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.
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.
Peter Daniel said:
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 ...
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.
'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.
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.edu/hbase/tables/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
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/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
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.
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.
Trying to explain the obvious...
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."
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."
carlosfm said:
Peter, look at your cute amp and think: heat goes up.
Heat doesn't go away from the chip.
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.
Re: Trying to explain the obvious...
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!
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.
carlosfm said:
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!
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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