Re: Heatsink fin area for given temp rise.


"Patrick Turner" <info@xxxxxxxxxxxxxxxxxx> wrote in message
news:47A93E0D.A3F28EAB@xxxxxxxxxxxxxxxxxxxxx


Trevor Wilson wrote:

"Patrick Turner" <info@xxxxxxxxxxxxxxxxxx> wrote in message
news:47A72B61.8AFA0E62@xxxxxxxxxxxxxxxxxxxxx

snip,


**All very well, except the you forge several things:

* The Quad is a Class B amplifier.
* The ME850 is a very heavily biased Class A/B amplifier, with
around
16
Watts of Class A power.

Which means having 32 watts in the heatsink at idle.

**WHAT! I suggest you consult your calculator once more. 16
Watts/channel
Class A, at a rail Voltage of +/- 50 - odd Volts does not correspond
to
32
Watts of PDiss. More like 300 Watts.

You cannot get more than 50% of the IDLE dissipation in class A audio
power,
and to get 16 watts of class A audio PO you must have a high RL if the
rails
are +/-50V. Don't tell me to use my calculator when you know I know
enough
and you won't convince the reading public with a detailed reply.

**I suggest you consult your calculator and text books.

I already have, and it appears your'e either too lazy and/or just too
incompetent
to prove something is correct about what YOU said about your favourite
ME amplifier workings.

**Then present your calculations. The rail Voltages are +/- 50 Volts.


The trouble with having anything to do with ME products is the complete
lack of online information.

Please remedy this situtation.

**I am not the manufacturer. It is neither my responsibility, nor am I
legally allowed to do so.


It'll only take you a few weeks to explain everything
and have all the service info and schematics in pdf.

Then I will offer you the full respect for your knowledge.
I am a real curmudgein I know, I expect people to proove themselves to
me before
I can respect them fully as i would like to.

I spent 6 months up-grading my website to stop ppl emailing me with dumb
questions.
The answers are there at my site, and it is NOT a pile of
uninformative sales bull***.

Before respect is given by anyone with any intelligence, you have to
show you really understand.



Its on YOU to convince me of the merits of the ME 850, but perhaps you
don't know all the numbers
about its workings.

**I know enough about how much power is dissipated in output devices,
when
the supply Voltage and bias current is known.


The ME 850 does not dissipate 300 watts per channel at idle, and cannot
make up to say 140 watts of class A.

**I NEVER siad the ME850 dissipated 300 Watts per channel at idle.

Nor did I.

**No. Here is what you (incorrectly) claimed:

"Which means having 32 watts in the heatsink at idle."

I said the ME 850 appears NOT to dissipate 300 watts at idle.

**Here is what you DID claim:

"Which means having 32 watts in the heatsink at idle."


But if it did, you could get about 140 watts of pure class A....

**Wrong. The rail Volts are +/- 50. I suggest you do your calculations with
that knowledge.


Who the hell would know anything about ME amps if ME never
made their amp details public and freely accessible????????

Anyway, with all due respect to Peter Stein, former ME CEO, readers need
to remember that
ME Technologies closed down business and amp productions a couple of
years ago due
to the conditions of a divorce settlement.

Peter seems to have retired, or escaped to Cairns, in North Queensland,
where no doubt he spends time relaxing under the coconut trees
and away from the hurly burly of running a business in cold climate
sothern states
where most of his sales were, and trying to preach the
benefits of his inventiveness to all and sundry in these sewers which
are called news groups.

So I doubt work is underway to place all the ME service info on a
website,
and available to all.




It produces quite low heat at idle, hence the very small amount of
class
A power,
but as audio power rises way beyond the class A to AB threshold, the
Pdiss then increases to your
stated 300 watts.

**No. The idle power consumption of the entire amplifier is approximately
300 Watts. Largely due to the 16 Watts of Class A biasing of the output
stages.

Well that makes 150W per channel at idle.
But you are saying there is 16 watts ( per channel?) od idle biasing

**NO. I stated that the ME850 delivers the first 16 Watts (@ 8 Ohms) in
Class A.


Make up you mind which of your statements is the truth.

**Misquoting me doesn't make me a liar. It merely makes you a person who
cannot quote correctly.





Please give all the details or make sure the details are avaliable at a
website
you can refer us to, with full explanations and all full schematics
like
my site has.

**Why? I am not the manufacturer. Are you suggesting that I should engage
in
breaching the copyright act?

Peter Stein should forget about protecting the copywrite he owns.

**I see. You should tell him that.


Its not worth anything. Nobody is EVER going to make money copying a
1976 amp design
by some relatively unknown Australian.

I don't suggest you breach copyright, but DO SUGGEST Peter Stein
stop being so darn secretive, and let the world know all his OLD
secrets.


Good design of SS amps does not need to have such precise temperature
control.

**Your OPINION is duly noted. Opinions are like arseholes. Everyone has
one.
The manufacturer of the ME860 has more than 30 years experience in the
construction of his amplifiers. He has determined (after using convection
cooling) that fan cooling, with is ability to provide precise temperature
control over output devices is the best way to go.

In an amp which is designed to operate in heavy class AB, after an
intiial few watts
of pure class A, there is nothing wrong with precise T control, except
the noise of the fan when it speds up to FORCE down the T when the T
rises above 60C.
Any decent amp should allow its devices and HS T to rise to 75C
without any problems.



Devices can be allowed to move within a range provided by fanless
heatsinks.

**Certainly. Conventional amplifiers, with large amounts of global NFB
will
work just fine in this way. The ME850 is far from a conventional high
global
NFB amplifier however.

But the basic ME amp design has in fact TWO loops of HIGH AMOUNTS of
NFB.
One around the driver stage and one around the output stage.

**Incorrect. The ME850 uses no Global NFB loop. The front end Voltage amp
uses a relatively small 15dB feedback loop. The output devices are not
contained within a Global Feedback loop. The DC servo loop operates only at
subsonic frequencies.


The reason ONE good loop of NFB COULD NOT be applied as simply as
everyone else has done it
is because there are too many amp stages, and the design would be
intractiably unstable if you tried.
Peter locked himself into his "unique" design he could then say was
superior,
and a whole raft of sales pitch and spiel hinges upon the basic design
which mainly
totally befuddles people when mentioned by yourself because there isn't
a schematic
available for ppl to check out what you are saying.

The ME amp IS VERY conventional in that it is in a black box, has HS, a
fan,
and uses lots of transistors and caps and resistors, and operates in
mainly class B,
and uses lots of NFB.

**Nope. Points:
* The ME850 uses no Global NFB.
* The ME850 delivers it's first 16 Watts in Class A.
* The ME850 DOES use lots of transistors. There are dual differential input
devices, with current sources. It uses far more output devices than
necessary, so that devices can be operated in the most linear region. All
transistors are carefully matched to within 1% of hFE and Vbe.
* The output devices can never saturate, thus Voltage limiting is always
smooth and relatively high order harmonic-free.
* The current limiters are not contained within a feedback loop, so current
limiting never involves gross distortion production.
* The 2,500VA power transformer (split wound) @ 4% regulation, coupled to
265,000uF of filter capacitance ensures that any load impedance can be
catered for.

These are NOT the characteristics of a VERY conventional amplifier. However,
please feel free to list all the amplifiers you know of, which offer the
above features.


Thye basic circuit elements and topologies in the ME amps were invented
by others,
but used by Stein. Similar to me using the UL connection in some of my
amps.

**So?


Nither Stein or myself present anything completely unique and
unconventional.

**So?


Please provide proof if you cannot agree.

It so happens the ME isn't too bad sounding. It does what's asked of it.

**Indeed.


The precise temp control does not have to depend on Peter Stein's
applications of well known circuit theory.

**The precise temperature control is an important element of the design.





Many makers realise this, and make good sounding/measuring reliable
amplifiers.

**Indeed. Many more manage to build garbage.

Indeed.




I may see you about getting one later.

**It is a pity you did not request one earlier.

I could make a foam barrier filter if I really needed to.



**And again. I was not commenting on your final solution. That is
entirely
up to you. I was merely correctly your misconception about fans.
Big,
slow
revving fans are quieter than fast revving small ones (all things
being
equal).

Sure, and they still make noise which is well above the noise floor
of my amps. Customers want INKY BLACK silence with zero signal,
not some damned slight shshshsh noise like feint tape hiss going on.

**And again, properly mounted, a fan can be quieter than even a potted
toroidal transformer. When I did my last measurement, I did so at
4:00AM,
with a doona over the whole shebang.

Huh? you smothered the amp with a doona?

**I covered the amp and entire rack of equipment with a doona. I wanted
to
do several things:
* I wanted to reduce extraneous noise to a minimum.
* I wanted to create the worst possible conditions for the amplifier.


That would reduce the fan noise eh?

**Nope. The mic was placed under the doona with the amplifier.


What is the full technical meaning of "shebang"?

**See above.

OK, I get the picture but a doona would not reduce LF noise much.

**It was all I could do. Fortunately, at 4:00AM noise levels are quite low.



**It's also very cold where youa re (in the Winter).

Well yes, but people have 25C in their rooms in winter,
and maybe 30C in summer, so the amps have to survive,
and ears must be sparred the whirring noises of fans....


I have found fans are noisy, period, and everyone I speak to
laments their presence in hi-fi amps.

Most hi-fi amps don't have fans.

**So?

It means that most makers have realised you don't need a fan in a
domestic
class AB hi-fi amp!!!!

**And again, so? Properly implemented, a fan can provide many benefits.



Fans belong in PA and industrial amps.

**Indeed.


Transformer noise is a problem with many hi-fi amps,
and most have audible noise within 600mm.

Potting isn't a bad idea because it is so difficult to supress the
100Hz
switching noise
generated in core and windings when Idc is high. In class AB amps where
Idc is low, its not such a problem.

The fan noise on the ME850 was loud when the amp "tests itself"
for a few seconds at turn on.

**Correct.

Then the fan seems to turn off or run real quiet, basically its doing
nearly nothing.
But then there isn't any need for the fan at all.

**16 Watts Class A, with +/- 50 Volt rails is a significant amount of
Pdiss.

In my 2x300W amp with 2 channels, there are +/- 65 volt rails and
6 mosfets to each channel, 3 x npn, 3 x pnp, source follower configured.
There is 100mA idle current in each mosfet for a total of 300mA
flow the two rails so the Pd at idle = 130V x 0.3A = 39 watts, more than
twice
what you claim is in the ME850, and so my amp produces more class A than
the ME850.
My amp has passive heatsinks and no fans and T rise is never beyond 75C
even with continuous sine wave and 300 W into 4 ohms.

The FULL DETAILS are at

http://www.turneraudio.com.au/solidstateamps1mosfets.html


* Moving air passes over ALL components in the amplifier, including
bypass
electros, thus prolonging their lifespan.

This is quite simply done passively in many amps.

**Very rarely. In most amps, such components are mounted horizontally and
sit in 'dead air'. In other designs, the components are subject to
radiated
or convected heat. Moving air across such components is just good design.



* Mass was kept lower, due to the abscence of huge amounts of
aluminium.

Then why is the ME so darn heavy????????

**The 2,500VA power transformer probably contributes significantly to
that.
With such a heavy transformer, there needs to be substantial steel in the
chassis to support it.

Its totally uneccessary to have a 2,500 watt rated power tranny
to supply 2 x 200 watt channels.

**Your opinion is duly noted.


Especially so for domestic hi-fi where the average
listener is unlikely to use more than 10 watts maximum per channel.

a 600W tranny would be more than enough.

**Your opinion is duly noted.


With my 2x300W amp, I can turn the mains off and it continues to play
music for
20 seconds and when you turn the power back on, there is no click, or
the
slightest hint that for the 20 seconds,
there was NO mains transformer present!!!

Several ppl have built samples of my 2x300 watter and shared their
experiences with me.

If someone wanted to build an ME, they couldn't; no information
available.

**So? They couldn't anyway. Matching transistors is simply beyond the
capacity of an amateur.



Only fools and idiots use a power amp standing on end, or in a
closeable
cabinet of any sort.
If something goes wrong, smoke pours out.......

**Nope. The fan will simply run faster to compensate for any porblems. At
90oC, the amp shuts down.

Mine does the same at 80C, but it never has, unless I held a gas torch
on the HS near the
T sensor.


BTW: The normal fan speed @ 25oC ambient is around 300 RPM. This is
dramatically slower than the 2,000 - odd RPM of an unregulated fan.
And
dramatically quieter.

So the fan is not doing much is it.

**That is the beauty of using a large, slow revving fan. Large volumes of
air are moved at low velocity, thus nboise is kept to a minimum. The nice
thing about forced air cooling, is that even minimal air movement
dramatically improves heat sink efficiency.

I found this is true, but you need to have room for the fans and
ductwork
to get a result.
Using the available space for more Al fins is a lot simpler and easier.



Look at some very top name SS amps made in the US.

No fans to be found.

**So? I fail to see your point.

Well do try to see it.

Many top name brands DON'T use fans.

**So? I fail to see your point.

You won't accept that MOST of the world disagrees with your
ideas about fans, no?

**I will accept that most domestic amplifiers do not use fans. I will also
accept that most cars are front wheel drive too. That won't stop me from
preferring rear drive cars. Fans offer some compelling advantages over
passive cooling.


Get used to the fact that most amps don't have and don't need fans.

**I am not bothered in the slightest. However, for the record: The vast
majority of modern, high powered surround sound amplifiers now use fans. Of
course, they're crappy, DC fans and not weel controlled, but they do use
fans.


This trend looks set to continue as more makers secumb to competition
and
retire their analog class AB designs in favour of super efficient ( 95%
) PWM amps
which need neither HS or fans.

**That much I agree with.



I've seen American amps which DO use fans.
I've top name amps which do use fans. I've seen top name amps which
don't.
I've crappy amps which do and crappy amps which do not.

I don't like fans, OK.

**I am starting to realise that.


You do like them.

**I don't like, nor dislike them. Badly implemented, fans are a bad idea.
PROPERLY implemented, fans can offer substantial and demonstrable
advantages.


I have had troubles with the complex ME 850 heat management system
and the fan whirred away when it wasn't supposed to be working.

**I know.


It'd have been a simpler amp and more reliable amp
if it had NO FAN, and just nice fat passive heatsinks.

**Yes, it would have been simpler. However, it also would have been:
* Much larger.

Total BS. My 2x300W is smaller than the ME850.

**I'm sure it is. It has not been designed to do what the ME850 can do.
They're fundamentally different amplifiers, designed for different markets
and different requirements.



* Much heavier.

Aluminium is a light material!!!!!!!!

**A fan allows the use of far less aluminium. 10kg of aluminium is still
10kg.



* Have exposed and very hot (60oC) heat sinks.


Can be enclosed with perforated casing as in the case of most other
makers.

Peter walker, the designer of the Quad 405, didn't agree with your ideas
either.

**And here we go again. The Quad 405 was a Class B amplifier. The ME850 is a
120 Watt Class A/B amplifier, which delivers the first 16 Watts in Class A.
BIG difference.



* More expensive.

Er, the ME was $8,000 some 15 years ago when my customer bought his kit.
It was an OUTRAGEOUS PRICE to pay for a bit of sound in the lounge.

**It would be, if you quoted the correct price. You didn't.


ME was NOT very good value compared to many other alternatives.

**I accept your opinion.


I ain't saying it was a poor choice of amp, but sheesh, it could have
been simper and cheaper.

**Sure. ME could have put in a crappy little, badly regulated 600VA, single
wound transformer, cut back on the the number of output devices, added some
Global NFB and dumped the fan assisted temperature maintenance. Hell, ME
could have backed the bias off, so that it delivered (say) 50mW of Class A
power like all the other ordinary amps. Guess what? It would have sounded
just like them too.




* Less reliable.

Er no, My client here has had all these bothers with the MANAGEMENT
CIRCUITRY
CONTROLLING FANS AND TEMPERATURE.
These very circuits SHOULD be far more reliable than the audio circuits
they manage
and guard.

**You failed to note that the temperature maintenance systems always
fail-safe. If they don't (which is never), the amp shuts down at 90oC.



* Slower to reach operating temperature.

Does not matter. Most ppl would find 20 minutes OK.
But most SS amps with lotsa NFB like the ME sound quite acceptable 1
minute afterturn on
or when used as soon as possible.


* Less able to deliver significant Class A power.

The ME delivers a very insignificant amount of class A power.

**16 Watts is much more than many SET amps. In fact, it is more than many
SET amps which cost MUCH more money too. It is, to put it into perspective,
around 2dB less power than the legendary Mark Levinson ML2.


You said above you fail to see my points, but you fail
to provide us with a URL to explain the plain simple facts about the
class A power from ME.

Hardly anyone, certainly none of the owners of audio gear I know have
the slightest
idea exactly what class A or AB means. They are utterly technically
illiterate.

**OK.


What matters to audiophiles is the sound, not the class of operation, so
don't go spouting
claims you can't or won't proove.

**I am simply correcting your misconceptions and explaining the necessity of
using fans to keep the amp cool.

Douglass Self has a goos site on SS amp design. Take a look, you'll
learn.

**I have the book. Self has a lot of good stuff to say.


Then armed with the idea of what should be on a website to explain your
favourite brand, go to it.

Douglas does not have the same opinions as Peter Stein, or yourself.

**So? Self doesn't share your opinions, either. He, like Peter Stein, feels
that modern BJTs are, by far, the best audio amplification device. Better
than triodes, better than MOSFETs.


All these designers guys all argue about what's the best of course.

**Of course.


There is no best, just what you end up with after some work.

**I would argue that point.



Al and Cu expand more than iron, no?

**I don't know what the specific coefficients of expansion are. I do know
that steel more closely matches silicon.

Go look up expansion coefficients in Google!!!!!!




Please don't try to tell me that cost was not a factor in device
material.

**I can only repeat what I read in the white paper. Copper cost may have
been a factor. Aluminium was definitely less reliable than steel.

But papers by makers don't often tell the whole story.
They say what they are doing perhaps, but leave out lots....

**Motorola dumped aluminium a long time ago.



Makers in 1970 knew that they had to make amps with millions of
devices.
So saving $1 on each device meant a handsome profit.

**I doubt that the cost difference between copper and steel would be
$1.00
per device. In fact, I just worked it out. At today's prices
(US$7k/tonne)
the amount of copper in a TO3 devices works out at close to US$0.14c. In
a
modern, TOP3 plastic device, there is approximately US$0.10c worth of
copper. Steel is around 10% of the cost of copper (give or take), but
requires more energy and is more difficult to work.

Yes but where 14c per device cab be saved, if that's what it is, it will
be saved.
Bean counters always penny pinch to be seen to be doing something.

**Sure.




I've not designed and built any amps where i have had troubles
with overheating devices, but then nothing I have built has seen
LONG service as a PA amp where they get some real hard work.

I lent my 2 x 300 watter to a guy for a test amp once to see if
the power was enough to fill a large school hall with 300 people.
It worked fine. No overheating, no fans needed.
Only 6 mosfets per channel. 8 would have been better.

**MOSFETs are an excellent choice for sound reinforcement. They're tough,
reliable and don't suffer any of the thermal problems associated with
BJTs.

Huh? how many amps have you designed and built?

**Several. What's your point?


I have repaired a few SS amps whose supposedly indestructable mosfets
have
fused to a short, or overheated in some way to make them into
oscillators or
a queer device.

However, I prefer them to bjts.

Ask Halcro what they use. They'll say class AB mosfets.

$50,000 per pair of amps.


OTOH, they generate far more distortion (at low bias currents) and lack
some
other benefits of BJTs. Having said that, MOSFETs would be my first
choice
for an amplifier where reliability is the prime factor.

The mosfet distortion at low Id, say 10mA per device, is overcome simply
by increasing Id at idle to above 60mA. Their fast switching speed
makes the AB action more seemless.
getting 0.004% thd at 200 watts and distortion so low at 5 watts that
its difficult to measure it
is a doddle with mosfets.

Mosfet reliablity isn't always as wonderful as one would like.
I have had TWO random short circuit failures in power mosfets bought at
Jaycar.
I would guess Jaycar get the worst ones made which are cheapest.

**That'll teach you for using Jaycar for mission critical stuff.







He bought a Yamaha 2200 which suited his purposes.

Got it cheap at CashConverters, the pawn shop.

I fixed all the multiple pcb dry joint faults it had.


Making things rugged, easily serviceable, simple as possible,
but with excellent sound, and good measurements costs money.

**Yup. And selecting fans takes more than 1 day.

I don't have to select ANY fans now.

No more days and daze of fucking around.
I have a contract to get on with which has time targets.

Use 40sq/cm of HS area per watt to be dissipated and all is well.
Simple and effective.

**Yep. And I wasn't taking issue with your final choice. You need to
do
what
is right for you. I was taking issue with a decision to condemn ALL
fans,
based on the choice of a couple of cheap and nasty Jaycar types.

BTW, someone said that Papst isn't making fans any more.

**Did they? Perhaps they should inform these guys:

http://www.ebmpapst.us/

Clearly, they think they're still in the fan business.

Indeed.

The noise in dbA varies from say 35 to 17 if the air volume rate is
halved.

I'll believe it when I hear it if they are quiet enough.


You are right about the Jaycar selection.

**Indeed I am. WES have a far better selection of cheap, halfway decent
fans. But Farnell have a much better choice, albeit at higher prices.

WES data is grim about what noise to expect if the fans are run slow.

**Sure. You need to suck it an see.


But I only bought a couple of
cheapies to
see what the effects of using fans would be, and if the fans
were of sufficient benefits then they'd warrant use if really quiet
ones
were easily available
at the right price.
But no matter how quiet they could be, the placement of 12 fins
on the casket full of resistors was the simplest easy solution in this
case
where there is NO need for precision cooling.

Can you recommend me an available fan now which might change my
attitude?
Please quote the brand, model number and approx price if you know it.

**Sure. I will cite you a 240VAC fan, since low Voltage fans are not as
good. I will also cite you a 120mm type, since they can be operated at
low
RPM, which will further reduce noise.

ebmpapst model # 4890N
Farnell Part # 959-9770
Air flow - 22 Litres/sec
Noise level - 25dBA @ 1 M
Farnell price - $100.75
In manufacturing quantities, the cost will fall dramatically. Farnell is
a
good choice for prototypes, but not a good choice for manufacturing
quantities.

I'll keep the info in mind for some later time when I think its
necessary to use a fan.

Maybe never.

I don't have buckets of cash around and loads of time for days and daze
of R&D.

Simple effectiveness wins.

**A fan cooled heat sink is cheaper than lots more aluminium. Even a tiny
amount of air flow, can increase the efficiency (read: reduce the size) of a
heat sink by 500% or more.

Trevor Wilson


.