Need opinions on heatsink mounting

thetube0a3 · 2nd February 2010, 11:12 PM

Was lucky enough to get a case from my boss to put the lm3886 stereo amp in.

I have a heatsink I tore out of a 5CH sony HT receiver, I'm thinking of mounting it inside the case, but now thinking maybe sticking out of the back

ALL opinions welcome.

The face panel will be swapped out for a custom one. Case is an ELMA.

pacificblue · 3rd February 2010, 11:05 AM

The image does not show up for me.

To make the right decision you need to know the heatsink's thermal resistance, the ambient temperature and the power dissipation of your amplifier. If you put the heatsink into the case, its ability to transfer heat to the surrounding air be greatly reduced, because the air flow is restricted and the inside of a case will always be warmer than the outside during operation.
But it also has advantages. You can use a non-isolated IC without additional electrical insulation, which can lead to improved heat transfer from the IC to the heatsink. A heatsink that sticks out, must remain colder than 60 °C to avoid burns, when touched and must be electrically isolated from a non-isolated IC. If you don't build double-insulated equipment, the heatsink must also be connected to PE.

Juergen Knoop · 3rd February 2010, 12:18 PM

the heatsink is fine for your LM3886 stereoamp. Me would mount it inside the case, because of the heatsinks sharp edges. You would cut your fingers with it every now and then, when you're moving the case around...believe me I have had my experience with such designs.

Just provide some ventilation through bottom and top of the case.
regards

thetube0a3 · 3rd February 2010, 05:15 PM

Yea, I may consider finding another sink as i would "prefer" it to be external. The case is very thick extruded aluminum and I'd almost cry drilling\cutting it. i'm told this case was over $200 which seems a bit much IMO.

I also have a separate small aluminum cage that mounts inside that i could use to shield a preamp "niice". Now all I need is a preamp circuit with a nice tone section and spots for regulators.

thetube0a3 · 5th February 2010, 04:08 PM

Was able to get two heatsinks from work that IMO are much nicer.
they are 5 1/2" long by 2" the base is 1/4" thick and the fins are around an inch long. not the largest heatsinks in the world but mounted outside of the case on the rear I think they will dissipate more then enough heat to run the LM3886's at 28+28 into 4 ohms.

They have a lot more mass then the sony one which is always nice.

jacco vermeulen · 5th February 2010, 04:30 PM

Quote:

Originally Posted by thetube0a3

i'm told this case was over $200 which seems a bit much IMO.

No, it doesn't.

thetube0a3 · 6th February 2010, 02:40 AM

These are the 2 new heatsinks I got from work. They seemed tiny until I laid the lm3886 on one. Both are identical tho they look slightly different in the picture. My plans are to mount them on the back of the case. This way they will be outside of the case and should cool very well.

Opinions?

nigelwright7557 · 6th February 2010, 02:59 AM

I tend to have my heatsinks internal but compensate by adding a couple of fans, one draws air in at one end of the case and the other blows it out at the opposite end.
Of course this means the extra expense of two fans and sorting out a power supply for the fans. You might get away with one fan.

thetube0a3 · 6th February 2010, 03:06 AM

Nigel : do you have any pics of your work?

I've thought about using fans mounted in the rear panel to circulate air in one side and out the other using a simple baffle inside. Thing that bothers me tho is dust and the noise I would have. This will be sitting on a shelf by my desk at work and when its dead silent the fans might drive me crazy. Tho there are some very quiet 80mm fans out there, I switched to 120-200mm fans on my pc's for a reason

And I'd have a tough time fitting one of those in the case on either end.

nigelwright7557 · 6th February 2010, 03:10 AM

Quote:

Originally Posted by thetube0a3

Nigel : do you have any pics of your work?

I've thought about using fans mounted in the rear panel to circulate air in one side and out the other using a simple baffle inside. Thing that bothers me tho is dust and the noise I would have. This will be sitting on a shelf by my desk at work and when its dead silent the fans might drive me crazy. Tho there are some very quiet 80mm fans out there, I switched to 120-200mm fans on my pc's for a reason

And I'd have a tough time fitting one of those in the case on either end.

I use PC cases which already have the fan mountings front and rear.
I get power from the amp DC rail dropped through a resistor with two fans in series.

2nd February 2010, 11:12 PM	#1
thetube0a3 diyAudio Member Join Date: May 2008	Need opinions on heatsink mounting Was lucky enough to get a case from my boss to put the lm3886 stereo amp in. I have a heatsink I tore out of a 5CH sony HT receiver, I'm thinking of mounting it inside the case, but now thinking maybe sticking out of the back ALL opinions welcome. The face panel will be swapped out for a custom one. Case is an ELMA.

3rd February 2010, 11:05 AM	#2
pacificblue diyAudio Member Join Date: May 2008	The image does not show up for me. To make the right decision you need to know the heatsink's thermal resistance, the ambient temperature and the power dissipation of your amplifier. If you put the heatsink into the case, its ability to transfer heat to the surrounding air be greatly reduced, because the air flow is restricted and the inside of a case will always be warmer than the outside during operation. But it also has advantages. You can use a non-isolated IC without additional electrical insulation, which can lead to improved heat transfer from the IC to the heatsink. A heatsink that sticks out, must remain colder than 60 °C to avoid burns, when touched and must be electrically isolated from a non-isolated IC. If you don't build double-insulated equipment, the heatsink must also be connected to PE. __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)

6th February 2010, 02:59 AM	#8
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	I tend to have my heatsinks internal but compensate by adding a couple of fans, one draws air in at one end of the case and the other blows it out at the opposite end. Of course this means the extra expense of two fans and sorting out a power supply for the fans. You might get away with one fan. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

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3rd February 2010, 12:18 PM	#3
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	the heatsink is fine for your LM3886 stereoamp. Me would mount it inside the case, because of the heatsinks sharp edges. You would cut your fingers with it every now and then, when you're moving the case around...believe me I have had my experience with such designs. Just provide some ventilation through bottom and top of the case. regards

3rd February 2010, 05:15 PM	#4
thetube0a3 diyAudio Member Join Date: May 2008	Yea, I may consider finding another sink as i would "prefer" it to be external. The case is very thick extruded aluminum and I'd almost cry drilling\cutting it. i'm told this case was over $200 which seems a bit much IMO. I also have a separate small aluminum cage that mounts inside that i could use to shield a preamp "niice". Now all I need is a preamp circuit with a nice tone section and spots for regulators.

5th February 2010, 04:08 PM	#5
thetube0a3 diyAudio Member Join Date: May 2008	Was able to get two heatsinks from work that IMO are much nicer. they are 5 1/2" long by 2" the base is 1/4" thick and the fins are around an inch long. not the largest heatsinks in the world but mounted outside of the case on the rear I think they will dissipate more then enough heat to run the LM3886's at 28+28 into 4 ohms. They have a lot more mass then the sony one which is always nice.

6th February 2010, 02:40 AM	#7
thetube0a3 diyAudio Member Join Date: May 2008	These are the 2 new heatsinks I got from work. They seemed tiny until I laid the lm3886 on one. Both are identical tho they look slightly different in the picture. My plans are to mount them on the back of the case. This way they will be outside of the case and should cool very well. Opinions?

6th February 2010, 03:06 AM	#9
thetube0a3 diyAudio Member Join Date: May 2008	Nigel : do you have any pics of your work? I've thought about using fans mounted in the rear panel to circulate air in one side and out the other using a simple baffle inside. Thing that bothers me tho is dust and the noise I would have. This will be sitting on a shelf by my desk at work and when its dead silent the fans might drive me crazy. Tho there are some very quiet 80mm fans out there, I switched to 120-200mm fans on my pc's for a reason And I'd have a tough time fitting one of those in the case on either end.

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