family body is a lower end TK9, and my best V15Vx body is a low end M35 ....

I would have assumed AT to have better QC than Shure.. but then there is that TK7 sitting among the very tightly specced AT20's and AT14.... is an outlier? or was Signet a marketing brand rather than a TOTL attempt?

bye for now

David

Actually, most of them are pretty good.  That errant AT20 has inductance within 1.1%  I would guess that impedance or DC whatever, would be much less critical. 

"It may be one of the few (quantifiable) justifications for megabuck cartridges.... To get a TOTL body you may need to manufacture 10 cartridges for each 1 that makes the grade...."

If dreams were wishes come true, dream on.  But they're not, and while a couple of high end MC companies are quite consistent, many are worse.  Some of the priorities might change a little.  Inductance matching might not mean as much for a LOMC, but it might reflect on output balance. 
What about that test report on the Clearaudio Concerto with the tip misaligned 10° ?  That cart went out the door an wound up on a test bench, but it could have been bought by a consumer who wastes hours scratching his head trying to figure out what's wrong.  This is after paying $3K for the privilege of doing CA's QC work.  We're also dealing with magnets and their inconsistencies.

In my last post I referred to Kiddman - he tests this stuff.  For those who missed this post:

http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1392385752&openfrom&1&4#1

"Come on, nearly all of these manufacturers make up the specs. Measuring lots and lots of high end analog, I've found the specs are dreams and wishes. MC's that show flat but have a rise of 8db by 14khz. Turntables that quote .01% wow + flutter but are really .3%.

Before you argue with me, buy some test gear and prove it for yourself. Measurrments mean a lot. But manufacturer quoted measurements, in this industry with no accountability, are meaningless."

I've measured, using state of the art equipoment (with AC test signal, the only way to do it right) 30% differences in impedance with some brands. Yes, "mass produced" ones, if you can call the bigger premium MC makers "mass produced".

A few manufacturers are quite consistent, and very consistent in sound. And with many manufacturers, I've never heard 2 sound close to identical, tested one right after the other."

eek!!  This is a painful subject, but it's a business and sometimes reality rears its ugly head, but it ain't necessarily so.  Maybe you'll get lucky and pick the right brand or that gem among the duds.  I bet that AT20SS with 1.1% inductance match, sounds pretty good.
neo

[neobop]

You need to start with a phono-cartridge and a cartridge body with identical inductance values. The 47 kohms series resistance is removed from the phono-stage input. It is replaced with a 5kohm series resistor,and a 5kohm resistor to ground. The phono-stage input is connected to the junction of these two 5kohm resistors.
The portion of the circuit connected to ground starts at the junction of the two resistors. The non-series connected 5kohm resistor is connected
to one of the positive pins of the cartridge body and the ground pin for that channel is connected to ground. The other channel is a duplicate of this.
 
Basically half of the cartridge's output is taken to ground from the junction of the two 5kohm resistors through the inductor in the cartridge body. This leaves on average 2.5 to 2 millivolts output which seems to be plenty for most phono-stages to work with.
Assuming that the two cartridge bodies have virtually the same inductance, the inductance of the phono-cartridge on the tonearm is cancelled out by the inductance to ground of the identical cartridge body. This gives you the same operating conditions as a MC with any phase shift in the upper mids and high frequencies a function of the mechanical resonance with zero phase shift due to electrical RCL phenomena.
 In addition there is a degree of electrical damping applied to the stylus mechanical resonance due to the 10kohm load the cartridge sees instead of the 47kohm which is standard practice.
In order for this circuit to function properly the basic input impedance of the phono amplifier stage circuit before any resistive loading network is added must be intrinsically above 100k ohms. Some Bipolar and most FET and Tube based phono-stages have this inherent impedance characteristic.
Cables connecting the TT to the phono-stage should be fairly low in capacitance per foot. If the capacitance does not get excessive the simple 6db/oct. filter pole could be above 100kHz. This would make the cartridge's high frequency extension primarily dependent upon the cartridge's mechanical characteristics.
Scotty
Edited for clarity

I was thinking about this hook-up.  Since the cartridge body is in parallel to the working cartridge, wouldn't the impedance of the body be part of the load?

In other words, 3200 ohms + 5000 ohms would be in parallel to whatever the preamp input impedance is. 
neo

[*Scotty*]

Only the DCR of the cartridge is add to the 10k sum of the two 5k resistors.  Because this same impedance is mirrored by the cartridge body to ground it ceases to be an independent factor that needs to be dealt with.
Scotty

[neobop]

That makes sense.  Reactance is grounded with inductance.

Finding the input impedance w/o the load resistors will be a problem for many.   Why not replace the preamp load resistors with 100K or whatever ?
neo

[*Scotty*]

Its not the same thing as the characteristic input impedance that the transistor or opamp might have. All FET and tube phono-stages with work just fine as will most bi-polar stages including opamp based circuits. If the intrinsic input impedance is not a minimum of 100k or higher the circuit just won't sound as good as it should, nothing is going to be damaged. Most manufactures brag about the circuitry used in their products and if they don't, an email, phone call or look at a service manual will provide the information.
 A lack of this specific knowledge is not a deal breaker.
Scotty

[neobop]

There might be some op amps that have lower than optimal impedance, but I'm not sure.  I was reading about that in DIY audio and it seems there are some that have impedance best suited for LOMC.  I'll see if I can find the numbers.

Anyone interested in downloading the Ortofon phase paper, it's here:
http://www.vinylengine.com/turntable_forum/viewtopic.php?f=46&t=33679&p=259517&hilit=phase#p259517

You have to be a VE member to download.
neo

[neobop]

The Ortofon 2M mono cart is 2 channels connected in parallel. 
http://ortofon.com/hifi/products/cartridges/2m-series/2m-mono

Internal impedance, DC resistance   700 Ohm
Internal inductance   350 mH

http://ortofon.com/hifi/products/cartridges/2m-series/2m-blue

Internal impedance, DC resistance   1,3 kOhm
Internal inductance   700 mH

Why doesn't inductance cancel or approach zero?
neo

[*Scotty*]

The fact that this is a phono cartridge doesn't change the behavior of inductors. They have shown us that they have strapped the two generators together internally thereby having the inductance value. There is no mechanism present to cause the remaining inductance to drop any further.
Scotty

[neobop]

I found it.
http://en.wikipedia.org/wiki/Series_and_parallel_circuits

" For two equal tightly coupled coils the total inductance is close to that of each single coil. If the polarity of one coil is reversed so that M is negative, then the parallel inductance is nearly zero or the combination is almost non-inductive. It is assumed in the "tightly coupled" case M is very nearly equal to L. However, if the inductances are not equal and the coils are tightly coupled there can be near short circuit conditions and high circulating currents for both positive and negative values of M, which can cause problems."

It has to do with the magnetic field of the coils.  In a loudspeaker crossover with multiple coils, they have to be oriented a certain way to retain proper value. 

Scotty,
Have you measured the inductance of your cancelling scheme?   I believe most stereo carts have 4 coils.  Your parallel coils aren't tightly coupled, so parallel inductance applies?
neo

[*Scotty*]

The basic electrical behavior of the circuit was verified by injecting an appropriate level signal through the cartridge and conducting a frequency sweep, which showed a 3dB down point of about 100kHz which indicates that the cartridge body to ground is compensating for the cartridge's normal high frequency roll off. The point in the circuit where the measurement is taken is at the junction of the two 5k ohm resistors which corresponds to the input of the phono-stage.
 If you were to measure the inductance of either the cartridge or the cartridge body while they were in the circuit there would still be measurable inductance. It is the complex behavior of the circuit as a whole that produces the desired result.
The uncompensated cartridge exhibits a rising source impedance with increasing frequency which produces the characteristic high frequency rolloff. It is the matching increase in the load impedance with respect to ground prevents the high frequency rolloff.
 It is perhaps my choice of descriptors which has engendered some confusion as to how circuit functions. I said that the the inductance is canceled out when I should said the the effects on frequency response and phase shift caused by the cartridges inductance is mitigated.
I am afraid my original description invited an overly simplified interpretation of what takes place when this circuit is used. 
 In the wiki example of tightly coupled inductors, the tight coupling is achieved by the inductors sharing a common core. A loudspeaker crossover generally does not have inductors that share a common core. In the course of my DIY speaker projects I have not encountered a case where the polarity of a single inductor has made any difference to how the crossover performed.The Goertz inductors I used were also unmarked as to polarity.
Scotty
Edited for clarity

[neobop]

When you have multiple coils in proximity on a circuit board, orienting the coils is usual.  They are often put at 90° to each other and might be on their side.   This is a 2-way 24dB/octave:



It's usual to see some laying flat and some on their side.  Also proximity to driver magnets could be a factor.   But that's not what this is about.

This is interesting.  Please excuse my remedial electronics, but exactly how did you "inject" an appropriate level signal and measure frequency response? 
It seems to me total inductance should be 245mH (490/2).  If there were no inductance wouldn't - 3dB be much higher?
neo

[*Scotty*]

You remove the stylus assembly from the cartridge and attach the signal generators leads to the hot pins on the cartridge attach the 5k resistors to the ground pins. You measure the resulting frequency response at the junction of the 5k resistors.
 The injection of the signal through the cartridge duplicates what the cartridge's inductance does to the stylus generated signal's frequency response.
 Scotty

[neobop]

You remove the stylus assembly from the cartridge and attach the signal generators leads to the hot pins on the cartridge attach the 5k resistors to the ground pins. You measure the resulting frequency response at the junction of the 5k resistors.
 The injection of the signal through the cartridge duplicates what the cartridge's inductance does to the stylus generated signal's frequency response.
 Scotty

Cool. 
The electrical resonance of a LOMC with 50 uH is 1.4 MHz.  50 uH is actually quite a bit for a MC.  Many are lower.  Here's documentation.  The phase part is BS, but the electrical resonance is what it is:
http://db.audioasylum.com/mhtml/m.html?forum=vinyl&n=856288&highlight=

That's why I suspect you've lowered inductance, not cancelled.  Still, a great achievement.
neo

[*Scotty*]

Neo, excellent link to the audio asylum post. It beautifully illustrates the reason for the inductance mirror circuit. With an AT 150 MLX stylus assembly and inductance effectively taken out of the equation, flat frequency response well beyond 20kHz might be possible without phase shift problems in the audio range. There is no electrical resonance peak near the audio band and the mechanical resonance is damped to a degree by the approximately 11k ohm resistive loading. I have been very happy with the results I have had from my AT440ML using this circuit.
 He is referring to phase shift due to purely electrical LCR phenomena, no BS, however mechanical resonance phenomena are not dealt with in his analysis.
Scotty

[neobop]

Neo, excellent link to the audio asylum post. It beautifully illustrates the reason for the inductance mirror circuit. With an AT 150 MLX stylus assembly and inductance effectively taken out of the equation, flat frequency response well beyond 20kHz might be possible without phase shift problems in the audio range. There is no electrical resonance peak near the audio band and the mechanical resonance is damped to a degree by the approximately 11k ohm resistive loading. I have been very happy with the results I have had from my AT440ML using this circuit.
 He is referring to phase shift due to purely electrical LCR phenomena, no BS, however mechanical resonance phenomena are not dealt with in his analysis.
Scotty

Not sure exactly what you mean by "phase shift problems", but it's those mechanical phenomena that determine MC phase shift.  In a MC, they are the sole determinant.  That's the mistake Ellison made, assuming electrical resonance determines frequency of phase shift.

Remember the MC200 ?  Phase shift occurred at 27KHz and was only extended out by mechanical damping.  Unfortunately, that damping also extended the lower end of the shift to 7 - 8KHz, well within the audio band.  The only way to have no shift in the audio band is to have an undamped boron/beryllium cantilever or one that resonates at a much higher frequency. 

I now think we're making more of this phase business than it warrants.  Look at Lyra carts.  Atlas best case HFR is 27KHz and double damper system makes it look like 20K.  Worst case - it is 20K.  Either way phase performance should be no better than MC200, maybe worse. 
Most audiofools prefer this to carts with "superior" phase performance like some Dynavectors or carts with short tubular boron cantilevers that are flat to 100K and beyond.  Personally, I like the more extended variety, but I'm the exception.
neo

[*Scotty*]

If you have a large collection of cartridges with duplicates you could try the mirror circuit and see what you hear.
Scotty