waht about attaching the LM3875 to a plate, and let the plate float on a air cusion(or what you call it) , just like a tonearm for a TT?
And if the plate/heatsink is properly designed the air flow beneath it can improve cooling dramatically.
Actually it can look pretty cool done properly with a 40 *40 cm aluminium sheet with a few wires going in and out.
Due to the flexible nature of the cables coming in and out from the amplifier these will dampen out most of the vibrations to.
FloatAmp (yes you may use the name Peter 🙂
/rickard
And if the plate/heatsink is properly designed the air flow beneath it can improve cooling dramatically.
Actually it can look pretty cool done properly with a 40 *40 cm aluminium sheet with a few wires going in and out.
Due to the flexible nature of the cables coming in and out from the amplifier these will dampen out most of the vibrations to.
FloatAmp (yes you may use the name Peter 🙂
/rickard
Peter Daniel said:
I just think the whole thing is foundamentally flawed. Putting aside the doubious sonic benefits of a "well damped" chip, I would have thought that one has to identify the source of the vibration, and figure out which part of it one wants to damp before going about doing something - hi, if a stupid banker can figure that out, a competent engineer should have done at least 100x better, 🙂.
I never understood why you wanted damp anything but that's another topic.
I would suggest that you first figure out your primary objectives in this whole project: damping or heat transfer, or something else. and then we can go from there. For heat transfer, I would suggest watercooling or heatpipes. Water (more accurately liquid) cooling is pretty mature and they are lots of cheap consumer products out there so it can be easily done. heatpipes are a lot more expensive but it is unique - I haven't heard of any amps using heatpipes.
for damping? I would suggest thick gel pads (those those gel mouse of insol). they are cheap but effective. I would use them to damp the who circuitry / heatsink so the whole thing is mechanically damped or isolated fromt he chassis.
rikkitikkitavi said:
or hang it from a ballon?
how about using the concept of air bearing? if it works for gyros, it should work here as well.
Steve Eddy said:
Off the top of my head.
SY will correct me since my freshmen chem is rusty but I think is
only between 55 times for water and maybe 5 times more molecules for greasy liquids than in gases. If it matters.
Liquids are still much better at subsonic damping than solids but air is used in optical tables which is clearly superior.
Peter I thought you had an optical table which was giving you enormous satisfaction.
I believe that air bearings are actually pretty stiff and don't isolate that well.
If you want to test your liquid damping idea, put your head in a metal bucket filled with water and have someone hit it with a stick.
The tonearms have a paddle that moves relative to the trough.
That's differnt then just popping a chip into a vial. IMHO
Heck, just put your circuit into cool monoblock towers so they look different
If you want to test your liquid damping idea, put your head in a metal bucket filled with water and have someone hit it with a stick.
The tonearms have a paddle that moves relative to the trough.
That's differnt then just popping a chip into a vial. IMHO
Heck, just put your circuit into cool monoblock towers so they look different
I could use silicone instead of oil for both damping and heat transfer. How good is silicone with heat transfering?
As to water cooling, I don't want to use any mechanical moving parts, like pumps or complicated piping and heat exchangers. The GC doesn't generate that much heat, to be really concerned with it.
As to water cooling, I don't want to use any mechanical moving parts, like pumps or complicated piping and heat exchangers. The GC doesn't generate that much heat, to be really concerned with it.
millwood said:
Let's keep it simple and let's keep an open mind. I think we are quite close to figuring it out😉
Peter Daniel said:
i assume you're talking about silicone thermal material(thermal paste eg?) if so... its performance over distances(think 1mm) is pathetic, as is water and oil without aggetation
grataku said:
I don't think "damping" is the right word here. We're talking about propagation through a medium, not a resonant system. So we're basically talking about absorption. And in any medium as far as I'm aware, absorption is frequency dependent, with the absorption increasing with frequency. And I'm not sure that low frequencies suffer more absorption loss in liquids than in solids. In fact, I'd hazard that it's just the opposite.
se
Peter Daniel said:
Ok, let's back up.
What exactly is it you want to do? Do you want to isolate the chip from external vibration so that the chip doesn't vibrate (or vibrates as little as possible) or do you want to damp the resonance of some existing vibration that is already affecting the chip?
What it is you're trying to do will determine how best to go about it. And damping and isolation are not one and the same.
se
Peter Daniel said:
the reason silicone is used is that it will form a think layer that touches both the device and heatsink. If you simply mount the heatsink and device together, there will be a thin layer of "air" together - and we all know that air is a pretty bad conductor of heat.
thermal conductivty
air 0,024 W/mC
water 0,6 W/mC
silicone 0,5-1 W/CK
thermal silicone paste 0,5-1
granite 2,5
solder 30
Al2O3 27
aluminium 120-220 (dural- pure 99,99 food grade)
copper 395 (OFC)
just a few examples, you can find most materials on google.
air 0,024 W/mC
water 0,6 W/mC
silicone 0,5-1 W/CK
thermal silicone paste 0,5-1
granite 2,5
solder 30
Al2O3 27
aluminium 120-220 (dural- pure 99,99 food grade)
copper 395 (OFC)
just a few examples, you can find most materials on google.
Steve Eddy said:
I guess I want both. The external vibrations (mostly from sound waves) are picked up by the chassis, both from the air and from supporting platform. So I want make the heatsink as small as possible to dissipate only enough heat. I would prefer to not mount the chip directly to heatsink as this increases the vibrations transfered to the chip. So I need some medium to transfer the heat from the chip to the heatsink. I already decided that heatsink area will be formed by a copper cylinder. It's easy to get from building suppliers. I believe that 1 1/4" tubing, 6" long will be enough to dissipate all the generated heat.
Variac said:
Optical table and other vibration damping systems are all based on air suspensions and they elimitate all subsonic vibrations quite well.
I can use your idea to prove my point too, remove the head from the bucket and have someone hitting it with a stick. You can probably walk away if your head is inside the bucket. That proves the great damping ability of water 😉
You are assuming that the transistor is as good a transducer as your ear.
It is actually a complicated problem, you need to distinguish between subsonic and ultrasound, audiofrequencies happen to be in between which is probably the worst case.
If you want to eliminate the subsonic vibrations or low audio freq vibrations that make your tone arm pickup jump or your cd skip or jitter any liquid will probably do well enough.
You can play with the inertias of the various components to be isolated and that helps.
Steve Eddy said:
Interesting discussion.
Maybe we should compile a table of frequencies and the common forms of matter and fill in the blanks as to what propagates and to what extent so we are all on the same page 😉
solid
liquid
gas
in order of decreasing energy
light
IR
phonons
microwaves
RF
ultrasound
audio
subsonic
DC
grataku said:
Talking about optical table, it is true that it isolates the audio unit on top of it from vibrations. It can be both heard and felt. For instance when I place my hand on the top panel of a CD player, which is on a table, I can't feel any vibrations. Another unit, which is one shelf below, vibrates like crazy (top panel).
But given that, there is still a difference, depending what I use between my stereo unit (CD player in this case) and the table. I made some experiments with acryilic plates and foam pieces, and the sound was greatly dependant on the combination I did choose. IIRC, foam, acrylic, foam was best sounding setup. This makes me very confused as the whole issue. You just cannot say that this and that is the beast, because it simply has to be tried out.
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