New page on Squares waves and amplifier performance
 

Jim Lesurf wrote:
In article , Trevor Wilson
wrote:

"Jim Lesurf" wrote in message
...

http://www.dynavector.com/etechnical/microstylus.html

Due to the deformation of the wall, simply having a physical contact
area of 2 microns does not gurantee that is the actual resolution.

The cartridge has an upper frequency limit of 100kHz.

How was that value measured? I can't see it on the above page.

**The usual way, presumably. A calibrated transducer is attached to
the stylus and is driven with a sweep signal.

Is that "the usual way"?

**As I best recall, yes. It's been a couple of decades since I read the
precise process, but you get the gist of it.

if so, it is news to me. I assumed
measurements would need to be done with a real test disc if you want
to assess the results with factors like stylus shape, wall
deformation, etc, taken into account.

**All very well, but the manufacturer would want to ensure that the
mechanics and electrics are as good as they can be, without entering into
the vagueries of real disks. Kinda like testing amplifiers into resistors,
rather than loudspeakers, I expect.

Without that, a claim that it
"has an upper frequency limit of 100kHz" become essentially
meaningless for the situations of actual use - i.e. playing vinyl
discs.

**Perhaps it is, but, in the case of the cited transducer, we can be secure
in the knowledge that it is as good as it gets.


I do recall that Shure used to use 45rpm test discs for some
measurements so as to help them to get test signals with higher radii
of modulation curvature. That is a little bit of a 'cheat' perhaps.
But not in the same class as basing a figure on directly driving the
stylus with a transducer. Presumably one made of harder material than
vinyl.

**Sounds like a plan.


All that said, you did state the above as a matter of fact. Where did
you get the figure from? Now you are just saying "the usual way,
presumably" which gives the impression that you don't actually know
how it was obtained.

**Like I said. I read about the system decades ago. My memory may not be
perfect in the precise details, but, I suspect, I am close to the mark.


--
Trevor Wilson
www.rageaudio.com.au

New page on Squares waves and amplifier performance
 

In article , Trevor Wilson
wrote:
Jim Lesurf wrote:
In article , Trevor Wilson
wrote:

The cartridge has an upper frequency limit of 100kHz.

How was that value measured? I can't see it on the above page.

**The usual way, presumably. A calibrated transducer is attached to
the stylus and is driven with a sweep signal.

Is that "the usual way"?

**As I best recall, yes. It's been a couple of decades since I read the
precise process, but you get the gist of it.

I can appreciate that some part of development testing would be done that
way. But it is clearly unlikely to be a relevant value to quote for any
purposes of use playing normal LPs. My understanding is that makers would
be using test records to make claims relevant to use. cf below.

if so, it is news to me. I assumed
measurements would need to be done with a real test disc if you want
to assess the results with factors like stylus shape, wall
deformation, etc, taken into account.

**All very well, but the manufacturer would want to ensure that the
mechanics and electrics are as good as they can be, without entering
into the vagueries of real disks.

Alas, this isn't simply a matter of the "vagueries of real disks". It also
includes the effects of things like choice of stylus shape, tip mass, etc.
So includes important parameters of the *stylus* which then affect intended
use after sale.

Kinda like testing amplifiers into resistors, rather than loudspeakers,
I expect.

Well I guess it is the case that by resorting to analogies you can
sometimes stretch a point out of all recognition or relevance to reality.
:-)

Without that, a claim that it
"has an upper frequency limit of 100kHz" become essentially
meaningless for the situations of actual use - i.e. playing vinyl
discs.

**Perhaps it is, but, in the case of the cited transducer, we can be
secure in the knowledge that it is as good as it gets.

Can we? Afraid that isn't obvious to me from what you've said. I'd expect
to be able to drive 100kHz though almost any cantilever system if I applied
enough force, etc. And if I didn't also say how tiny an output I was happy
to accept as showing it 'worked'... Tells me nothing about use with an LP,
though.


All that said, you did state the above as a matter of fact. Where did
you get the figure from? Now you are just saying "the usual way,
presumably" which gives the impression that you don't actually know
how it was obtained.

**Like I said. I read about the system decades ago. My memory may not be
perfect in the precise details, but, I suspect, I am close to the mark.

So just a figure you think you recall, produced by a method you aren't sure
of, either. And assuming a measurement method essentially irrelevant to
real use, and with unspecified conversion efficiency, drive level, etc.
Can't say that strikes me as being very reliable as a guide to what a
stylus system can actually do in the intended use!

TBH Trevor it does look to me like the kind of technobabble argument that
riddles audio. If you or someone else can now come up with more actual info
it might tell us more. But on the basis of what you've said I confess it
doesn't look like worth taking very seriously to me.

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
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New page on Squares waves and amplifier performance
 

"Trevor Wilson" wrote in message

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



As for vinyl, a typical minimum groove radius is 6cm.
That means a linear velocity of about 210 mm/sec. So
the wavelength of a 60kHz signal is .0035mm. What is
the sidewall contact area of even the smallest stylus?

**This one seems to do the trick:

http://www.dynavector.com/etechnical/microstylus.html

Due to the deformation of the wall, simply having a
physical contact area of 2 microns does not gurantee
that is the actual resolution.
The cartridge has an upper frequency limit of 100kHz.

How was that value measured? I can't see it on the above
page.

**The usual way, presumably. A calibrated transducer is
attached to the stylus and is driven with a sweep signal.

Ignores many aspects of the actual operational enviroment. Wavelength
effects due to the stylus radius is ignored. Deformation of the vinyl by the
mass of the stylus is ignored. It may produce interesting effect, but it is
wildly asymmetrical with actual operation.

New page on Squares waves and amplifier performance
 

"Arny Krueger"

"Trevor Wilson = Incorrigible TROLL "


It may produce interesting effect, but it is wildly asymmetrical with
actual operation.


** Arny just described the demented TW ****wit to a T.





.... Phil

New page on Squares waves and amplifier performance
 

In article , David Looser
wrote:

OK, let's take your example. With a 220k cathode resistor and 1.2mA the
cathode voltage will be 264V, seems excessively high but let that pass.
With no signal the 10n capacitor is charged to that voltage. Now we
apply a fast 0.5V negative going pulse to the grid so the negative grid
bias on the valve increases by 0.5V. Now if the gm of the AX7 is about
1.5mA/V the valve current drops by 1.5 x 0.5 = 0.75mA, so it is now 1.2
- 0.75 = 0.45mA. The valve has not cut-off, but it's current is no
longer capable of supporting 264V across the cathode resistor. The
"missing" current is, instead, supplied by the discharge of the 10n
capacitor. As that capacitor discharges the cathode voltage falls,
reducing the negative grid bias, and the valve current increases until
the cathode voltage has fallen by fractionally under 0.5V, by which
time the valve current is now capable of supporting a volt drop of
263.5V across the 220k cathode resistor. The point is, this takes
*time*, time dependant on the time-constant of the 220k resistor and the
10n load capacitor. With a current of 0.75mA and 10nF the time for an
0.5V drop is about 6.6 microseconds. In this case that is modified by
the fact that valve current increases as the voltage falls, but this is
clearly still slew-rate limiting.

IIUC a point I can perhaps make about the above is as follows.

If you had made an abrupt change of a slightly different amount - say 0.55V
instead of 0.5V - for your step-change then the initial rate of change of
the output would be different to the 0.5V example.

If so, the basic behaviour you have described is essentially an RC low pass
filter. In effect, the output response is an exponential (assuming linear
gain for the sake of simplicity) rise, scaled in value by the amplitude of
the input step-change.

If so, that is essentially a linear process. Any small extra variations in
input during the time just after the step would also vary the output,
subject to the same LPF being applied.

IIUC Ian's point may be that the above isn't the same as the situation
where you have cut off or saturated the gain device since whilst it is cut
off or saturated you get an output that does not depend on the details of
the input during that period.

'Classic' slew rate limiting presumably is taken to be signified by a
uniform rate of change of the output voltage - e.g. as you might see from a
constant current source driving the capacitance. i.e. what can occur with
the gain device saturated.

I'd also regard the cut off case as producing slew rate limiting, but in
that situation the slew rate can vary exponentially as the drive is now
just the bias resistor. So like the above it may show exponential behaviour
in response to a step at the input. The distinction being that whilst the
device is cut off you can't vary this exponential by alterations of the
input during the period of cutoff. But with the smaller example with no cut
off or saturation, you can.

Hence there are at least three situations here IIUC. Perhaps this is what
has led to some confusion and some arguments at cross-purposes.

The interesting case to me is the cutoff one. That - like the RC low pass -
gives exponential shapes. But is still a form of distortion due to the
input being unable to affect the output. So I'd regard it as slew limiting
even though the rate falls with time.

I think I now appreciate one of the points that Ian was making and I didn't
follow at first. Hence my comments above. But I'll wait and see what
reactions I get. :-)

BTW I had no idea what an 'AX7' was beyond the obvious point that it was a
small signal valve. Afraid it is decades since I did anything with audio
valves. But the above seems to me to also apply to other device types
provided you scale the values as appropriate.

That said, my interest wrt amplifiers here is cases where the required
signals tend to *not* be 'small' as they are power amps, and may be
connected to arbitrary - and sometimes awful! - loads. ;-

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

New page on Squares waves and amplifier performance
 

"Trevor Wilson" wrote

**It's a strawman. because I SPECIFICALLY referred to Red Book CD. Nothing
else. I have never, nor will I ever, argue that higher sampling rates do
not allow superior square wave performance. Any nong knows that. We're
discussing RED BOOK CD.

You may be. Jim, who started this thread, was discussing amplifiers. You
don't have the power to put limits on the discussion.


For the record: I am not arguing that a cheap Red Book CD cannot
outperform even high end vinyl in most areas. However, in ONE, VERY
SPECIFIC area (namely: high frequency square waves), SOME vinyl
reproduction systems are capable of superior performance.

So bloody what?, since no one actually listens to squarewaves.


I question the ability of even that sort of thing to consistently deliver
100kHz. One of the reasons the CD4 'quadraphonic' system failed was the
inabilty of vinyl technology to reliably deliver the subcarrier to the
decoder.

**No. It failed for a host of reasons.

I *said* "one of the reasons"!

The appalling software was one and the high cost was another.

Also the fact that there were several incompaible quadraphonic systems on
the market. One thing that the history has shown time after time is that
having incompatible rival systems around puts people off buying any of them.
Though it's a lesson that rival manufacturers don't want to learn.

The short life-span of the disks was a relatively minor issue.

That may be your opinion, it hardly qualifies as a fact. My recollection is
that the poor technical performance of CD4 was a significant reason for it's
particular lack of success.

David.

New page on Squares waves and amplifier performance
 

"David Looser" wrote in message
...
"Trevor Wilson" wrote

**It's a strawman. because I SPECIFICALLY referred to Red Book CD.
Nothing else. I have never, nor will I ever, argue that higher sampling
rates do not allow superior square wave performance. Any nong knows that.
We're discussing RED BOOK CD.

You may be. Jim, who started this thread, was discussing amplifiers. You
don't have the power to put limits on the discussion.

**I'll say it again: _I_ was SPECIFICALLY referring to Red Book CD, with
reference to the comment about sources. If I had wished to mention higher
sampling rate digital sources, I would have included them.



For the record: I am not arguing that a cheap Red Book CD cannot
outperform even high end vinyl in most areas. However, in ONE, VERY
SPECIFIC area (namely: high frequency square waves), SOME vinyl
reproduction systems are capable of superior performance.

So bloody what?, since no one actually listens to squarewaves.

**Another strawman. We are discussing square wave performance of various
devices and it's relevance in testing. Further and for the record: Square
waves can be an excellent predictor to the sonic performance of a device.



I question the ability of even that sort of thing to consistently
deliver 100kHz. One of the reasons the CD4 'quadraphonic' system failed
was the inabilty of vinyl technology to reliably deliver the subcarrier
to the decoder.

**No. It failed for a host of reasons.

I *said* "one of the reasons"!

**And I included a bunch of those reasons.


The appalling software was one and the high cost was another.

Also the fact that there were several incompaible quadraphonic systems on
the market.

**Yep.

One thing that the history has shown time after time is that
having incompatible rival systems around puts people off buying any of
them.

**Not as much as you'd think. Witness Beta vs. VHS. Sony *only* managed a
pitiful 20 years out it's system. VHS, a few years more. Having said that, I
agree that incompatible systems are an impediment to overall sales, but not
necessarily a death knell.

Though it's a lesson that rival manufacturers don't want to learn.

**It's not that simple. The word you are grasping for is 'royalties'.
Success for a specific manufacturer can spell huge profits.


The short life-span of the disks was a relatively minor issue.

That may be your opinion, it hardly qualifies as a fact. My recollection
is that the poor technical performance of CD4 was a significant reason for
it's particular lack of success.

**When released CD4 decoders cost more than the amplifiers they were
connected to (here in Australia, a typical CD4 decoder cost AUS$400.00+). SQ
and QS decoders, by comparison, cost a minute fraction of that price. The
high cost of entry into CD4 was the killer for the system. Then there were
the extra amplifiers, speakers, space to place them, etc. The sound quality
of SQ and QS was appalling, as was the software quality. The systems
deserved to fail.


--
Trevor Wilson
www.rageaudio.com.au

New page on Squares waves and amplifier performance
 

"Jim Lesurf" wrote

IIUC a point I can perhaps make about the above is as follows.

If you had made an abrupt change of a slightly different amount - say
0.55V
instead of 0.5V - for your step-change then the initial rate of change of
the output would be different to the 0.5V example.

If so, the basic behaviour you have described is essentially an RC low
pass
filter. In effect, the output response is an exponential (assuming linear
gain for the sake of simplicity) rise, scaled in value by the amplitude of
the input step-change.

If so, that is essentially a linear process. Any small extra variations in
input during the time just after the step would also vary the output,
subject to the same LPF being applied.

IIUC Ian's point may be that the above isn't the same as the situation
where you have cut off or saturated the gain device since whilst it is cut
off or saturated you get an output that does not depend on the details of
the input during that period.

'Classic' slew rate limiting presumably is taken to be signified by a
uniform rate of change of the output voltage - e.g. as you might see from
a
constant current source driving the capacitance. i.e. what can occur with
the gain device saturated.

I'd also regard the cut off case as producing slew rate limiting, but in
that situation the slew rate can vary exponentially as the drive is now
just the bias resistor. So like the above it may show exponential
behaviour
in response to a step at the input. The distinction being that whilst the
device is cut off you can't vary this exponential by alterations of the
input during the period of cutoff. But with the smaller example with no
cut
off or saturation, you can.

Hence there are at least three situations here IIUC. Perhaps this is what
has led to some confusion and some arguments at cross-purposes.

The interesting case to me is the cutoff one. That - like the RC low
pass -
gives exponential shapes. But is still a form of distortion due to the
input being unable to affect the output. So I'd regard it as slew limiting
even though the rate falls with time.

I think I now appreciate one of the points that Ian was making and I
didn't
follow at first. Hence my comments above. But I'll wait and see what
reactions I get. :-)

BTW I had no idea what an 'AX7' was beyond the obvious point that it was a
small signal valve. Afraid it is decades since I did anything with audio
valves. But the above seems to me to also apply to other device types
provided you scale the values as appropriate.

That said, my interest wrt amplifiers here is cases where the required
signals tend to *not* be 'small' as they are power amps, and may be
connected to arbitrary - and sometimes awful! - loads. ;-


Useful comments, thanks.

I lashed up a CF today based on the circuit that Ian referred to. The only
changes I made were that I used a 100k cathode resistor to keep the d.c.
cathode voltage at a reasonable level, and I used a 12AX7 as I didn't have
an "AX7" :-) (does Ian *really* expect everyone to realise that when he
says "AX7" he means a 12AX7?)

Unfortunately I didn't get much time to play with it before I had to be
elsewhere, but what was apparent in the short time I had was that the output
level rolled off very quickly with frequency, it seemed to me to do so a lot
faster than the simple 6dB/octave that one would expect from the output
impedance of the CF and the 10n load capacitor; but I'll check this point
more thoroughly when I get the chance.

If the input level was increased in an attempt to bring the output back to
the same level as it had at low frequencies the clear signs of slew-rate
limiting rapidly became apparent. As I expected fast output slew-rates in
excess of the rate allowed by the time constant of the 100k resistor and 10n
capacitor were never possible, at low input signal levels the amplitude of
the output signal was simply too low, at higher input levels the output was
slew-rate limited and the output level became independent of the input
level. When that happened the asymmetry of the slew-rate limiting was
clearly visible.

I take the point that until the output signal amplitude becomes slew-rate
limited the CF behaves in a linear manner. It had seemed to me that Ian was
suggesting that, at high frequencies but low signal levels, the output could
slew negative faster than the rate determined by the cathode resistor and
load capacitor. It doesn't because the HF roll-off always keeps the output
signal level below the amplitude which would make that happen.

David.

New page on Squares waves and amplifier performance
 

In article , David Looser
wrote:
"Jim Lesurf" wrote
[snip]

Useful comments, thanks.

I lashed up a CF today based on the circuit that Ian referred to. The
only changes I made were that I used a 100k cathode resistor to keep
the d.c. cathode voltage at a reasonable level, and I used a 12AX7 as I
didn't have an "AX7" :-) (does Ian *really* expect everyone to realise
that when he says "AX7" he means a 12AX7?)

I've now found the basic characteristics for 12AX7 listed in the back of my
ancient (1966) copy of "Basic electronics for scientists" by Brophy that
was the textbook when I took my 1st year course back in the year
mumble-mumble! :-) So far as I recall, the actual course ignored small
signal valves entirely as things had moved on.

Amusing aspect of this is that I got this year's 'Electronics' scripts to
mark last night, and I'll be spending today and tomorrow marking them.[1]
So at the same time as I'm looking up 12AX7s from when I was given such a
course I am marking the papers of my students now I am a quasi-retired
'Honorary Reader'. The more things change... ;-

Slainte,

Jim

[1] Oh, joy of joys! :-/ I hate setting and marking exams.

--
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