Aleph Temperature Sweet Spot

I know some of us have touched on heatsink size recently, but but does the Aleph (2) have an ideal operating temperature for best sound/distortion?

Mr Pass indicates 25 c rise above ambient for 50 - 55c and after 1 hour will reach best performance subjectively, and measured.

But how important is this? Obviously if it runs too hot say above 65 there may be some reliability issues, but what if you buy hugh heatsinks and it cruises at say 40 c.

Will this matter to best performance?

The curves for the 244/240 IRF show gentle rise through most parameters and perhaps there is a sweet spot.

My other point is that I assume that it is the top running temperature and not rise above ambient that is important.

Guys how about some feedback!

regards

macka
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
50 degrees C has been a standard for me for a
long time, not because it necessarily results in
better sound per se, but is the most ideal high
temperature for sale to consumers. At this point
human skin is quite sensitive to small changes in
temperature. At 45 degrees, you can keep your
hand on a sink for quite a long time, and at 50
you cannot.

Aside from assuring that a consumer or his family
will not be injured by the temperature, when I get a
call from wondering if an amp is biased properly, I can
ask the question, "How long can you put your hand on
the sink?" and get the information I need.

At home I have stuff running hotter, say 65 degrees,
which have not yet died, but then again, I don't lay awake
at night about a potential transistor failure.
 
This is a question that I have considered. On the face of it, it would seem silly that the temperature would have an effect on the sound quality.
But...
There are so many other things that defy rational explanation (cable directionality is my favorite example--makes no sense at all, logically speaking) that it might...just might be worth investigating. Basically those who choose to use passive heat sinks will have a tough time investigating this because the creation of heat via bias vs. the dissipation via the heat sinks is going to be fixed by the original mechanical design.
But for those who choose water-cooled circuits, the intriguing option of varying the water flow or the efficiency of the heat exchanger (air flow) would allow one to explore temperature questions independent of bias (to a first approximation--I'm ignoring the fact that the bias will vary with the temperature).
It's one of those things that's on my to-do list for about the year 2010. If anyone gets to it ahead of me, let me know how things turn out.

Grey
 

macka

Member
2001-12-15 3:07 am
Australia
Alpeh Temperature Sweet Spot

I appreciate your point on chip temperature.

I had this problem with my first class A diy project .. A JLH which only has one pair of output devices.

I used cheap SiIicon washers from Jaycar.They appeared to shrink after the first use and l cooked the output stage in 5 minutes because the devices had come loose.

I always use Mica washers now, but I undestand there are better quality self greasing washer available.

Do you have a preference for heatsinks with or without flanges?

I expect I will have to allow for any temperature gradient across the flange and heatsink junction as the flange appears hotter than the heatsink.

My current project for the Aleph 5 uses 1 x heatsink rated at 0.25 c /watt / channel. Theyhave twin flanges which makes it easier to mount the devices, this seems the main advantage.

I will refer this point to my heatsink manufacturer Conrad Engineering.

Thankyou for your assistance.

regards

macka
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
I always use Mica for TO-3's, as the silicone insulators
shear at the hole edges. Usually we use silicon for the
plastic devices which have a plastic insulating ring on
the mounting hole.

Thermalloy white grease is my favorite for Micas.
 
Output stage temperature

I find that a output stage temperature range of 145-165 degrees F is quite acceptable. I useally test my amps to 205 degrees F.

With proper temperature compensation circuits the output stage currents can be kept at a near constant value from 85 to 185 degrees F fairly easy. Heatsink design plays an important factor and most be considered when building compensation circuits.

All power amplifiers should have some type of temperature compensation. That is unless you believe that this is not important.

John Fassotte
Alaskan Audio
 
optimum temperature

Hello all,
Regarding temperature, I have read comment in the past by Peter Stein, http://www.me-au.com/sound.html , that he temperature regulates (variable speed fan) to 50*C or something because he finds this to be a sonically optimum operating temperature.

"There are so many other things that defy rational explanation (cable directionality is my favorite example--makes no sense at all, logically speaking) that it might...just might be worth investigating. "

Possible rational explanation is that temperature is affecting noise characteristics of output devices, combined with negative loop feedback system causing change in final output noise.
Concept of wire direction is perfectly rational according to a nuclear physicist I knew.
His explanation was that the copper ingot takes up a magnetic alignment during manufacture and this stays in the copper.
I have done audio experiments that demonstrated this directional characteristic very clearly.
Remember, all materials have some magnetic property.
Search "paramagnetic and diamagnetic, ferromagnetic etc " http://hyperphysics.phy-astr.gsu.edu/hbase/solids/magpr.html

Maybe this helps,
Regards , Eric.
 
Any thing can have magnetic properties. If you have a powerfull enough magnet. I saw this on TV. A bug floated in a small highly concentrated magnetic field created in a small three inch cylindrical chamber. To create the field required the same amount of electrical power needed for a small town. You could do it to a person if you wanted to spend a few billion dollars to make a powerful enough magnetic field.
 
Re: optimum temperature

mrfeedback said:
Possible rational explanation is that temperature is affecting noise characteristics of output devices, combined with negative loop feedback system causing change in final output noise.

Wasn't the Lavardin amps about this ('constant power' biasing to have the transistors not changing their operating points)? It does make sense to me.
 
Thankyou all for your technical and creative input.

Decision Time: Do I build a rectangle box or an Aleph cube?

Should I follow other or choose to be different or re create it in the mold of the original? How about we case a vote!

I have two options.

1. Build the Alpeh 2 in a rectangle (like the A60 and recent Aleph
2 project in the gallery) using available PCB's and two 35 x 15
x 5 cm heatsinks rated at 0.21 c/watt.

Given an ambient temperature in Melbourne of 19-22 c this will in theory give an operating temperature of about 50 to 53 c. Even in summer on a hot day at 30 c the temperature should still be about 60-63c.

The box is self would be the main contruction challenge.

2. Build the Alpeh in a cube (like the original) using (4) 20 - 25 x 15 x 5cm heatsinks each rated at 0.38 - 0.36 c/watt.

Based on the same conditions as above the operating temperature would be slightly lower in theory at about 46 - 49c and on a hot day still only 59 c.

The heatsinks could easily be bolted together with L angle aluminium and say a 3 inch deep plinth at the bottom to add some depth and form a base. The total size would be 25 x 25

But fitting everything in and assembling it and wiring it up could be a challenge.


Does anyone have any ideas?

All input is most welcome!


regards

macka