Safe Operating Area calculation for audio power amps

[Clifford Heath]

Ok, so I've seen all Leo Simpson's designs and his articles on
designing audio power amps, and I understand the principles
of reactive loads etc. Problem is, I can't find an algebraic
derivation of the power curves he plots, and though I have
derived an expression for it, I can't see how to integrate it
over one half-cycle.

My goal is to bridge two ETI-480's together from a +-37 V
supply, and I'm trying to work out whether the output devices
need to be upgraded. The accepted bridge configurations for
the ETI480 assume it swings to within 5 V of the rail, so
that gives me 255W into a resistive load.

Do folk do the dissipation/SOA calculation numerically, or
can someone point me to an algebraic formula for it?

Clifford Heath.

 

[Phil Allison]

"Clifford Heath"

Ok, so I've seen all Leo Simpson's designs and his articles on
designing audio power amps, and I understand the principles
of reactive loads etc. Problem is, I can't find an algebraic
derivation of the power curves he plots, and though I have
derived an expression for it ......


I can't see how to integrate it over one half-cycle.

** Errr - the whole idea is NOT to do that. Excursions outside the safe
region when driving a complex load occur only for PART of a CYCLE.

My goal is to bridge two ETI-480's together from a +-37 V
supply, and I'm trying to work out whether the output devices
need to be upgraded. The accepted bridge configurations for
the ETI480 assume it swings to within 5 V of the rail, so
that gives me 255W into a resistive load.

** What about supply regulation ????????


BTW Bridged 8 ohm = single channel 4 ohms.





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

 

[Clifford Heath]

Phil Allison wrote:

** Errr - the whole idea is NOT to do that. Excursions outside the safe
region when driving a complex load occur only for PART of a CYCLE.

The SOA contains more than one curve, the objective is to stay
inside them all, including the max-current "curve" and the max
instantaneous power curve. I think I can calculate the max current,
but not the peak and average dissipation at peak (max non-clipping
sine-wave) output.

Now I'm sure that if I was smart enough I could arrive at an
algebraic solution and avoid the need to integrate, but I'm
not. Leo plots these conic sections, and I want a formula for
them. Fair?

** What about supply regulation ????????

1400 watt xformer weighing 15Kg, 67,000uF capacitors top and
bottom. I don't think it'll move much. Fair question though.

BTW Bridged 8 ohm = single channel 4 ohms.

Yup, the bridge isn't the point, I just mentioned it for context.

BTW, what are the chances that DS has supplied devices that meet
the 2N3055/2955 spec?

Clifford Heath.

 

[Phil Allison]

"Clifford Heath"

Phil Allison wrote:

** Errr - the whole idea is NOT to do that. Excursions outside the
safe region when driving a complex load occur only for PART of a CYCLE.

The SOA contains more than one curve,

** It is only one curve - for the 2N 3055 it is 15 amp max up to 8
volts ( bonding wire limited) , a max power of 120 watts diss up to 40 volts
and a reducing max power at higher voltages ( second breakdown limited)
until the max voltage is reached. Also note the 1 mS curve that allows a
much higher power for that short time - ie part of a cycle.

BTW All these figures assume an infinite heatsink with case temp held at
25C - ie a total impossibility.

the objective is to stay
inside them all, including the max-current "curve" and the max
instantaneous power curve. I think I can calculate the max current,
but not the peak and average dissipation at peak (max non-clipping
sine-wave) output.

** For a resistive load, the peak device power is at half supply out -
ie 18 volts into 4 ohms or 81 watts for the two paralled devices.

** What about supply regulation ????????

1400 watt xformer weighing 15Kg, 67,000uF capacitors top and
bottom. I don't think it'll move much. Fair question though.

** Bizarre overkill - IMO.

BTW Bridged 8 ohm = single channel 4 ohms.

Yup, the bridge isn't the point, I just mentioned it for context.

** Err - the SC 480 ( with 4 devices ) was designed for 4 ohm speaker
loads - what is your problem ??

Everything really depends on the nature of the particular load this amp
will be used with - have you measured the impedance curve for that ?




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

 

[Clifford Heath]

Phil Allison wrote:

The SOA contains more than one curve,
** It is only one curve

Ok, I understand what you mean, though you still indicate that the
"one curve" is made up of different segments. But I was meaning a
different thing, which is the safe zone for the amp as a whole.

1400 watt xformer weighing 15Kg, 67,000uF capacitors top and
bottom. I don't think it'll move much. Fair question though.
** Bizarre overkill - IMO.

You're quite right, but I have two of them and they cost $0 .
I was thinking about building a 100W pure class-A stereo amp, but
decided it was just a wank.

** Err - the SC 480 ( with 4 devices ) was designed for 4 ohm speaker
loads - what is your problem ??

At the supply voltage I'll be using looks like it could exceed a safe
power level. I don't think the DS hardware (transistor mounting bracket
esp.) will get the heat away fast enough. I have a huge heatsink and
will mount a quiet fan for it. I just wanted to be able to do the
calculations myself to verify things - actually I think I can, just
have to roll out the complex impedance math I studied 25 years ago.

Everything really depends on the nature of the particular load this amp
will be used with - have you measured the impedance curve for that ?

No. It's one of these, for use with bass guitar (no x-over):
http://www1.jaycar.com.au/productView.asp?ID=CW2145

I'm going to build the amp in a separate box so it could be un-bridged
as a stereo PA amp also. The box is a custom 19" case with a separate
housing to make it stand alone when necessary (good idea?).

Clifford Heath.

 

[Phil Allison]

"Clifford Heath"
Phil Allison wrote:

Everything really depends on the nature of the particular load this amp
will be used with - have you measured the impedance curve for that ?

No. It's one of these, for use with bass guitar (no x-over):
http://www1.jaycar.com.au/productView.asp?ID=CW2145

* That is a 12inch hi-fi woofer - no suitable for bass guitar at all.

Put your $229 towards a proper instrument speaker.




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

 

[Clifford Heath]

Phil Allison wrote:

* That is a 12inch hi-fi woofer - no suitable for bass guitar at all.

I see you're a musician now in addition to all your other attributes.

Bass guitar is completely unlike lead. You want a smooth, linear,
largely undistorted response, much like HiFi, but as powerful as
you can afford... contrary to what the makers of musical instrument
speakers might have you believe.

Do you actually have anything to offer on my original question, or
is the maths beyond you? Three responses without attempting to answer
my question, sheesh.

 

[Phil Allison]

"Clifford Heath"

Phil Allison wrote:

No. It's one of these, for use with bass guitar (no x-over):
http://www1.jaycar.com.au/productView.asp?ID=CW2145

* That is a 12inch hi-fi woofer - no suitable for bass guitar at all.

I see you're a musician now in addition to all your other attributes.

** Don't be a smartarse - musicians do not design bass amps.

I have designed and made amps for bass guitar, also their speaker systems
and repaired hundreds of bass amps over the last 30 years for a living.

PA system and stage amplification gear is what I do.

Bass guitar is completely unlike lead. You want a smooth, linear,
largely undistorted response, much like HiFi, but as powerful as
you can afford... contrary to what the makers of musical instrument
speakers might have you believe.

** Bullshit - bass guitar speakers are not like hi-fi ones, it is a big
error to confuse the two.

Hi-fi bass drivers are too in-efficient and too fragile for electric bass
guitar - what you plan to do will produce disappointing results and/or the
driver will not last long.

Do you actually have anything to offer on my original question, or
is the maths beyond you?

** Your original question made no sense - as do your other assertions.
You have fundamentally misunderstood the problems involved. There is little
chance that SOA or dissipation will be issues at all - plus in any case is
NOT directly calculable for your application since it depends on playing
style and the particular speaker and enclosure design used.

Three responses without attempting to answer
my question, sheesh.

** I was attempting to put you on the right track - instead of the
irrelevant tangent you were off on.

BTW Grow up anytime.




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

 

[Alan Rutlidge]

"Phil Allison" <philallison@tpg.com.au> wrote in message
news:35j820F4mpsg5U1@individual.net...

"Clifford Heath"
Phil Allison wrote:

No. It's one of these, for use with bass guitar (no x-over):
http://www1.jaycar.com.au/productView.asp?ID=CW2145

* That is a 12inch hi-fi woofer - no suitable for bass guitar at
all.

I see you're a musician now in addition to all your other attributes.


** Don't be a smartarse - musicians do not design bass amps.

I have designed and made amps for bass guitar, also their speaker systems
and repaired hundreds of bass amps over the last 30 years for a living.

PA system and stage amplification gear is what I do.


Bass guitar is completely unlike lead. You want a smooth, linear,
largely undistorted response, much like HiFi, but as powerful as
you can afford... contrary to what the makers of musical instrument
speakers might have you believe.


** Bullshit - bass guitar speakers are not like hi-fi ones, it is a big
error to confuse the two.

Hi-fi bass drivers are too in-efficient and too fragile for electric bass
guitar - what you plan to do will produce disappointing results and/or
the
driver will not last long.


Do you actually have anything to offer on my original question, or
is the maths beyond you?


** Your original question made no sense - as do your other assertions.
You have fundamentally misunderstood the problems involved. There is
little
chance that SOA or dissipation will be issues at all - plus in any case is
NOT directly calculable for your application since it depends on playing
style and the particular speaker and enclosure design used.


Three responses without attempting to answer
my question, sheesh.


** I was attempting to put you on the right track - instead of the
irrelevant tangent you were off on.

BTW Grow up anytime.




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

Cliff,

Phil is correct about guitar speakers. Drivers are usually specially
constructed to be highly efficient in the desired operating frequency range.
Bass guitar speakers typically have a fundamental resonance at about 45 -
55Hz (not set in concrete) and are designed for sustained high power
operation. A hi-fi speaker would simply not stand up to the punishment and
fail very quickly - most likely from voice coil burn out.

You might want to consider drivers made by Etone, Electrovoice etc.

Cheers,
Alan

 

[Clifford Heath]

Phil Allison wrote:

** Don't be a smartarse - musicians do not design bass amps.

Ok, sorry, that was out of line.

My frustration was because I was hoping to learn (remember some
maths here as well as get an answer on the amp.

There is little chance that SOA or dissipation will be issues at all

Sounds like you don't think the ETI-480 with +-37V won't have any
trouble into 4 ohms? Because on the raw numbers it looks to me like
it could. If it swings to +-32 into a resistive 4Ohm load, that's
130W RMS already, before the load gets inductive or clips.

** Bullshit - bass guitar speakers are not like hi-fi ones, it is a big
error to confuse the two.

Although Jaycar sell this speaker under their hifi division, the same
unit in 4 ohm is sold for use as a car subwoofer - surely they get a
bit of serious punishment also? Would a suitable speaker protector
help here, given that it's expected *not* to run into clipping much
of the time (see below)?

Resonant frequency is much lower than Alan indicates preferable, though
the right enclosure will raise that a lot (Jaycar's suggested sealed box
resonates at 43 Hz, almost in Alan's suggested range). Did you mean free
air resonance Alan, or in the box?

A possible replacement is the Eminence Delta Pro-12A. It has the same
high-freq response, but less low end. Sensitivity is 100dB (1W 1m),
much higher than the Jaycar 93dB - point taken. And 400W power handling.
A bit more expensive though.

Does anyone stock Eminence (or Etone/Electrovoice) speakers in
Melbourne? Otherwise shipping from the USA will kill me.

** Your original question made no sense

On the contrary, go and review it.

Leo Simpson plots his curves from calculations, I've seen the tables
of numbers but not the algebra. I just wanted to know if someone could
point me to a presentation of the maths behind these. Whether the plots
make sense or not, I wasn't asking. I just wanted to know how they're
made, so I can make my own, and use that to make some judgements about
what OP devices and heatsinking I need.

plus in any case is
NOT directly calculable for your application since it depends on playing
style and the particular speaker and enclosure design used.

Obviously. My aim for a clean linear amp/speaker combo is based
on advice from Neil Kennedy, one of the foremost bass players,
teachers and boutique builders in this country, who also teaches
sound engineering. He got the Protools teaching license exclusive
for Box Hill TAFE not 200 metres from here, where my son had
lessons with him in the studio for a year or two while we were also
building a bass. Neil's words were "as powerful as you can afford,
so you never get clipping". Entirely a different thing from an
amp for lead guitar, which must clip to get a lead sound.

I haven't opened the box from Jaycar yet, and since I bought it
with the avowed intention of using it for bass guitar, I can still
return it. Fitness for purpose and all that jazz.

Clifford Heath.

 

[Phil Allison]

"Clifford Heath

Phil Allison wrote:

There is little chance that SOA or dissipation will be issues at all

Sounds like you don't think the ETI-480 with +-37V won't have any
trouble into 4 ohms? Because on the raw numbers it looks to me like
it could. If it swings to +-32 into a resistive 4Ohm load, that's
130W RMS already, before the load gets inductive or clips.

** Output device dissipation is only a few watts in that condition. Vce
drops to around 1 volt at clipping.

BTW What is the persistent ETI 480 stuff

Do you mean the SC 480 ?????

DSE sell both, but Leo Simpson had nothing to do with the ETI one.

** Bullshit - bass guitar speakers are not like hi-fi ones, it is a
big error to confuse the two.

Although Jaycar sell this speaker under their hifi division, the same
unit in 4 ohm is sold for use as a car subwoofer - surely they get a
bit of serious punishment also? Would a suitable speaker protector
help here, given that it's expected *not* to run into clipping much
of the time (see below)?

** Live electric bass guitar is another ball game entirely compared to
recorded music.

A possible replacement is the Eminence Delta Pro-12A. It has the same
high-freq response, but less low end. Sensitivity is 100dB (1W 1m),
much higher than the Jaycar 93dB - point taken. And 400W power handling.
A bit more expensive though.

Does anyone stock Eminence (or Etone/Electrovoice) speakers in
Melbourne? Otherwise shipping from the USA will kill me.

** Pretty sure there is an Eminence agent here - also consider
Celestion.

WES sell a decent 15 inch bass speaker for circa $100 - the
"IS15 -150 " .

** Your original question made no sense

On the contrary, go and review it.

** I did, many times - it is based on a false assumption.

Leo Simpson plots his curves from calculations, I've seen the tables
of numbers but not the algebra. I just wanted to know if someone could
point me to a presentation of the maths behind these.

** Errr - you have never aid where these curves are to be found.

Which issues of SC ???

I have most but not all SC issues.

plus in any case is NOT directly calculable for your application since it
depends on playing style and the particular speaker and enclosure design
used.

Obviously.

** Errr - then don't constantly ignore that fact as you have been.




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

 

[Clifford Heath]

Phil Allison wrote:

** Output device dissipation is only a few watts in that condition. Vce
drops to around 1 volt at clipping.

Yup, fair point. It's when you get a reactive load that the current
can be near a peak while the output voltage is approaching zero
(maximum voltage across the output devices). At some frequencies,
you can even get negative impedance - +ve current and negative
voltage at the output. But that's the type of complexity that I
think you were assuming I was unaware of.

BTW What is the persistent ETI 480 stuff

No, it's the ETI-480 - but probably the higher distortion figure
won't matter.

DSE sell both, but Leo Simpson had nothing to do with the ETI one.

Ahh, ok. I'm more familiar with Leo's more recent work, including his
first article on the subject, entitled "A discussion of some of the
design problems in High Power Amplifiers", published in WE, October
1979, pp 66-68. The text is online as a PDF somewhere, but Fig 4
contains the first instance I know of of the type of diagram I'm
talking about. It plots current vertical against voltage horizontal,
and shows the SOA, resistive and two inductive dissipation curved.
I assumed that this was used in the ETI-480, but maybe it was what
Leo learnt from blowing up a few of them .

A subsequent article "The ETI-480 amp module - barefoot and bridged"
had a table of some known single-ended and bridged configurations.
I can see that the power results presented are likely correct, but
the table is very sparse, and again, there's no formula to help in
completing it.

The recent (Jan/Feb '04) 300W amplifier in SC also shows the same
type of graph, page 14 inthe January issue.

** Pretty sure there is an Eminence agent here - also consider
Celestion.

Ok, I'll get on the phone. I would have already, but when I google
for "eminence speakers", it seems impossible to find the manufacturer,
you only get resellers.

WES sell a decent 15 inch bass speaker for circa $100 - the
"IS15 -150 " .

Ok, I was thinking 12" because I have a cabinet that suits one, but
the front plate can be replaced. It's a good price, thanks for the
pointer. Must get a WES catalogue, shame it's not online.

** I did, many times - it is based on a false assumption.

Perhaps now that you've reviewed the articles I referred you to,
it makes more sense?

Clifford.

 

[Phil Allison]

"Clifford Heath"

Phil Allison wrote:
** Output device dissipation is only a few watts in that condition.
Vce
drops to around 1 volt at clipping.

Yup, fair point.

** No fooling ...................

It's when you get a reactive load that the current
can be near a peak while the output voltage is approaching zero
(maximum voltage across the output devices).

** That is what SOA concerns are all about - that *fraction* of a cycle
when high peak device dissipation happens.

At some frequencies,
you can even get negative impedance - +ve current and negative
voltage at the output.

** Soon as there is ANY phase angle between V and I there is a period
( near zero crossing) when the two are of opposite polarity.

But that's the type of complexity that I
think you were assuming I was unaware of.

** Nope - it was this drivel " ....I can't see how to integrate it over
one half-cycle. "

BTW What is the persistent ETI 480 stuff...

No, it's the ETI-480 - but probably the higher distortion figure
won't matter.

DSE sell both, but Leo Simpson had nothing to do with the ETI one.


Ahh, ok. I'm more familiar with Leo's more recent work, including his
first article on the subject, entitled "A discussion of some of the
design problems in High Power Amplifiers", published in WE, October
1979, pp 66-68.

** Huh ?? What is WE ?????

Sounds more like the EA articles re their 1980, 300 watt amp

I have no copies of stuff 25 years old.

The text is online as a PDF somewhere, but Fig 4
contains the first instance I know of of the type of diagram I'm
talking about. It plots current vertical against voltage horizontal,
and shows the SOA, resistive and two inductive dissipation curved.
I assumed that this was used in the ETI-480, but maybe it was what
Leo learnt from blowing up a few of them .

** I repeat - the ETI 480 design is not connected with Leo.

The recent (Jan/Feb '04) 300W amplifier in SC also shows the same
type of graph, page 14 inthe January issue.


** Pretty sure there is an Eminence agent here - also consider
Celestion.

Ok, I'll get on the phone. I would have already, but when I google
for "eminence speakers", it seems impossible to find the manufacturer,
you only get resellers.

** And who did you expect to buy one from ??

WES sell a decent 15 inch bass speaker for circa $100 - the
"IS15 -150 " .

Ok, I was thinking 12" because I have a cabinet that suits one, but
the front plate can be replaced. It's a good price, thanks for the
pointer. Must get a WES catalogue, shame it's not online.

** I did, many times - it is based on a false assumption.

Perhaps now that you've reviewed the articles I referred you to,
it makes more sense?

** What articles ???

Post some URLs - the ETI 480 history and data is on the web.




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

 

[Clifford Heath]

Phil Allison wrote:

** Soon as there is ANY phase angle between V and I there is a period
( near zero crossing) when the two are of opposite polarity.

Yup, but that's not what I meant, as you know. To get significant
power, you have to have significant current. When the phase shift is
more than 90 degrees, you get into an area of negative resistance
(which is what I meant when I said negative impedance), where you can
have *peak* current at negative voltage.

** Nope - it was this drivel " ....I can't see how to integrate it over
one half-cycle. "

A formula for instantanous power doesn't give you the average power
over one half-cycle (of current), it needs to be integrated, you
know, that calculus stuff? But I since remembered that using complex
numbers is easier for this stuff than calculus.

** Huh ?? What is WE ?????

Typo, should have been EA.

Sounds more like the EA articles re their 1980, 300 watt amp

Yup, it was just before ETI-466 was published.

I have no copies of stuff 25 years old.

I got rid of mine also, along with the 30+ year-old stuff in which
I had a circuit published as a kid :-(.

** I repeat - the ETI 480 design is not connected with Leo.

Yeah, got that message. It was Graeme Dicker.

Most of what I now have is from <http://www.alphalink.com.au/~cambie/>.
Some of the related material (not Leo's) is under the ETI-466 in ZIP
files Prac1.zip and Prac2.zip

you only get resellers.
** And who did you expect to buy one from ??

A local dealer (not one of the thousands of US ones that google finds),
found by perusing the "dealers" section of the manufacturer's web page.
How else?

** What articles ???
Post some URLs - the ETI 480 history and data is on the web.

This one, for example, from my previous mail:

The recent (Jan/Feb '04) 300W amplifier in SC also shows the same
type of graph, page 14 inthe January issue.

Leo's article I found somewhere as a PDF which I can send, but I don't
know where I got it from now.

Clifford.

 

[Phil Allison]

"Clifford Heath"

** Soon as there is ANY phase angle between V and I there is a period
( near zero crossing) when the two are of opposite polarity.

Yup, but that's not what I meant, as you know.

** There is no way known to know what you mean.

To get significant power, you have to have significant current. When the
phase shift is more than 90 degrees,

** When does that ever happen ??

Not with speaker loads for sure.

** Nope - it was this drivel " ....I can't see how to integrate it
over one half-cycle. "

A formula for instantanous power doesn't give you the average power
over one half-cycle (of current), it needs to be integrated, you
know, that calculus stuff? But I since remembered that using complex
numbers is easier for this stuff than calculus.

** The power dissipation averaged over a cycle is less with reactive than
for the simple resistive load case.

** Huh ?? What is WE ?????

Typo, should have been EA.

** That is one HELL of a typo !!!!

Ok, I'll get on the phone. I would have already, but when I google
for "eminence speakers", it seems impossible to find the manufacturer,
you only get resellers.

** And who did you expect to buy one from ??

A local dealer (not one of the thousands of US ones that google finds),
found by perusing the "dealers" section of the manufacturer's web page.
How else?

** Still a dealer - not the manufacturer.

** What articles ???

Post some URLs - the ETI 480 history and data is on the web.

This one, for example, from my previous mail:

The recent (Jan/Feb '04) 300W amplifier in SC also shows the same
type of graph, page 14 inthe January issue.

** I have not got that one.

Try reading this one:

http://sound.westhost.com/vi.htm


and get that nonsense about 90 degree+ phase angles out of your head.





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

 

[Clifford Heath]

Phil Allison wrote:

** The power dissipation averaged over a cycle is less with reactive than
for the simple resistive load case.

Yes. I want to know how much less. Because when you turn it around
and measure 100W delivered RMS power into the reactive load, you
need an amp that's capable of delivering more then 100W into a
resistive load by the same ratio.

** Still a dealer - not the manufacturer.

Obviously. But have you checked the cost of shipping one of these
heavy beasts from the USA?

** I have not got that one.

But now you have the one I emailed you directly, last night.
I have others if you need them, or can scan the '04 SC one.

Try reading this one:
http://sound.westhost.com/vi.htm

Thanks, excellent reference. Would you recommend me adding a VI
limiter to the ETI480 outputs, assuming they're operating from
+-37V into 4 ohms?

 

[Phil Allison]

"Clifford Heath"

Phil Allison wrote:
** The power dissipation averaged over a cycle is less with reactive
than for the simple resistive load case.

Yes. I want to know how much less.

** That it IS less means you do not need extra heatsinking over what is
needed for resistive loads.

Because when you turn it around
and measure 100W delivered RMS power into the reactive load, you
need an amp that's capable of delivering more then 100W into a
resistive load by the same ratio.

** Pure gobbledegook - until you define the nature of the reactive load,
this makes no sense.

The article on the ESP site makes is clear what to expect from a
woofer.

** Still a dealer - not the manufacturer.

Obviously. But have you checked the cost of shipping one of these
heavy beasts from the USA?

** Non sequiturs are your speciality ?

** I have not got that one.

But now you have the one I emailed you directly, last night.

** My email addy is fake.

I have others if you need them, or can scan the '04 SC one.

Try reading this one:
http://sound.westhost.com/vi.htm

Thanks, excellent reference. Would you recommend me adding a VI
limiter to the ETI480 outputs, assuming they're operating from
+-37V into 4 ohms?

** Nope - long as you are using the 4 device version of the amp.




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

 

[Clifford Heath]

Phil Allison wrote:

Because when you turn it around
and measure 100W delivered RMS power into the reactive load, you
need an amp that's capable of delivering more then 100W into a
resistive load by the same ratio.
** Pure gobbledegook - until you define the nature of the reactive load,
this makes no sense.

It's really quite simple - I'll try again:

If the speaker is modelled as 5ohms+5mH for example,
and an amp puts 100WRMS into it, the amp is operating at
a voltage level that would put more than 100WRMS into an
resister or equivalent impedance. Maybe 120W or 140W for
example (that's what I want to figure). So should this
amp be claimed to be a 100W amp or a 140W amp? Obviously
a manufacturer will claim the latter. Would anyone use
the former?

But now you have the one I emailed you directly, last night.
** My email addy is fake.

Resent under this subject line to a.b.s.e - I'd appreciate
your comments.

Clifford.

 

[Phil Allison]

"Clifford Heath"

Phil Allison wrote:

Because when you turn it around
and measure 100W delivered RMS power into the reactive load, you
need an amp that's capable of delivering more then 100W into a
resistive load by the same ratio.

** Pure gobbledegook - until you define the nature of the reactive load,
this makes no sense.

It's really quite simple - I'll try again:

** Lose the smartarse attitude !!!

The problem is being created by YOU posting ambiguous rubbish and
constantly moving the goalposts.

If the speaker is modelled as 5ohms+5mH for example,
and an amp puts 100WRMS into it, the amp is operating at
a voltage level that would put more than 100WRMS into an
resister or equivalent impedance.

** Not relevant to your ETI 480 - as the DC rails are a given.

The supply rails set the output power limit into a load.

Maybe 120W or 140W for
example (that's what I want to figure). So should this
amp be claimed to be a 100W amp or a 140W amp? Obviously
a manufacturer will claim the latter. Would anyone use
the former?

** Amps are always quoted with resistive loads - just to avoid this silly
issue. The same amp with a ( series ) reactive load will always deliver
less - since voltage is lost across the reactive component.


BTW

I make this the fourth time you have **totally changed** the nature of your
question re SOA.

Wanna go for five ??


BTW 2 Nothing visible on my ABSE (courtesy of tpg)



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

 

[Clifford Heath]

Phil Allison wrote:

** Lose the smartarse attitude !!!

I've been biting my tongue real hard for a while here.
I don't need to say what everyone else is already thinking.

** Not relevant to your ETI 480 - as the DC rails are a given.
The supply rails set the output power limit into a load.

Not entirely. If I can't make the thing safe at +-37 volts,
I'll buy a different supply tranny. In fact the monster is
likely to be so annoying that I will anyhow. I just thought
that adding another bridged pair might be useful in future.

** Amps are always quoted with resistive loads

Ok, that's what I thought.

BTW 2 Nothing visible on my ABSE (courtesy of tpg)

It'll propagate from Optarse soon.