| budwiser |
Here is a picture of my Legacy GC converted to use new snubber PS.
Enjoy,
Pete |
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| carlosfm |
| Great, but those 'heatsinks' are too thin...:xeye: |
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| budwiser |
Dimensions are one eigth inch thick by 6" by 3.5" Had it cranked for about 30 minutes and did not even get close to warm. They cam out of an old dynaco st120.
Pete |
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| phoneisbusy |
Hi Pete,
How would you describe the differences between the two configurations?
regards
Dave |
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| thomas997 |
| quote: | Originally posted by carlosfm
Great, but those 'heatsinks' are too thin...:xeye: |
Depends on the voltage though.. If hes running it at 10-20V the thing wont even get warm.
Plus it kinda connects to the chassi. |
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| carlosfm |
| quote: | Originally posted by thomas997
Depends on the voltage though.. If hes running it at 10-20V the thing wont even get warm. |
Yes, at lower voltages it won't get hot.
| quote: | Originally posted by thomas997
Plus it kinda connects to the chassi. |
If the heatsink is thin there will be a "hot-spot" right on the back of the chip. The heat doesn't spread properly.
The heatsink will be almost cold at the extremes, and :hot: on the chip. Even if it's connected to the chassis. |
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| peranders |
| As long as the SPiKe protection doesn't trigger it's alright, no need to worry but in general it's better to have as low temperatures as possible if it's a question of the life time. |
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| budwiser |
Opppps Tranny is 25-0-25. I have 37v coming out of the PS board. Looks like I need to rethink my heat sinks real quick.
Thanks for the info,
Pete
I do notice more punch and amybe more low end with this new PS. |
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| carlosfm |
| quote: | Originally posted by budwiser
Opppps Tranny is 25-0-25. I have 37v coming out of the PS board. |
:hot:
| quote: | Originally posted by budwiser
Looks like I need to rethink my heat sinks real quick.
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You do.
This is no Dynaco.:D |
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| budwiser |
| How about this for one chip. |
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| budwiser |
| Here is another picture of heatsink |
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| Eric Weitzman |
| quote: | Originally posted by carlosfm
If the heatsink is thin there will be a "hot-spot" right on the back of the chip. The heat doesn't spread properly.
The heatsink will be almost cold at the extremes, and :hot: on the chip. Even if it's connected to the chassis. [/B] |
Would you mind providing a reference to support this statement?
I've noticed that gaincloner's have a penchant for thick heatsinks.
As far as my research shows, a heatsink's thermal transmission (degrees/watt) depends on it's surface area and finish, and has nothing to do with it's mass. In fact, mass will increase it's thermal inertia, making the heatsink heat up and cool down slower. Take a look at an air conditioner or car radiator: you won't find any massive conducting structures, just LOTS of surface area from LOTS of extremely thin fins.
- Eric |
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| carlosfm |
| quote: | Originally posted by Eric Weitzman
Would you mind providing a reference to support this statement? |
Yes.
My post, your quote.:D
| quote: | Originally posted by Eric Weitzman
I've noticed that gaincloner's have a penchant for thick heatsinks. |
I thought it was very obvious, but here it goes...:rolleyes:
If you use transistors you can spread them through a heatsink.
One small chip concentrates the heat on a single point.
:att'n: This is also the reason for the sligh less power of the LM4780 against the LM3886, even if in practice it has two of them inside.
The 2-channel LM4780 concentrates the heat of two LM3886s on a single, small package.
A thin heatsink with no fins doesn't spread the heat away from the chip.
I've been there, done that, years ago.
You can burn your finger and leave a peace of your skin on the heatsink right on the back of the chip. Right next to it, it's just warm. |
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| SheldonD |
Eric:
".... car radiator: you won't find any massive conducting structures, just LOTS of surface area from LOTS of extremely thin fins."
I don't think this a very valid comment relating to the Dyna heat sinks.
The reason for the thin fins is to maximize the surface area to the air which is passing by at a high velocity. Inside the radiator ( if you like, on the other side of the fins) you have a moving liquid which has a very high specifiic heat. This combination allows very rapid heat transfer to the air, from the fluid either water or freon (in a liquid state). In other words the thermal resistance is low.
The thickness in a GC heatsink has to be thick enough to rapidly spread out the heat, from the CHIP which is a concentrated heat and rather tiny heat source Perhaps an analogy would be a thick enough conductor for high current in an electrical circuit.
If we had a very thin heat sink for GC with water passing by this would work as well. |
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| Eric Weitzman |
| quote: | Originally posted by carlosfm
If you use transistors you can spread them through a heatsink.
One small chip concentrates the heat on a single point.
|
There are single transistors in TO-220 packages with comparable dissipation to the LM3886, such as the IRF9Z34N power mosfet, which can dissipate 68 watts. The spec sheet (just like the LM3886 spec sheet) is silent on the question of thickness.
I have never come across a spec sheet for a device that said how "thick" the heatsink had to be, only the thermal resistance (TR). It appears that if a heatsink's TR is 1 degree per watt, it's thickness is irrelevant.
| quote: | Originally posted by carlosfm
A thin heatsink with no fins doesn't spread the heat away from the chip.
I've been there, done that, years ago. |
It was clearly your folly to not have fins on your thin heatsink. It's TR would have been extremely high, since TR is proportional to SURFACE AREA (not thickness AFAIK).
| quote: | Originally posted by carlosfm
You can burn your finger and leave a peace of your skin on the heatsink right on the back of the chip. Right next to it, it's just warm. |
All that matters is the junction temperature of the transistors on the chip. This should be kept below 155 degrees on the LM3886. It doesn't matter if the heatsink burns your fingers at 150 degrees under the chip if it has the right TR. There's a chart on page 14 of the LM3886 spec sheet showing minimum TR for various ambient temperatures and power levels. You may want to extend the life of the component with lower TR, but lower TR has nothing to do with thickness.
Carlos, I was truly hoping for a reasonable answer from you that might have explained your assertion. This idea of "spreading heat" is naive. IIRC my high school physics, if the temperature gradient is high, the heat will be conducted away even faster.
Anyone interested in the subject of heatsinks may like to review http://sound.westhost.com/heatsinks.htm. The author, like all other sources I've read (except carlos) is mute about thickness. |
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| Eric Weitzman |
| quote: | Originally posted by SheldonD
Eric:
".... car radiator: you won't find any massive conducting structures, just LOTS of surface area from LOTS of extremely thin fins."
I don't think this a very valid comment relating to the Dyna heat sinks.
The reason for the thin fins is to maximize the surface area to the air which is passing by at a high velocity. Inside the radiator ( if you like, on the other side of the fins) you have a moving liquid which has a very high specifiic heat. This combination allows very rapid heat transfer to the air, from the fluid either water or freon (in a liquid state). In other words the thermal resistance is low.
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Precisely. The thermal resistance is low. The way to accomplish this is with large surface area and fast moving air. I have never seen thickness or mass of the heatsink mentioned in any document I've read as a factor in increasing thermal resistance.
BTW, the fact that the coolant is a liquid or freon has little to do with the thermal resistance, and everything to do with transporting the heat from the source to the cooling device. The surface area of the contact between the piping and the fins determines the TR of that junction similar to the TRjc of a semiconductor device. |
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| dsavitsk |
Assuming, for the sake of argument, that the thichness of a HS does matter, how much does the material the HS is made out of matter? For instance, could a copper sink be made of thinner material than something else, assuming that heat moves through copper more easily than other substances?
I ask this as I have a sheet of copper that is 4"x10"x0.25" that I was thinking of using. It has lots of surface area per volume, so it seemed ideal to me. But if this is inadequate, i'll find something else.
-d |
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| Eric Weitzman |
| quote: | Originally posted by dsavitsk
Assuming, for the sake of argument, that the thichness of a HS does matter, how much does the material the HS is made out of matter? For instance, could a copper sink be made of thinner material than something else, assuming that heat moves through copper more easily than other substances?
I ask this as I have a sheet of copper that is 4"x10"x0.25" that I was thinking of using. It has lots of surface area per volume, so it seemed ideal to me. But if this is inadequate, i'll find something else. |
Here's a quick'n'dirty formula from Rob Elliott's web page I listed above to determine TR for a heatsink:
TR = 50 / squareroot(A), where A is area in square centimeters.
So your copper sheet, assuming both sides are exposed to outside air, would have TR=2.2^C/w.
Looking at the chart on page 14 of the LM3886 spec sheet, you could run the amp at about 38 watts total dissipation if the outside air temperture is 25^C. The case temperature of the chip would be about 105^C. If you were driving 8 ohm speakers, you could use a +/-38VDC supply and get about 28W audio power. You could get up to 60 watts dissipation at this voltage, but you'd need better heatsinking with lower TR.
There's also a link on that page to a site for building your own heatsinks from folded sheet metal.
I don't think the material's inherent TR is that big an issue as long as it is significantly smaller than than the TR between the heat sink and air. Unfortunately, Rod Elliott doesn't have any data on the metals per se. |
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| SheldonD |
"I ask this as I have a sheet of copper that is 4"x10"x0.25" that I was thinking of using. It has lots of surface area per volume, so it seemed ideal to me."
copper will move heat about 2x as fast as aluminum, there is anice article referencing CPU heatsinks at
http://www.overclockers.com/articles223/index.asp
http://www.overclockers.com/articles223/index02.asp
On page 2 :
"Aluminum will have a higher temperature difference between the point of contact and the heatsink extremities. This becomes and important factor because the heat must be removed from the heatsink along...."
This supports Carlos' contention that one could overheat the chip.
You have to consider that the heat flow at the contact between chip and heatsink is in three dimensions. It is quite possible that the heat flux density is too high at the chip and therefore the thermal resistance is too high, simply because the sink thickness is too small. Again similar to an undersized wire for electrical currents
I believe your 0.25 inch thickness is much more than required, as to the consideration brought up by Carlos. The total heat capacity will hav
e to be calculated. |
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| sek |
Hi,
| quote: | Originally posted by Eric Weitzman
There are single transistors in TO-220 packages with comparable dissipation to the LM3886, such as the IRF9Z34N power mosfet, which can dissipate 68 watts. The spec sheet (just like the LM3886 spec sheet) is silent on the question of thickness. |
I think you're cheating here. ;)
A power mosfet can withstand much higher temperatures than a chipamp. After all, we're talking about sound, not chip failure. It's the protection circuit that limits the desired chip junction temperature, not the question wether it burns.
| quote: | | I have never come across a spec sheet for a device that said how "thick" the heatsink had to be, only the thermal resistance (TR). It appears that if a heatsink's TR is 1 degree per watt, it's thickness is irrelevant. |
Heat sink construction can't be fixed by the chip (or transistor) manufacturer, as it depends on the actual need of the 'user'.
| quote: | | All that matters is the junction temperature of the transistors on the chip. |
Again, the internal protection circuit measures the chip temperature and kicks in, ruining the sound if the chip overheats it's junction(s).
| quote: | It doesn't matter if the heatsink burns your fingers at 150 degrees under the chip if it has the right TR.
[...]
but lower TR has nothing to do with thickness. |
Imagine the so called thermal resistance as an actual impedance. It's value is frequency dependent. The term TR refers to the heat sinks property of conducting a steady heat flow, which can be imagined as it's property at zero heat change (an ideal figure).
If you constantly (e.g. slowly enough) heat up your metal bracket, it will warm up as a whole, sinking the specified amount of temperature differential to it's surrounding air.
If you modulate it's temperature from a single heat source (e.g. a transistor small compared to the heat sink area), the more remote areas of your bracket will 'receive' this heat significantly later than the heating had it's peak amplitude. This is a typical behaviour of impedances: it's reaction has a phase shift from it's stimulus.
Now, if your LM3886 tries to heat up to 150 centidegrees, the heat sink's performance depends on the rate (and duration) of the temperature increase. If you heat up slowly the temperature differential between chip and remote metal areas will be small (due to the 'heating slew' being much slower than the bracket's inherent lag in transporting that heat away).
But if an instantaneous power peak heats up the chip very quickly, it migh heat up near it's max. junction temperature before the heat is drawn away.
If I may conclude (;)), among all heat sinks of the same thermal resistance, there are faster and slower ones...
And you want one that is fast enough four the protection circuit not to limit the output, as this would mean severe distortion in dynamic music passages, especially when listening loud.
Hope, this helps,
Sebastian. :) |
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| Eric Weitzman |
Ah, a reference by an engineer with an emphasis in heat transfer. Fantastic. But ...
I just skimmed the article. He talks about "thermal conductance", which is where you got your "copper is 2x better than aluminum" from. Higher conductivity moves heat faster. But this constant relates temperature and distance, not heat and cross-sectional area. So he doesn't answer the question at hand.
Besides, you can move the heat as quickly as you like to the extremeties of the heatsink, but if the extremeties have a small surface are, heat conduction to the air and subsequent convection away from the heatsink will be small and the heat will accumulate.
The analogy of a thicker heatsink with higher conductance being like a fatter wire carrying more current seems attractive, but I don't know that it's correct. This is physics, not intuition. |
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| Eric Weitzman |
| quote: | Originally posted by sek
I think you're cheating here. ;)
A power mosfet can withstand much higher temperatures than a chipamp. After all, we're talking about sound, not chip failure. It's the protection circuit that limits the desired chip junction temperature, not the question wether it burns.
[/B] |
No cheating here! The LM3886 protection kicks in at 165^C, then lets the chip run again when the temp drops to 155^C. The IRF9Z34N's max Tj is 175^C. They're comparable, even though a bit different.
| quote: | | Heat sink construction can't be fixed by the chip (or transistor) manufacturer, as it depends on the actual need of the 'user'. |
Of course not, which is why spec sheets list the maximum temp only, leaving heatsink design to the engineer. The engineer will then figure out the TR of the heatsink necessary to keep the junction at or below the maximum based on the power consumption in the application.| quote: | ...snip...
But if an instantaneous power peak heats up the chip very quickly, it migh heat up near it's max. junction temperature before the heat is drawn away.
If I may conclude (;)), among all heat sinks of the same thermal resistance, there are faster and slower ones...
And you want one that is fast enough four the protection circuit not to limit the output, as this would mean severe distortion in dynamic music passages, especially when listening loud.
|
I think you're talking about short-duration phenomena that are of no concern here. Why? Read the LM3886 notes:
| quote: | LM3886 spec sheet
With high power pulses of duration longer than 100ms, the case temperature will heat up drastically without the use of a heatsink |
So we're all heatsinking because the bass notes in our music may last for longer than 1/10th of a second. If we weren't, then pulse length and temperature lag, etc, would be something to think about. National has clearly taken instantaneous power into consideration when specifying the behavior of the chipamp. |
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| Eric Weitzman |
And furthermore :)
| quote: | Originally posted by sek
Now, if your LM3886 tries to heat up to 150 centidegrees, the heat sink's performance depends on the rate (and duration) of the temperature increase. If you heat up slowly the temperature differential between chip and remote metal areas will be small (due to the 'heating slew' being much slower than the bracket's inherent lag in transporting that heat away).
But if an instantaneous power peak heats up the chip very quickly, it migh heat up near it's max. junction temperature before the heat is drawn away. |
This raises the question: does heat flow faster when there's a bigger temperature gradient or smaller one? I bet it's the former. (think about it for a minute or two...) So, when the device suddenly heats up due to instantaneous peaks, the heat will be conducted into the heatsink faster, especially if the edges of the sink are relatively cool. If I'm right, the system is self-correcting in a way, more responsive when it needs to be to peaks. But I'll be dam*ed if I know this for sure ... thus, all the questions. |
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| sek |
Hello Eric,
After writing my above post, it appears clear to me that the described effect of 'thermal phase lag' will lead to a quantitative increase in heat spreading performance if you increase the number of spreading dimensions (or in this case, increase the third dimension's contribution to the performance).
After all, the speed of heat conduction in metal is finite... just imagine the heat flux capacity as non-linear vs. temperature.
I don't yet see how a (scalar, time-invariant) figure of thermal resistance can be all that counts. ;)
| quote: | | This raises the question: does heat flow faster when there's a bigger temperature gradient or smaller one? I bet it's the former. (think about it for a minute or two...) So, when the device suddenly heats up due to instantaneous peaks, the heat will be conducted into the heatsink faster, especially if the edges of the sink are relatively cool. If I'm right, the system is self-correcting in a way, more responsive when it needs to be to peaks. But I'll be dam*ed if I know this for sure ... thus, all the questions. |
I thought about it at an earlier time... and please try to think about the finite nature of heat flux speed for a minute or two; wouldn't it help if there were more directions for the heat to spread?
The higher temperature gradient leads to a higher 'acceleration', not speed. After the surroundings of the chip are hot, the gradient is reduced, and so is the 'acceleration'...
Sebastian. :) |
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| SheldonD |
"The analogy of a thicker heatsink with higher conductance being like a fatter wire carrying more current seems attractive, but I don't know that it's correct. This is physics, not intuition. "
You MUST consider all three dimensions in regard to extracting the heat from the chip.
With large area heat sink the heat transfer to the air is primarily on area, but we are concerned here about the heat transfer from chip to heat sink.
The valid reason one can think in electrical terms is that heat transfer in metals is in fact carried out by electrons, and because of this there is an extremely close relationship in electrical and heat conductivity for metals. |
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| carlosfm |
| quote: | Originally posted by Eric Weitzman
It was clearly your folly to not have fins on your thin heatsink. |
It was not exactly a heatsink, I mounted the chips directly to the chassis, which was not thick enough.
Anyway, one ot the reasons why I pointed out that the heatsinks on the pic are not enought was because, besides thin, they have no fins.
Get it?;) |
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| Eric Weitzman |
| quote: | Originally posted by sek
so what's your actual question, then? |
I originally asked carlosfm in post #13 to support his statement that a thin heatsink would have a hot-spot on the back of the chip. I then said that none of my research refered to heatsink thickness, only TR being a function of surface area. I observed that gaincloner's like thick heatsinks. Flat, too :)
The question is, simply, does thickness matter?
| quote: | | After writing my above post, it appears clear to me that the described effect of 'thermal phase lag' will lead to a quantitative increase in heat spreading performance if you increase the number of spreading dimensions (or in this case, increase the third dimension's contribution to the performance). |
I don't know what "heat spreading performance" is, and I've never seen it mentioned before. I also don't see how you can increase the number of dimensions of a heatsink -- is this string theory applied to heatsinks? :)
| quote: | After all, the speed of heat conduction in metal is finite... just imagine the heat flux capacity as non-linear vs. temperature.
I don't yet see how a (scalar, time-invariant) figure of thermal resistance can be all that counts. ;) |
I don't see how a single metric is sufficient either, but pragmatically speaking, that's all I ever see in spec sheets. Maximum junction temperature for the device, and a bunch of TR values (TRjc, TRca). So I can't help but wonder if our "intuitive" thoughts are misguided, and the engineers have in fact reached a single metric based on hard science that I'm ignorant of.
I think car radiators clear demonstrate that surface area (and so TR) is the most important factor. If thickness was, wouldn't car radiators have just a few massive fins instead of thousands of paper-thin ones? |
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| sek |
| quote: | | there is an extremely close relationship in electrical and heat conductivity for metals |
That's why I thought about coming up with analogies to AC signals, impedances and phase lags. ;)
I think, another term to consider is thermal inertia (which is only losely related to thermal resistance, as manufacturers specify that with a convective heat flow, another lagging transport system with extremely low time constant).
Sebastian. :) |
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| Mr Evil |
Let me try and elucidate heat transfer. There are two things here which are being confused:
1) Thermal resistance. This is the temperature difference caused by a given power. This is the most important figure as it determines what temperature the chip will be at relative to the air. It can also be expressed as thermal conductance.
2) Thermal inertia. This is how 'fast' heat is conducted. High thermal inertia means it takes longer to reach the final steady-state temperature. High thermal inertia is helpful to smooth out peaks, but not essential.
Copper is superior to aluminium for both of these. |
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| carlosfm |
| quote: | Originally posted by Eric Weitzman
The question is, simply, does thickness matter? |
Yes.
Otherwise I'll start making heatsinks out of kitchen aluminium sheets.:D
With thermal paste, perfect contact, minimum resistance between the chip and the "heatsink".:cool: |
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| Peter Daniel |
| quote: | Originally posted by carlosfm
It was not exactly a heatsink, I mounted the chips directly to the chassis, which was not thick enough.
Anyway, one ot the reasons why I pointed out that the heatsinks on the pic are not enought was because, besides thin, they have no fins.
Get it?;) |
What about this design, that seems to be working pretty well, although the heatsink wall is even thinner that the plate at the beginning of this thread. |
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| carlosfm |
| quote: | Originally posted by Peter Daniel
What about this design, that seems to be working pretty well, although the heatsink wall is even thinner that the plate at the beginning of this thread. |
It doesn't seem thinner.
At what voltage are you using the chips?
Up to around +/- 24V should be OK.
Also important: what speakers? |
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| Eric Weitzman |
| quote: | Originally posted by SheldonD
You MUST consider all three dimensions in regard to extracting the heat from the chip. |
Says you ... ;)
| quote: | | With large area heat sink the heat transfer to the air is primarily on area, but we are concerned here about the heat transfer from chip to heat sink. |
The reason that I must disagree with you is again pragmatic. There are three pages on heat, power, and heatsink design in the LM3886 spec sheet. They mention, strongly and several times, that the TRcs (thermal resistance from case to sink) is determined by proper heatsink compound and insulator. They talk about mica, thermalcote, and silicon pads. They ONLY FACTOR THEY MENTION AND USE IN THE DESIGN EQUATIONS is TR for thermalcote, mica, and silicon. THEY SAY NOTHING ABOUT THICKNESS OF THE HEATSINK. I'm not trying to be rude by saying this, but you have not presented any science that makes heatsink thickness a factor. I don't think this is a situation where subjectivism (like about sound quality) can substitute for hard facts.
The Larsen article cited what looks like a text book, "Fundamentals of Heat and Mass Transfer" by Incropera and De Witt. Does anybody have a copy of this? |
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| carlosfm |
| quote: | Originally posted by Eric Weitzman
They ONLY FACTOR THEY MENTION AND USE IN THE DESIGN EQUATIONS is TR for thermalcote, mica, and silicon. THEY SAY NOTHING ABOUT THICKNESS OF THE HEATSINK. |
Why should a chip's datasheet be the heatsink's encyclopedia?
The datasheets never say it all.
Or would they also have to include a complete book on op-amps on every datasheet?:eek: |
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| dsavitsk |
"The Larsen article cited what looks like a text ook, "Fundamentals of Heat and Mass Transfer" by Incropera and De Witt. Does anybody have a copy of this?"
You can look in the TOC and the Index (and a bit of the first chapter) on Amazon. Fwiw, there is a chapter on 1 dimension, and another on 2, but none on 3. :) |
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| sek |
| quote: | Originally posted by Eric Weitzman
The question is, simply, does thickness matter?
|
And as difficult seems to be the answer: it depends.
My answer would be: if you use your device as a heater (slowly heated up and kept constant in power dissipation) then it does not matter.
| quote: | | I don't know what "heat spreading performance" is, and I've never seen it mentioned before. I also don't see how you can increase the number of dimensions of a heatsink -- |
You're starting to blame me for not being native in your mother language ;)
(Joke)
| quote: | | is this string theory applied to heatsinks? :) |
No, this is just assuming that if there is a third dimension too thin to contribute, the situation is similar to having only two dimensions to encounter (as the third will always be 'saturated', e.g. too hot, immediately).
| quote: | | Maximum junction temperature for the device, and a bunch of TR values (TRjc, TRca). So I can't help but wonder if our "intuitive" thoughts are misguided, and the engineers have in fact reached a single metric based on hard science that I'm ignorant of. |
To my awareness, thermal dynamics is one of the most complex topics in practical engineering. Bolting it down to a set of numbers that summarize what heat sink engineers gather from simulations, measurements and graphs is always a simplification.
After all, the model theory (!!!) of thermal resistances makes some certain (and practical) assumptions, e.g. that you have enough steady airflow available so that the claimed thermal resistance can be achieved. Another one is that matter conducts in a homogenous way...
| quote: | | I think car radiators clear demonstrate that surface area (and so TR) is the most important factor. If thickness was, wouldn't car radiators have just a few massive fins instead of thousands of paper-thin ones? |
Again, you seem to forget the (effective) thermal inertia. With something like water for storing the heat and forced air flux to sink it, the comparison doesn't fit.
If you stop the airflow, will the car overheat? Suddenly not in an instant, but wouldn't it happen more quickly if you also stopped the water flow?
For the car radiator, the water is just a heavily massive thickness as the water only transports the heat, it doesn't dissipate enough (that's what the fins and the airfan are for).
| quote: | | THEY SAY NOTHING ABOUT THICKNESS OF THE HEATSINK. I'm not trying to be rude by saying this, but you have not presented any science that makes heatsink thickness a factor. |
;)
So you basically state that you need a lesson in how to calculate a proper heat sink according to a datasheet Rth specification?
Sebastian. |
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| Eric Weitzman |
| quote: | Originally posted by carlosfm
It was not exactly a heatsink, I mounted the chips directly to the chassis, which was not thick enough. |
Your post said it was a heatsink, so that's what I responded to.
| quote: | Originally posted by carlosfm
Anyway, one ot the reasons why I pointed out that the heatsinks on the pic are not enought was because, besides thin, they have no fins.
|
Your post said nothing about lack of fins. Here's what you said:| quote: | Originally posted by carlosfm in post #2
Great, but those 'heatsinks' are too thin...:xeye: |
Back on topic,
| quote: | | quote: | Originally posted by Eric Weitzman
The question is, simply, does thickness matter? |
Yes.
Otherwise I'll start making heatsinks out of kitchen aluminium sheets.
With thermal paste, perfect contact, minimum resistance between the chip and the "heatsink". |
Reasserting yourself again, offering only opinion for proof.
I've read many of your posts, carlosfm, and I realize that this is your "style". But I was hoping you could explain why thickness matters.
I admire your tenacity, but not your opinions. |
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| Eric Weitzman |
Lots of good info, sek, but little on topic. We don't need to argue if the water in a radiator is "thickness" or heat source, etc. So I'll keep this short.
| quote: | Originally posted by sek
So you basically state that you need a lesson in how to calculate a proper heat sink according to a datasheet Rth specification?
|
(I'm assuming that "Rth" is a typo ...)
No and yes. I do not need a lesson using junction temperatures and thermal resistance. If thickness is a factor, then YES, I need a lesson. Can you provide me with the design equations that I should use that incorporate thickness? I'm not joking about this. |
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| carlosfm |
| quote: | Originally posted by Eric Weitzman
I've read many of your posts, carlosfm, and I realize that this is your "style". But I was hoping you could explain why thickness matters.
I admire your tenacity, but not your opinions. |
I'm not willing to discuss this, as I'm just sharing my experience.
Take it or leave it.
A thin heatsink, with thin fins, only works with forced cooling (fans).
If it's not written on any "paper", then maby I invented something, which I doubt.
You read less, practice more.:angel:
There are diyers that make it.
There are other ones that just theorize and never make anything.
I never thought that a good advice could turn into a big discussion.
But I should know better by now...:xeye: |
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| Eric Weitzman |
| quote: | Originally posted by carlosfm
Why should a chip's datasheet be the heatsink's encyclopedia?
The datasheets never say it all. |
If the thickness of the heatsink was important to their products being used sucessfully, they would say so. In fact, the three pages on heat/power issues, coupled with the two or three preceding pages of graphs, is the most comprehensive (should I say encyclopedic?) treatment of these issues I've ever seen in a spec sheet. |
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| Eric Weitzman |
| quote: | Originally posted by carlosfm
I'm not willing to discuss this, as I'm just sharing my experience.
Take it or leave it. |
Yes, I can see this clearly. :smash:
| quote: | There are diyers that make it.
There are other ones that just theorize and never make anything.
|
Of course your implication is that I just theorize and never make anything. I've probably built more in my 20 years of being a DIYer than most people. Some of us look for reasons, look to theory, to explain those things that we're just learning about. Others just make it up as they go along.| quote: | I never thought that a good advice could turn into a big discussion.
But I should know better by now...:xeye: |
I'm sorry that you cannot provide any rationale for "thickness". I was hoping to learn something from you. At least I have from others. |
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| sek |
budweiser,
sorry for having helped to turn this into an off-topic discussion...
| quote: | | I do notice more punch and amybe more low end with this new PS. |
Wanna describe what exactly you had, and what you did to it (e.g. which values, pictures)? ;)
Cheers,
Sebastian.
PS: Eric,
Rth is the common symbol for thermal resistance, [Rth] = 1 K/W.
It's commonly also noted RTH, but I was lazy ;)
You need a good book on the topic, not a diy forum to find the answer... sometimes in life it's not sufficent to yell at others for not answering a question.
Philosophical question for you: does thickness not matter just because noone here can satisfy you with an answer?
Can you say Texas?... :devilr: |
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| carlosfm |
| quote: | Originally posted by Eric Weitzman
Of course your implication is that I just theorize and never make anything. I've probably built more in my 20 years of being a DIYer than most people. Some of us look for reasons, look to theory, to explain those things that we're just learning about. Others just make it up as they go along. |
Let me put it this way:
Are the heatsinks on the pics fine for an LM3886 working at +/- 37V?
| quote: | Originally posted by Eric Weitzman
I'm sorry that you cannot provide any rationale for "thickness". |
I did, but you didn't understand, or don't want to.
Or you don't understand my english, which is not as good as yours.
| quote: | Originally posted by Eric Weitzman
I was hoping to learn something from you. At least I have from others. |
I did my part on this thread, helping a diyer to make a better amp.
You didn't help.
I do not intend to teach you anything.
I don't know how to explain better than what I did.
Sorry to disappoint you.:D |
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| carlosfm |
| quote: | Originally posted by sek
Philosophical question for you: does thickness not matter just because noone here can satisfy you with an answer? |
That's a question one should make to a woman, not us.:D :D :D |
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| SheldonD |
Eric:
You may be right, those of us who consider that the heatsink thickness is a factor must be wrong. It may not be a three dimensional consideration at all. Heat must only travel on the surface, i.e it is only a 2 dimensional phenomenom.
You are so very sure thickness matters not at all.
Therefore you should make all your heat sinks out of aluminum foil!
Think of the money you could save, make them as large as you want.
Pick up your heat sinks at the grocery store! |
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| Eric Weitzman |
| quote: | Originally posted by sek
Rth is the common symbol for thermal resistance, [Rth] = 1 K/W.
It's commonly also noted RTH, but I was lazy ;) |
I see, common in Germany perhaps... Here it's θ (theta), as in θjs or θsc.
| quote: | | You need a good book on the topic, not a diy forum to find the answer... sometimes in life it's not sufficent to yell at others for not answering a question. |
First, a "good book" on the subject would probably be at 3rd year mechanical engineering level. I don't have the spare time to engage in such a study. A forum is just the right place for experts like yourself to provide novices like me with design equations, or at least references to them. [Note: I'm still waiting for you to provide a lesson, see end of your post #37 and my reply post #39]
Second, I only responded appropriately when carlosfm started to yell at me. Please review the posts in the thread more carefully. I asked carlosfm very politely to if he could provide a reference to support his assertion. His first answer was a snotty "Yes. See my post ..." Most other posts have been civil.
| quote: | | Philosophical question for you: does thickness not matter just because noone here can satisfy you with an answer? |
Realistic answer: It appears to NOT matter because spec sheet writes never mention it and none of my textbooks mention it. Philosophical answer: In my state of little knowledge, I put more faith in National Semiconductor than carlosfm.
| quote: | | Can you say Texas?... :devilr: [/B] |
I don't get this. Can you explain this to me? |
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| Eric Weitzman |
| quote: | Originally posted by carlosfm
Let me put it this way:
Are the heatsinks on the pics fine for an LM3886 working at +/- 37V? |
That would depend on knowing the materials and dimensions, data that I do not have available to me right now.
| quote: | I did my part on this thread, helping a diyer to make a better amp.
You didn't help.
|
Further demonstration of your .... ? I have been helping budwiser with his problem via email. |
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| budwiser |
I really appreciate everyones input. Based on the dimensions for the current heat sinks for the LM3875 running off +/- 37v in my amp. I think I need to look closer at replacing them. The c/w came to 2.8.
Thanks,
Pete
The amp really sounds good, but I have not used it since the tread started. Maybe being over cautious.
Pete (budwiser) |
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| Eric Weitzman |
| quote: | Originally posted by SheldonD
You may be right, those of us who consider that the heatsink thickness is a factor must be wrong.
....snip...
You are so very sure thickness matters not at all.
...snip...
Think of the money you could save, make them as large as you want. Pick up your heat sinks at the grocery store! |
You're saying that "[I am] so very sure thickness matters not at all." I am not sure of that. I have asked for a credible explanation of why thickness matters, or for at least a reference to an explanation. None of the explanations have been conclusive, some have been easily refuted, many ideas have been interesting, and no references have answered the question (except for the amazon index of a text that omits heat transfer in three dimensions?) I'm very open to the possibility that it does matter, it seems intuitively so, so please show me why.
Perhaps you're just upset that I observed that gaincloners have a penchant for thick blocky heatsinks. I agree that they look cool, but a simple analysis of a 3" x 3" x 1/2" piece of aluminum (as I've seen recommended) shows that it's not a very good heatsink. The surface area of a medium size case may be good for some applications, but the thickness, AFAIK (and which so far hasn't been disproved) has nothing to do with it.
You really should look under the hood of your car to see just how much resemblence your car radiator bears to aluminum foil. |
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| grege |
I just had a good idea. :eek: Just have a look at the commercially available heatsinks. All the hi efficiency heatsinks I'm familiar with have have reasonable mass (width, thickness etc) with a large surface area (fins).
I think you need the mass for conduction and large surface area for convection. BTW, I failed thermodynamics. :bawling:
budwiser,
Don't stop using you amp, just make sure you monitor the temperature. You learn more when you experiment and maybe blow a few things up. ;) I just use aluminium angle for heatsinks on my GCs and have found it sufficient for my requirements. |
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| Mr Evil |
| quote: | Originally posted by Eric Weitzman
...You really should look under the hood of your car to see just how much resemblence your car radiator bears to aluminum foil. |
How long are the 'fins' in a car radiator? Not much more than a couple of cm away from the heat source (water). This is an important factor, since the thermal resistance of a lump of material is proportional to area and inversely proportional to length.
In a heatsink for an amp the lengths involved are greater, and thus the thickness must also be greater to maintain the same overall thermal resistance.
If this were not so then a huge sheet of aluminium foil would be sufficient, as suggested earlier. However even an infinite sheet of foil would have a high thermal resistance. |
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| sek |
| quote: | | A forum is just the right place for experts like yourself |
To my understanding this is a DIY forum and I am no expert.
It's of course true that a forum is the right place to ask. But if noone knows it, noone knows it...
| quote: | | Realistic answer: It appears to NOT matter because spec sheet writes never mention it and none of my textbooks mention it. |
Do you see the contradiction?
First, you say that noone here can be right, because everyone refuses to deliver proof.
Then, you say that the datasheets must be right, because not a single one mentions it?
The key in understanding this discussion is: We are not speaking about missing facts in datasheets, we speak about the limit of the thermal resistance model theory. Or more specifically: it's applicability to transistor heat sinking under all circumstances.
Put a transistor on a thick heat sink with a too low thermal resistance specification and load it with only short but large power peaks. It will very likely survive. Power it with a constantaneous load that is too high for the heat sink capability and the transistor will fail (after a significant amount of time).
Put a transistor on a (too) thin heat sink with a high (enough) thermal resistance specification and again load it with a constantaneous load as high as the constantaneous load above. It will very likely survive, too. Power it, again, with short but large power peaks and it will very likely overheat.
Even if nobody here can prove why this is possible, some claim that they have experienced such a phenomenon, including me. So it obviously appears to matter for some, does it?
This is the reason why you never see heat sinks with low thermal resistance and thin mounting plates (or high-theta sinks with a waste of material in plate thickness, for that matter).
Practical calculations with thermal resistances work because the manufacturers care for the numbers. But for their validity, the mounting considerations are of importance.
| quote: | | Philosophical answer: In my state of little knowledge, I put more faith in National Semiconductor than carlosfm. |
So far, Carlos did not contradict with any datasheet. He just said that they are usually far from complete and somtimes provide biased data.
As for his explanations: I liked the analogy of taking a kitchen roll of aluminium foil, making it infinitely large, and then claim it to be a suitable heatsink... It won't be, thickness does matter in this case. One could now argue that if it was ideally flat and void free, in theory it should. But is a thin mounting plate ideal?
It's a running gag on the forum(s), nothing of importance...
Sebastian. |
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| Peter Daniel |
Here's the picture of my current amp. It's using 2" brass rod (about 6" long) as the heatsink (it also serves as a chassis). I expected it to be quite enough for heat dissipation, as the surface of the rod is about the same as other plates I was using successfuly for heatsinking. However, it's no the case.
Even if amp is idle, the rod is always warm, (normally it should be cold), and when amp is pushed, it gets much warmer than usually, sometimes in excess of 50 deg, which not comparable with my other amps.
I expect that a 1/8 plate of similar surface area would be more efficient in heat dissipating. |
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| Eric Weitzman |
| quote: | Originally posted by sek
Do you see the contradiction?
First, you say that noone here can be right, because everyone refuses to deliver proof.
Then, you say that the datasheets must be right, because not a single one mentions it? |
Either you're backing you "contradiction" by distortion, pure and simple, or you're skipping over the literal meaning of the words I choose. I have never said nobody is right, I have never said I am right. I am debating the issue and asking those making strong assertions to back them up. I offer what I've read in spec sheets as support for my doubt that thickness matters, not as proof that everyone else is wrong. I have even conceded that some of the intuitive arguments are appealing several times.
| quote: | | The key in understanding this discussion is: We are not speaking about missing facts in datasheets, we speak about the limit of the thermal resistance model theory. Or more specifically: it's applicability to transistor heat sinking under all circumstances. |
It seems that you've been in a different conversation that I have been. Nobody has presented any formal model of thermal resistance, let alone discussed the limitations of the model. Maybe this is where your thinking is at, but not your posting.
Anyways, nothing has been proven either way. We only have several more datapoints to consider now, especially those presented by Peter.
- Eric |
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| Eric Weitzman |
| quote: | Originally posted by Peter Daniel
Here's the picture of my current amp. It's using 2" brass rod (about 6" long) as the heatsink (it also serves as a chassis). I expected it to be quite enough for heat dissipation, as the surface of the rod is about the same as other plates I was using successfuly for heatsinking. However, it's no the case. |
Peter,
I'd suggest two reasons for the higher temperature:
1. the smooth surface and curved shape severely limits turbulent air flow, limiting heat transfer to the air
2. shiny surfaces (like your brass has) have terrible emissivity (0.07 for polished copper compared to 0.9 for anodized aluminum)
- Eric |
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| Peter Daniel |
I will try to mill out the grooves on the length; this might help in dissipation.
Besides being inefficient, this type of heatsink arrangement has certain advantages not only for the sound, but also building a chassis gets pretty simple. |
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| Eric Weitzman |
| quote: | Originally posted by Peter Daniel
I will try to mill out the grooves on the length; this might help in dissipation. |
Just put it in the baby walker and let your kid walk it around... |
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| chipco3434 |
| Peter, it might look really sharp if you were to turn (as in lathe)some grooves in the rod. Clearly not the best (OK, the worst) arrangement for airflow but there's plenty of rod there to get lots of surface area from with turned grooves. |
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| grege |
| quote: | Originally posted by Peter Daniel
I will try to mill out the grooves on the length; this might help in dissipation.
Besides being inefficient, this type of heatsink arrangement has certain advantages not only for the sound, but also building a chassis gets pretty simple. |
Peter have you ever determined if there is a relationship between chip temperature and sound quality. It seems to me that there is a lot of GCs with inefficient heatsinks so maybe running the chips warmer has an advantage. Heat is the only way I can think of to influence the internal circuitry. |
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| Peter Daniel |
I've never really did any test with regards to temperature, but I've heard quite a few of those amps running cold and sounding pretty good.
I believe that chassis influences the sound to some extent. That's why I decided on that brass rod. It makes for one part chassis only (no screws, additional panels or brackets) and one spike to support it. Seemingly a perfect setup.
So far, it's also the best sounding amp I've built. |
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| Peter Daniel |
| quote: | Originally posted by chipco3434
Peter, it might look really sharp if you were to turn (as in lathe)some grooves in the rod. Clearly not the best (OK, the worst) arrangement for airflow but there's plenty of rod there to get lots of surface area from with turned grooves. |
As I don't have any machining tools at home, I will run it on a table saw and cut vertical grooves (maybe 3/16 deep) on the length of the rod. This is also good arrangement for air flow. |
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| Eric Weitzman |
| quote: | Originally posted by Peter Daniel
So far, it's also the best sounding amp I've built. |
Peter,
Of course it's the best sounding so far.
<sarcasm-mode>
* It won't have any hot spots because the heatsink is 6" thick below the chip.
* The heatsink is very compact but with a high surface area. So it must be very massive. This gives it great thermal inertia which must be a good thing because it's great.
* Because of the great thermal inertia, there won't be much "acceleration" as the heat tries to navigate it's way from high temperature zones to low temperature zones. This lack of accelerated slaloming causes less heat collision, which is another way of saying that the thermal resistance is lowered.
*With great thermal inertia, the heatsink won't have any cold spots or cold toes. This will make it less cranky (as you, being a Torontonian, well understand) and less reluctant to stand in the way of the heat particles trying to find a way out.
</sarcasm-mode>
To press "Submit Reply" or not to press, that is the question ... |
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| Eric Weitzman |
| quote: | Originally posted by Peter Daniel
So far, it's also the best sounding amp I've built. |
Peter,
Of course it's the best sounding so far.
Maybe the transistors' sweet spots are attained when they run hotter.
Think microphonic caps. Maybe the mass of the heatsink reduces vibration. Maybe some other mechanical aspect has improved things. |
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| skyraider |
Peter,
Briliant work as usual! I assume in this setup your RCA sockets is mechanically isolated from the chip? |
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| skyraider |
Just want to add aditional comments to the heatsink issue...
'uniliterately speaking', as long as heat can be transfered fast enough from the chip before thermal shutdown temp is reached, it should be ok. Even though NSC did not specify thickness, common sense should be employed.
Some people just mount the chips on heatsink, some people (like what budweiser did) uses conductor to transfers the heat to the chasis.
In my BPA200 subwoofer circuit, I am using 1/8"thick L-bend as heat transfer from the chip to a massive 'proper' heatsink. Initially I am worried, but the amp works without thermal shutdown occuring. It runs on +/-37V dc, btw.
I guess if it aint broke, it aint need no fixing. budweiser, I suspect your heatsink is ok. Just drive it hard, and if it doesnt shut down leave it as it is. Dont worry, you cant blow those chips. Theyre built like tank. |
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| carlosfm |
| quote: | Originally posted by Eric Weitzman
Second, I only responded appropriately when carlosfm started to yell at me. Please review the posts in the thread more carefully. I asked carlosfm very politely to if he could provide a reference to support his assertion. His first answer was a snotty "Yes. See my post ..." Most other posts have been civil. |
Was that yelling?
I was joking.:bawling:
If inserting a smile isn't enough, then what is?:confused:
I didn't start anything, I just gave an advice to a member. |
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| jackinnj |
| here's a heat sink nomograph from an old issue of "Radio Electronics": |
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| filholder |
The reason that the brass might be heating up so much might be becuase brass has very poor thermal conductivity.
http://hyperphysics.phy-astr.gsu.ed...bles/thrcn.html
One quater as conductive as copper and half as conductive as aluminium. Only twice as conductive as steel.
Thermal conductivity
(W/m K)
Silver 406
Copper 385
Aluminium 205
Brass 109
Steel 50
Brass is pretty poor choice for a heat sink.
No disrespect Peter, the amp looks superb and that lump may well be enough, it is however a far from ideal material.
Phil |
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| Peter Daniel |
Good point Phil.
I didn't realize that brass is so poor in that regard, I thought it was more like copper.
But anyway, it's not that bad, and the idea to make it in this way was dictated by the reason that I already had a brass rod material and wanted to do something about it.
Whith regards to sound though, I think brass is better than copper, the latter seems to create too much damping, which somehow influences high frequency extention. ;) |
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| filholder |
Hey Peter
When Brass has so much copper in it is does seem weird but i checked a while back when i was building some cpu waterblocks for an overclocking project. My Dad had a fair bit of scrap brass and i was planning on using until i did a bit of googling.
Oh well |
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| carlosfm |
| quote: | Originally posted by Eric Weitzman
Further demonstration of your .... ? I have been helping budwiser with his problem via email. |
Curious... me too.:cool: |
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| carlosfm |
| quote: | Originally posted by Peter Daniel
Good point Phil.
I didn't realize that brass is so poor in that regard, I thought it was more like copper. |
Peter, look at your cute amp and think: heat goes up.:D
Heat doesn't go away from the chip.
| quote: | Originally posted by Peter Daniel
Whith regards to sound though, I think brass is better than copper, the latter seems to create too much damping, which somehow influences high frequency extention. ;) |
:confused: |
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| carlosfm |
http://sound.westhost.com/heatsinks.htm
Quote:
"Even if one were to obtain an infinitely large block of aluminium, if a bracket or other mounting arrangement directly underneath the heat source (the transistors) is not thick enough, it will have significant thermal resistance, and the transistors may just overheat anyway, so we do need to look at all the resistances in the thermal circuit, not just the heatsink itself.
It is not uncommon to have transistors operating at well in excess of their ratings, but a casual "finger" test of temperature on the surface of the heatsink will appear to indicate that all is well." |
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| steenoe |
| quote: | | "finger" test of temperature on the surface of the heatsink will appear to indicate that all is well." |
Do the 'fingertest' on the chip, and you will see:hot:
Steen. |
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| carlosfm |
| quote: | Originally posted by steenoe
Do the 'fingertest' on the chip, and you will see:hot:
Steen. |
I've been saying that since the beginning.:bawling: |
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| Peter Daniel |
| quote: | Originally posted by carlosfm
Peter, look at your cute amp and think: heat goes up.:D
Heat doesn't go away from the chip.
:confused: |
In that case you are seriously mistaken. The brass rod had a uniform temperature all over, no hot spots, no ups or downs.
As to your assumption that heat goes up in a brass material, can you elaborate? I'm curious what you come up with this time. |
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| carlosfm |
| quote: | Originally posted by Peter Daniel
In that case you are seriously mistaken. The brass rod had a uniform temperature all over, no hot spots, no ups or downs. |
I don't doubt it, because of your arrangement.
But put the amp to work upside-down and push it hard.
Observe it the temperature is the same. |
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| SheldonD |
Carlos:
there is a saying " you can lead a horse to water but you can't make him drink"
rather approriate I think. |
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| Eric Weitzman |
| quote: | Originally posted by carlosfm
http://sound.westhost.com/heatsinks.htm
Quote:
"Even if one were to obtain an infinitely large block of aluminium, if a bracket or other mounting arrangement directly underneath the heat source (the transistors) is not thick enough, it will have significant thermal resistance, and the transistors may just overheat anyway, so we do need to look at all the resistances in the thermal circuit, not just the heatsink itself.
It is not uncommon to have transistors operating at well in excess of their ratings, but a casual "finger" test of temperature on the surface of the heatsink will appear to indicate that all is well." |
Rod is clearly talking about the thickness of a bracket or other mounting arrangement directly underneath the heat source that connects the transistor to the heatsink, and not the heatsink itself. Why? Because that's what his words say! :xeye: Another reason, which ought to be obvious, is because he's talking about the theoretical case where one were to obtain an infinitely large block of aluminium. An infinitely large block of aluminum would not only be infinitely wide and infinitely long, it would be infinitely thick, so he can't be talking about the thickness of the heatsink. In summary, he's talking about inadequate thickness of various mounting schemes such as using L-channel to connect a transistor to a heatsink.
It is not uncommon to have transistors operating at well in excess of their ratings, but a casual "finger" test of temperature on the surface of the heatsink will appear to indicate that all is well. Well, where does one do a casual finger test? On a heat fin that extends outside of the enclosure.
Nice misreading. Nice try. |
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| grege |
| quote: | Originally posted by carlosfm
Peter, look at your cute amp and think: heat goes up.:D
Heat doesn't go away from the chip.
|
I think you're thinking of hot air (or liquid) going up because it is less dense. I would imagine this effect in solids would be very very minimal. :xeye: |
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| Eric Weitzman |
| quote: | Originally posted by Peter Daniel
In that case you are seriously mistaken. The brass rod had a uniform temperature all over, no hot spots, no ups or downs.
As to your assumption that heat goes up in a brass material, can you elaborate? I'm curious what you come up with this time. |
He may be thinking about the heated air rising. Intuitively, this would seem to expose the chip to a bit more heat, that is, recycled heat. Quantitatively, it's probably insignificant. Would it be easy for you make some air temp measurements, Peter?
Speaking of which, do any of the fingertip testers among us use a remote-sense IR thermometer? I've seen some on sale at MCM and was wondering if they're worth getting. |
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| planet10 |
| quote: | Originally posted by Eric Weitzman
the fingertip testers among us |
Not me... my current output devices are EL84s and they surely get to skin blistering temps :)
dave |
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| steenoe |
| quote: | | do any of the fingertip testers among us use a remote-sense IR thermometer? |
Yes, I use one. Mine is fairly precise. It really comes in handy for this kind of work. Highly recommended. I even had it for free:) Some kind of commerciel present from a company, trying to sell me something at work;)
The readings from it are always as I would expect. So I think it is fairly trustworthy.
Steen. |
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| Peter Daniel |
| quote: | Originally posted by carlosfm
I don't doubt it, because of your arrangement.
But put the amp to work upside-down and push it hard.
Observe it the temperature is the same. |
I don't expect any difference here. Can you explain, so far those are only your assumptions, and it seems that you have no clue about laws of thermodynamics. |
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| Eric Weitzman |
| quote: | Originally posted by planet10
Not me... my current output devices are EL84s and they surely get to skin blistering temps :) |
Strange place to meet a fellow traveller: my output devices are 300Bs. |
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| Peter Daniel |
| quote: | Originally posted by Eric Weitzman
He may be thinking about the heated air rising. Intuitively, this would seem to expose the chip to a bit more heat, that is, recycled heat. Quantitatively, it's probably insignificant. Would it be easy for you make some air temp measurements, Peter?
|
I suspect that this is what he talks about, but because of relatively large mass of brass rod, short length comparing to diameter and small emission surface (and the surface that is not really friendly to release heat, as it was mentioned already before), the rising air has insignificant effect here. So it doesn't really matter if you place your chip on top bottom or side, the temperature will be more or less similar.
Unfortunately I don't hve any special devices to measure temp. However, my fingertips are quite sensitive ;) |
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| steenoe |
| quote: | | I would imagine this effect in solids would be very very minimal. |
You are right, Grege. The heat transfer in solid metal, does not behave as hot air. The heat spreads evenly in metal, no matter the orientation, more or less at least. Thats why you want to place the chip in the middle of the heatsink.:cool:
Steen. |
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| carlosfm |
| quote: | Originally posted by Eric Weitzman
Another reason, which ought to be obvious, is because he's talking about the theoretical case where one were to obtain an infinitely large block of aluminium. An infinitely large block of aluminum would not only be infinitely wide and infinitely long, it would be infinitely thick, so he can't be talking about the thickness of the heatsink. |
Misreading again.:rolleyes:
Don't read only my post, read the article on that part.
He is talking about thickness.
But I'm really convinced that you won't accept anything, you're on your own.:apathic: |
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| Peter Daniel |
| quote: | Originally posted by steenoe
Thats why you want to place the chip in the middle of the heatsink.:cool:
|
That's actually a good point, but with regards to construction, it would be rather complicated. Besides I wanted to have the spike directly on the opposite side (as the chip). Don't ask me why.:cool:
Though the thermal issues might not be optimised, the amp is playing without problem for last 4 months, and I wouldn't probably change much here. |
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| Eric Weitzman |
| quote: | Originally posted by Peter Daniel
Unfortunately I don't hve any special devices to measure temp. However, my fingertips are quite sensitive ;) |
Nice discrete measurement system. One ouch, two ouches, or an OUUUUUH. |
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| carlosfm |
| quote: | Originally posted by Peter Daniel
I don't expect any difference here. Can you explain, so far those are only your assumptions, and it seems that you have no clue about laws of thermodynamics. |
I was just asking you to try it upside-down, because the pic you posted is not enough to have an idea of the whole assembling of your amp.
I think that more heat will be transmitted to the tube instead of concentrating on | | | |
