lm3886 heating problem

[aniruddha]

Hi,

I am trying to build a subwoofer amplifier, subwoofer i am using is a 8 inch, 6 ohm JVC subwoofer with 135W rms rating. I tried to test it using single LM3886 amp. IC gets heated and woofer stops for few second and again started, and this happens continuously. I used a heat sink of PC which is standard for pentium 4 processor. also sound dosent feel good, feels like i need more powerful amp may be because i was giving input from my laptop directly without any preamp.

neway IC is getting heated , so what should i do to solve this problem

1) bigger heatsink
2) two parallel 3886 (current needed may be more because of 6 ohm)
3) 4 bridge/parallel 3886 (i feel power is less for subwoofer)

or i have to try all the above to get the proper solution?

please suggest me for this.

Thanks
Aniruddha

 

[aniruddha]

power supply i used was +/-35V DC and transformers and bridge rectifier are good enough to provide 5-6 amps easily

 

[ratza]

1. Get a decent heatsink. The cooler may not be enough if it gets that hot. If you cannot keep your fingers on the heatsink, then you need a bigger one.
2. Better not. Use them in bridge configuration.
3. See above

 

[AndrewT]

Hi,
don't go to either bridged or parallel just yet.
Get this one working properly first.
The complicated setups using parallel only achieve an extra 3db of SPL.

+-35Vdc is quite high for a 6ohm speaker.
Have you looked at and followed the design procedure in National's datasheet?

 

[aniruddha]

Hi AndrewT ,

thermal and heat sink procedure is followed, i didt understood it properly. also LM3886 is not at the edge of the PCB which i am using, so heat sink is connected from the bottom of it, not at the center.

but, this amplifier was made almost an year ago, and at that time I tested it on my friend's setup ( dual 12 inch subwoofers 8ohm connected in parallel) with a good headphone preamp. and the bass was amazing that time without having these heating problems. I almost tested it for around 30 min at very high volume.

So, if i need to try on this amplifier then ,
1) i will make a preamp with variable gain using NE5532
2) apply heatsink paste again and fix the heat sink properly

one more point, heat sink is not getting heated up too much, but the IC is gettini heated, so one problem may be heat is not getting transferred to heat sink properly.

if i make the fan on the heat sink running, will it improve the performance???

please advise if you feel that i should follow some more extra steps and correct me if i am doing wrong.

Thanks
Aniruddha

 

[aniruddha]

sorry one correction

*thermal and heat sink procedure is not followed

 

[pjp]

Aniruddha, if the chip is hot and the heatsink is not, you obviously haven't mounted it right. Buy some heatsink compound, tap a hole in the heatsink and attach the chip to the heatsink with a *screw*. I'm guessing you've not done that.
Did you buy the JVC and the chip in pune ? If you did, please let me know the shop and how much you paid for it ? I only know of Chaudhary Trading in Bombay who sells this driver. :-(

 

[aniruddha]

Yes, i bought JVC driver from Chaudhary Trading in Bombay and LM3886 from Chip Components

Do you have any idea where i can get good mid range drivers??
Chaudhary Trading was having very expensive 6 inch woofers which he suggested me to use it as mid range(625 for each woofer)

I got local 6 inch 90mm magnet woofer for mid range, i am not sure if it will give good sound or not, can only say after trying.

I got good Philips dome tweeters from parvail sons lamington road .

are you also in pune??

 

[aniruddha]

i have mounted heat sink using screw, but i think paste is not applied properly, i will do that and try again. I got JVC subs for 1400

 

[sukyone]

I think -+35v for load 6 Ohm
quite to height and sub-woofer
use height current amp.
for single chip warning to blow
( if temp protection in chip not work).

BPA are good for sub-woofer amp.

sorry my english is not good.

 

[pjp]

Chaudhary is good, http://www.corrson.com/ is also good.
Unfortunately, the thing about speakers is that quality is directly proportional to price.
I have a bunch of speakers lying around that I can't bear to listen to because I tried to get good speakers cheap.

 

[TheMG]

Keep in mind that CPU heat sinks are designed for forced-air cooling only. They are very poor performers when it comes to passive (convection) cooling since the spacing between the fins is very small.

So if you're going to use a CPU heat sink you best have the fan running otherwise it's going to get mighty hot after you run it for a while.