Heat pipe cooling in power amps

[MCH]

Hi,
Computer CPUs dissipate a lot of heat and from what I understand (very little) their cooling systems are very much developed and performant. I never see heat pipes assemblies in power amps (I am not interested in water cooling). Is there a reason for that or is it just that is not usually necessary?
Thank you for your comments.


PS: the reason I am asking is that I am thinking on, maybe, building (that is, PCB included, not premade module) a multichannel TPA3xxx amp, but the condition is that it is possible to make it very small. What worries me most is of course the cooling, and before even starting I want to know if it would be possible to clamp the amp chips to a laptop CPU like cooling system (heat pipes - radiator - fan) with no additional heat sink other than the enclosure. The amp would be hidden and the fan noise is not expected to be an issue. I am not interested in any commercially available amps.

 

[Doodski]

I never see heat pipes assemblies in power amps (I am not interested in water cooling). Is there a reason for that or is it just that is not usually necessary?

The heatpipes where used sometimes in the 1980s by Matsushita Electric also known as Technics. It was a very effective cooling system and was found to be very reliable, very cool running and lightweight too. Check out this fine SU-V303 integrated amplifier as a example.

Technics SU-V303 Stereo Integrated Amplifier Manual | HiFi Engine

www.hifiengine.com

 

[antcollinet]

Hi,
Computer CPUs dissipate a lot of heat and from what I understand (very little) their cooling systems are very much developed and performant. I never see heat pipes assemblies in power amps (I am not interested in water cooling). Is there a reason for that or is it just that is not usually necessary?
Thank you for your comments.


PS: the reason I am asking is that I am thinking on, maybe, building (that is, PCB included, not premade module) a multichannel TPA3xxx amp, but the condition is that it is possible to make it very small. What worries me most is of course the cooling, and before even starting I want to know if it would be possible to clamp the amp chips to a laptop CPU like cooling system (heat pipes - radiator - fan) with no additional heat sink other than the enclosure. The amp would be hidden and the fan noise is not expected to be an issue. I am not interested in any commercially available amps.

Heat-pipes are a means of effectively transferring heat from one place to another. In the case of a CPU, from the small surface area of the top of the CPU to the heatsink. Typically in a sitution where the CPU needs to be in the middle of the PCB and therefore not easy to put in good contact with a heatsink. You also have all the heat loss concentrated in one realtively small device.

This is not so necessary in Audio amps where:
The power devices can be located at the edge of the PCB in close proximity to the heatsink.
There are multiple devices all - combined - perhaps dissipating the same (if ClassA or Class AB) or less heat as a single CPU - much easier to get the lower heat per device out.
Class D amps (Such as you are thinking of designing) have much lower heat loss than a typical CPU - again spread over multiple devices. Cooling them is even less of a problem, and is typically achieved by putting the power device(s) in contact withe a heat-spreader, which an then make contact with the housing.

EDIT - though as pointed out by @Doodski heat pipes have clearly been used in amps.

Nothing to stop you using a CPU heatsink with heat-pipes though if that makes your home built mechanical design easier.

 

[MaxwellsEq]

Also the Sony TA F80 used a heat pipe

 

[staticV3]

Computers routinely produce hundreds of watts in form of heat, and therefore need sophisticated cooling solutions.

In contrast, modern Class D Amps like the TPA3255 have a peak heat output of <100W:


However, the nature of music signals (~15dB crest factor) make the average heat output be closer to 1-5W.

That severely relaxes the requirements for heat dissipation, which makes solutions like heat pipes just plainly unnecessary.

That being said, I'm very much a fan of over engineered and overkill cooling solutions, so if you want to get fancy with it, no complaints from me

 

[MCH]

Heat-pipes are a means of effectively transferring heat from one place to another. In the case of a CPU, from the small surface area of the top of the CPU to the heatsink. Typically in a sitution where the CPU needs to be in the middle of the PCB and therefore not easy to put in good contact with a heatsink. You also have all the heat loss concentrated in one realtively small device.

This is not so necessary in Audio amps where:
The power devices can be located at the edge of the PCB in close proximity to the heatsink.
There are multiple devices all - combined - perhaps dissipating the same (if ClassA or Class AB) or less heat as a single CPU - much easier to get the lower heat per device out.
Class D amps (Such as you are thinking of designing) have much lower heat loss than a typical CPU - again spread over multiple devices. Cooling them is even less of a problem, and is typically achieved by putting the power device(s) in contact withe a heat-spreader, which an then make contact with the housing.

EDIT - though as pointed out by @Doodski heat pipes have clearly been used in amps.

Nothing to stop you using a CPU heatsink with heat-pipes though if that makes your home built mechanical design easier.

Thank all for your answers, I have reasons now to waste a bit of time digging a bit deeper.

@antcollinet what I see in laptops is a big clamp for the CPU and then the heat pipe going above the smaller heat releasing components with heat tape/resin whatever to the pipe. That is what I had in mind. Not sure if this is feasible with, i.e. inductors thought.

 

[MCH]

That severely relaxes the requirements for heat dissipation, which makes solutions like heat pipes just plainly unnecessary.

The objective is a 6-8 channel power amp half the size of a cigar box (PSU not included).
Stupid? Sure, that's why I need to dyi it.

 

[mcdn]

The objective is a 6-8 channel power amp half the size of a cigar box (PSU not included).
Stupid? Sure, that's why I need to dyi it.

Your bigger issue is going to be that you may need to design a custom board in order to meet your size constraint. Cooling it will be relatively simple. The TI reference design is easy enough to implement I suppose, with maybe a single tunnel style heat sink with 2 chips mounted to each side?

 

[mcdn]

I should have added some extra context. In practice an 8ch TPA3255 made of 4 2ch modules and an 800w SMPS idles at around 30W. With a 2U steel case and a small fan it stays around 10c above ambient.

 

[MCH]

Your bigger issue is going to be that you may need to design a custom board in order to meet your size constraint.

This is the intention

Cooling it will be relatively simple. The TI reference design is easy enough to implement I suppose, with maybe a single tunnel style heat sink with 2 chips mounted to each side?

The idea is to make a few identical 2 channel (1 chip) little boards and use them as modules. Before posting this i was thinking on designing the PCB so that i can use CPU style clamps to attach to the heat pipes but after reading the answers here i will probably go simpler and just use some heat transfer tape between the chips and the pipe. I still think the clamps are a good idea to make sure the connection is robust. Will see how difficult to find these parts are. Regarding on how to lay out the modules, i don't know yet, until i research a bit how easy is to work with the pipes.
I was thinking after reading the answers that i might try first a 3D printed PTMG or ABS enclosure (i can do both) what would give me much more freedom.
I have been experimenting the past couple of weeks with 2 aiyima A07 max at different voltages and the difference in themperature at >45V vs <42V is very significant, so if i run into trouble with my build i can always lower a bit the voltage, or at least feed the surround channels with a lower voltage.

In terms of fan, i currently have my DSP electronics in an enclosure with a little noctua 4x4cm fan that never goes beyond 50% duty and i cannot hear it even with the door of the cabinet open. If i force the fan to 100% then yes, i can hear it when the door is open. This gives me confidence that a slightly bigger good quality fan will not be an issue whatsoever and i can have it working all the time at a low speed and program it to go faster only if necessary.

 

[Dunring]

Some computer fan controllers have temperature probes so from the panel on it you can program when a fan comes on. I'd just use it on a USB to 3 pin connector and leave it in all the time. There's power reducers and 3 position switches to lower the speed.

 

[dlaloum]

Studer/Revox in the late 70's and 80's used to have heatpipes for their power amp cooling... (B251, B242, maybe other models?)

Their power amps are an oft overlooked gem....

 

[Doodski]

Studer/Revox in the late 70's and 80's used to have heatpipes for their power amp cooling... (B251, B242, maybe other models?)

Their power amps are an oft overlooked gem....

Yesss, I opened a Studer Revox small integrated and it was like I had walked into a analytical art exhibit. It was perfect in every way. I serviced it and when the customer came to pick it up and pay I offered to buy it for a good price and he said, "NO!"

 

[dlaloum]

Yesss, I opened a Studer Revox small integrated and it was like I had walked into a analytical art exhibit. It was perfect in every way. I serviced it and when the customer came to pick it up and pay I offered to buy it for a good price and he said, "NO!"

I lent my Revox integrated to a friend, while I was travelling overseas... a few years later when I came back, he had sold it....
To him it was an old redundant, used piece of kit... he got a brand new sparkly heapie cheapie setup.... sigh.

 

[Doodski]

I lent my Revox integrated to a friend, while I was travelling overseas... a few years later when I came back, he had sold it....
To him it was an old redundant, used piece of kit... he got a brand new sparkly heapie cheapie setup.... sigh.

Awww, that would hurt for sure...

 

[howard416]

I lent my Revox integrated to a friend, while I was travelling overseas... a few years later when I came back, he had sold it....
To him it was an old redundant, used piece of kit... he got a brand new sparkly heapie cheapie setup.... sigh.

Sold it... so he gave you the proceeds in full, plus at least interest for your trouble, right?

 

[MCH]

Guys, i believe it is very feasible.
Here is a simulation of how the modules would look like with the BOM of TPA3255 eval board. This contains all the parts needed for balanced input and stereo and bridged operation and also the PFFB net and a radiator with a 4cm fan. I left out the 12V voltage regulators (I would use a USB power delivery chip) and microcontroller (for fan control, amp restart and master/slave board controls etc) that would go in a different board. Each module is 11x7 cm. The idea would be to put other two boards on top (all bulky components pointing outwards) for a total of 4 heat pipes (represented by the yellow lines. Each amp would have one heat pipe for the amp chips and another one to the ground plane somewhere around the inductors/output stage.
I think the whole 8 channels amp could fit a ca. 22x13x8 cm enclosure. Ok, a bit more than half a cigar box, but still a smallish cigar box

I might be even go ahead and do it, but it won't be a cheap project, i calculate roughly 150-200 eur + PSU...

 

[dlaloum]

Sold it... so he gave you the proceeds in full, plus at least interest for your trouble, right?

Yeah right... he basically gave it away... it was a "piece of junk", "old clunker" of no real value...

 

[antcollinet]

Each amp would have one heat pipe for the amp chips and another one to the ground plane somewhere around the inductors/output stage.

How are you coupling the heat pipes to the ICs? You are going to need some sort of heat transfer block with the pipe soldered to it.

And I've no idea how you will transfer the heat from a ground plane to a heat pipe.

 

[Doodski]

with the pipe soldered to it.

I have seen where the block and the heat pipe thermal conduction is done by using thermal paste instead of solder. It works very well.