On Sun, 16 Dec 2012 11:49:44 +0000,
(D.M. Procida) wrote:

Johny B Good wrote:

Since the drag from the stylus is pretty closely aligned to the
offset angle the drag force is trying to pull the stylus towards the
spindle and is only restrained from doing so by the resultant increase
of force on the inner groove wall. The best analogy I can think of is
that of keeping a horse drawn barge away from the bank the towpath is
on by judicious use of the tiller to compensate the shorward component
in the towing force vector provided by the horse.

I'm still struggling with all this.

Still:

* the horse (tonearm pivot) stands firmly stationary by the side of the
canal

* the horse is connected to the barge (stylus) not with a rope, but a
rigid bar, that means horse and barge must always face the same
direction

* the rapidly-flowing canal (the vinyl groove) tugs at the barge as it
goes by

* because the horse is offset from the direction of the water's tug, the
whole assembly of horse, bar and barge wants to rotate around the horse,
towards the bank

I think I understand that, but it must be more complicated.

It isn't. That analogy is just simply an alternative example of the
classic tone arm case.


For example, when the needle is in the middle of the side (assuming
that's where the tonearm is parallel to the tangent of the groove) that
would be like having the horse directly upstream of the barge, not to
one side.

It must be nearly forty years ago since I last saw any magazine
articles on the subject. I think the figure of three points came from
the fact that the _two_ points of exact alignment traversed by the
stylus creates three sections along the angular error curve where two
of them produce a small positive excursion from the ideal and one
other where the error is in the negative direction.

Without the overhang and offset, you could only get a perfect
tangential contact at the mid point with the error becoming larger the
further away that the stylus is from this single point of perfect
alignment. In fact the rate at which the error grows as the stylus
scans beyond this point increases (the error curve for the preceding
points simply mirrors this).

Very approximately, the two points of perfect alignment would occur
somewhere around the 25 and 75 percent mark. Off the top of my head, I
reckon a straight tone arm without overhang and offset would triple
the error angle variation range.

And, either side of that middle, the force on the tonearm must always be
towards the middle of the side, suggesting you'd need positive bias
adjustment for the first half and negative bias for the second.

That would only be true for a straight arm without overhang and
offset. However, in the case of the classic tone arm configuration the
side thrust compensation will always remain in the same direction. The
effect of angular variations from the tangent will simply cause a
modest variation[1] in the sidethrust force.

[1] Modest compared to those due to variations in the amplitude and
wavelength of the recorded signal. A given frequency of a test tone
will produce a much shorter wavelength near the end of the groove
compared to the start of the groove. This proves to be rather
detrimental to any piece of music that builds up to a loud finale
which is typical of a lot of musical works (including a lot of rock
and pop performances).

Although it is nominally the velocity of the stylus tip that
corresponds to the waveform voltage (maximum speed at the zero
deviation point corresponding to the voltage peak with maximum
excursion equating to a zero crossing), the use of equalisation, as
per the RIAA curve, means we see equal amplitudes in the groove wall
modulation for the same voltage level output from the cartridge. At
the shorter wavelengths near the end of the groove this produces a
steeper curve which not only increases drag but also causes tracing
distortion[2] to become more pronounced.

[2] Tracing distortion arises because the cutter head creates the
modulation from a line contact with the groove wall which the typical
stylus cannot recreate due to the fact the contact involves a curved
surface on the stylus tip which leads to the point of contact
advancing and retarding as the groove wall angle changes according to
the shape of the modulation impressed into the groove.

Modifying the basic round tipped conical shape of the stylus to
include an additional curve or two (eliptical and Shibata types)
significantly reduces this type of distortion. Also, I believe that
some records were experimentally cut with a pre-distorted signal
designed to counter tracing distortion during playback.

After googling around for more info on the subject of tracing
distortion, it seems the idea of using pre-distortion on the cutter
amp feed fell out of favour rather swiftly, in part on account it had
been calibrated for a conical stylus tip profile and so could
introduce more distortion when the eliptical and Shibata stylus
profiles were used. This was at a time when virtually no quality
cartridge maker would cheapen their product with a conical stylus tip.

This link to a forum thread titled "Is Dynagroove Really Bad?"
(Dynagroove being RCA's system to reduce tracing distortion for
conical stylii) might be of interest.

http://www.audiokarma.org/forums/archive/index.php/t-277978.html

--
Regards, J B Good

On Sun, 16 Dec 2012 14:35:47 +0000 (GMT), Jim Lesurf
wrote:

On 16 Dec, wrote:

I suspect a diagram is needed to clarify this. I'll have a look on Mike
Fremer's site and Keith Howard's. They may something as they've done
articles, etc, on these topics. If I can't find a diagram I'll generate
one when I get a chance. They appear in various books on audio as well.

Can't find what I had in mind, so I've mashed something from John Crabbe's
book. I'm certain he'd be happy for me to do so if he were still with us.
You can find it at

http://jcgl.orpheusweb.co.uk/temp/geometry.png

I've added a blue blob to emphasis where the stylus tip will be contacting
the LP. This is the usual arrangement. And I've added a red blob for where
it **would** be **if** there were no overhang or end-angle on the arm.
No-one does this with a conventional arm so far as I know as it gives other
serious problems.

In both locations the cartridge would be aligned parallel to the
circumference. But the overhang involved in placing the stylus at the blue
point means that the drag force does *not* go along a line parallel to the
arm back to the pivot. You can see how it creates a torque on the arm and
tries to move the stylus toward the center of the LP rotation.

You can find out more at

http://www.stereophile.com/reference...try/index.html

http://www.hi-fiworld.co.uk/vinyl-lp...-geometry.html

http://www7a.biglobe.ne.jp/~yosh/armdata.htm

Embarrased that HFW have a relevant page, but HFN don't that I can find!
However the Stereophile page is good for details, and written by Keith
Howard who has done a lot of work on this. His article also provides two
protactor designs you can use.


Thanks for providing those links. Trying to get useful, fact laden
articles with google is rather like trying to squeeze blood out of a
stone.
--
Regards, J B Good

On Sun, 16 Dec 2012 09:57:51 +0000 (GMT), Jim Lesurf
wrote:

In article , Johny B Good
wrote:
On Fri, 14 Dec 2012 13:54:30 +0000,
(D.M. Procida) wrote:

RJH wrote:


=========huge snip=============

When I was doing this, some 30 odd years ago, I was staggered by how
much of the highest level of 300Hz test tone energy was reaching the
pivot of the SME3009 (detected by the vibration that could be detected
by a finger tip pressed to the junction of the arm's pivot bearing
mounting and the baseboard.

I have long felt that the growth in anxiety about 'tone arm resonances'
stemmed from the MC carts that grew popular having much lower compliance
and tip mass than the Shure/Empire/etc MMs. Thus injecting much higher
vibrational force into the arm.


I feel that I should add that I was (still am) using an ADC XLM
cartridge with this setup and that was classed as being a high
compliance cartridge!

And, to further clarify, This was built onto a Thorens TD125 Mk I
motorboard that I mounted into a chinese copy of the plinth as
pictured in the HiFi Yearbook ('75 istr), which I made made out of
10mm thick perspex sheet glued together instead of the wood used in
the original.

The very idea of sending the cartridge output directly to phono
sockets on a seperate amplifier via a yard or so of screened cable
didn't appeal one iota to me. After all, you don't do this to the
replay head of a tape deck.

I built an RIAA pre-amp (along with a headphone driver) directly into
the record deck so that the cartridge signals wouldn't have to face
the unknown conditions of the outside world. The signal connection is
at line out levels which eliminates the usual problems with hum loops
and noise pickup that tends to plague the more traditional setup.
--
Regards, J B Good

On Sun, 16 Dec 2012 14:54:42 +0000, Eiron
wrote:

On 16/12/2012 09:57, Jim Lesurf wrote:

I have long felt that the growth in anxiety about 'tone arm resonances'
stemmed from the MC carts that grew popular having much lower compliance
and tip mass than the Shure/Empire/etc MMs. Thus injecting much higher
vibrational force into the arm.

And according to Trevor, those groove-straighteners would lift SME arms
off their bearings during the loud passages.

Wow! Now, that _is_ impressively low compliance! The SME design
deliberately uses a large counter balance mass very close in to the
knife edge bearing to explicitly prevent this behaviour.


Now, why is my arm S-shaped instead of straight with an angled headshell?

I suspect because it looked 'stylish' just as the J shape of the
SME3009 arm does. If the arm has a detachable headshell or the design
started out that way and, like the SME, no longer does, then it's most
likely a design choice to maximize stiffness of the arm and head
assembly.
--
Regards, J B Good

On Sun, 16 Dec 2012 15:21:18 +0000 (GMT), Jim Lesurf
wrote:

In article , Eiron
wrote:

Now, why is my arm S-shaped instead of straight with an angled headshell?

I suspect the makers simply decided the 'S' shape was easy enough to make
and looked good. FWIW I'm happy enough with the arm of that shape on my
Technics DD. But I'd also have loved to have an old SME fitted as the
'standard' companion for a V15.

Alas, my ideal dream combination of the Technics SP10 + SME + V15 was
stolen at an audio show. Not encountered one since. But what I have suits
me OK.

That said, drifting way from topic... my main concern of late has been
transferring old reel tapes rather than LPs.


Aha! so I'm not the only one trying to optimise this process. I've
googled the subject of a software dolby B decoder (plus tape
distortion canceller) but only found very few mentions of this sort of
request and all with negative replies.

However, a mere Dolby B decoding DSP plugin doesn't really cut it.
What I'm after is a self calibrating intelligent DSP that will adapt
to the actual distortions introduced by the magnetic
recording/playback process itself as well as provide a dolby B decode
function that precisely matches the inverse of the encoding actually
used.

My idea being that a blank part of the tape can be used to record the
test signals from such a utility during the calibration phase with the
record EQ and sensitivity and bias switch settings adjusted to match
those used during the original recording. I don't mind having to do
two or even three passes (with and without dolby processing enabled)
in order to 'train' the DSP software if it means that _all_ errors are
virtually cancelled out.

Realistically, I don't think such DSP software exists and the number
of potential customers for such an application is pitifully too low to
attract commercial interest. Having said that, there might be some way
we could throw this out as a challenge to a computer sciences dept in
a university. Better yet, plant the idea that this could be the basis
of an inter university competition within the halls of academia
(preferably, as an open source project). ;-)

--
Regards, J B Good

In article , Johny B Good
wrote:
On Sun, 16 Dec 2012 14:35:47 +0000 (GMT), Jim Lesurf
wrote:

Can't find what I had in mind, so I've mashed something from John
Crabbe's book. I'm certain he'd be happy for me to do so if he were
still with us. You can find it at

http://jcgl.orpheusweb.co.uk/temp/geometry.png

http://www.stereophile.com/reference...try/index.html

http://www.hi-fiworld.co.uk/vinyl-lp...-geometry.html

http://www7a.biglobe.ne.jp/~yosh/armdata.htm


Thanks for providing those links. Trying to get useful, fact laden
articles with google is rather like trying to squeeze blood out of a
stone.

FWIW I gave up on google ages ago. I now tend to use duckduckgo to avoid
google's interest in harvesting data about me to 'monetise' via junk.
Baffles me that I keep hearing meeja types on the BBC moaning that although
they can biycott Starbucks there is "no alternative to google".

Maybe it is time for a "how it works" article on LP replay on audiomisc. Or
even in HFN. Wasn't until this thread that I realised the lack of recent
info on what I'd regarded as basic points like the cause of the radial
force for normal LP replay. Seems to have been forgotten with all the more
recent fuss about vertical and rake angles, etc.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article , Johny B Good
wrote:
On Sun, 16 Dec 2012 09:57:51 +0000 (GMT), Jim Lesurf
wrote:

The very idea of sending the cartridge output directly to phono sockets
on a seperate amplifier via a yard or so of screened cable didn't appeal
one iota to me. After all, you don't do this to the replay head of a
tape deck.

Actually, back in the 1950s/60s people did often buy the tape 'deck' with
no electronics and seperately buy or DIY the electronics, using a
reasonably length of coax between the head and the preamp! People like
Armstrong used to sell PABO units (playback amp and bias oscillator) units
for this to punters.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article , Johny B Good
wrote:
On Sun, 16 Dec 2012 15:21:18 +0000 (GMT), Jim Lesurf
wrote:


That said, drifting way from topic... my main concern of late has been
transferring old reel tapes rather than LPs.


Aha! so I'm not the only one trying to optimise this process. I've
googled the subject of a software dolby B decoder (plus tape distortion
canceller) but only found very few mentions of this sort of request and
all with negative replies.

My reel tapes are all without Dolby, so it isn't a concern for them. I only
have to worry about replay being 'correct'. e.g. using the original deck
with eq, level, azimuth, etc, matching what it recorded.

However many of my cassettes are Dolby B. cf below.

However, a mere Dolby B decoding DSP plugin doesn't really cut it. What
I'm after is a self calibrating intelligent DSP that will adapt to the
actual distortions introduced by the magnetic recording/playback process
itself as well as provide a dolby B decode function that precisely
matches the inverse of the encoding actually used.

You might be able to use the mcompand feature of sox, or devise something
similar. There may be something dedicated, though. I was pleasantly
surprised to find that recent releases of ffmpeg now have an HDCD decoding
switch. Presumably the developers spotted as I did that the patents are now
lapsing.


Personally, though, I just use a decent cassette machine for my old
cassettes. (Nakamichi) Then digitise the output from that. Old cassette
recorders seem more available these days than old reel recorders.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

On Mon, 17 Dec 2012 08:48:47 +0000 (GMT), Jim Lesurf
wrote:

In article , Johny B Good
wrote:
On Sun, 16 Dec 2012 14:35:47 +0000 (GMT), Jim Lesurf
wrote:

Can't find what I had in mind, so I've mashed something from John
Crabbe's book. I'm certain he'd be happy for me to do so if he were
still with us. You can find it at

http://jcgl.orpheusweb.co.uk/temp/geometry.png

http://www.stereophile.com/reference...try/index.html

http://www.hi-fiworld.co.uk/vinyl-lp...-geometry.html

http://www7a.biglobe.ne.jp/~yosh/armdata.htm


Thanks for providing those links. Trying to get useful, fact laden
articles with google is rather like trying to squeeze blood out of a
stone.

FWIW I gave up on google ages ago. I now tend to use duckduckgo to avoid
google's interest in harvesting data about me to 'monetise' via junk.
Baffles me that I keep hearing meeja types on the BBC moaning that although
they can biycott Starbucks there is "no alternative to google".

Maybe it is time for a "how it works" article on LP replay on audiomisc. Or
even in HFN. Wasn't until this thread that I realised the lack of recent
info on what I'd regarded as basic points like the cause of the radial
force for normal LP replay. Seems to have been forgotten with all the more
recent fuss about vertical and rake angles, etc.

Slainte,

Jim

Jim, you can keep using Google. Just make sure you have Ghostery
installed. It traps any spy scripts that try to send info from your
machine.

d

In article , Don Pearce
wrote:
On Mon, 17 Dec 2012 08:48:47 +0000 (GMT), Jim Lesurf
wrote:
[snip]

Jim, you can keep using Google. Just make sure you have Ghostery
installed. It traps any spy scripts that try to send info from your
machine.

I prefer to avoid google for now. I am wary of quasi-monopolies or
companies that seek to collect and exploit data or seem to not pay much
tax. I would prefer to support their being *many* genuinely competing
search engines, mapping systems, etc, etc. Put not your faith in princes...
except possibly for the tinned salmon. :-)

That said, I do sometimes still use google. But only either on a system
with no scripting, flash, etc. Or one with none of my personal data, etc.
And in both cases I regularly clean out the systems. So my main concern
isn't anxiety about them learning about me. It is the dislike of
companies becoming effective monopolies - if only by assumption -
and feeling they may then treat the rest of us in whatever ways they may
fancy that they can get away with.


Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html