Don Pearce wrote:

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



Big endians vs. little endians?



No, bring back 24 bit ICL kit, octal made sense then.

--
Nick

In article , Ian Bell
wrote:


A colleague of mine did his PhD on fuses about 30 years ago.

If you are still in contact with him it would be interesting to see what
info he could provide on the topic of how they might affect impedance and
distortion.

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 , 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 :-)

"Correct" or not as an equation, like Don, it is not a usage I tend to
employ. It can confuse some students in my experience who are puzzled by
thinking they somehow have to divide the values by 'mA' or think of it as
being a 'current per mA'. I think the meaning of Current (mA) is fairly
clear, but of course, anything may be misunderstood. :-)

TBH I'm more concerned that I only obtained some fairly rough data over a
small range, etc.

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 , Oddjob
wrote:


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 :-))

Is *this* why Germany, etc, were called the "Axis Powers" during WW2? :-)

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 , Nick Gorham
wrote:
Don Pearce wrote:

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



Big endians vs. little endians?



No, bring back 24 bit ICL kit, octal made sense then.

I still have a bundle of blank punch-cards somewhere. Threw away all the
old paper tapes of data, though... :-)

First learned about computing on ICL1900's.

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 , 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

Jim

My boss was more concerned about £10 amplifiers failing, followed by a claim
for £100 speaker damage.

Graham

Jim Lesurf wrote:

In article , Pooh Bear
wrote:

Recently acquired some new dummy loads for amplifier testing.

The measured THD figures seemed rather high. Swapping to an earlier
dummy load reduced the THD.

Concluded that the resistance element was thermally modulating on a
cycle by cycle basis. The cable to the load acted like a potential
divider in series withe lon-linear load.

Measuring THD directly at the amplifer output itself proved the point.

Was the 'suspect load' THD high at HF or at LF?

Seemed to be pretty much independent of frequency IIRC which seemed odd. I was
more interested in just sorting it to spend too much time though.


Not all dummy loads are equal it seems ! The best I've found in this
respect are the alumium clad bolt down types.

Agreed. I think I know the type of loads you mean, and if so, they are the
sort I used to use many years ago. However the reason I ask the above
question is that I recall a review in HFN of the Armstrong 600 range where
the reviewer got much higher THD values than the company had measured.
Investigation lead to us deciding that the reviewer's load had a high
series inductance which was changing the distortion. (However it may have
been a thermal effect, despite our conclusion at the time.)

I used to think that too. I even measured the inductive component of some of
our loads. It wasn't that high.

The ceramic tubular loads appear to be the ones with the problem. More recent
ones seem worse too. Different resistance wire ?

Graham

Arny Krueger wrote:

"Pooh Bear" wrote in message


Recently acquired some new dummy loads for amplifier testing.

The measured THD figures seemed rather high. Swapping to an earlier
dummy load reduced the THD.

oops!

Concluded that the resistance element was thermally modulating on a
cycle by cycle basis. The cable to the load acted like a potential
divider in series with the non-linear load.

Been there, done that.

Measuring THD directly at the amplifer output itself proved the point.

Perhaps.

Not all dummy loads are equal it seems ! The best I've found in this
respect are the alumium clad bolt down types.

Interesting. What were these new dummy loads composed of, exactly?

2 of these in series to make a 600W 4 ohm load. Tubular ceramic wirewound type.

http://uk.farnell.com/jsp/endecaSear...=1840290&N=401

They're still fine for soak tests.


The biggest problem I've found with my dummy loads is variation of actual DC
resistance with lnger-term heating and cooling.

I have acquired a stash of precision NI wirewound resistors from Mouser for
my next pass at the problem.

These take my fancy. Supposed to be non-inductive.

http://uk.farnell.com/jsp/endecaSear...=3067920&N=401

Hugely expensive though.


Graham

"Pooh Bear" wrote in message

Arny Krueger wrote:

"Pooh Bear" wrote in message


Recently acquired some new dummy loads for amplifier testing.

The measured THD figures seemed rather high. Swapping to an earlier
dummy load reduced the THD.

oops!

Concluded that the resistance element was thermally modulating on a
cycle by cycle basis. The cable to the load acted like a potential
divider in series with the non-linear load.

Been there, done that.

Measuring THD directly at the amplifer output itself proved the
point.

Perhaps.

Not all dummy loads are equal it seems ! The best I've found in this
respect are the alumium clad bolt down types.

Interesting. What were these new dummy loads composed of, exactly?

2 of these in series to make a 600W 4 ohm load. Tubular ceramic
wirewound type.

http://uk.farnell.com/jsp/endecaSear...=1840290&N=401

They're still fine for soak tests.


The biggest problem I've found with my dummy loads is variation of
actual DC resistance with lnger-term heating and cooling.

I have acquired a stash of precision NI wirewound resistors from
Mouser for my next pass at the problem.

These take my fancy. Supposed to be non-inductive.

http://uk.farnell.com/jsp/endecaSear...=3067920&N=401

Hugely expensive though.

Interesting design. Seem to be very compact about 1 x 3".

Thay are in about the same price range as my 300 watters, of which I have 8.
They are huge - about 2 inches in diameter and about 8 inches long.

Here is the catalog page I order precision NI wirewounds from - I have a
mixture of sizes and wattage ratings related to my reactive and non-reactive
loads:

http://www.mouser.com/catalog/620/411.pdf

In my tests these are amazingly stable over a large temperature range. Rated
power puts the surface temp up in the 400F range. The resistance barely
changes. This is quite a contrast with other cheaper NI parts I have tested
(and regrettably used).

"Jim Lesurf" wrote in message
...
In article , Oddjob
wrote:


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 :-))

Is *this* why Germany, etc, were called the "Axis Powers" during WW2? :-)

Even today, Bush et al declare war on the "Axis of Evil" this is also very
much open to interpretation ;-)