LM386 measurements
Everyone seems to hate the LM386 audio amplifier chip yet it abides well into the 20th century. What do they hate ? Noisy output, distorted output, low power output - let me paraphrase the opening story from "Annie Hall" with the two old ladies at the Catskills resort:
first lady: "the food here is terrible"
second lady: "yes, and such small portions !"
Looking at the TI data sheet description:
the chip is meant for battery operation in consumer electronics. Low standby power is the big selling point. And the ability to increase the gain by 20 db by adding a single bypass cap is another selling point. I don't think it was meant to be an all-purpose device. I'm reminded of when I was a kid, I would have a transistor radio going under the pillow, and since I'd usually fall asleep and not turn it off, low power operation let those silly 9V batteries last. Also, the radio had to be physically robust since it would often end up hitting the hardwood floor during the night. I had one of these (this one is from ebay):
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A GE P1710 - a classic design with an unusual speaker but not that great a radio, the case was pretty tough though :)
There were two vendors of the LM386 that I've used, National (now TI) and New Japan Radio (aka Japan Radio Corp) version.
Let's compare them. Test circuit used:
National LM386N-4 specs:
National LM386N-4 data:
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| National LM386 yellow trace is output, blue trace is input |
Quiescent current at 9V was 5.3 mA. Undistorted maximum power at 9V was 4.4V p-p or 300 mW into 8 ohms (probably higher with a 3.2 ohm speaker), voltage gain was 22, current at max. power was 145 mA
NJR NJM386D spec:
NJR NJM386D data:
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| yellow trace is the somewhat distorted output, blue is the input |
Quiescent current at 9V was 2.7 mA. Undistorted maximum power at 9V was 3.4V p-p or 180 mW into 8 ohms (450 mW with 3.2 ohm speaker ?), voltage gain was 17, current at max. power was 110 mA
Bottom line: the NJM386D was more frugal batterywise but not as much oomph as the National. To be fair, the NJR part was the D low power version, the National part is the -4 higher powered version. Also, the National part was new out of the tube while the NJR part was pulled from a socket.
Although the TI LM386 still is sold in 2023 the NJR part has been discontinued. The continuing quest will be to find a discrete circuit that operates with a low standby current but delivers "better" performance than the LM386, more to follow !
Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm
