LM3886 audio cutting out

NINfan · 25th December 2005, 03:09 AM

Hi all,

I'm having a bit of an issue with an lm3886 amp I just built(using the amp kit from www.chipamp.com). When I crank the volume into excessive levels the sound on one of my channels cuts out for about 2 seconds and comes back in and does this every so often, it's very random, and occurs alot. I'm using a CPU heatsink, which from what I've read is adequate for this amp. This problem is just for 1 channel, the other channel stays on.

At first I thought something may have been loose in the speakers and amp, but everything is pretty secure and connected. So it does'nt seem to be anything intermittent. Has anyone else had this issue? I'm thinking it maybe heat because the chips do get warm, but then would'nt both channels cut out? I'm seriously considering rebuilding it, which might be the only choice I have if I can't figure this out.

abid_rehan · 25th December 2005, 03:47 AM

i would work on the mute section area....

neutron7 · 25th December 2005, 04:01 AM

is it the isolated or non isolated 3886?

NINfan · 25th December 2005, 04:24 AM

Sorry? but I'm not familiar with isolated and non isolated. If I had to guess, I think you'd mean is it seperate from the power supply? which it's not, it's all housed in the same chassis. I'm not sure what the mute section are is either, sorry for my bit of ignorance.

Greg Erskine · 25th December 2005, 04:49 AM

Hi NINfan,

The LM3886 comes in 2 types, the LM3886T and LM3886TF. The LM3886TF is the isolated version which means it can be mounted on the heatsink with only heat transfer compound between the chip and the heatsink. The LM3886T on the other hand needs an isolating material such as a mica washer, to insulate it from the heatsink.

neutron7 was implying that maybe one of the chips has a intermittent short to the heatsink, I think???

regards
Greg

xplod1236 · 25th December 2005, 05:12 AM

I'm thinking that the heat from that chip isn't going into the heatsink, and the chip goes into thermal shutdown. What we need to know is which version of the chip it is (T or TF), and if you used a mica washer/heat transfer compound between the chip and the heat sink.

NINfan · 25th December 2005, 06:00 AM

Thanks for that definition. Well, I checked chipamp.com and the kit I ordered comes with the LM3886TF. I am using heatsink compound, but I have a feeling it may not be making good contact with heatsink.

xplod1236 · 25th December 2005, 06:16 AM

If the heatsink doesn't get too hot, then you are right, the chip is not making good contact with the heatsink. Pull off the chip, clean off the contact areas, make sure that the heatsink contact area is straight, reapply the heat transfer compound, and bolt the chip to the heatsink, making sure it sits flat against the mounting surface.

NINfan · 25th December 2005, 06:37 AM

Just redid it, thanks for the adivice. I'll have to crank it tommorow because everyones getting some sleep right now. I'll tell you all how it goes in a few hours, thanks for all your help.

peranders · 25th December 2005, 06:38 AM

NINfan, how big is your heatsink? Maybe it's too small? If the heatsink is rather cool but the IC is hot, then you have a problem with the heat transfer between IC and heatsink. If the heatsink is hot, then it is too small.

25th December 2005, 03:09 AM	#1
NINfan diyAudio Member Join Date: Jun 2005 Location: mem	LM3886 audio cutting out Hi all, I'm having a bit of an issue with an lm3886 amp I just built(using the amp kit from www.chipamp.com). When I crank the volume into excessive levels the sound on one of my channels cuts out for about 2 seconds and comes back in and does this every so often, it's very random, and occurs alot. I'm using a CPU heatsink, which from what I've read is adequate for this amp. This problem is just for 1 channel, the other channel stays on. At first I thought something may have been loose in the speakers and amp, but everything is pretty secure and connected. So it does'nt seem to be anything intermittent. Has anyone else had this issue? I'm thinking it maybe heat because the chips do get warm, but then would'nt both channels cut out? I'm seriously considering rebuilding it, which might be the only choice I have if I can't figure this out.

25th December 2005, 04:49 AM	#5
Greg Erskine diyAudio Member Join Date: Jan 2002 Location: Sydney/Australia	Hi NINfan, The LM3886 comes in 2 types, the LM3886T and LM3886TF. The LM3886TF is the isolated version which means it can be mounted on the heatsink with only heat transfer compound between the chip and the heatsink. The LM3886T on the other hand needs an isolating material such as a mica washer, to insulate it from the heatsink. neutron7 was implying that maybe one of the chips has a intermittent short to the heatsink, I think??? regards Greg __________________ Greg Erskine

25th December 2005, 06:38 AM	#10
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	NINfan, how big is your heatsink? Maybe it's too small? If the heatsink is rather cool but the IC is hot, then you have a problem with the heat transfer between IC and heatsink. If the heatsink is hot, then it is too small. __________________ /Per-Anders (my first name) or P-A as my friends call me

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25th December 2005, 03:47 AM	#2
abid_rehan diyAudio Member Join Date: Mar 2007	i would work on the mute section area....

25th December 2005, 04:01 AM	#3
neutron7 diyAudio Member Join Date: Dec 2003 Location: Toronto Canada	is it the isolated or non isolated 3886?

25th December 2005, 04:24 AM	#4
NINfan diyAudio Member Join Date: Jun 2005 Location: mem	Sorry? but I'm not familiar with isolated and non isolated. If I had to guess, I think you'd mean is it seperate from the power supply? which it's not, it's all housed in the same chassis. I'm not sure what the mute section are is either, sorry for my bit of ignorance.

25th December 2005, 05:12 AM	#6
xplod1236 diyAudio Member Join Date: Dec 2003 Location: On the couch	I'm thinking that the heat from that chip isn't going into the heatsink, and the chip goes into thermal shutdown. What we need to know is which version of the chip it is (T or TF), and if you used a mica washer/heat transfer compound between the chip and the heat sink.

25th December 2005, 06:00 AM	#7
NINfan diyAudio Member Join Date: Jun 2005 Location: mem	Thanks for that definition. Well, I checked chipamp.com and the kit I ordered comes with the LM3886TF. I am using heatsink compound, but I have a feeling it may not be making good contact with heatsink.

25th December 2005, 06:16 AM	#8
xplod1236 diyAudio Member Join Date: Dec 2003 Location: On the couch	If the heatsink doesn't get too hot, then you are right, the chip is not making good contact with the heatsink. Pull off the chip, clean off the contact areas, make sure that the heatsink contact area is straight, reapply the heat transfer compound, and bolt the chip to the heatsink, making sure it sits flat against the mounting surface.

25th December 2005, 06:37 AM	#9
NINfan diyAudio Member Join Date: Jun 2005 Location: mem	Just redid it, thanks for the adivice. I'll have to crank it tommorow because everyones getting some sleep right now. I'll tell you all how it goes in a few hours, thanks for all your help.

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