"Don Pearce" wrote in message

On Mon, 29 Nov 2004 16:24:29 +0000 (GMT), Jim Lesurf
wrote:

Yes. In fact IIRC some of our older sinewave oscillators in the
teaching labs use a small incandescent lamp to stabilise the gain of
the oscillator. (That makes me also recall that I think the old
'Sound Technology THD analyser I used to use also did something
similar.)

Slainte,

Jim

I have a home-built Wien bridge oscillator stabilized by a thermistor
- a tiny bead sealed in a glass tube. It is very good above a hundred
Hz, but its attempts to stabilize the oscillator down around 10Hz are
really pretty pathetic.

Been there did that, with the same results. I moved on to one based on a CdS
cell driven by a LED and precision rectifier/integrator.

In article , Graham Holloway
wrote:


"Pooh Bear" wrote in message
...


One of the fuses will blow before the other.

What happens to the voltage at the speaker output then? And could it
toast the speaker?

Sounds well dangerous to me.

Far more reliable is to fit 'crowbar protection' on the output to guard
against
excessive DC. Whatever else - the speaker won't see prolonged DC.
Supply
rail
fuses will blow.


Graham


If either fuse blew, the output would float to zero.

My experience was similar. I tried various kinds of 'problems and faults'
on the designs I played with and they tended to either:

1) Blow one fuse and the output floaded down to zero with no real ability
to o/p current.

2) Blow both fuses almost at the same moment.

I assume this depends a lot on the design details, but I concluded that I
could omit any d.c. crowbar, etc and just depend on the fuses. My concern
was more for the amp than the speakers, though... 8-]

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

In article , Arny Krueger
wrote:
"Jim Lesurf" wrote in message



My assumption until quite recently was that no-one would now use fuses
in the o/p of a power amp as the effect would depend upon the speaker
- a factor outwith the control of the amplifier designer. :-/

Fuses inside the feedback loop seem to be less problematical from the
standpoint of distortion.

Yes. That seems like a much wiser location that outside the loop. I did
wonder about that when working on amps. But I suspected that having a pair
of fuses on the +/- rails also meant they 'shared' the current as a result
of the duty cycles on music, but would individually protect in the event of
a 'd.c.' problem and that the I2t behaviour made this useful. No real
evidence for this, though, just a feeling that made me chose the rails for
the fuses.


Perhaps ironically, light bulbs have their own
time/resistance/current nonlinearity problems.

Indeed, In fact one of our 1st/2nd year experiments used to be to use
an incandescent lamp to do some measurements on Stephan's Law, and
this used the rise in bulb resistance to determine the temperature of
the bulb as a function of the applied power. The snag with doing this
with fuses is their tendency to 'evaporate' half-way through a
measurement unless you are careful. :-)

The trick is to do your measurements quickly.

Indeed. :-) Alas, these day the only things I do 'quickly' are forget
what I was intending to do, or run out of breath. :-)

Did the rough fuse measurements by briefly touching two wires together to
connect the test circuit to the PSU I used. this meant I could do 1-2
second 'on' tests, but I decided not to push my luck beyond approaching
double the fuse rating. To do better I'd need to arrange an 'automated'
method of the kind you mentioned, but I decided that just a rough check
would be enough to confirm that the resistance *does* rise.

Not yet read the ref you mentioned, but intend to tomorrow. Also got hold
of a copy of our physics lab experiment that uses incandescent lamps to
experiment with Stephan's Law. These give info that relates the current,
resistance, etc. Will have a read through these things when I get a chance.

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

"Jim Lesurf" wrote in message
...
Following on from some discussions in other threads I couldn't find any
existing data on the resistance-current properties of fuses, so did a
quick
measurement as a simple experiment.

The results are shown on the graph at

http://www.st-and.demon.co.uk/temp/fuseplot.gif

Note that this is fairly rought data and I only chose one 0.5A fuse for
test purposes. Other individual types and values of fuse can be expected
to
differ in detail. However the results do show the tendency for the fuse
resistance to rise with current. Only used an AVO and a cheap DVM so the
lower current values are subject to random reading errors producing a
scatter of points.

For these measurements I only applied the current for a few seconds for
each reading. To get to higher currents I would probably need to do pulsed
measurements. These would also be needed to look at the details of the
time-dependent behaviour when the current level varies.

Although I fitted a parabola for illustrative purposes, I doubt that is
the
correct function for making reliable predictions, particarly for fuses of
values that differ a lot from 0.5A. So the results are perhaps
'interesting' rather than particularly significant.


Nice graph Jim :-)

The labelling of your x y axis would be better (mathematically correct) by
using / instead of ( )

Current / mA instead of Current (mA)

Oddjob ;-)

On Tue, 30 Nov 2004 20:01:56 -0000, "Oddjob"
wrote:

Nice graph Jim :-)

The labelling of your x y axis would be better (mathematically correct) by
using / instead of ( )

Current / mA instead of Current (mA)

Oddjob ;-)


I've never bought this theory - that the axis of a graph is the other
side of an equation. As far as I am concerned the graph axis is the
current in milliamps - not one-over-milliamps (or current per milliamp
as you have it, which is dimensionless).

So it is Current (mA) - a good label
Not Current / mA - an incorrect representation of what is on the
graph.

d
Pearce Consulting
http://www.pearce.uk.com

"Don Pearce" wrote in message
...
On Tue, 30 Nov 2004 20:01:56 -0000, "Oddjob"
wrote:

Nice graph Jim :-)

The labelling of your x y axis would be better (mathematically correct) by
using / instead of ( )

Current / mA instead of Current (mA)

Oddjob ;-)


I've never bought this theory - that the axis of a graph is the other
side of an equation. As far as I am concerned the graph axis is the
current in milliamps - not one-over-milliamps (or current per milliamp
as you have it, which is dimensionless).

So it is Current (mA) - a good label
Not Current / mA - an incorrect representation of what is on the
graph.

But the axis is the description of the quantity on the graph, so that:

Current / mA = 300 therefore

Current = 300 mA this is correct :-)


Current (mA) = 300 transposes as:

Current = 300 per mA this is not correct

The above must be correct :-))

On Tue, 30 Nov 2004 20:20:37 -0000, "Oddjob"
wrote:

"Don Pearce" wrote in message
...
On Tue, 30 Nov 2004 20:01:56 -0000, "Oddjob"
wrote:

Nice graph Jim :-)

The labelling of your x y axis would be better (mathematically correct) by
using / instead of ( )

Current / mA instead of Current (mA)

Oddjob ;-)


I've never bought this theory - that the axis of a graph is the other
side of an equation. As far as I am concerned the graph axis is the
current in milliamps - not one-over-milliamps (or current per milliamp
as you have it, which is dimensionless).

So it is Current (mA) - a good label
Not Current / mA - an incorrect representation of what is on the
graph.

But the axis is the description of the quantity on the graph, so that:

Current / mA = 300 therefore

Current = 300 mA this is correct :-)


Current (mA) = 300 transposes as:

Current = 300 per mA this is not correct

The above must be correct :-))


No what I want from an axis label is a description of the units I must
attach to the value I read on the graph. If the value is 300, and the
unit is mA of current, then current (mA) is the label I want to read.
It is not a formula - it is a description.

d
Pearce Consulting
http://www.pearce.uk.com

"Don Pearce" wrote in message
...
On Tue, 30 Nov 2004 20:20:37 -0000, "Oddjob"
wrote:

"Don Pearce" wrote in message
...
On Tue, 30 Nov 2004 20:01:56 -0000, "Oddjob"
wrote:

Nice graph Jim :-)

The labelling of your x y axis would be better (mathematically correct)
by
using / instead of ( )

Current / mA instead of Current (mA)

Oddjob ;-)


I've never bought this theory - that the axis of a graph is the other
side of an equation. As far as I am concerned the graph axis is the
current in milliamps - not one-over-milliamps (or current per milliamp
as you have it, which is dimensionless).

So it is Current (mA) - a good label
Not Current / mA - an incorrect representation of what is on the
graph.

But the axis is the description of the quantity on the graph, so that:

Current / mA = 300 therefore

Current = 300 mA this is correct :-)


Current (mA) = 300 transposes as:

Current = 300 per mA this is not correct

The above must be correct :-))


No what I want from an axis label is a description of the units I must
attach to the value I read on the graph. If the value is 300, and the
unit is mA of current, then current (mA) is the label I want to read.
It is not a formula - it is a description.

Point taken, it depends on one's education I suppose, my Physical Chemistry
lecturer pointed this out to me and I always label my axis as though it were
equal to the values on the graph. I have seen both types of label used with
total success. I'm sure some of the group will agree with you and some with
me....

hope we don't get a war of the axis label :-))

On Tue, 30 Nov 2004 20:37:58 -0000, "Oddjob"
wrote:

No what I want from an axis label is a description of the units I must
attach to the value I read on the graph. If the value is 300, and the
unit is mA of current, then current (mA) is the label I want to read.
It is not a formula - it is a description.

Point taken, it depends on one's education I suppose, my Physical Chemistry
lecturer pointed this out to me and I always label my axis as though it were
equal to the values on the graph. I have seen both types of label used with
total success. I'm sure some of the group will agree with you and some with
me....

hope we don't get a war of the axis label :-))


Big endians vs. little endians?

d

Pearce Consulting
http://www.pearce.uk.com

Big endians vs. little endians?

My bell-end is big, so I'll go for big-endian.

tie


Martin