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LM386 minimal circuit

unclejed613

Well-Known Member
Thread starter #1
i remember a thread a while back where somebody wanted to use an LM386 amp, and they were trying to keep it simple. i found this in one of the 400+ page TAB circuit collection books. this one is about as simple as it gets...

lm386-2.png


all it needs is a battery and speaker.
 

MikeMl

Well-Known Member
Most Helpful Member
#2
Might take off. I built one once without the shunt RC network shown across the speaker on the data sheet, and it made a great oscillator at about 500kHz. Clobbered an AM radio....:banghead:
 

audioguru

Well-Known Member
Most Helpful Member
#3
Maybe the IC was made 50 years ago when the magazine printed their article about it was different and today's IC MUST have the RC Zobel network at its output. My datasheet of the LM386 is 18.5 years old and shows it in its "minimalist" schematic.
The datasheets for the similar LM380 and LM390 also show the Zobel network at the IC output. An applications document about the LM380 discusses the important Zobel network that the magazine article ignored.
 

JimB

Super Moderator
Most Helpful Member
#5
The datasheets for the similar LM380 and LM390 also show the Zobel network at the IC output. An applications document about the LM380 discusses the important Zobel network that the magazine article ignored.
I recently resurrected a little LM380 amplifier which I made about 30 years ago.
As I was testing it, I noticed on the scope that it was oscillating at some high frequency.
A quick look over the circuit showed that the resistor was missing from the Zobel network. There were holes in the circuit board for it, but no resistor.
I guess that at the time I built it, I did not have a nice low value resistor handy, so I missed it out, saying to myself "I will fit a resistor when I get one".
I guess that I soon forgot about it.
Meanwhile back in the present day, as soon as I fitted a 3.3 Ohm resistor, the oscillation stopped.

So, the moral of this boring tale is: "Don't forget the Zobel network".

JimB
 

gophert

Active Member
#6
i remember a thread a while back where somebody wanted to use an LM386 amp, and they were trying to keep it simple. i found this in one of the 400+ page TAB circuit collection books. this one is about as simple as it gets...

View attachment 116026


all it needs is a battery and speaker.
I remember reading a TAB electronics book and it described why the Zobel network was critical to the old '386.
 

gophert

Active Member
#8
I've never considered TAB books as canonical sources of lnowledge.
And where do you propose finding a canonical source of knowledge about the buzzy piece-of-crap LM386 that needs a sober network to insure it doesn't go into a self-oscillating rage?
 

JonSea

Well-Known Member
#9
I made no proposal regarding excellent references. I suggest Google if you need help.

I stand by my statement that for the most part, TAB books were pretty low quality. If you'd like to prove me wrong, please save your typing for somebody who places some value on what you have to say.
 

dr pepper

Well-Known Member
Most Helpful Member
#12
I had a Lm386 go nuclear when I threw a circuit together last year & forgot to ground the zobel network on the output, the chip appears to need it.
 

JimB

Super Moderator
Most Helpful Member
#14
What Nigel said.
JimB
 

unclejed613

Well-Known Member
Thread starter #15
the TAB books were basically compilations of schematics from data sheets and magazine articles. quite often there's a component that says " * see text" but since the schematic has been lifted from another source, there is no text. it seems that a good 5 to 10 percent of the schematics in those TAB compilations had a LM386 in them maybe that's an exaggeration, but if you wanted to write a book that was just circuits using the LM386, you could find a ton of them in those books.
 

unclejed613

Well-Known Member
Thread starter #16
#17
never built using the '386-
but successfully used many other building block schematics from this vintage Radio Shack pub by Forrest Mimms
 

Attachments

#18
I use this circuit, which seems to be stable and doesn't whistle. :)

View attachment 116029
Your circuit is the same but better written and with a filter capacitor(c3) and an RC filter (C1, R1). Since we have never used these circuits it will be hard to tell their efficiency. If you can share the inpout voltage/current and output voltage current and the what kind of a speaker you are using.

Simple is not always better. The circuit with the filters is more advised and more efficient. In engineering you can not afford to make that 1 mistake which blows up the device, thats why you put more, even if does work in 95% of the cases without it.
 

ChrisP58

Well-Known Member
#19
Your circuit is the same but better written and with a filter capacitor(c3) and an RC filter (C1, R1). Since we have never used these circuits it will be hard to tell their efficiency. If you can share the inpout voltage/current and output voltage current and the what kind of a speaker you are using.

Simple is not always better. The circuit with the filters is more advised and more efficient. In engineering you can not afford to make that 1 mistake which blows up the device, thats why you put more, even if does work in 95% of the cases without it.
The manufacturer gives typical values for that circuit in section 9.2.1 of the datasheet.
http://www.ti.com/lit/ds/symlink/lm386.pdf
 

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