Hi! I just finished building an LM3886 surround amplifier, and it works like a charm. I got 3x LM3886 in parallell for the subwoofer, on a heatsink rated at 0.9 degC/W and 5 separate LM3886's on another, identical heatsink. This is installed in a closed enclosure, with a temperature controlled fan on the back. The problem is that the heatsink with the 5 LM3886's gets really hot (50-55 degC) even when idle. They are not muted, but doesn't have anything connected to them, except power.
Should I worry about this? Does the LM3886 take any damage by operating near its maximum temperature (85 degC)?
Should I worry about this? Does the LM3886 take any damage by operating near its maximum temperature (85 degC)?
just to clarify, when you say 'closed enclosure' is the heatsink inside the enclosure or outside?
The 3886 has temperature protection so will shutdown if it gets too hot, but that temperature at idle seems wrong. Assuming 20 degrees room temp you are talking about 6W per device and I would not expect anything that high at idle.
The 3886 has temperature protection so will shutdown if it gets too hot, but that temperature at idle seems wrong. Assuming 20 degrees room temp you are talking about 6W per device and I would not expect anything that high at idle.
I guess there may me many parameters that I've ignored. At first I only used the enclosure (with the heatsink inside) as a subwoofer amplifier. I just had one heatsink with 3x LM3886, and my back plate was not finished yet, so it got all the air it wanted. I've been finising up this amp the last few days, and I've installed the rest on the amplifiers (5 LM3886's on one heatsink) and a laser cut backplate. I guess I may need to make some more vent holes, or/and add a fan that blows directly on the heatsink.
What's the temperature inside the enclosure? A heatsink's degC/W rating is normally for a single central heat source, I'd expect 5 chips to distribute the heat and hence get a slightly better overall rating. A single LM3886 is about 3.5W at 35V supplies so you have in theory 17W. This would make sense if the internal temp was around 40degC.
Yes, I'll have to fix that. The best would be to make the vent holes invisible from the front and the side, but big enough so the fan didn't need to run when the amp is idle. Anyway, here is a picture if it 
All the LM3886's is running ~ +-36v, and I guess the internal temp is arround 40 degC when the amp is idle.
All the LM3886's is running ~ +-36v, and I guess the internal temp is arround 40 degC when the amp is idle.
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The schematic for each amplifier can be found in this forum post:
LM3886 Schematic
I've also added a zobel network at the output, and soldered a 220pF cap across R5
LM3886 Schematic
I've also added a zobel network at the output, and soldered a 220pF cap across R5
Well...That board has a very poor layout, PS mid and high frequency bypass caps entirely missing, feedback path is too far from chip pins, and the grounding scheme looks a little wonky to my eyes.
I highly recommend checking out Tomchr's site on "Taming the 3886" here: http://www.neurochrome.com/audio/?page_id=941#RealWorldDesignExample. There's a lot of good helpful info there.
Mike
I highly recommend checking out Tomchr's site on "Taming the 3886" here: http://www.neurochrome.com/audio/?page_id=941#RealWorldDesignExample. There's a lot of good helpful info there.
Mike
I have a bunch of those little blue chinese LM3886 kit boards, they oscillate, and get really hot. They're easy to fix.
Some details here: http://www.diyaudio.com/forums/anal...n-motor-powered-turntables-4.html#post4079081
More here: http://www.diyaudio.com/forums/anal...n-motor-powered-turntables-4.html#post4079764
I am using several of them in parallel to drive an EI step up transformer with appreciable capacitance and leakage inductance. I added both a zobel and thiele network in addition to many other changes, see the posts referenced for all of the details. You probably don't need the thiele network - or just one after you sum all of the amp outputs together
Some details here: http://www.diyaudio.com/forums/anal...n-motor-powered-turntables-4.html#post4079081
More here: http://www.diyaudio.com/forums/anal...n-motor-powered-turntables-4.html#post4079764
I am using several of them in parallel to drive an EI step up transformer with appreciable capacitance and leakage inductance. I added both a zobel and thiele network in addition to many other changes, see the posts referenced for all of the details. You probably don't need the thiele network - or just one after you sum all of the amp outputs together
They all need to be done to make the board stable under all conditions I believe with the exception of the thiele network (parallel RL) on the output. In terms of the thiele network I would probably include one between all of the amps and the speaker - it's very cheap/easy insurance although it should not be needed in this instance.
You can use 18 - 27pF COG/NPO ceramic across the feedback resistor - this is used primarily to compensate for stray capacitance in the layout at the inverting input of the LM3886.
The board is quite poorly laid out and takes a number of short cuts to save cost like deleting critical supply decoupling components, but in spite of this I still think it is a good deal if you know how to fix it!
You can use 18 - 27pF COG/NPO ceramic across the feedback resistor - this is used primarily to compensate for stray capacitance in the layout at the inverting input of the LM3886.
The board is quite poorly laid out and takes a number of short cuts to save cost like deleting critical supply decoupling components, but in spite of this I still think it is a good deal if you know how to fix it!
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