"Patrick Turner" <info@[EMAIL PROTECTED]
> wrote in message
news:47A574B3.5D9FA06@[EMAIL PROTECTED]
>
>
> Trevor Wilson wrote:
>>
>> "Patrick Turner" <info@[EMAIL PROTECTED]
> wrote in message
>> news:47A478B2.BFE8A725@[EMAIL PROTECTED]
>> >
>> >
>> > Trevor Wilson wrote:
>> >> > Fins are vertical, and have natural unobstructed air flow not
>> >> > dependand
>> >> > of fans.
>
>
>> >>
>> >> **I trust they are anodised black, as this will improve cooling
>> >> efficiency
>> >> somewhat.
>> >
>> > Blacking the heatsink makes them only 10% more efective; ie, instaed
of
>> > 24C t rise.
>> > maybe you get 22C T rise, not a huge difference.
>
> snip...
>> >
>> > HS are blacked mainly for appearances sake.....
>>
>> **Nope. They're black to ensure highest possible efficiency.
>> Manufacturers
>> could choose any colour they like, but most choose black, because it
>> works
>> best. Your figure of 10% is close to the mark. At 100oC that makes a
10oC
>> difference.
>
> Manufacturers DO NOT always colour HS black at all and they mostly try
> to avoid the cost
> of doing so.
>
> Quad didn't with their 405....
>
> Some do make them black, some don't, and appearances matter for sales
> appeal.
>
> MOST generic mainly class B SS amps have many very thin Al fins crimped
> onto a
> 4mm thick extruded plate base without even any silicone grease.
>
>
> snip
>
>> >> **The best fans (by far) are 240VAC types. They are tough, quiet and
>> >> easy
>> >> to
>> >> control.
>> >
>> >
>> > Sure they are tough...
>> >
>> > But you CANNOT run then full bore because the noise is INTOLERABLE.
>>
>> **That would depend on the fan. I have an ancient Boxer fan (made in
the
>> US)
>> which is amazingly silent at full RPM. Having said that, the noise is
>> pro****tional to air flow VELOCITY.
>
> But even with fans barely turning around the howl across the room is
> still
> audible to finer ears than mine for whom I make my amps.
>>
>> > OK with a an RF transmitter or industrial or PA amp, but NOT
>> > something in someone's lounge with audiophiles with perfect hearing
>> > able to hear a pin drop or low level fan whine or transformer hums.
>>
>> **That would depend on the fan, how it is mounted and how it is used.
>> I've
>> measured a fan in a piece of audio equipment (at 4:00AM) which was not
as
>> noisy as the transformer in that equipment. The transformer was a
potted,
>> toroidal type and was VERY quiet. Of course, the fan was large, 240VAC
>> type
>> and mounted on compliant rubber.
>
> All the fans I tested were noisy.
>
> Even if the fans are quieter than a power trans one doesn't want the
> added noise.
> The fans produce noise at F where fine ears are very sensitive; PT
> make noise mainly at lower F with the switching noise harmonics from
> 100Hz
> rectifiers on B+ usually being the worst to control.
>
> My 845 amps have TWO separate choke input supplies for the two 845
> cathodes
> needing 3.4A at 10V dc for the Chinese 845 or 211 which I am likely to
> use.
> With B= turned off, the choke inputs are very quiet, even with unpotted
> chokes.
> I will have to probably choose R between diodes and C1 of the B+
> supplies and a higher voltage
> HT tap to reduce peak rectifier charge currents and hence reduce the
> noise a bit more.
>
> This means even more hot running resistors, worth it though.
> In for a penny, in for a pound...
>
>
>>
>> >
>> > I tried using a few spare 120mm dia fans here with 240, and they are
>> > effective
>> > when fed only 95Vrms instead of full blast 240, so you have to series
a
>> > pair
>> > and use dropping resistance They are plainly audible even at low
speed,
>> > and
>> > trying to get them slower and quieter is self defeating and an
exposed
>> > fin passive HS is then
>> > just as good if the fin area is large enough.
>>
>> **Here are some specs I gleaned from a single manufacturer (Papst) for
>> two
>> fans. One, 80mm and one 199mm. Both are 230VAC types.
>>
>> Size Air flow (L/min) dBa@[EMAIL PROTECTED]
>> 80 13.7 24
>> 119 22 25
>>
>> These fans are rated by Papst as "super low noise". You'll note that
for
>> a
>> miniscule increase in SPL (1dB), with the 119mm fan you get nearly
double
>> the air flow of the 80mm fan.
>
> OK, I have not investigated Papst fans, just the lowest noise types
> which the project can afford.
>
> The two $16 x 80mm 12Vdc fans from Jaycar were rated for 32dB and
> terribly noisy
> with 12Vdc, but cooled the HS WITHOUT the added fins very well even with
> only 6V and barely turning, and where noise may have been at
> 25dB if the full bore 32dB was to be believed.
>
> But those fans were still way too noisy.....
> I could hear them easily at 3M, and my old ears are much worse than some
> sharp
> younger man at 30.
>
> Nothing so silent as NO fans, and I don't have to
> muck around with fan control circuits and making special metal work.
>
>
>> Decrease the speed of the fan to match the
>> volume of air from the 80mm fan and the noise will be dramatically
lower.
>> My
>> rough measurements in the past indicate an approximate 10dB fall in
noise
>> levels. An excellent trade-off. BTW: Looking at 80mm 12/24 Volt DC fans
>> from
>> Papst, indicate noise levels in the range of 23 - 32dB. An
insignificant
>> decrease in noise, for far less controllability.
>
> The motor noise is the least of one's troubles; its the air noise,
> and blades cutting the air to give maybe a 500Hz whine plus harmonics.
>>
>> >
>> > My experience with ME amps and their fan control and heat control
>> > leads me to think I'd always rather have a passive HS like Quad 405
>> > etc.
>>
>> **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.
> This is easy to do.
>
> My 2X300 amp has 40 watts for each channel at idle with passive HS.
> Each of the two HS are sized 300mm long, 30 fins 150 long each, 2mm
> thick extruded.
>
> No fans are needed even when using 4 ohms and running 300 watts.
>
> Music taken to clipping hardly affects Temp.
>
>
>> * The ME is SPECIFICALLY designed to operate at a constant temperature
of
>> between 50 - 60oC.
>
> Yes, good practice, and achievable with passive HS with lotsa fins
> poking into
> a natural rising airflow.
**Nope. Not even close. The ME850 will maintain it's heat sink
temperature,
REGARDLESS of ambient temperature. If the ambient temperature is 0oC the
heat sink will be maintained at 50-60oC. If the ambient temperature is
40oC,
the heatsink temperature will be maintained at 50-60oC. This is not
possible
with convection cooling.
>
> My mono class A 50 watter mosfet amps with home made HS have 100W at the
> HS at all times,
> and T never rises above 50C.
**I did say that the temperature is a constant 50-60oC.
>
> No fans needed at all.
>
>
>>
>> >
>> > The ME850 has a nice fan system, surrounded by foam.
>> > In the last one I repaired the foam is on its last legs and will have
>> > to
>> > be replaced in
>> > a a year perhaps. Foam rots and falls to bits, and the foam in the ME
>> > isn't
>> > an exception to this.
>>
>> **Indeed. Which is why I ALWAYS replace the sup****t foam, if I consider
>> it
>> has less than a few year's life left. I see no point in gouging
customers
>> unnecessarily. This way, they only pay for one labour charge, rather
than
>> two. In normal operation, the sup****t foam last between 10 and 15
years.
>> Not
>> an unreasonably short period of time, IMO.
>
> Not bad for foam lasting ability.
>
> The amps are about 15 years old.
>
> What's the foam part cost?
**Dunno. 30 Bucks or so. That's my best guess. I purchased a bunch awhile
ago and I can't recall the exact price.
>
> It needs to have been manufactured last year, not be 15 year old stock>
**Of course.
>
> Meanwhile the guy whose ME 850 I repaired re****ted that in his AR9
> speakers,
> all 4 x 11" bass drivers and the two large bas/mids have rotted
> surrounds.
> I told him not to use these speakers until they are fixed when I get
> time
> because they might damage the amp, although it probably would cope
> with the occasionally jamming cones with the resulting reduced
> impedance when they jam.
> He has a stand by pair of speakers until repairs/upgrades are done over
> winter.
>
> The amp foam can be replaced in the work ahead....
>
>
>>
>> >
>> > Modern DC fans are not so easy to control quietly. The motor is
>> >> usually a brushless, AC type. The difficulty arises with the
>> >> controller.
>> >
>> >> Just alterning the input Voltage can cause 'cogging' which
translates
>> >> to
>> >> noise. Best to use an AC type, with a suiable controller, or even a
>> >> resistor.
>> >
>> > The fan noise is caused mainly by the speed of blades whipping tiny
>> > eddy
>> > air currents.
>> > Its basically PROPELLER NOISE that we have to face, not "cogging".
>>
>> **You have cogging problems with DC fans.
>
> I couldn't hear cogging noise, but its the AIR noise that seemed worst
> with the dc fans.
>>
>> >
>> > I tried resistors to drop the AC or the DC voltage.
>> >
>> > And, like ALL fans, the bigger the quieter.
>> >
>> > I found a pair of 80mm 1vDC fans were much quieter than ONE 120mm
fan.
>>
>> **That would depend on the choice of fans. Two good fans will be
quieter
>> than one crappy fan.
>
> I meant 12Vdc fans BTW....
>
> Choice and cost are/were im****tant, but best idea is zero fans.
>>
>> >
>> > The dc fans waste far less resistor feed current, and ran at 6V OK
>> > for reducing T rise by 50%. But that's all.
>> >
>> > This is for a class A amp so once up to running temp the heat is
>> > STABLE.
>> > Its not a class AB amp where Pd of the devices and HS swing wildly
due
>> > to signal levels.
>>
>> **I understand that.
>>
>> >
>> >
>> >
>> >> A large, slow revving
>> >> fan, will be quieter and move as much, or more air, than a smaller
>> >> type.
>> >> In
>> >> general. I have a bunch of 175mm fans, which I operate at 50% of
their
>> >> rated
>> >> Voltage and they are inaudible. Mind you: They are old, mad ein
Japan
>> >> and
>> >> very high quality.
>> >
>> > I have a few old fans; none are quiet, all are audible, and a passive
>> > HS
>> > is the best solution for me. I have no room left on the chassis to
>> > accomodate a
>> > suitably formed metalwork plenum to flow the air without turbulence.
>>
>> **Fair enough. I wasn't commenting on your final solution. I was
>> commenting
>> on what I feel to be your misconception about certain fans and their
>> noise
>> levels. You say it yourself, in your reference to turbulence. Lower
>> velocity
>> air creates less turbulence. Lower velocity air, with higher volume can
>> pay
>> big dividends.
>
> So far to get any benefit with any fan the air turbulence noise is a
> problem still, and with any sort of ducted plenum, you get a defacto
> resonator to increase noise; the air tube path acts like a horn.....
> or like an organ pipe... maybe a foam plenum is needed,
> but its all fancy smancy gee whizery, where having a simple
> passive HS will do fine.
>
>
>> >> >
>> >> > So where one was building a 25 watt class A SS amp, one might have
>> >> > to
>> >> > dissipate 55Watts,
>> >> > so you'd need a total Al fin and plate surface area 55 x 40 =
2,200
>> >> > sq.cm to get a T rise of about 24C.
>> >>
>> >> **Which is where using a large, slow revving fan, makes perfect
sense.
>> >
>> > Sure, but all ther fans I have tried are too noisy for anyone I know.
>> >
>> > Its better to use the extra one kG of Al in a custom made amp.
>>
>> **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. I mounted the wideband (40kHz)
microphone 2cm from the air intake and took measurements. First, with the
amp switched off. Then with the amp switched on, but with the fan off.
Then
again, with the fan on. The results were impressive. By ear, I could hear
the transformer noise, when I was under the doona and my ear about 10cm
away
from the intake vent. I could not hear the fan noise, nor could my
measurement equipment (LinearX LMS system) detect any change, when the fan
came on. When I moved more than 30-40cm away from the amp, I was unable to
hear anything. I readily acknowledge that in a country area, background
noise may be even lower than Sydney at 4:00AM however.
>
>
>>
>> >
>> > High bias Class A or AB amps will not have varying heat once up to
>> > working temp. Some examples I have seen are plain awful like Sugden
who
>> > have horizontal HS fins, YUK!! when will these doltheads learn??
>>
>> **They probably won't. Musical Fidelity have made similar stupid
>> mistakes.
>
>> >> > This is what I have for my resistor pack on the mono 845.
>> >> >
>> >> > The placement of mosfets and any hot parts must be so they are
>> >> > spread
>> >> > out as much as possible or else
>> >> > you get devices being hotter than you'd want if they are clustered
>> >> > together
>> >> > and a heatsink running too hot near the devices and too cold
further
>> >> > away from the devices,
>> >> > so the devices are stressed and the heatsink would be inefficient.
>> >>
>> >> **Which is why fan cooling makes perfect sense.
>> >
>> > We will have to agree to disagree Trevor.
>> >
>> > I just spent a day ****ing around with fans and decided they are a
>> > miserabally Royal Pain In The Arse.
>>
>> **A whole day! Gee! I've spent weeks mucking about with fans. Big, slow
>> revving fans are quieter than small fast revving ones (all things being
>> equal).
>
> Its not as if I don't know the basics about fans Trevor.
**It seems you miss the fundamental principle about velocity of air vs
volume.
>
> I agree with you in principle, but as I have argued over the years,
> having no fans and just convection/radiation cooling is all that's
> really needed.
>
> I do not know why ME went to the fan option. A waste
> of time and op****tunity IMHO.
**Nope. ME chose fans for some good reasons:
* Output stage temperature was able to be kept constant with great
precision.
* Warmup times were dramatically reduced.
* Since air flow p***** through capacitor banks, lifespan is extended.
* Moving air p***** over ALL components in the amplifier, including bypass
electros, thus prolonging their lifespan.
* Mass was kept lower, due to the abscence of huge amounts of aluminium.
* Case size was reduced substantially, due to the abscence of huge amounts
of aluminium.
* Customer choice of mounting has been dramatically improved. The amp may
be
used in ANY orientation. The amp may be placed in a cabinet, with doors
closed (inadvertently) and the fan will increase speed to cool the amp.
BTW: The normal fan speed @[EMAIL PROTECTED]
25oC ambient is around 300 RPM. This is
dramatically slower than the 2,000 - odd RPM of an unregulated fan. And
dramatically quieter.
>
> Look at some very top name SS amps made in the US.
>
> No fans to be found.
**So? I fail to see your point. 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.
>
> Fans have been tried in tube amps as well. ARC has them fitted
> but of course ARC have no idea how to properly bias output tubes so the
> fans don't
> help overheating tubes, and who likes music with the drone similar
> to two circling B17's over berlin in 1944?
>
> snip,
>
>> > I tried it out today with shed C = 28C, and got HS at 52C. Actual R
>> > might be
>> > 62C.
>> >
>> > Reliability in general for R drops 5% for each 10C rise in Temp.
>> >
>> > So at 100C, the R are 50% unsafe, and at 200C, VERY likely to fail.
>> >
>> > Solid state device reliability falls 10% for each 10C rise.
>>
>> **Nope. A common misconception. Capacitors, maybe, but not semis.
>> Operating
>> semis at a constant elevated temperature can pay big dividends in
>> reliability. This research was done decades ago by RCA engineers. For
>> that
>> reason, RCA chose to use steel rather than aluminim for their TO3
>> devices.
>> It is the thermal cycling which kills the devices, not the absolute
>> temperatures (assuming the devices are kept below (say) 100oC.
>
> Doncha reckon RCA used steel because it was FAR cheaper than copper or
> Al???
**Nope. I may even have the white paper somewhere. Steel was chosen due
it's
similar thermal expansion characteristics to silicon. Back in the 1970s,
RCA
and Motorola were batting heads. Motorola chose aluminium and RCA chose
steel. Before too long, Motorol switched to steel as well, as they
discovered, through thermal cycling, their aluminium devices were failing
prematurely. Not that it is relevant, but when I was service manager for
Marantz, one model stood out as being slightly less reliable than it
should
be. The Model 140 power amp (and it's derivatives - the 2270 reciever).
Unusually, it did not use Japanese output transistors Which were steel or
copper cased), but it used Motorola devices. Although an in-house code was
used, I believe the output devices were probably MJ15003/4s. Not only were
they less reliable than usual, when the outputs failed, the silicon would
usually burn a small hole in the case, as it ejected itself from the
amplifier. Not possible with steel, of course.
>>
>> >
>> > So with 100C rise, BJTs etc are 100% likely to fail soon.
>>
>> **100oC is too hot for semis.
>>
>> >
>> > And these things do fail. My shed if full of amps that
>> > have failed due to heat resulting from failed bits and peices,
>> > and very often it goes back to the designer who reliaes ona Hail Mary
>> > or
>> > Allah to
>> > prevent failure.
>> > Dry joints are very likely when the leads, tracks, boards get hot;
heat
>> > causes expansion differentials
>> > on PCBs and some things are not mounted to allow for the microscopic
>> > movements that occur.
>>
>> **Sure. And, strangely enough, I rarely find dry joints on hand
soldered
>> PCBs and American machine soldered equipment. I don't know why.
>>
>> >
>> > 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 ****ing 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.
Trevor Wilson
|
