hi guys,
I am new in this: hope u guys can help. recently Ive built an amp using the LM3886 IC. I followed the exact schematics from the application datasheet. When the amp is first turned on, it sounds really sweet, untill something like 5 minutes. then it started to distorts heavilly, and the volume decreases. After shutting it down and turning it on again, it sounds ok, and the whole distortion process starts again....-(
I suspected thermal problems, but Ive changed the heatsink to a super duper large one, Ive even installed a fan to cool it. still the problem stays. can anyone help me with this? thanks
I am new in this: hope u guys can help. recently Ive built an amp using the LM3886 IC. I followed the exact schematics from the application datasheet. When the amp is first turned on, it sounds really sweet, untill something like 5 minutes. then it started to distorts heavilly, and the volume decreases. After shutting it down and turning it on again, it sounds ok, and the whole distortion process starts again....-(
I suspected thermal problems, but Ive changed the heatsink to a super duper large one, Ive even installed a fan to cool it. still the problem stays. can anyone help me with this? thanks
What speaker are you running? and... how big of a heatsink are you using? When it starts distorting badly, feel the heatsinks you are using...see if they are scorching hot...i suspect they are...which means they are too small or you are running a speaker that this amp can't handle
-Matthew K. Olson
-Matthew K. Olson
You may want to post this in the chip amps forum if you haven't already.
I agree you should check your heatsink temp and the top of chip (metal part, t model) for burning heat and if there is a noticable diff in the temp's between the 2 you may need to look at your chip to sink junction.
Unless the chip is faulty or your power supply/load are incorrect this is all I can think of.
Could you post a pic of your setup in question?
I agree you should check your heatsink temp and the top of chip (metal part, t model) for burning heat and if there is a noticable diff in the temp's between the 2 you may need to look at your chip to sink junction.
Unless the chip is faulty or your power supply/load are incorrect this is all I can think of.
Could you post a pic of your setup in question?
I seem to recall something similar, where it turned out the centre tap of the transformer wasn't connected to ground.
Rune
Rune
yep
that was the problem with my second set of gainclones.
I had connected every ground cable that was there, except I had overlooked one thing, to test the IEC receptacle
You see I recycle them from PC enclosures, and after i remove them i trim then, it is to say I desolder the pieces of wire that hang on the rear end. Well I do that with a solder GUN 100 watts.
I must have burned something while doing so because after I checked out the ground wiring( i did that after havind sought for 2 days... to test oout everything from the schematic to my building outlay, I noticed it was obstructed because of the faulty receptacle.
and the description you give is exactly the same !
same thing!!! first few minutes nice sound, then hum and some music at very low volume! Must be the groundloop somewhere obstructed from going to the earth......
J-P.
that was the problem with my second set of gainclones.
I had connected every ground cable that was there, except I had overlooked one thing, to test the IEC receptacle
You see I recycle them from PC enclosures, and after i remove them i trim then, it is to say I desolder the pieces of wire that hang on the rear end. Well I do that with a solder GUN 100 watts.
I must have burned something while doing so because after I checked out the ground wiring( i did that after havind sought for 2 days... to test oout everything from the schematic to my building outlay, I noticed it was obstructed because of the faulty receptacle.
and the description you give is exactly the same !
same thing!!! first few minutes nice sound, then hum and some music at very low volume! Must be the groundloop somewhere obstructed from going to the earth......
J-P.
thanks guys, i am going to check on my earth line again. Matt, youve mentioned about speakers, that the amp could not handle. Currently I am using a pair of cheap speakers salvaged from a panasonic hi-fi, rated 8 ohms. Would this effect the amp?
another thing, Im pretty sure my heatsink is big enough, could it be the thermalpaste that i am using is not conductive? I will try to post the photo after i can rob a camera off someone-)
another thing, Im pretty sure my heatsink is big enough, could it be the thermalpaste that i am using is not conductive? I will try to post the photo after i can rob a camera off someone-)
I had the same problem with one of my gainclones when I first started biamping with passive XO.
The problem was crossed wires (0 ohm impedance) in the crossover.
It would play nice for a few seconds or at low volume, but then started to distort big time.
The problem was crossed wires (0 ohm impedance) in the crossover.
It would play nice for a few seconds or at low volume, but then started to distort big time.
Skyrader, if you have a multimeter, stick it in the terminals of the speakers and give us a reading of the resistance in ohms. ...do this to both speakers, you may have a short
-Matthew K. Olson
-Matthew K. Olson
I have tried using a spare transformer, checked my earth lines, yet the amp still behaves badly. Sorry I dont have any digicams with me. The syptoms as follows: sweet music for about 5 minutes, then distortion buildup, untill there is a loud humming.
Ive tried using other speaker sets, but no improvements. Could it be my amp oscillating?
Ive tried using other speaker sets, but no improvements. Could it be my amp oscillating?
thanks for the tips guys, Ive finally solved my problems.
The improper ground lines thats causing oscillations. Previously, my old circuit looks like this:
Previously, I wired all the external components to a stripboard, and I connect the chip to the board using wires(about 3 inches long). Ground loops happens because it seems that all the components are plugged into a single earth line, and to make it worse, the line is a very small PCB track.
This morning I took everything apart, I used P2P wiring, and connected all the earth wiring to a star, making it like an ideal sink. I kept all the wires short, and bypass caps as close to the chip as possible LM3886 has been abusing my neighbours for two hours now.
I get lower noise floor than before, and I think I am hearing extra noises from my carbon resistors. from here I understand 2 things:
1) how to identify an amp oscilating.
2) all ground line is best connected to a centre point, making a star shape. For this, P2P wiring is and advantage.
Thanks for helping out, guys. Now Im looking into making a good casing.
skyraider has attached this image:
The improper ground lines thats causing oscillations. Previously, my old circuit looks like this:
Previously, I wired all the external components to a stripboard, and I connect the chip to the board using wires(about 3 inches long). Ground loops happens because it seems that all the components are plugged into a single earth line, and to make it worse, the line is a very small PCB track.
This morning I took everything apart, I used P2P wiring, and connected all the earth wiring to a star, making it like an ideal sink. I kept all the wires short, and bypass caps as close to the chip as possible LM3886 has been abusing my neighbours for two hours now.
I get lower noise floor than before, and I think I am hearing extra noises from my carbon resistors. from here I understand 2 things:
1) how to identify an amp oscilating.
2) all ground line is best connected to a centre point, making a star shape. For this, P2P wiring is and advantage.
Thanks for helping out, guys. Now Im looking into making a good casing.
skyraider has attached this image:
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