Why moving coil
 

On Fri, 17 Mar 2006 14:14:30 -0000, "Keith G"
wrote:


"Bill Taylor" wrote


I recently changed my turntable. The only reasonably priced one that I
felt that I could trust was the Technics DJ turntable (basically a
1970s HiFi turntable with a speed control). The supplied arm has
quite a high effective mass and with the Shure V15-V that I had to buy
as well the LF resonance is plainly much to low, this cartridge has a
more reasonable compliance of about 23c.u., but it is still too high.
Forunately the Shure damper more or less controls the resonance.


I ran the same cart on a (presumably) similar deck - the Technics SL1210 Mk
2 - and found that the damping brush had virtually no effect on sound
quality.

Yes, it's the same deck. If you're lucky enough to have perfectly flat
discs and the Turntable isn't subject to vibration, then it shouldn't
have any effect, but if you have any records with a bit of a ripple in
them, the cartridge will oscillate at LF and that can produce an
audible effect. The degree of audibility depends largely on the type
of music you're listening to. On the previous V15 the brush could act
as a stylus itself and it could transmit noise from the adjacent
grooves into the cartridge. The type 5 doesn't seem to suffer from
this so much.

Interesting to see that word is slowly spreading on the massy, non-suspended
decks (direct drive in particular) - I've been 'into' them for years now and
have been watching with some amusement as the the 'bouncing brigade' have
slowly woken up to the fact that suspension causes as many problems as it
solves (apparently) and is a bugger to keep maintained.....

Afraid that you can't claim credit for my conversion. The 1210 was
bought to replace a Technics DD parallel tracker that was failing to
parallel track after 20 odd years!


Bill

Why moving coil
 

In article , Bill Taylor
wrote:
On Fri, 17 Mar 2006 09:52:29 +0000 (GMT), Jim Lesurf
wrote:



If I look at Goddard's article in the 1963 "hi fi yearbook" he gives a
graph of the minimum acceptable compliance as a function of weight.

Simply to ensure contact this rises from 8 cu at 3g up to 20 cu at 1g
playing weight. This ignores tip mass which will also contribute, s
you'd want a lower value to ensure avoiding mistracking. Also, due to
the finite compliance of the vinyl - which is more significant with
small contact profiles - you'd want a low compliance to minimise vinyl
deformation - and hence reduce distortion and wear.


Tip mass adds to the downforce neede to keep the stylus in contact with
the groove but I don't think you can trade off tip mass by increasing
compliance.

I'd agree. In practice you have to ensure both are satisfactory.

[snip]

Walton makes a very convincing case that the most significant cause of
groove damage is high stylus tip mass. He reckoned that a tip mass of
.6mgm or less would cause relatively low rates of wear. In 1968 this was
something of a stringent rquirement,

Again, I'd agree - but in part this is on the basis that makers *can*
deliver a reasonably high compliance to ensure that isn't much of a
problem. Delivering a low tip mass is perhaps more difficult - particularly
with a MC since the coils have to be moved, whereas an MM may use variable
reluctance of a small piece of material.

Looking in the 67/68 'Yearbook' it is notable that many makers quote
compliance values, but then fail to mention a value for effective
tip mass. Some simply claim something like "less than 1mg".


Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Why moving coil
 

"Arny Krueger" wrote in message
. ..
"Keith G" wrote in message

"Arny Krueger" wrote in message
...
"Trevor Wilson" wrote
in message



**Er, not quite. The FR plots of MC carts, in some
cases, CAN be shown to be superior.

In some cases the FR of MM cartriges are at worst the
equal. No, the true hard parameter in the design of a cartridge
is the moving mass, not the inductance of its pickup
coils. Less moving mass for a given amount of brute
force strength, the greater the potential of the design.

Brute force strength is an important parameter of a
cartrdige for two main reasons:

(1) Durabilty.
(2) Ability to tracking the rapid undulations of the LP
groove. The beauty of the MM design is that the moving magnet
can be structural as well as being the primary signal
generating element. With modern high-energy magnetic
materials the magnetic generating element can be made as
virtually as small as is desired. A moving coil cartridge's coils can't
be as strong of a
structural element. The coils work best if there is also
a moving magnetic core. This adds up to excess weight. Furthermore it is
far more difficult to make small coils
of wire and wire leads to transmit the signal, as
opposed to simple small blocks of solid magnetic
material that itself has considerable inherent strength.
The reason, of course, is
blindingly simple. It's all about inductance. The
inductance of (LOW OUTPUT) MC carts is very low, indeed.

The inductance of a MC cartrridge is irrelevant because
it can be made to be whatever is desired. The cost of
reducing it is reduced output, but that is pretty much a
given with MC cartridges. The inductance of a coil is proportional to
the square
of the number of turns. The output voltage of a coil in
a varying magnetic field is proportional to the number
of turns. Thus, if a cartridge is allowed to have a mere
3 dB less output, it has half the inductance. In fact the inductance of
MM cartridges is optimized to
provide smooth response, not minimize inductance. Fools
that they are, designers of MM cartrdiges tend to be
most interested in high fidelity.
This enables them to produce a very flat, very wide (up
to around 60kHz) frequency response, with a
correspondingly superior rise time.

All of which are well-known to have zero audible
benefits.
The real benefit of
such a system is that LC resonance effects are often
well outside the audible range.

Ignores the fact that the resonance that actually
dictates the response of a cartridge in ways that can't
be managed is the resonance between the moving mass of
the cartridge stylus and paraphenalia that is attached
to it, and the compliance of the vinyl.
This means that a low output
MC cart may exhibit a very flat phase response within
the audio band.

Which is again well-known to have zero audible benefits.

This may not be the case with high output MC
carts nor with some MM carts.

For the record: Many, well designed, MM carts do not
exhibit any resonance problems without the audio band.

Thus invalidating Trevor's entire argument.

Interesting, succinct and AFAIAC (from what little I
know) right on the money - quite surprising really, as it
comes from Usenet's No1 antivinyl bigot!! :-)

There's a huge difference between being a bigot and being well-informed
about the properties of various media. I simply know vinyl and digital's
strengths and weaknesses and speak accordingly.

In fact I have an average vinyl rig that I use for making digital
transcriptions. So I'm a funny kind of antivinyl bigot - one who has a
vinyl rig of his own and uses it from time to time for a productive
purpose. It's not as good as the vinyl rig I had when I switched to
digital, but its good enough for the purpose.



Well, we've come a long way from the 'dangers of vinyl' from a few years
back (IIRC), I suppose we should be grateful....

Why moving coil
 

"Jim Lesurf" wrote in message
...
In article , Keith G
wrote:

"Bill Taylor" wrote


I recently changed my turntable. The only reasonably priced one that I
felt that I could trust was the Technics DJ turntable (basically a
1970s HiFi turntable with a speed control). The supplied arm has
quite a high effective mass and with the Shure V15-V that I had to buy
as well the LF resonance is plainly much to low, this cartridge has a
more reasonable compliance of about 23c.u., but it is still too high.
Forunately the Shure damper more or less controls the resonance.


I ran the same cart on a (presumably) similar deck - the Technics SL1210
Mk 2 - and found that the damping brush had virtually no effect on
sound quality.

That isn't particularly surprising. The main effect in practice would show
up on LPs with pronounced levels or warp or surface ripples. If the discs
are fairly flat, then the damper wouldn't be doing much.

FWIW I use my V15/III with an old technics TT/arm so the arm mass is 'too
high', but in general I don't hear any problems as a result, despite the
LF
resonance being lower than nominally ideal.


Quite. IME less problems are experienced by people who are not *listening*
for them - I use V15 IIIs and a V in 'medium mass' S-shaped headshell
tonearms and don't find too much to object to either....

Why moving coil
 

"Bill Taylor" wrote in message
...
On Fri, 17 Mar 2006 14:14:30 -0000, "Keith G"
wrote:


"Bill Taylor" wrote


I recently changed my turntable. The only reasonably priced one that I
felt that I could trust was the Technics DJ turntable (basically a
1970s HiFi turntable with a speed control). The supplied arm has
quite a high effective mass and with the Shure V15-V that I had to buy
as well the LF resonance is plainly much to low, this cartridge has a
more reasonable compliance of about 23c.u., but it is still too high.
Forunately the Shure damper more or less controls the resonance.


I ran the same cart on a (presumably) similar deck - the Technics SL1210
Mk
2 - and found that the damping brush had virtually no effect on sound
quality.

Yes, it's the same deck. If you're lucky enough to have perfectly flat
discs and the Turntable isn't subject to vibration, then it shouldn't
have any effect, but if you have any records with a bit of a ripple in
them, the cartridge will oscillate at LF and that can produce an
audible effect. The degree of audibility depends largely on the type
of music you're listening to. On the previous V15 the brush could act
as a stylus itself and it could transmit noise from the adjacent
grooves into the cartridge. The type 5 doesn't seem to suffer from
this so much.


I found the worst thing with the brush was that it made little or no effect
on the sound but could become very clogged up with fine dust which created a
double (needle *and* brush) cleaning problem!!



Interesting to see that word is slowly spreading on the massy,
non-suspended
decks (direct drive in particular) - I've been 'into' them for years now
and
have been watching with some amusement as the the 'bouncing brigade' have
slowly woken up to the fact that suspension causes as many problems as it
solves (apparently) and is a bugger to keep maintained.....

Afraid that you can't claim credit for my conversion. The 1210 was
bought to replace a Technics DD parallel tracker that was failing to
parallel track after 20 odd years!


I don't claim credit it for *anyone's* conversion, I merely state that I
find it amusing to see more and more people latch on to 'non-suspended' (and
frequently direct drive) decks these days. The downside is that the
*suitable* carts and needles on eBay are going for *double* the usual price
now!!

(No names - I Shure as hell don't need even *more* competition for the stuff
on eBay I would like to grab!! ;-)

Why moving coil
 

"Jim Lesurf" wrote in message
...
In article , Trevor
Wilson wrote:


Similarly, frequency response plots of moving magnets and moving coils
don't show any particular benefit to the MC, nor does stereo
separation or harmonic and intermodulation distortion. So why *are*
MC cartridges throught to be better?

**Er, not quite. The FR plots of MC carts, in some cases, CAN be shown
to be superior. The reason, of course, is blindingly simple. It's all
about inductance. The inductance of (LOW OUTPUT) MC carts is very low,
indeed. This enables them to produce a very flat, very wide (up to
around 60kHz) frequency response, with a correspondingly superior rise
time.

The problem with this is that the mechanical resonances will still exist.
:-)

Also bear in mind that with a decent MM cartridge you can arrange the
loading to give quite a flat response if that is your concern. I've not
personally had any worries on that score with my own Shure V15/III...

Alas, magazines and makers now tend to avoid giving any useful data on
cartridges. Hence we usually can't now assess the level of compliance, tip
mass, etc, etc. Nor, indeed the levels of distortion.

My recollection was that MC's became 'flavour of the year' with some
subjective reviewers precisely because the ones in question did *not* have
a flat response, and they liked the changes, but then ascribed this to
'magic'... :-)



More and more these days, I'm finding there comes a time when it pays not to
read the ingredients when you are eating something.

Without any knowledge of the 'claimed specifications' of the kit in use, I
did indeed experience some 'magical' qualities with a number of 'nothing
special' old (freebie) MC carts a while back - *all* of which I would have
expected to be some way off claimed, original performance specifications,
due to age and infirmity.

The MC10 I mentioned in an earlier post actually had quite a badly bent
cantilever which had obviously had one or two attempts to straighten it
(including 2 attempts by me) which eventually slowly sank to its death,
still sounding quite unutterably *sublime* until the bodywork was actually
riding the vinyl! It was almost a tragical experience!! ('Sublime = 'sweet,
delicate, sonorous, detailed' and *captivating' in this instance...)

Not too 'scientific' I know, but there is more in it for me than just the
numbers. (Perhaps I'm more of a 'mystic' myself than I would care to admit!!
;-)

Why moving coil
 

"Bill Taylor" wrote


snippage


FWIW the best cartridge that I have owned was a Technics P205CMk4.
This tracked better than the Shures v15s that I've owned and has a
flatter FR. According to the makers spec it has a compliance of only
12c.u. but an effective tip mass of 0.11 mg, which agrees with Waltons
argument about the importance of low tip mass. I think that it is a
better cartridge than the V15-V, but my sample has got a collapsing
suspension and replacement styluses seem to be unavailable.



Also FWIW, I haven't found the V15s to be that much better at tracking than
the M75 and M95 carts I own and use - was the Technics cart you mention
above used on the linear tracker you mentioned elsewhere/earlier...???

I have a linear tracker and even the lowly (but well worthy) cheepie AT110E
tracks like a good un on it!!

Why moving coil
 

"Ian Iveson" wrote in message
o.uk...
Trevor Wilson said

I took the question to be general. Do you mean that it is obvious that
MC has less inductance than MM? Why is that please?

**MUCH less wire in the coils (to keep moving mass within reasonable
limits). High output MC carts negate many of these advantages.

I see, although the restriction may have more to do with space than
weight. But it is possible to have low output MM with low inductance, or
high output MC with high inductance. Similarly, all magnets are not by
definition heavier than all coils. What is not simple is how the process
of optimisation led MM and MC to be so different in practice.

**Indeed. IN fact, Stanton did release a low output MM cart, which exhibited
many of the advantages of MCs. A big part of the difference (IMO) lies with
the fact that almost all MC carts do not have replacable stylii, whilst
almost all MMs do have.


I know nothing of cartridges and the last one I heard was in a Dansette,
but there are other machines similarly categorised, such as ammeters and
generators. I remember the change from MC dynamos to MM alternators, which
had much greater output for a similar size and weight. Initially they were
unreliable on motorcycles because their extra rate of work had not been
taken into account properly, mechanically and thermally.

MM meters are generally not linear, if I remember, because the magnetic
field is not constant over the travel of the coil. With a moving coil, you
can have a magnet with a hole in it, or two magnets, or a ring magnet with
a gap, with a much more constant field in the space between, in which a
small coil can move. It would be impractical to have such a magnet
assembly as the moving part.

A problem for MC dynamos is the need for commutator or slip-rings. A MC
cartridge with two coils needs at least three connections brought to a
stationary point, with attendant compromises in suspension.

I assume MM cartridges were initially high output, simple, cheap, not very
linear, and had a high mechanical impedance. MC were the opposite in all
respects.

**Not really. Generally, MC carts possess a higher mechanical impedance.

Advances in magnetic materials and their fabrication, and
smaller-scale boutique production, will have allowed carts to use more
complex and lighter magnets, and hence MM with more linearity, and MC with
larger coils perhaps? Or how else is linearity and high output achieved
simultaneously?

**AFAIK, MC carts have always used high energy magnets. Same as quality MM
carts. MC carts with larger coild tend to be high output types and, IME,
exhibit a number of annoying flaws. Notably a 'peaky' response in the 20kHz
area. This can give rise to a 'hotter' top end response.


Does one tend to have more crosstalk than the other?

**Not AFAIK.


BTW, has anyone mentioned the problem of noise in the early stages of
amplification from a low output source?

**Not really a problem with modern SS equipment. Given that the impedances
are almost always very low, then the thermal noise is also minimised.

Largely solved now, perhaps, but it was
a real problem during most of the development of cartridges.

**With valve products, certainly.


--
Trevor Wilson
www.rageaudio.com.au

Why moving coil
 

"Jim Lesurf" wrote in message
...
In article , Trevor
Wilson wrote:


Similarly, frequency response plots of moving magnets and moving coils
don't show any particular benefit to the MC, nor does stereo
separation or harmonic and intermodulation distortion. So why *are*
MC cartridges throught to be better?

**Er, not quite. The FR plots of MC carts, in some cases, CAN be shown
to be superior. The reason, of course, is blindingly simple. It's all
about inductance. The inductance of (LOW OUTPUT) MC carts is very low,
indeed. This enables them to produce a very flat, very wide (up to
around 60kHz) frequency response, with a correspondingly superior rise
time.

The problem with this is that the mechanical resonances will still exist.
:-)

**True. Some manufacturers go to extreme lengths to deal with such problems.


Also bear in mind that with a decent MM cartridge you can arrange the
loading to give quite a flat response if that is your concern. I've not
personally had any worries on that score with my own Shure V15/III...

**And one of my favourites happens to be the V15 VMR. An extremely neutral
cartridge. In fact, I did a recording of an LP from the V15 VMR onto a CD
and compared it to the CD, in uncontrolled conditions, but, apart from the
obvious surface noise, the result was bloody hard to pick.


Alas, magazines and makers now tend to avoid giving any useful data on
cartridges. Hence we usually can't now assess the level of compliance, tip
mass, etc, etc. Nor, indeed the levels of distortion.

My recollection was that MC's became 'flavour of the year' with some
subjective reviewers precisely because the ones in question did *not* have
a flat response, and they liked the changes, but then ascribed this to
'magic'... :-)

**Not necessarily, but maybe. Certainly, some MC carts, like the Linn Asak
had an appallingly bad response, which was preferred by many listeners. Same
deal with the onld Talisman S (sapphire cantilever). Ironically, the cheaper
Talisman B (Boron cantilever) was a more neutral cartidge. Not only was the
Talisman B very flat accross the audile range, but sample to sample
variations was very impressive. Best of all (IMO) was the fabulously neutral
Dynavector 17DII. Not only does/did the 17DII exhibit a very neutral
response, but it can do so over a wide temperature range (unlike almost
every other cartridge). Try your V15III in sub 10oC temps and get back to
me. The rubber suspension hardens, along with the sound. Not so the
Dynavector.



The real benefit of such a system is that LC resonance effects
are often well outside the audible range. This means that a low output
MC cart may exhibit a very flat phase response within the audio band.
This may not be the case with high output MC carts nor with some MM
carts.

For the record: Many, well designed, MM carts do not exhibit any
resonance problems without the audio band.

Indeed. Thus this isn't really a reason for arguing that MCs as a class of
object are 'better' to MMs as a class. :-)

**Perhaps. The fact that MCs can be made to operate well in the many tens of
kHz means their phase repsonse is very good in the audio range.


The reality is that there will be 'good' and 'bad' examples in each class,
and a 'good' one in either may deliver excellent results.

**Agreed. In fact, for an easy to live with, easy to tolerate (arm-wise) and
very accurate cart, it is hard to go past the (now deleted) V15 VMR.


FWIW I don't know of any MCs that can provide the same levels of tracking,
etc, of something like a Shure V15. But this may be because no-one for
years can be bothered to even consider such things in 'reviews'. sic

**Yep.


--
Trevor Wilson
www.rageaudio.com.au

Why moving coil
 

On Mon, 20 Mar 2006 16:47:58 -0000, "Keith G"
wrote:


"Bill Taylor" wrote


snippage


FWIW the best cartridge that I have owned was a Technics P205CMk4.
This tracked better than the Shures v15s that I've owned and has a
flatter FR. According to the makers spec it has a compliance of only
12c.u. but an effective tip mass of 0.11 mg, which agrees with Waltons
argument about the importance of low tip mass. I think that it is a
better cartridge than the V15-V, but my sample has got a collapsing
suspension and replacement styluses seem to be unavailable.



Also FWIW, I haven't found the V15s to be that much better at tracking than
the M75 and M95 carts I own and use - was the Technics cart you mention
above used on the linear tracker you mentioned elsewhere/earlier...???

Yes, but it wasn't the one supplied with the turntable, that was
pretty nasty. The Technics cartridge would work well on the 1210,
because the low compliance matches the cartridge/arm mass.

I have a linear tracker and even the lowly (but well worthy) cheepie AT110E
tracks like a good un on it!!