I'm in the process of building a small stereo powered speaker box using LM380Ns. I've got the amp set up and working on my prototype board. It is essentially this circuit:
I've got two questions.
1st, I've notice that with the RF suppression components, R1,C5 in place, the heat sinks become very hot. Without them, there is no change in sound, but the heat sinks are about at room temperature. Here's the really weird thing. The heat sinks only get hot when those parts are in place in both amps. 😱 If either one is left out, but the other left in place, both ICs run cool! It doesn't matter which is in place, and which is left out.
2nd, That cap between the pin 2 and 6 inputs. I can't detect any difference in sound whether it's installed or not, so what is it there for? I've seen some schematics that show pin 6 being grounded through a resistor, but it seems to work fine if I just let it float.
I've got two questions.
1st, I've notice that with the RF suppression components, R1,C5 in place, the heat sinks become very hot. Without them, there is no change in sound, but the heat sinks are about at room temperature. Here's the really weird thing. The heat sinks only get hot when those parts are in place in both amps. 😱 If either one is left out, but the other left in place, both ICs run cool! It doesn't matter which is in place, and which is left out.
2nd, That cap between the pin 2 and 6 inputs. I can't detect any difference in sound whether it's installed or not, so what is it there for? I've seen some schematics that show pin 6 being grounded through a resistor, but it seems to work fine if I just let it float.
That schematic came from LM380 Stereo Amplifier ? x2Jiggy.com
There is a similar one here - Mini audio amplifier circuit | Eleccircuit.com
It isn't much different from the Minimum Component Configuration shown in the AN-69 specs or the phono amp shown in the datasheet.
There is a similar one here - Mini audio amplifier circuit | Eleccircuit.com
It isn't much different from the Minimum Component Configuration shown in the AN-69 specs or the phono amp shown in the datasheet.
In my electronics class in 1980 about 20 of us built this circuit.
Every one got hot then blew up.
Decoupling is important as close to the power supply pins as possible.
It sounds like the 380 is oscillating so the RC on the output becomes low impedance and overloads the 380.
Every one got hot then blew up.
Decoupling is important as close to the power supply pins as possible.
It sounds like the 380 is oscillating so the RC on the output becomes low impedance and overloads the 380.
You can't actually float the input terminals since both of them are loaded to ground internally by 150k. Your oscillation condition cries out "layout problem". It's difficult on on a proto board but attempt as much of a single point ground as possible. Lead/wire lengths should be minimized, usually to the point where the components can't be re-used. 🙁
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Thanks! I believe you solved it!
I hadn't bother using decoupling caps on the power supply pin.
I just did several tests whereby I inserted the caps, and the heat sinks cooled down, when I pulled them out, the heat sinks got hot.
Interestingly, before I built the 2nd channel amp, I ran just one amp for a long time, and it never warmed up.
Now what about that cap across pins 2 and 6? Should I leave it there
I hadn't bother using decoupling caps on the power supply pin.
I just did several tests whereby I inserted the caps, and the heat sinks cooled down, when I pulled them out, the heat sinks got hot.
Interestingly, before I built the 2nd channel amp, I ran just one amp for a long time, and it never warmed up.
Now what about that cap across pins 2 and 6? Should I leave it there
In your configuration it shouldn't be necessary, but leaving it will cause an input roll-off to start just above the audio band, with the negative input impedance left internally set at 150k.
The c on pins 2 & 6 helps prevent RF pickup due to the highish input impedance. You can take it out but may experience radio station pickup. I always get a french LW station if I miss an input c off my amps lol..
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