I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?

Thanks in advance

Iain

http://www.pcabx.com/product/amplifiers/ -- see the dummy load they use. I
believe that there is one on Stereophile's website, and one in D'Appolito's
book.



"Iain M Churches" wrote in message
...
I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?

Thanks in advance

Iain

"Iain M Churches" said:

I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?

Thanks in advance

Iain

I use switcheable capacitors across a 6.8 ohms/30 watts resistor.
The caps vary from 1 nF to 2 uF max.

--
Sander de Waal
" SOA of a KT88? Sufficient. "

"Iain M Churches"
I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?


** Real loudspeakers do not follow any particular pattern in regard to
impedance curves - so no such test load exists.

This is why people use resistive loads - if there is *no* problem over a
range of resistance values above and below nominal then the (tube) amp can
be expected to drive most speakers OK.

If you own a speaker with an unusual characteristic ( like an
electrostatic ) then simulate that. Of course you will have to measure it
first.





............... Phil

"Iain M Churches" wrote in message
...
I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?

http://www.duncanamps.com/technical/dummyload.html

Sander deWaal wrote:

"Iain M Churches" said:

I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?

Thanks in advance

Iain

I use switcheable capacitors across a 6.8 ohms/30 watts resistor.
The caps vary from 1 nF to 2 uF max.

--
Sander de Waal
" SOA of a KT88? Sufficient. "

There are a range of R+L+C arrangements which mimic speaker loads,
and all are usable, but usually if a *non inductive* resistor
is used, some idea of most tube amp's power performance can be gained.

I use a switchable set of R,
1,2,3,4,5,6,8,12,16,32,64 ohms, and when i test an amp
I record full power into all these loads where thd does not exceed 1%,
and therefore I can plot a max power vs load value graph for the amp.

But that doesn't tell me if the amp is stable at HF, and for that I have
to
record the sine wave response with solely capacitive loads,
so I use 0.1uF, 0.22uF, 0.47uF, 1uF, 2uF, and 4.7uF, but with the
output voltage set at 1/10 of the maximum, so the tests at up to 200 kHz
don't wreck
any internal components.

Square wave and sine wave tests are done, and all the responses plotted.

You can also use an L across the output.
But speakers rarely ever present a purely inductive load to any amp.
The voice coils of all speakers have some dc resistance, and as F falls,

the load becomes purely a resistance, and so there is not a big enough
extra
phase shift caused to make the amp oscillate at LF.

But nevertheless, sine wave response should always be checked down to 1
Hz, since
many amps poorly designed will be marginally stable at LF, or depend on
a load being connected
to maintain LF stablity, or have a large peak in the response below 20
Hz, indicating
all isn't well with the margin of stability.

Sometimes the use of 0.22 uF will make a tube amp oscillate even before
a signal is applied, and such an amp is not unconditinally stable, and
it should be
unconditionally stable, because one never knows if a speaker may have a
cap across its terminals.
Some give a very peaked sine wave response into say 2 uF,
with a 6 dB peak at 20 kHz, and this shows the leakage inductance of the
OPT
is high, and / or the circuit has not been critically damped properly,
and that
using such amps with ESL may give a bright harsh sound.

Testing amps with only one value of R doesn't tell you much about the
amp.

Patrick Turner.

"kyser"
"Iain M Churches"

I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?

http://www.duncanamps.com/technical/dummyload.html



** The info in that link relates ONLY to guitar amps and how that may
behave when OVERDRIVEN.




................ Phil

"Patrick Turner"
"Iain M Churches"

I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

There are a range of R+L+C arrangements which mimic speaker loads,
and all are usable, but usually if a *non inductive* resistor


** Why do so called "non-inductive" resistors matter so damn much ??????

They are very hard to find and there is *no point* as standard wire wound
types have so little inductance that a metre of lead connecting them to the
amp has more.


But that doesn't tell me if the amp is stable at HF, and for that I have
to record the sine wave response with solely capacitive loads,


** Which is a *stupid* test since no loudspeaker made presents such a load
to the amp.



You can also use an L across the output.
But speakers rarely ever present a purely inductive load to any amp.


** ESLs have step up transformers - ie inductors with bad attitude.


Sometimes the use of 0.22 uF will make a tube amp oscillate even before
a signal is applied, and such an amp is not unconditinally stable, and
it should be unconditionally stable, because one never knows if a speaker
may have a
cap across its terminals.


** By that logic the Turneroid must go about wearing a steel helmet all
ay - since **no-one knows** when a meteorite may strike !!!!!


Some give a very peaked sine wave response into say 2 uF,
with a 6 dB peak at 20 kHz, and this shows the leakage inductance of the
OPT is high, and / or the circuit has not been critically damped properly,
and that using such amps with ESL may give a bright harsh sound.


** To simulate the impedance of even the notorious Quad ESL 57 requires a
4 uF film cap in **SERIES** with a 1.2 ohm resistor - plus a 16 ohm
dummy load.

The series resistor must not be omitted or the test is **absurd**.




................ Phil

Phil Allison wrote:

"Patrick Turner"
"Iain M Churches"

I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

There are a range of R+L+C arrangements which mimic speaker loads,
and all are usable, but usually if a *non inductive* resistor

** Why do so called "non-inductive" resistors matter so damn much ??????

They are very hard to find and there is *no point* as standard wire wound
types have so little inductance that a metre of lead connecting them to the
amp has more.

I have used normal coil wound RLs for amp tests, only to find the
L component too large to permit accurate HF assessments.

So I switched to non inductive R, and no more problems with L;
the R stayed constant up to a Mhz.




But that doesn't tell me if the amp is stable at HF, and for that I have
to record the sine wave response with solely capacitive loads,

** Which is a *stupid* test since no loudspeaker made presents such a load
to the amp.

Its not stupid.

One needs to be able to tweak the phase at HF with a cap load to make sure the
margin
of stability is adequate.

I have a client whose midrange ESL are the equivalent of 0.47 uF..

Nothing leaves my shed unless its can cope well with capacitor loads as
described.




You can also use an L across the output.
But speakers rarely ever present a purely inductive load to any amp.

** ESLs have step up transformers - ie inductors with bad attitude.

That's right, and the "8ohm" transformer input has L across it.



Sometimes the use of 0.22 uF will make a tube amp oscillate even before
a signal is applied, and such an amp is not unconditinally stable, and
it should be unconditionally stable, because one never knows if a speaker
may have a
cap across its terminals.

** By that logic the Turneroid must go about wearing a steel helmet all
ay - since **no-one knows** when a meteorite may strike !!!!!

Well, I build my amps to be able to sustain any type of load,
and it makes them better for it.


Some give a very peaked sine wave response into say 2 uF,
with a 6 dB peak at 20 kHz, and this shows the leakage inductance of the
OPT is high, and / or the circuit has not been critically damped properly,
and that using such amps with ESL may give a bright harsh sound.

** To simulate the impedance of even the notorious Quad ESL 57 requires a
4 uF film cap in **SERIES** with a 1.2 ohm resistor - plus a 16 ohm
dummy load.

There would be many amps where the peaking may still occur with the 1.2 ohms in
series.
Its not enogh series R to prevent peaking.

If the amp is set up to give no more than a 3 dB peak in the measured response
at
any value of C, then indeed the response with a series R of 1.2 ohms usually
results in a flat response, dropping only at HF as a function of increasing Ro
and as the load finally becomes nearly purely resistive where C has a reactance
well below R at some HF.


The series resistor must not be omitted or the test is **absurd**.

Its no absurd.

If the amp can handle any value of capacitor at low power levels up to
300 kHz without having a peak in the sine wave response of more than 6 dB,
then it will be OK to use with any ESL with some series R.

When car makers test a prototype, they drive the car for months at
high speeds on terrible roads, and try to make the car fail.
If it doesn't, then they know the average city buyer is unlikely
to ever bust it.

So testing should be always more difficult than real world conditions.

They used to test new models of TVs in a small room with 20 other sets, and
allow the temperature to rise dangerously.

The sets which expired were repaired, perhaps beefed up, and retested,
and when they could all make it through a few days of torture, they were deemed
saleable to the public, who always surprize is with new ways of killing
electronics.

So I believe in unconditionally stable amplifiers, and building them
without any compromise to the sound quality even though the
gain step networks have been used within the amp to limit open loop
gain at the extremes just outside the audio band, but not affecting the
frequencies within the band.
In a tube amp, there is at least the pure input shunt capacitance of the OPT
which is effectively like a C across the output terminals, although is really
exists from anode to anode, and it can cause stability problems.

There are many amps which cannot be stabilised when no load is connected, and
such amps
require RC networks to achieve this.
To make the stability maximal, whilst maintaining the response into the rated R
load
out to 65 kHz involves testing with pure cap loads gretaer than the one already
there in the amp; 600 pF from a-a on an OPT is like having 0.37 uF across the
output
in an amp with a 600:1 impedance ratio using a "perfect OPT" which does not
exist;
its common in tube amps.

With SS amps, there is usually a parallel LR "zobel" network between the
transistors and the load
to effectively prevent any C load from upsetting the stability of the amp,
or allowing excessive current to flow at HF if there was a cap load, or too low
a value of R load.
But such networks are *outside the NFB loop* and are passive networks which
themselves
do not enchorage instablity like the leakage inductance of an OPT,
which is *included within the NFB* loop, along with the capacitances in the OPT.



Anyway, you stabilise your amps your way, but I will do mine my way.

Patrick Turner.



............... Phil

"Phil Allison" wrote in message
...

"kyser"
http://www.duncanamps.com/technical/dummyload.html

** The info in that link relates ONLY to guitar amps and how that may
behave when OVERDRIVEN.

From the text, which you obviously _didn't bother to read, without leaping
in:

"Here is a copy of my design for a circuit that will simulate the
impedance variations you get with a 16 ohm speaker cabinet. The real speaker
will probably vary depending upon how hard it is driven, due to motional
restrictions of the cone, which this circuit will not do".

So, impedance aspects aside (as I don't think too many hifi speakers would
be 16 ohm these days and, in any case Aiken's circuit could be adjusted to
simulate lower impedances), what difference whether it's driven by a clean
or overloaded amp?

Goose ......

I'd say that it is very difficult to try and simulate a real load, and
particularly how it reflects on actual SOUND. OK, the flatter the better,
but in this case why some sand state units having tons of feedback and
giving out 500W with a frequency response from DC to light sound so awful?
Maybe we can find 2 solutions to 2 different problems:
1 - if You are a pro and You get paid for Your units like Mr. Turner, You
need to be sure they will work in a stable way under any mistreatment and
any load: shorts, blown loudspeakers, You name it. This means You'll have
to test 'em even with purely capacitive loads or with all the rest of the
torture machines used by our OZ fellow. "Sound" is a further aspect, 'cause
it involves a certain peculiar speaker and it's not feasible to test an amp
with 500 different boxes.
2 - if You are an amateur like I am, a test with a small set of plain
resistors (say 2 to 64 ohms, I just use 8 to be sure that all connections
have been properly done) will show You if the unit is safe enough to be
connected to Your expensive speakers, then You can test it (@ no more than
1W out to avoid frying some mega-$ coil) and see if anything is wrong in
real-world terms.

Ciao

Fabio


"Iain M Churches" ha scritto nel messaggio
...
I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?

Thanks in advance

Iain

I have a newbie question about dummy loads. Is there any reason I
can't go to my local car stereo shop and get speakers (hopefully out of
their garbage can) with damaged cones and use them as a dummy load? If
one cuts the cone out completely and tapes the coil into the magnet the
speaker should be nearly silent.

-Jim

On 2004-11-02 08:38:24 -0700, "Fabio Berutti"
said:

I'd say that it is very difficult to try and simulate a real load, and
particularly how it reflects on actual SOUND. OK, the flatter the
better, but in this case why some sand state units having tons of
feedback and giving out 500W with a frequency response from DC to light
sound so awful?
Maybe we can find 2 solutions to 2 different problems:
1 - if You are a pro and You get paid for Your units like Mr. Turner,
You need to be sure they will work in a stable way under any
mistreatment and any load: shorts, blown loudspeakers, You name it.
This means You'll have to test 'em even with purely capacitive loads or
with all the rest of the torture machines used by our OZ fellow.
"Sound" is a further aspect, 'cause it involves a certain peculiar
speaker and it's not feasible to test an amp with 500 different boxes.
2 - if You are an amateur like I am, a test with a small set of plain
resistors (say 2 to 64 ohms, I just use 8 to be sure that all
connections have been properly done) will show You if the unit is safe
enough to be connected to Your expensive speakers, then You can test it
(@ no more than 1W out to avoid frying some mega-$ coil) and see if
anything is wrong in real-world terms.

Ciao

Fabio


"Iain M Churches" ha scritto nel messaggio
...
I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?

Thanks in advance

Iain


--
-Jim Strickland

That speaker is now pretty much a cross between a wire wound resistor
and a choke, as there is no cone movement, hence back emf, etc.


\
Jim Strickland wrote:

I have a newbie question about dummy loads. Is there any reason I
can't go to my local car stereo shop and get speakers (hopefully out of
their garbage can) with damaged cones and use them as a dummy load? If
one cuts the cone out completely and tapes the coil into the magnet the
speaker should be nearly silent.

-Jim

On 2004-11-02 08:38:24 -0700, "Fabio Berutti"
said:

I'd say that it is very difficult to try and simulate a real load, and
particularly how it reflects on actual SOUND. OK, the flatter the
better, but in this case why some sand state units having tons of
feedback and giving out 500W with a frequency response from DC to light
sound so awful?
Maybe we can find 2 solutions to 2 different problems:
1 - if You are a pro and You get paid for Your units like Mr. Turner,
You need to be sure they will work in a stable way under any
mistreatment and any load: shorts, blown loudspeakers, You name it.
This means You'll have to test 'em even with purely capacitive loads or
with all the rest of the torture machines used by our OZ fellow.
"Sound" is a further aspect, 'cause it involves a certain peculiar
speaker and it's not feasible to test an amp with 500 different boxes.
2 - if You are an amateur like I am, a test with a small set of plain
resistors (say 2 to 64 ohms, I just use 8 to be sure that all
connections have been properly done) will show You if the unit is safe
enough to be connected to Your expensive speakers, then You can test it
(@ no more than 1W out to avoid frying some mega-$ coil) and see if
anything is wrong in real-world terms.

Ciao

Fabio


"Iain M Churches" ha scritto nel messaggio
...
I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?

Thanks in advance

Iain

Bob H.

Just grab that plate in one hand, the chassis in the other,
and FEEL the power of tube audio!!!
(not literally, of course, just kidding. DON'T DO THAT!)

Jim Strickland wrote:

I have a newbie question about dummy loads. Is there any reason I
can't go to my local car stereo shop and get speakers (hopefully out of
their garbage can) with damaged cones and use them as a dummy load? If
one cuts the cone out completely and tapes the coil into the magnet the
speaker should be nearly silent.

Don't bother doing this with a busted speaker whose
impedance will be completely different to an operational
speaker with freely movable cone attatched.

Best to just use a 50 watt resistor as a start, and for
more investigative measurements, see my other posts on the subject.

Patrick Turner.

-Jim

On 2004-11-02 08:38:24 -0700, "Fabio Berutti"
said:

I'd say that it is very difficult to try and simulate a real load, and
particularly how it reflects on actual SOUND. OK, the flatter the
better, but in this case why some sand state units having tons of
feedback and giving out 500W with a frequency response from DC to light
sound so awful?
Maybe we can find 2 solutions to 2 different problems:
1 - if You are a pro and You get paid for Your units like Mr. Turner,
You need to be sure they will work in a stable way under any
mistreatment and any load: shorts, blown loudspeakers, You name it.
This means You'll have to test 'em even with purely capacitive loads or
with all the rest of the torture machines used by our OZ fellow.
"Sound" is a further aspect, 'cause it involves a certain peculiar
speaker and it's not feasible to test an amp with 500 different boxes.
2 - if You are an amateur like I am, a test with a small set of plain
resistors (say 2 to 64 ohms, I just use 8 to be sure that all
connections have been properly done) will show You if the unit is safe
enough to be connected to Your expensive speakers, then You can test it
(@ no more than 1W out to avoid frying some mega-$ coil) and see if
anything is wrong in real-world terms.

Ciao

Fabio


"Iain M Churches" ha scritto nel messaggio
...
I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?

Thanks in advance

Iain

--
-Jim Strickland

Fabio Berutti wrote:

I'd say that it is very difficult to try and simulate a real load, and
particularly how it reflects on actual SOUND. OK, the flatter the better,
but in this case why some sand state units having tons of feedback and
giving out 500W with a frequency response from DC to light sound so awful?
Maybe we can find 2 solutions to 2 different problems:
1 - if You are a pro and You get paid for Your units like Mr. Turner, You
need to be sure they will work in a stable way under any mistreatment and
any load: shorts, blown loudspeakers, You name it. This means You'll have
to test 'em even with purely capacitive loads or with all the rest of the
torture machines used by our OZ fellow. "Sound" is a further aspect, 'cause
it involves a certain peculiar speaker and it's not feasible to test an amp
with 500 different boxes.

How the amp "sounds" can't be assessed with a dummy load.

I am not so sure *all* 500w sand amps with a zillion dB of NFB all sound
awful, but some sand amps do.
Is the sound of measured accuracy horrid?
Trouble is the inaccuracy of tube amps is so negligible at normal listening
levels that
the arguments about their euphonics and mistakes don't stack up,
because its all below the threshold of audibility.
For more info on that sunject go to
http://www.godoftriodes.com/soundbjtvstubes

Sure I have to cater for the most improbable use of my amps,
bit so to should the amateur, lest he find he has built an oscillator,
rather than an amplifier.
An oscillator is an amplifier that oscillates.



2 - if You are an amateur like I am, a test with a small set of plain
resistors (say 2 to 64 ohms, I just use 8 to be sure that all connections
have been properly done) will show You if the unit is safe enough to be
connected to Your expensive speakers, then You can test it (@ no more than
1W out to avoid frying some mega-$ coil) and see if anything is wrong in
real-world terms.

An oscilliscope might be very handy, and a square wave.
If they are not available, then some means of detecting the presence of
F above 20 kHz should be used, and ppl did use a diode plus C&R to detect RF,
and watch for a change in direct voltage across the C.
A lotta guys used to build amps without oscilliscopes.

Patrick Turner.



Ciao

Fabio

"Iain M Churches" ha scritto nel messaggio
...
I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?

Thanks in advance

Iain

"Patrick Turner"
Phil Allison wrote:

There are a range of R+L+C arrangements which mimic speaker loads,
and all are usable, but usually if a *non inductive* resistor

** Why do so called "non-inductive" resistors matter so damn much
??????

They are very hard to find and there is *no point* as standard wire wound
types have so little inductance that a metre of lead connecting them to
the
amp has more.

I have used normal coil wound RLs for amp tests, only to find the
L component too large to permit accurate HF assessments.


** Typical Turneroid self referencing /meaningless reply.



So I switched to non inductive R, and no more problems with L;
the R stayed constant up to a Mhz.


** Ever thought of adding a simple zobel network to get that - ****head
?????


But that doesn't tell me if the amp is stable at HF, and for that I
have
to record the sine wave response with solely capacitive loads,

** Which is a *stupid* test since no loudspeaker made presents such a
load
to the amp.

Its not stupid.


** Everything the Turneroid fool says is stupid.



One needs to be able to tweak the phase at HF with a cap load to make sure
the
margin of stability is adequate.

I have a client whose midrange ESL are the equivalent of 0.47 uF..

Nothing leaves my shed unless its can cope well with capacitor loads as
described.


** Typical Turneroid self-referencing /meaningless reply.



** By that logic the Turneroid must go about wearing a steel helmet all
ay - since **no-one knows** when a meteorite may strike !!!!!

Well, I build my amps to be able to sustain any type of load,
and it makes them better for it.


** Asinine, self aggrandising **** - from a notorious ****wit.



** To simulate the impedance of even the notorious Quad ESL 57
requires a
4 uF film cap in **SERIES** with a 1.2 ohm resistor - plus a 16 ohm
dummy load.

There would be many amps where the peaking may still occur with the 1.2
ohms in
series.


** But now the test is realistic instead of insane - like theTurneroid.



The series resistor must not be omitted or the test is **absurd**.

Its no absurd.


** Yes it ****ing is.


So testing should be always more difficult than real world conditions.


** Typical pedantic, autistic, ****wit, Turneroid, self- serving, trumpet
blowing CRAP !!


Anyway, you stabilise your amps your way, but I will do mine my way.


** Never the issue - ****HEAD .


YOU are insisting that EVERYONE MUST do such tests YOUR INSANE way.


And that is *******BAD******** advice to give others.





............... Phil

"kyser"
"Phil Allison"

http://www.duncanamps.com/technical/dummyload.html

** The info in that link relates ONLY to guitar amps and how that may
behave when OVERDRIVEN.

From the text, which you obviously _didn't bother to read, without leaping
in:


** Don't make such arrogant assumptions - you vile little **** head.


"Here is a copy of my design for a circuit that will simulate the
impedance variations you get with a 16 ohm speaker cabinet. The real
speaker
will probably vary depending upon how hard it is driven, due to motional
restrictions of the cone, which this circuit will not do".



** All relates to a guitar amp "cabinet" - just as I said.


So, impedance aspects aside (as I don't think too many hifi speakers would
be 16 ohm these days and, in any case Aiken's circuit could be adjusted to
simulate lower impedances), what difference whether it's driven by a clean
or overloaded amp?


** The test is of the amp - you masturbating moron.

To see what *it* does with a load that is much like a speaker cabinet and
not a simple resistor - particularly when being overdriven.


Goose ......


** ****ing donkey.




................ Phil

"Phil Allison" wrote in message
...

"kyser"
"Phil Allison"

http://www.duncanamps.com/technical/dummyload.html

** The info in that link relates ONLY to guitar amps and how that may
behave when OVERDRIVEN.

From the text, which you obviously _didn't bother to read, without
leaping in:

** Don't make such arrogant assumptions - you vile little **** head.

I'm quite a substantial **** head actually, as you'll find out if I drop in
to see you personally on my next visit to Sydney. LOL

"Here is a copy of my design for a circuit that will simulate the
impedance variations you get with a 16 ohm speaker cabinet. The real speaker
will probably vary depending upon how hard it is driven, due to motional
restrictions of the cone, which this circuit will not do".

** All relates to a guitar amp "cabinet" - just as I said.

So, impedance aspects aside (as I don't think too many hifi speakers
would be 16 ohm these days and, in any case Aiken's circuit could be
adjusted to simulate lower impedances), what difference whether it's driven
by a clean or overloaded amp?

** The test is of the amp - you masturbating moron.

Of course it is, this is a circuit for a dummy load, dummy! And at least my
hand isn't _permanently_ attached to my appendage like yours, Philthy!!!

To see what *it* does with a load that is much like a speaker cabinet and
not a simple resistor - particularly when being overdriven.

But the OP asked (which has been lost, as usual in these threads, with all
your bluster, abuse and obfuscation):

" .. I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required. What should I add to my 50W resistor to
make a load closer to a real world situation .. "?

Isn't this what Aiken's simulated load does, irrespective of whether it's
connected to a hifi amp, or an overloaded guitar amp?

** ****ing donkey.

You still a well-known patron at King's Cross, Phil?

"kyser"
"Phil Allison

( snip waste )


But the OP asked (which has been lost, as usual in these threads, with all
your bluster, abuse and obfuscation):

" .. I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required. What should I add to my 50W resistor to
make a load closer to a real world situation .. "?

Isn't this what Aiken's simulated load does, irrespective of whether it's
connected to a hifi amp, or an overloaded guitar amp?


** NO.

It in no way simulates **hi-fi speaker system** load.

It simulates a typical guitar cab.

The difference is enormous.




............ Phil

"Phil Allison" wrote in message
...

Isn't this what Aiken's simulated load does, irrespective of whether
it's connected to a hifi amp, or an overloaded guitar amp?

** NO.

It in no way simulates **hi-fi speaker system** load.

It simulates a typical guitar cab.

The difference is enormous.

Then can you enlighten us with your words of wisdom, O Mighty Guru, and
explain the difference to ordinary mortals?

(Bearing in mind, of course, that this particular serf already owns a couple
of Marshalls .... ).

"kyser"
"Phil Allison"

Isn't this what Aiken's simulated load does, irrespective of whether
it's connected to a hifi amp, or an overloaded guitar amp?

** NO.

It in no way simulates **hi-fi speaker system** load.

It simulates a typical guitar cab.

The difference is enormous.

Then can you enlighten us with your words of wisdom, O Mighty Guru, and
explain the difference to ordinary mortals?



** Do your own Google search, post a question here.

Or just go learn something about speakers.

Not my job to teach a fence post.




.............. Phil

Iain M Churches wrote:

I realise that a resistive load when testing a valve/tube
amp does not tell the whole story, and that some capacitance
and inductance is also required.

What should I add to my 50W resistor to make a
load closer to a real world situation?

'Closer' is all you'll get.

Even a single driver has both inductive and capacitive elements
depending on frequency. Add a crossover network and you'll get something
really complex.

Then of course you get ppl like me who 'compensate' the driver to make
it mainly resistive - so there !

Specs are tested with resistive loads in the absence of any meaningful
standard to the contrary.


Graham

On Wed, 03 Nov 2004 10:55:23 +1100, Patrick Turner
wrote:

Fabio Berutti wrote:

I'd say that it is very difficult to try and simulate a real load, and
particularly how it reflects on actual SOUND. OK, the flatter the better,
but in this case why some sand state units having tons of feedback and
giving out 500W with a frequency response from DC to light sound so awful?

In 2004, they mostly don't - but they *do* sound like their input
signals, which is more than can be said for 5W sand amps with no
global feedback. BTW, I use the term 'sand amp' for the type which has
the most silicon in it - you know, those big glass bottles..... :-)

Maybe we can find 2 solutions to 2 different problems:
1 - if You are a pro and You get paid for Your units like Mr. Turner, You
need to be sure they will work in a stable way under any mistreatment and
any load: shorts, blown loudspeakers, You name it. This means You'll have
to test 'em even with purely capacitive loads or with all the rest of the
torture machines used by our OZ fellow. "Sound" is a further aspect, 'cause
it involves a certain peculiar speaker and it's not feasible to test an amp
with 500 different boxes.

How the amp "sounds" can't be assessed with a dummy load.

True, but a good dummy load is a reasonable predictor of whether the
amp will run into trouble with a real speaker - which won't usually
like 50 watts at 20kHz!

I am not so sure *all* 500w sand amps with a zillion dB of NFB all sound
awful, but some sand amps do.

Sand amps? Please remind us how glass is made! Which has the more
'sand' in its active devices, solid-state or hollow-state? :-)

Is the sound of measured accuracy horrid?

No, it's excellent if you use the right measurements.

Trouble is the inaccuracy of tube amps is so negligible at normal listening
levels that
the arguments about their euphonics and mistakes don't stack up,
because its all below the threshold of audibility.
For more info on that sunject go to
http://www.godoftriodes.com/soundbjtvstubes

Hmmm. It depends on the amp, and reverberation exists even at low
powers, if you have efficient speakers. Sure there are some *good*
tubed amps, but there are also bad ones, in the sense of not being
true to the input signal. If a tubed amp sounded *exactly* like the
input signal, i.e. it had no artifacts, euphonic or otherwise, then it
would ipso facto sound *exactly* like any good SS amp, no?

Sure I have to cater for the most improbable use of my amps,
bit so to should the amateur, lest he find he has built an oscillator,
rather than an amplifier.
An oscillator is an amplifier that oscillates.

2 - if You are an amateur like I am, a test with a small set of plain
resistors (say 2 to 64 ohms, I just use 8 to be sure that all connections
have been properly done) will show You if the unit is safe enough to be
connected to Your expensive speakers, then You can test it (@ no more than
1W out to avoid frying some mega-$ coil) and see if anything is wrong in
real-world terms.

Indeed, you can't beat hooking up a 'scope to the real speaker
terminals - bravery is a pre-requisiste! :-)

An oscilliscope might be very handy, and a square wave.
If they are not available, then some means of detecting the presence of
F above 20 kHz should be used, and ppl did use a diode plus C&R to detect RF,
and watch for a change in direct voltage across the C.
A lotta guys used to build amps without oscilliscopes.

Indeed, but 'scopes aren't expensive nowadays, and you really, really
do want to know if your amp is oscillating at 23 kHz *before* you
leave it hooked up to your 'high end' speakers!

Personally, I'd whack it onto a dummy load along the lines of that
used by Stereophile, and check the output with a 'scope, long before
letting a new homebuilt amp anywhere near my speakers.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Wed, 03 Nov 2004 10:55:23 +1100, Patrick Turner
wrote:

Fabio Berutti wrote:

I'd say that it is very difficult to try and simulate a real load, and
particularly how it reflects on actual SOUND. OK, the flatter the better,
but in this case why some sand state units having tons of feedback and
giving out 500W with a frequency response from DC to light sound so awful?

In 2004, they mostly don't - but they *do* sound like their input
signals, which is more than can be said for 5W sand amps with no
global feedback. BTW, I use the term 'sand amp' for the type which has
the most silicon in it - you know, those big glass bottles..... :-)

Maybe we can find 2 solutions to 2 different problems:
1 - if You are a pro and You get paid for Your units like Mr. Turner, You
need to be sure they will work in a stable way under any mistreatment and
any load: shorts, blown loudspeakers, You name it. This means You'll have
to test 'em even with purely capacitive loads or with all the rest of the
torture machines used by our OZ fellow. "Sound" is a further aspect, 'cause
it involves a certain peculiar speaker and it's not feasible to test an amp
with 500 different boxes.

How the amp "sounds" can't be assessed with a dummy load.

True, but a good dummy load is a reasonable predictor of whether the
amp will run into trouble with a real speaker - which won't usually
like 50 watts at 20kHz!

I am not so sure *all* 500w sand amps with a zillion dB of NFB all sound
awful, but some sand amps do.

Sand amps? Please remind us how glass is made! Which has the more
'sand' in its active devices, solid-state or hollow-state? :-)

Is the sound of measured accuracy horrid?

No, it's excellent if you use the right measurements.

Trouble is the inaccuracy of tube amps is so negligible at normal listening
levels that
the arguments about their euphonics and mistakes don't stack up,
because its all below the threshold of audibility.
For more info on that sunject go to
http://www.godoftriodes.com/soundbjtvstubes

Hmmm. It depends on the amp, and reverberation exists even at low
powers, if you have efficient speakers. Sure there are some *good*
tubed amps, but there are also bad ones, in the sense of not being
true to the input signal. If a tubed amp sounded *exactly* like the
input signal, i.e. it had no artifacts, euphonic or otherwise, then it
would ipso facto sound *exactly* like any good SS amp, no?

Sure I have to cater for the most improbable use of my amps,
bit so to should the amateur, lest he find he has built an oscillator,
rather than an amplifier.
An oscillator is an amplifier that oscillates.

2 - if You are an amateur like I am, a test with a small set of plain
resistors (say 2 to 64 ohms, I just use 8 to be sure that all connections
have been properly done) will show You if the unit is safe enough to be
connected to Your expensive speakers, then You can test it (@ no more than
1W out to avoid frying some mega-$ coil) and see if anything is wrong in
real-world terms.

Indeed, you can't beat hooking up a 'scope to the real speaker
terminals - bravery is a pre-requisiste! :-)

An oscilliscope might be very handy, and a square wave.
If they are not available, then some means of detecting the presence of
F above 20 kHz should be used, and ppl did use a diode plus C&R to detect RF,
and watch for a change in direct voltage across the C.
A lotta guys used to build amps without oscilliscopes.

Indeed, but 'scopes aren't expensive nowadays, and you really, really
do want to know if your amp is oscillating at 23 kHz *before* you
leave it hooked up to your 'high end' speakers!

Personally, I'd whack it onto a dummy load along the lines of that
devised by Ken Kantor and used by Stereophile,
http://www.stereophile.com//reference/60/
and check the output with a 'scope, long before letting a new
homebuilt amp anywhere near my speakers.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Wed, 3 Nov 2004 15:49:46 +1100, "Phil Allison"
wrote:

Not my job to teach a fence post.

OTOH, you could obviously share your world view with one......
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Phil Alliso

So testing should be always more difficult than real world conditions.

** Typical pedantic, autistic, ****wit, Turneroid, self- serving, trumpet
blowing CRAP !!

Anyway, you stabilise your amps your way, but I will do mine my way.

** Never the issue - ****HEAD .

YOU are insisting that EVERYONE MUST do such tests YOUR INSANE way.

And that is *******BAD******** advice to give others.

.............. Phil

Pure capacitor load testing is widely recommended elsewhere
in the audio world, so I am not alone in what I said, and not the only
one who uses the same methods I do, and it was from these others I learnt my
methods.

Not only that, the stability of my valve amps is better than many solid state
amps I have tested.


The LR zobel found at the output of many SS amps is rather like the leakage
inductance
found in all transformer coupled amps, except that the tube amp hasn't got an
equivalent R across
the leakage inductance.

But first let's think about the tube amp.

For those confused, the leakage is usually quoted as being
the equivalent series inductance between the anode to anode load and the anode
to anode
resistance.
Typically, this might be 10 mH, and it is "referred" to the primary.
Say the OPT is 5K to 8 ohms, then the Z ratio is 625:1, so this 10mH
becomes 16 uH when looking into the tube amp at its secondary.
So the nature of the output of the tube amp is inductive.
Now such inductance adds to the phase shift caused by miller effects, where
at least two lots of CR couplings cause a pahse lag, and then the leakage
adds yet another filter, only its LR, so more phase shift lag is added.
With pure C load at the output, the C causes yet another lot of phase lag.

Yet we are forced to connect NFB from the seconday all the way back to the
cathode of V1,
so we need to have critically damped the circuit to minimise the phase lag of
the amp
before NFB is connected to bet the best stability margin.
Basically, it means we make sure the *phase* shift is as low as possible
at extremes of F so that some NFB is actually possible without oscillations,
and the best way to test all that is to connect NFB,
and adjust critical damping RC values, and use a range of cap loads
until the amp displays the minimum overshoot on square waves, even with a cap
load.

Critical damping is one huge PITA for the novice, and especially for anyone who
fails to understand the concept of the tube amp being a rather limited bandpass
filter
and one that employs and relies on NFB around an active circuit
to get a final result.

The nature of the open loop phase shift character is of great importance,
and because a tube amp has more CR and LR poles in its "filter structure"
than an SS amp.
It is thus inevitable that the amount of applied NFB is limited so about 26dB,
and best I have ever achieved with R loads only is about 40 dB, but such a test
amp oscillated
at RF immediately 0.05 uF was connected across the output.
I rarely ever use more than 15 dB, and the stability with any cap loads is fine,

so I know the "margin of stability" is really good.

Let's consider the SS amp again.

There are inbuilt CR phase lag causing interfaces within the SS gain structures,

ie, the signal gets delayed in the transistors, but usually the open loop
response
has a dominant pole at say 1 kHz, so that by 10 kHz, the open loop response is
down
20 dB abd the phase shift is - 90 degrees.
The application of say 50 dB of a typical amount of global NFB = 50 dB
applies delayed signal back to the input, and the phase shift at 10 kHz
may be reduced to 5 degrees, and the response is flat.

But just imagine if you had 16 uH on the output of the SS amp, and then
applied the feedback from the output of the inductor to the input pair.
because yet another reactance was added, the phase shift would be all the
greater,
and so would the tendency for the amp to oscillate, and most certainly so,
with all that NFB.

So we place the zobel *after* the NFB take off point, and we add the LR zobel to

never allow the amp with its NFB to ever experience the
phase shift caused by too low a load value, or by a capacitor.

Hence SS amps can be stable with such LR networks.

But they often display a very large amount of ring on square waves
with cap loads because the L in the LR network resonates with the C load.
This ring isn't see at the amp output ahead of the zobel, so all is well with
the amp.

Now one could use a similar zobel network in a tube amp,
but I have always found them to be a real PITA to get right,
so one gets a nice response into cap loads, ( minimum sq.wave overshoot )
at low power levels, and still get 65 kHz of response with an R load at **full
** power.

I have explored other ways of doing it all, such as applying NFB from the OPT
primary
back to a previous stage, and that works fine, but my ears tell me
time after time it isn't isn't as good as a combination of local cathode
feedback
in the output stage from tertiary windings, like Quad II,
and then have some applied global NFB.

And without the OPT included in the NFB loop, the amp will display
an output resistance equal to the sum of the
tubes with NFB plus the winding resistance of the OPT, and this sum is usually
too high a figure for my liking, more than 1 ohm, and not good if you have
speakers which are 4 ohms.

For those who like their triode amplifiers without NFB, then
all they have to do is make sure the response is flat, and the
the issues of stability don't arise, since the open loop
triode amp is always going to be stable regardless of load.

I don't have to use any bandwidth limiting networks at the input of my tube
amps,
and nor do I have to use any zobel network at the output.
By reducing the leakage inductance to less than 5 uH measured at the
secondary output, and by *minimal* critical damping CR networks,
I get a good measured response, and ppl tell me after a listen,
" I guess NFB isn't so bad..."

With SS, I need to employ both measures.




PA is welcome throw a tantrum over what I said,
but it won't change a thing.

Patrick Turner.

"Patrick Turner"


Pure capacitor load testing is widely recommended elsewhere.....


** Pure Turneroid excrement.

The fools thinks in clichés and borrowed ideas - all of them irrelevant
and wrong.





............ Phil

"Stewart Pinkerton"
"Phil Allison"

Not my job to teach a fence post.

OTOH, you could obviously share your world view with one......



** Like you share your semen with a blow up doll ????



Stewart Pinkerton | Music is Art - Audio is Engineering


** But Pinkerton is not a musician nor engineer's bootlace.





............... Phil

Stewart Pinkerton wrote:

On Wed, 03 Nov 2004 10:55:23 +1100, Patrick Turner
wrote:

Fabio Berutti wrote:

I'd say that it is very difficult to try and simulate a real load, and
particularly how it reflects on actual SOUND. OK, the flatter the better,
but in this case why some sand state units having tons of feedback and
giving out 500W with a frequency response from DC to light sound so awful?

In 2004, they mostly don't - but they *do* sound like their input
signals, which is more than can be said for 5W sand amps with no
global feedback. BTW, I use the term 'sand amp' for the type which has
the most silicon in it - you know, those big glass bottles..... :-)

We welcome your opinion, but too many folks tell me tubes
do better with the input signal than a solid state 500 watter.

Its not down to me to guide or change folks opinions.

And I am building a decent SS amp right now, with
5 x MJL21193 and 5 x MJL21194 in each channel.
I hope it sounds well; the output devices are much better than 30 years ago.



Maybe we can find 2 solutions to 2 different problems:
1 - if You are a pro and You get paid for Your units like Mr. Turner, You
need to be sure they will work in a stable way under any mistreatment and
any load: shorts, blown loudspeakers, You name it. This means You'll have
to test 'em even with purely capacitive loads or with all the rest of the
torture machines used by our OZ fellow. "Sound" is a further aspect, 'cause
it involves a certain peculiar speaker and it's not feasible to test an amp
with 500 different boxes.

How the amp "sounds" can't be assessed with a dummy load.

True, but a good dummy load is a reasonable predictor of whether the
amp will run into trouble with a real speaker - which won't usually
like 50 watts at 20kHz!

I know of nobody who ever uses 50 watts at 20 kHz in a domestic amp,
but sure, the dummy load should test the amp like a speaker does,
so that HF performance can be examined.


I am not so sure *all* 500w sand amps with a zillion dB of NFB all sound
awful, but some sand amps do.

Sand amps? Please remind us how glass is made! Which has the more
'sand' in its active devices, solid-state or hollow-state? :-)

I don't care wtf they are called.....


Is the sound of measured accuracy horrid?

No, it's excellent if you use the right measurements.

I won't make a comment.



Trouble is the inaccuracy of tube amps is so negligible at normal listening
levels that
the arguments about their euphonics and mistakes don't stack up,
because its all below the threshold of audibility.
For more info on that sunject go to
http://www.godoftriodes.com/soundbjtvstubes

Hmmm. It depends on the amp, and reverberation exists even at low
powers, if you have efficient speakers. Sure there are some *good*
tubed amps, but there are also bad ones, in the sense of not being
true to the input signal. If a tubed amp sounded *exactly* like the
input signal, i.e. it had no artifacts, euphonic or otherwise, then it
would ipso facto sound *exactly* like any good SS amp, no?

If only it were so simple....

But it isn't, and I have to deal with all thse ppl who vote with their ears....



Sure I have to cater for the most improbable use of my amps,
bit so to should the amateur, lest he find he has built an oscillator,
rather than an amplifier.
An oscillator is an amplifier that oscillates.

2 - if You are an amateur like I am, a test with a small set of plain
resistors (say 2 to 64 ohms, I just use 8 to be sure that all connections
have been properly done) will show You if the unit is safe enough to be
connected to Your expensive speakers, then You can test it (@ no more than
1W out to avoid frying some mega-$ coil) and see if anything is wrong in
real-world terms.

Indeed, you can't beat hooking up a 'scope to the real speaker
terminals - bravery is a pre-requisiste! :-)

After testing the amp after I have set it up, any test with any speaker
gives not the slightest surprise.
I have done it often, and what I see on the CRO is usually a function
of what you would see with a speaker in series with a voltage source in series with
say 0.5 ohms,
which is the output resistance.
Using purely capacitive loads reveals a hidden series inductance is also
in series with the amp.




An oscilliscope might be very handy, and a square wave.
If they are not available, then some means of detecting the presence of
F above 20 kHz should be used, and ppl did use a diode plus C&R to detect RF,
and watch for a change in direct voltage across the C.
A lotta guys used to build amps without oscilliscopes.

Indeed, but 'scopes aren't expensive nowadays, and you really, really
do want to know if your amp is oscillating at 23 kHz *before* you
leave it hooked up to your 'high end' speakers!

I agree, but for some diyers starting out, a CRO is a major cost,
and all they might ever make is one amp.


Personally, I'd whack it onto a dummy load along the lines of that
used by Stereophile, and check the output with a 'scope, long before
letting a new homebuilt amp anywhere near my speakers.

Indeed.

Patrick Turner.



--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Phil Allison" wrote in message
...

"kyser"
Then can you enlighten us with your words of wisdom, O
Mighty Guru, and explain the difference to ordinary mortals?

** Do your own Google search, post a question here.

Or just go learn something about speakers.

Not my job to teach a fence post.

So you don't really know yourself, then?

Stewart Pinkerton said:

snip

Why are you trolling in RATubes, Pinky?
Now be a good 'borg and stay overthere in uk.rec.audio.

--
Sander de Waal
" SOA of a KT88? Sufficient. "

Stewart Pinkerton wrote:

On Wed, 3 Nov 2004 15:49:46 +1100, "Phil Allison"
wrote:

Not my job to teach a fence post.

OTOH, you could obviously share your world view with one......

I think our Phil sees himself surrounded by a palisade of tall
threatening
fence posts.

Patrick Turner.


--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Wed, 03 Nov 2004 14:30:29 +0100, Sander deWaal
wrote:

Stewart Pinkerton said:

snip

Why are you trolling in RATubes, Pinky?
Now be a good 'borg and stay overthere in uk.rec.audio.

I'm not trolling, ****head, I'm providing useful advice on dummy
loads. Now be a good tweako and stop sounding like that **** Allison.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

Stewart Pinkerton said:

Why are you trolling in RATubes, Pinky?
Now be a good 'borg and stay overthere in uk.rec.audio.

I'm not trolling, ****head, I'm providing useful advice on dummy
loads. Now be a good tweako and stop sounding like that **** Allison.

Tweako? Now you sound like Ferstler.
Time to open another bottle I'd guess.

--
Sander de Waal
" SOA of a KT88? Sufficient. "

"Stewart Pinkerton" wrote in message
...
On Wed, 03 Nov 2004 14:30:29 +0100, Sander deWaal
wrote:

Stewart Pinkerton said:

snip

Why are you trolling in RATubes, Pinky?
Now be a good 'borg and stay overthere in uk.rec.audio.

I'm not trolling, ****head, I'm providing useful advice on dummy
loads. Now be a good tweako and stop sounding like that **** Allison.


Stewart.
I posted on RAT specifically to avoid your "useful advice".


Iain

"Iain M Churches" said:

Stewart.
I posted on RAT specifically to avoid your "useful advice".

3rd strike..........OUT!

--
Sander de Waal
" SOA of a KT88? Sufficient. "

On Wed, 3 Nov 2004 20:20:53 +0200, "Iain M Churches"
wrote:


"Stewart Pinkerton" wrote in message
.. .
On Wed, 03 Nov 2004 14:30:29 +0100, Sander deWaal
wrote:

Stewart Pinkerton said:

snip

Why are you trolling in RATubes, Pinky?
Now be a good 'borg and stay overthere in uk.rec.audio.

I'm not trolling, ****head, I'm providing useful advice on dummy
loads. Now be a good tweako and stop sounding like that **** Allison.


Stewart.
I posted on RAT specifically to avoid your "useful advice".

In that case, you simply prove that you are indeed the arsehole that
you appeared to be on UKRA.............
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Wed, 03 Nov 2004 19:11:55 +0100, Sander deWaal
wrote:

Stewart Pinkerton said:

Why are you trolling in RATubes, Pinky?
Now be a good 'borg and stay overthere in uk.rec.audio.

I'm not trolling, ****head, I'm providing useful advice on dummy
loads. Now be a good tweako and stop sounding like that **** Allison.

Tweako? Now you sound like Ferstler.
Time to open another bottle I'd guess.

RAT used to be such a nice sociable group. What happened?
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Stewart Pinkerton said:

RAT used to be such a nice sociable group. What happened?

You.

--
Sander de Waal
" SOA of a KT88? Sufficient. "

On Wed, 03 Nov 2004 20:48:58 +0100, Sander deWaal
wrote:

Stewart Pinkerton said:

RAT used to be such a nice sociable group. What happened?

You.

How predictable, but in fact, first there was Phil Allison, then there
were clowns like you who instantly attack a newcomer whose name you
recognise, regardless of what he actually posts. Who's the troll here?
Not me.
--

Stewart Pinkerton | Music is Art - Audio is Engineering