MC Carts: Poor Specs!

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   One very important factor in ensuring the correct sound balance from a moving coil cartridge according to one website is being able to control the extreme rising response which, according to a graph on the same website, can be up to plus 10dB at 16kHz!

Bang goes the supposed benefits of moving coil cartridges then?

I know this simply doesn't happen with moving magnet!

But does this happen at all? Or is this website a lone voice?

Excluding forums where it is known that members can imagine all sorts of things and convince themselves and others of all sorts of myths and magical things (this doesn't happen here because our members still have most of the sense they were born with, plus I have the delete button...), the website in question IS a lone voice. So where's the link I hear you ask? Sorry, it's a competitor is my answer.

I spent most of Friday trying to substantiate this claim of "wickedly" rising response, which is due to the inductance of the cartridge, but unless my search terms were way off base, I couldn't substantiate it.

So what is the inductance of a moving coil cartridge? Most manufacturers don't seem to have a clue - or don't give a hang!

The only manufacturer's website to specify inductance is Goldring!

So with only their inductance to go on I decided to do a spice model of the parasitics: if you model pure inductance into a load you will get a frequency response "kick" which would suggest the website in question has a point. But then the cartridge manufacturer also specifies the DC resistance of the coil - this is a constant. Model that in series with the inductor and suddenly the "kick" is gone!

So will the "kick" be an acoustic phenomenon? And if it is - is the website in question therefore saying moving coil cartridge manufacturers have it wrong? I would have thought they'd be equipped with the odd test record and some test gear to be able to plot their cartridge's response - wouldn't you? In fact I'm sure I received such a plot with my Audio Technica OC9!

So is this guy kidding? Trying to frighten the buying public by saying "see here, I'm the only guy who knows his stuff and if you buy anything else you're in for a bad time"? Could that be possible? 

Or does the fact that I can't find any MC cart specs that list inductance mean that the cartridge manufacturers have something to hide (except Goldring)?

If the last case is true, then it would be a case of just one cartridge manufacturer's products being any good!

So my using Audio Technica and Ortofon moving coils in the listening tests of our phono stages is wrong?.... I should be using Goldring?

Well, if that is the case, then our phono stages will sound just fine with every single MC cart apart from Goldring.....  ?!? 

And that gentlemen, is why so many of you can get so totally confused!

My advice is to avoid the singleton! The singleton with what seems to be an attitude problem who wishes to suggest you can only get the RIGHT result with him, and him alone!

Which is exactly what every hi-fi manufacturer is about which equates to one thing...

MONEY LUST, period!

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Graham Slee Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16314	Post Options Post Reply Quote Graham Slee Report Post Thanks(0) Quote Reply Topic: MC Carts: Poor Specs! Posted: 03 May 2009 at 6:02am
	One very important factor in ensuring the correct sound balance from a moving coil cartridge according to one website is being able to control the extreme rising response which, according to a graph on the same website, can be up to plus 10dB at 16kHz! Bang goes the supposed benefits of moving coil cartridges then? I know this simply doesn't happen with moving magnet! But does this happen at all? Or is this website a lone voice? Excluding forums where it is known that members can imagine all sorts of things and convince themselves and others of all sorts of myths and magical things (this doesn't happen here because our members still have most of the sense they were born with, plus I have the delete button...), the website in question IS a lone voice. So where's the link I hear you ask? Sorry, it's a competitor is my answer. I spent most of Friday trying to substantiate this claim of "wickedly" rising response, which is due to the inductance of the cartridge, but unless my search terms were way off base, I couldn't substantiate it. So what is the inductance of a moving coil cartridge? Most manufacturers don't seem to have a clue - or don't give a hang! The only manufacturer's website to specify inductance is Goldring! So with only their inductance to go on I decided to do a spice model of the parasitics: if you model pure inductance into a load you will get a frequency response "kick" which would suggest the website in question has a point. But then the cartridge manufacturer also specifies the DC resistance of the coil - this is a constant. Model that in series with the inductor and suddenly the "kick" is gone! So will the "kick" be an acoustic phenomenon? And if it is - is the website in question therefore saying moving coil cartridge manufacturers have it wrong? I would have thought they'd be equipped with the odd test record and some test gear to be able to plot their cartridge's response - wouldn't you? In fact I'm sure I received such a plot with my Audio Technica OC9! So is this guy kidding? Trying to frighten the buying public by saying "see here, I'm the only guy who knows his stuff and if you buy anything else you're in for a bad time"? Could that be possible? Or does the fact that I can't find any MC cart specs that list inductance mean that the cartridge manufacturers have something to hide (except Goldring)? If the last case is true, then it would be a case of just one cartridge manufacturer's products being any good! So my using Audio Technica and Ortofon moving coils in the listening tests of our phono stages is wrong?.... I should be using Goldring? Well, if that is the case, then our phono stages will sound just fine with every single MC cart apart from Goldring..... ?!? And that gentlemen, is why so many of you can get so totally confused! My advice is to avoid the singleton! The singleton with what seems to be an attitude problem who wishes to suggest you can only get the RIGHT result with him, and him alone! Which is exactly what every hi-fi manufacturer is about which equates to one thing... MONEY LUST, period!
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tg [RIP] Members Profile Send Private Message Find Members Posts Add to Buddy List Moderator Group Joined: 19 Jan 2008 Location: Sydney Status: Offline Points: 1866	Post Options Post Reply Quote tg [RIP] Report Post Thanks(0) Quote Reply Posted: 03 May 2009 at 9:29am
	Interesting theory. My bog standard professional broadcast cartridge (DL103) came with a frequency plot that drops gently from 2KHz to around 9KHz - by about 1dB then rises gently to about 0.5dB at around 17KHz dropping again to -1 dB @ 20KHz. Is this some kind of fraud on their part ? - it does look like a section torn from a continuous roll of recorder paper, rather what one would expect to be used in such testing equipment and does have an official "chop" mark along with various testing parameters for reference. Perhaps the official mark of the tester makes it some form of legal document ? - rather like a sworn statement ? - would they dare to falsify such a thing ? - particularly one not intended for a consumer market ? That is no doubt why this one displays such "atypical" behaviour - it is a broadcast cartridge not a "hifi" cartridge. I hope our friends at Nippon Columbia understand the use of irony - don't want any flak from there - after all, I am a fan of their products. BTW I have seen inductance figures for some AT cartridges on a resellers website so they must be published somewhere - perhaps in Japanese. Edited by tg - 03 May 2009 at 9:34am

Analog Kid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 07 Mar 2008 Location: Germany Status: Offline Points: 209	Post Options Post Reply Quote Analog Kid Report Post Thanks(0) Quote Reply Posted: 03 May 2009 at 8:45pm
	Some manufacturers even display a lack of consistency in their specifications. For example for their 17D3, Dynavector specificies a DC resistance of 38 ohms. But they refer to the same specification as impedance for their new top-of-the-line XV-1t which is listed as having an impedance of 24 ohms. Is "impedance" and "DC resistance" not two words for the same thing? And when looking at the DC resistance of a cartridge, lower is better, yes? To make it even more confusing, the previous model the XV-1s has the following listed: "Impedance: R=6 ohms, L=18 micro Henry" And what does that mean? Edited by Analog Kid - 03 May 2009 at 8:55pm

Graham Slee Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16314	Post Options Post Reply Quote Graham Slee Report Post Thanks(0) Quote Reply Posted: 04 May 2009 at 4:51am
	Nice question AK! Here we need to differentiate between the recommended load impedance and the little understood property of source or driving impedance. Also we need to learn the difference between impedance and resistance. We'll do the last first... Resistance is that thing we were taught about in elementary science at school - remember Ohms Law? That is DC resistance. Impedance is a bit more complicated, but is still stated in Ohms: the complication being that it includes "resistance" from things other than actual resistors - in the case of a phono cartridge, it includes the AC resistance of the coil winding. A straight piece of wire has resistance, but when wound into a coil it becomes an inductor too! Inductors are only resistive when an alternating signal is in them - and that's what audio is - an alternating signal. Therefore the AC resistance is called IMPEDANCE because it includes both the DC resistance and the alternating signal resistance... If this were a math class we would represent the alternating signal resistance as A, the DC restance as C because it is a constant, with the result B being a sum of both... A + C = B The textbook explanation is much more complicated so we'll not go there. Right, now for the difference between load impedance and driving or source impedance - this will have you in command of the situation from now on... Because the signal is generated in a coil of the cartridge by a magnetic influence (stylus movement causing the coil to move with it in a magnetic field) it works just like the alternator of your car - except in miniature and the voltage isn't constant but IS in sympathy with the music... As we found above, the coil has its own "straight wire" resistance as well as AC resistance and lumped together they're called impedance - so the voltage is developed across this impedance - THE DRIVING IMPEDANCE. In the case of the XV-1s, the DRIVING IMPEDANCE is 6 Ohms plus 18 micro Henry. The constant C which is DC resistance is 6 Ohms, and the AC resistance is 18 micro Henrys but to put it into our equation we want the 18 micro Henrys in Ohms. Luckily there is an equation for this... XL (AC resistance) = 2 x Pi (approx 22/7) x F (Frequency) x L (Inductance in Henrys) So for an audio bandwidth of 20kHz, 18 micro Henrys gives a resistance of... 2.2619 Ohms So the maximum driving impedance is... (A) 2.2619 + (C) 6 = (B) 8.2619 Ohms (in the frequency domain to 20kHz) You see, IMPEDANCE has to be quoted for a given frequency domain whereas DC resistance is constant. And now you will see that the driving impedance of a cartridge (in fact all coils) rises with frequency. So what about LOAD IMPEDANCE? The source or driving impedance is seen as being in-series with the signal, therefore the load will divide that signal down, but by how much? If we made the load the same as the driving impedance (8.2619 Ohms) the signal would be divided in half... ....but would it? Not exactly - at a very low frequency the driving impedance is nearer 6 Ohms than 8.2619! So it would not be evenly loaded - the highs (20kHz) would be divided by two, but the lows would be divided by a bit less. We have to hit a load impedance that will have a less pronounced difference. Many MC inputs are 100 Ohms - that would fit the bill! But maybe the cartridge manufacturer noticed a slight tendency for the highs to get a bit loud? This being a mechanical or acoustic thing, he decides he can use the load to improve the tonal balance - and this is possibly why Dynavector have specified a load impedance of 30 Ohms? Yes! Actually that is the case. The previous model of the Dynavector XV-1t was obviously much different - possibly a weaker magnetic system requiring more ampere turns to produce its 0.35mV output: more ampere turns = greater DC resistance as well as more Henrys of inductance so the driving impedance is as quoted 24 Ohms. So then they specify greater than (>) 75 Ohms for the load. Again, with the Dynavector 17D3 you have an even weaker magnetic system calling for even more ampere turns of wire - being thinner wire so as to be of small bulk to fit the cartridge and weigh light enough, its resistance is going to be higher and so is its inductance. But here you find they only specify DC resistance - maybe the inductance is a tad embarrasing to them? But why should it?... ...The load now needs to be greater than (indicated by the symbol > ) 100 Ohms. In fact with a source resistance of 38 Ohms I would have expected a load impedance of say 380 Ohms ( x 10 ), but maybe it does have a rising output with frequency? Maybe 100 Ohms keeps that in check? The math we went through above suggests that is the case! Should we therefore assume moving coil is still in its experimental state? At least moving coil cartridges from some manufacturers? It would seem so. Now how can the phono preamp designer be all things to all men? He simply cannot - all he can do is try to cover as many bases as possible! So where is the justification for all those quick to put down one design or another? That place is called hypocrissy! The hypocrissy comes about from not understanding - more like a refusal or stubborness in understanding? Like I said a million times (with very little exageration) it is no good getting into vinyl without understanding it, or at least trying... ...vinyl is not for the plug and play (foot note on magnetic systems: a weaker magnetic system is not necessarily a bad thing - it can actually reduce the Q or peaking in the cartridge system. The downside being that the majority of manufacturers don't do the same, so the weaker magnetic system finds itself out of place - it doesn't fit easily with the majority...)
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MC Carts: Poor Specs!

Cadman Enterprises Limited
7 Kirkstall Close
South Anston
Sheffield S25 5BA
England

+44 (0) 1909 568739
+44 (0) 7947 107188

john at gspaudio.co.uk

MC Carts: Poor Specs!

Cadman Enterprises Limited7 Kirkstall CloseSouth AnstonSheffield S25 5BAEngland

+44 (0) 1909 568739+44 (0) 7947 107188

john at gspaudio.co.uk

Cadman Enterprises Limited
7 Kirkstall Close
South Anston
Sheffield S25 5BA
England

+44 (0) 1909 568739
+44 (0) 7947 107188