In article , Arny Krueger
wrote:

[snip]

There's an old JAES paper by Greiner of the University of Wisconson that
charted nonlinear distoriton due to fuse thermal effects.

Ah! Thanks for that info. I'll do a search on the CDROM set of papers I
have and see if I can unearth a copy. May save me wondering or having to
re-do measurements that have already been done! I had the feeling that
surely someone *had* done this, but could not recall ever seeing it.

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. :-/

Speaker voice coils do this as well.

Although I assume (?) that in the short and medium term the thermal time
constants will be longer due to the mass involved. That said, I suppose the
coils dissipate lots more power than the fuse! :-)
[snip]

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. :-)

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

In article , Arny Krueger
wrote:

[snip]

There's an old JAES paper by Greiner of the University of Wisconson
that charted nonlinear distoriton due to fuse thermal effects.

Ah! Thanks for that info. I'll do a search on the CDROM set of papers
I have and see if I can unearth a copy. May save me wondering or
having to re-do measurements that have already been done! I had the
feeling that surely someone *had* done this, but could not recall
ever seeing it.

Glad that you have the CDs. I have them online here, but I'm getting tired
of searching it.

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.

The real problem is with fuses that are reasonable for protecting speakers,
as opposed to fuses that are appropriate for protecting the amplifier.

Speaker voice coils do this as well.

Although I assume (?) that in the short and medium term the thermal
time constants will be longer due to the mass involved. That said, I
suppose the coils dissipate lots more power than the fuse! :-)
[snip]

That's it. Part of the problem is that fuses are often made up of materials
that are intentionally chosen to be nonlinear, to assist the process of
protection.

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.

These days I do most of my measurements by playing a test suite with one or
two channel of a sound card, and making the measurements with the record
side of said card, or something like that.

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

In article , Arny Krueger
wrote:

[snip]

There's an old JAES paper by Greiner of the University of Wisconson that
charted nonlinear distoriton due to fuse thermal effects.

Thanks again for pointing this out. I've now had a chance to read it. Two
things strike me as remarkable:

1) That he mention fuse effects in just a couple of pages at the end of a
paper largely on other things like cables. Yet I'd say that what he reports
there almost as a throw-away aside is *much* more interesting than the main
topic. THD values up to a percent or more in quite plausible example cases!

2) That no-one else seems to have much of an issue of this.

OK, I assume that most designer's reactions would be like mine and just
avoid using fuses where the distortion would show up. But only once they
realise this is a problem. Yet it seems to pass almost without comment in
many textbooks, and in magazines, and I can't recall any systematic and
widely known data on this. Given how some people beat their brains out over
tiny effects, seems weird this isn't better known!

I've now put onto my "must do one day" list to do some more measurements
and try and work out a basic model of the effect. Some of the papers I've
mentioned will help with that if I ever get around to it. I'll also do a
search of Electronics World and see if they've ever covered this.

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

In article , Arny Krueger
wrote:

[snip]

There's an old JAES paper by Greiner of the University of Wisconson
that charted nonlinear distortion due to fuse thermal effects.

Thanks again for pointing this out. I've now had a chance to read it.
Two things strike me as remarkable:

1) That he mention fuse effects in just a couple of pages at the end
of a paper largely on other things like cables. Yet I'd say that what
he reports there almost as a throw-away aside is *much* more
interesting than the main topic. THD values up to a percent or more
in quite plausible example cases!

2) That no-one else seems to have much of an issue of this.

OK, I assume that most designer's reactions would be like mine and
just avoid using fuses where the distortion would show up

Greiner's article suggests that separate fuses for woofers and tweeters
would do a lot of good.

. But only
once they realise this is a problem. Yet it seems to pass almost
without comment in many textbooks, and in magazines, and I can't
recall any systematic and widely known data on this. Given how some
people beat their brains out over tiny effects, seems weird this
isn't better known!

Well, we all *know* that speakers are very dirty, and some of us know that
rooms can be at least as dirty.

However, realizing the audible implications of the fact that audio
reproduction involves a chain that is only as good as the weakest link,
seems to be less common.

Many people seem to think that speaker distortion is a separate breed that
always flies under our auditory radar. In fact nonlinear distortion of a
given magnitude and order is audibly what it is, no matter what the source.

I've now put onto my "must do one day" list to do some more
measurements and try and work out a basic model of the effect. Some
of the papers I've mentioned will help with that if I ever get around
to it. I'll also do a search of Electronics World and see if they've
ever covered this.

The conventions for use of protective devices seem to be separate protection
devices in each driver's line or even more common, just the tweeter line.
This probably makes most of the problems Greiner finds vanish below
perceptibility.

"Don Pearce" wrote in message
...
On Mon, 29 Nov 2004 13:55:30 +0000 (GMT), Jim Lesurf
wrote:

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.

Slainte,

Jim

Jim, for the purposes of seeing how a fuse might affect linearity,
some sort of frequency response of resistance change vs frequency
would be needed. If a fuse has a very low thermal inertia, it might
change its resistance significantly during a cycle, particularly at
low frequencies. This would cause distortion if it was in series with
a speaker. At higher frequencies which it could not track, it would
simply cause amplitude compression - I've used a light bulb for this
in the past.

d

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


When I worked for ILP Electronics many years ago, they suggested the use of
a fuse in series with the loudspeaker as protection against a DC fault. I
found that distortion was significant due to the modulation of the fuse
resistance by low frequencies. I have no records of the tests I did.
However, I did suggest an alternative, and that was to put a fuse in each (+
and -) supply rails. It was possible to use fuses of a lower rating than
that in the output line because of the lower (half cycles) duty.

Graham Holloway
WPS Electronics.

"Graham Holloway" wrote
Jim, for the purposes of seeing how a fuse might affect linearity,
some sort of frequency response of resistance change vs frequency
would be needed. If a fuse has a very low thermal inertia, it might
change its resistance significantly during a cycle, particularly at
low frequencies. This would cause distortion if it was in series with
a speaker. At higher frequencies which it could not track, it would
simply cause amplitude compression - I've used a light bulb for this
in the past.

d

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


When I worked for ILP Electronics many years ago, they suggested the use of
a fuse in series with the loudspeaker as protection against a DC fault. I
found that distortion was significant due to the modulation of the fuse
resistance by low frequencies. I have no records of the tests I did.
However, I did suggest an alternative, and that was to put a fuse in each (+
and -) supply rails. It was possible to use fuses of a lower rating than
that in the output line because of the lower (half cycles) duty.

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.


Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk

Fleetie wrote:

"Graham Holloway" wrote
Jim, for the purposes of seeing how a fuse might affect linearity,
some sort of frequency response of resistance change vs frequency
would be needed. If a fuse has a very low thermal inertia, it might
change its resistance significantly during a cycle, particularly at
low frequencies. This would cause distortion if it was in series with
a speaker. At higher frequencies which it could not track, it would
simply cause amplitude compression - I've used a light bulb for this
in the past.

d

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


When I worked for ILP Electronics many years ago, they suggested the use of
a fuse in series with the loudspeaker as protection against a DC fault. I
found that distortion was significant due to the modulation of the fuse
resistance by low frequencies. I have no records of the tests I did.
However, I did suggest an alternative, and that was to put a fuse in each (+
and -) supply rails. It was possible to use fuses of a lower rating than
that in the output line because of the lower (half cycles) duty.

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

"Pooh Bear" wrote in message
...
Fleetie wrote:

"Graham Holloway" wrote
Jim, for the purposes of seeing how a fuse might affect linearity,
some sort of frequency response of resistance change vs frequency
would be needed. If a fuse has a very low thermal inertia, it might
change its resistance significantly during a cycle, particularly at
low frequencies. This would cause distortion if it was in series with
a speaker. At higher frequencies which it could not track, it would
simply cause amplitude compression - I've used a light bulb for this
in the past.

d

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


When I worked for ILP Electronics many years ago, they suggested the
use of
a fuse in series with the loudspeaker as protection against a DC
fault. I
found that distortion was significant due to the modulation of the
fuse
resistance by low frequencies. I have no records of the tests I did.
However, I did suggest an alternative, and that was to put a fuse in
each (+
and -) supply rails. It was possible to use fuses of a lower rating
than
that in the output line because of the lower (half cycles) duty.

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.

We used it because it was cheap. In fact, the 100W amplifier modules cost
under one UKP (circa 1982) in parts, including the heatsink.

Graham Holloway.

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