On 21/07/2013 09:46, Don Pearce wrote:
On Sun, 21 Jul 2013 09:16:41 +0100, Eiron
wrote:


snip


I think you are missing the point. The internal pots are adjusted in the
factory
to give 33 1/3, 45 etc. rpm, then the external one is for the user to tweak
if he wants to play his records too fast or slow, or to match the mains
frequency more accurately.

Of course a quartz oscillator would be better - in fact I had one in 1976
driving an LED as well as the mains neon lamp to more accurately check
my turntable speed. But that would not give you the speed adjustment.

No, this isn't how these things work - that is a naive view. It is
what marketing people do - try and sell a bug as a feature.

I'd agree that it's a bit odd for a domestic user to speed up or slow
down music. But there are other variables, mostly related to wear (but
also marketing!), that might require speed adjustment.

--
Cheers, Rob

"RJH"

I'd agree that it's a bit odd for a domestic user to speed up or slow down
music. But there are other variables, mostly related to wear (but also
marketing!), that might require speed adjustment.


** Thorens knew what they were doing with the TD125.

A very high quality, belt drive turntable with 33.3, 45 & 78 rpm available
at the flick of a switch was highly marketable.

The simplest way to do it was with an electronic, variable frequency sine
wave drive and a special 24V motor. Fitting fine speed adjustment was
essential - so why not give it a fairly wide range? Someone will like it.

It was NOT done to allow for errors in the oscillator frequency.

In the 1980s, I saw a few TD125s and all the speeds were exact with the trim
wheel set very near the middle.

Pearce has never seen one, is just not listening to facts and does not give
a hoot about reality.

The guy is totally up himself and completely nuts.

Been that way for decades too.



.... Phil

When I design indoor equipment for my main customer I have to meet
spec over 0 to 45C. I was being kind with just a 20C range. This is
about absolute accuracy as well as intra-track drift. What can you get
with a Wien, 1% if you go for the best components? Well, that will be
half a Hz right there.

The right way to do this job is to stop messing and put in a crystal
oscillator. Hell, these days it is probably as cheap to use an off-air
time standard. Modules for those cost a few pence in bulk. That is
going to be cheaper than a Wien bridge that almost certainly needs
select-on-test components to get close enough to the right frequency.

Except thats off air for maintenance more times than hot dinners in a
week;!...


d

In the meantime the grid speed is;?..

http://www.gridwatch.templar.co.uk/
--
Tony Sayer

On Sun, 21 Jul 2013 15:46:50 +0100, tony sayer
wrote:


When I design indoor equipment for my main customer I have to meet
spec over 0 to 45C. I was being kind with just a 20C range. This is
about absolute accuracy as well as intra-track drift. What can you get
with a Wien, 1% if you go for the best components? Well, that will be
half a Hz right there.

The right way to do this job is to stop messing and put in a crystal
oscillator. Hell, these days it is probably as cheap to use an off-air
time standard. Modules for those cost a few pence in bulk. That is
going to be cheaper than a Wien bridge that almost certainly needs
select-on-test components to get close enough to the right frequency.

Except thats off air for maintenance more times than hot dinners in a
week;!...


d

In the meantime the grid speed is;?..

http://www.gridwatch.templar.co.uk/

The grid speed is, as ever, just fine. Not surprising really, because
there are so many power stations that must match their frequency and
phase to the finest of degrees in order to be able to switch on and
off line as needed. They have to be really tight whether on or off
line.

d

On Sun, 21 Jul 2013 19:06:52 +1000, "Phil Allison"
wrote:


"Eiron"

I think you are missing the point. The internal pots are adjusted in the
factory to give 33 1/3, 45 etc. rpm, then the external one is for the user
to tweak if he wants to play his records too fast or slow, or to match the
mains
frequency more accurately.


** Pearce is just not listening and does not give a hoot about realities.

The guy is totally up himself and completely nuts.


Of course a quartz oscillator would be better - in fact I had one in 1976
driving an LED as well as the mains neon lamp to more accurately check
my turntable speed.


** That is highly obsessive behaviour, just like JBG .

I think that's a case of the pot calling the kettle... no wait, bone
china teacup black.

My "obsession", as you call it, with the deficiencies of using the
mains as a speed calibration reference lies with the fact that it does
suffer short term drift throughout the day.

As a reference capable of allowing electric wall clocks to stay
within a minute of the correct time throughout the day, 365 days a
year decade by decade, it's an excellent one. It just doesn't cut it
as a turntable speed reference and a quartz crystal driven one is the
only cost effective alternative worth considering in a deck of this
calibre.

I can't speak for everyone but I prefer my calibration references to
have a stability or accuracy that's at least an order of magnitude
better than whatever it is I'm trying to calibrate rather than one
that is an order or two worse.


But that would not give you the speed adjustment.

** I have built several sine wave, variable frequency drives for TTs, the
first in about 1977. My last design was published in " Electronics
Australia" in July 1998.

All of them allowed belt drive turntables like the " Linn Sondek" to be
simply switched between 33.3 rpm and 45 rpm and fine adjusted over a small
range to compensate for built in speed errors and varying belt condition.

Early ones used a Wien bridge, self oscillating 15W amplifier driving a
valve output transformer in reverse to generate 240VAC at 50Hz and 270VAC at
67.5 Hz.

The published design used a driven amplifier ( TDA1514A ) and separate RC
oscillator with readily available, 30VA toroidal mains transformers for both
DC power supply and output.

So, you do have some credentials in regard to turntable design after
all.

I've been watching your previous exchanges with Pierce with some
interest where you have, in essence, argued against his attacks on my
previous post that you had rubbished without offering any clue as to
how you'd come to that conclusion.

It seems to me that you must have been in a rather angry mood when
you speed read my post and fired off that reply since you've been
restating pretty well all of the salient points I made in that post.

Regarding the speed wheel adjustment range, circa a 10% total range
(+/-5% of nominal), there isn't only the issue of allowing the end
user to fine tune for component tolerances in the Wein bridge
oscillator and variations in the belt drive (manufacturing tolerances,
environmental and aging effects) but also to cater for cutting speed
variations of older material, specifically for the early 78s and to a
lesser extent 45s and 33 1/3 rpm LPs.

There's a very good article on the subject he

http://www.charm.rhul.ac.uk/history/p20_4_3.html

The +/-5% adjustment wasn't purely a marketing ploy, there is a
legitimate use for those who wanted to replay their vintage 78s at the
original speeds they were cut at[1]. It's true that it's a feature
most users would regard as extraneous to their needs and would be
quite happy if the design bypassed the need to manually recalibrate
the speed to a reference source (preferably one not reliant on the
vagaries of the mains supply).

Direct drive decks can also offer speed adjustment such as the famous
Technics SL-1200 with its pitch slider control (+/-8% range) so it's a
feature deemed worthy enough to include on a deck that has intrinsic
speed accuracy built in by design.

There are pros and cons to both approaches, BD or DD (Idler wheel
drive, imho, is not really a contender), and, as you said previously,
"Thorens knew what they were doing with the TD125", a statement I can
agree with (settiing to one side the issue of relying on the mains
frequency as a calibration reference).

[1] These days, such pitch controls are, to a large extent, rendered
superfluous by digital processing techniques that can be applied to
digitally captured recordings of such material (who would care to
subject their precious antiques to further wear and tear than is
absolutely necessary - those disks are a lot less durable than modern
vynil pressings).
--
Regards, J B Good

"Johny B Good" wrote in message
...
On Sat, 20 Jul 2013 12:18:46 +1000, "Phil Allison"
wrote:

Most LPs would have been *made* using machines that relied on the supply
frequency for speed.

I rather think the kit was a lot more sophisticated in that regard,
possibly using servo braking speed control in the very early days
before transistors allowed for more sophisticated servo speed
controlled motors to be used. You assume too much, methinks.

Think again.

Unlike you, Phil and I worked with the turntables and cutting lathes of the
day.

"Don Pearce" wrote in message
...
On Sat, 20 Jul 2013 10:32:19 +0100, Eiron

wrote:

"An order or two identical" was a humorous remark.
And I hadn't remembered that the TD125 used a synchronous motor driven
from a Wein-bridge oscillator rather than the mains like the OP's deck.

But how stable do you think your oscillator is?
Let's have some facts. Set the speed at the start of an LP (with a cold
turntable)
and let us know how fast your strobe dots are drifting by the end.

A Wien bridge? Seriously? Then it isn't even remotely stable. That's
just silly.

No, its what the TD125 used. Both Thorens (TD 125) and Revox (A77) used a
locally generated AC signal for motor drive that was not crystal-controlled.
I suspect that having a product that could be sold on the world market with
one model was the goal. Also the AC power frequency in some parts of Europe
was not comparable to what we had in the US, based on living in Bavaria for
a year in 1969. I saw AC power that was so heavily modulated by an area
that received power from two out-of-synch generating stations that the
incadescent room lighting literally flashed. If you wanted to read after
dark, you found some flourescent fixtures to sit by.

"Don Pearce" wrote in message
...
On Sat, 20 Jul 2013 17:55:52 +0100, Johny B Good
wrote:

On Sat, 20 Jul 2013 10:16:29 GMT, (Don Pearce) wrote:

====snip====


A Wien bridge? Seriously? Then it isn't even remotely stable. That's
just silly.

It depends on what level of accuracy is required for the job. Aside
from an initial warm up period of some 5 to 10 minutes, it's more than
accurate enough for the job considering the residual mechanical causes
for speed variation in the system (and those of the reference source).

Let's put it this way, it's more than accurate enough to show up the
variations in mains frequency in the short term (half hour segments).

Right, but that wasn't the standard of the day which was audible pitch.

Whilst such an oscillator can't compete against a quartz crystal
oscillator reference for stability, it's main charm is that it can be
readily trimmed to speed by the end user. It's just a pity that the
chosen reference source is a mains driven neon strobe lamp.

In the US a neon strobe is still a pretty good standard, depending on the
performance levels you are interested in.

If the reference against which it is measured is the AC mains, I can't
see a good reason for not using the AC mains to set the speed too.

Two words: World market.

The ear's sensitivity to long term speed errors is on the order of 0.25-0.5%
.. From an electronics standpoint, that isn't a very high bar.

"Don Pearce" wrote in message
...

The 10% variation tells me that 10% was about as close as they could
get with the component tolerances available to them.

The actual parts were better than that. More likely they were trying to
make the 78 rpm setting usable with legacy recordings that might be 5-10%
off.

They had to put
in a trimmer pot for the user to adjust. Rather worse than I had
imagined, I suppose there weren't any cheap 1% caps around.

Simply not true. On the worst day of their lives people were buying large
lots of 5% parts and picking the middle 1%.

Get the
speed right, and there is no need for that variation. Three speeds -
you really think that is a problem with a crystal or off-air
stabilized oscillator? I'm paying 2.3C right now for an Analog Devices
synth chip that will do this job.

Believe it or not, the cost of parts was different in 1969 than they are
today.

On Tue, 23 Jul 2013 07:54:51 -0400, "Arny Krueger"
wrote:


"Don Pearce" wrote in message
...
On Sat, 20 Jul 2013 10:32:19 +0100, Eiron

wrote:

"An order or two identical" was a humorous remark.
And I hadn't remembered that the TD125 used a synchronous motor driven
from a Wein-bridge oscillator rather than the mains like the OP's deck.

But how stable do you think your oscillator is?
Let's have some facts. Set the speed at the start of an LP (with a cold
turntable)
and let us know how fast your strobe dots are drifting by the end.

A Wien bridge? Seriously? Then it isn't even remotely stable. That's
just silly.

No, its what the TD125 used. Both Thorens (TD 125) and Revox (A77) used a
locally generated AC signal for motor drive that was not crystal-controlled.
I suspect that having a product that could be sold on the world market with
one model was the goal.

That was just a handy side effect that would undoubtedly have counted
as plus factor in the design choice (no need to move the belt between
a 50 or 60 Hz pulley - just a suitable 240v 50Hz mains transformer
with with 100/117/120 voltage taps or WHY to cater for most of the
worldwide national domestic mains voltage / frequency standards).

Also the AC power frequency in some parts of Europe
was not comparable to what we had in the US, based on living in Bavaria for
a year in 1969. I saw AC power that was so heavily modulated by an area
that received power from two out-of-synch generating stations that the
incadescent room lighting literally flashed. If you wanted to read after
dark, you found some flourescent fixtures to sit by.


Think again! :-)

The AC power frequency would have been a nominal 50Hz. Even if you
were in a region that was "Off Grid" and reliant upon its own locally
generated islanded power source, your supposition about out-of-synch
generators simply doesn't hold water. The symptoms you witnessed would
have been due to some other problem with the supply.

Furthermore, conventionally ballasted fluorescent light fittings
would exagerate the effect you saw with the incandescent lamps.
Perhaps you meant it was the other way around or else you were talking
about fluorescent lamps fed from a regulated independent high
frequency supply (a system commonly to be found in large offices and
retail stores today).
--
Regards, J B Good