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triden 29th January 2006 01:14 AM

lm386 amp without negative power supply
Hey everyone,

I am really new to building amps and find it a really interesting hobby to dabble in. Lately I've been building small o-amp circuits using our test equipment provided at school. The nice thing is that the power supplys there have a negative supply rail.

Now while at home I have an amp built, but only a single positive source power supply. I am wondering if there is a way to bias it so that I can somehow get a -v and +v output out of it. So say it can output +20v, can I somehow bias it so that 10v is common and it can swing either way? Does this seem like a realisitc thing to do, or should I build a new supply with a positive and negative rail?

Hopefully I made my first post in the right place :cool:

sivan_and 29th January 2006 01:56 AM

Welcome to this forum..Yes it is possible to run power amps with single psu...Do search the forum..

Goodluck !!

lineup 29th January 2006 03:44 AM

2 Attachment(s)

Low Voltage Audio Power Amplifier

General Description

The LM386 is a power amplifier designed for use in low voltage
consumer applications. The gain is internally set to 20 to
keep external part count low, but the addition of an external
resistor and capacitor between pins 1 and 8 will increase the
gain to any value from 20 to 200.

The inputs are ground referenced while the output automatically
biases to one-half the supply voltage. The quiescent
power drain is only 24 milliwatts when operating from a 6 volt
supply, making the LM386 ideal for battery operation.

Normal version of LM386 can have power supply 4-12 Volt.
You should download and study: LM386 Datasheet PDF

LM386 is NOT designed for use of dual supply, positive, 0V and negative.
It is designed for single supply.

If you use maximal 12 Volt supply, with +V and Ground connections,
the input terminals will be at Ground level.
This means you can use input without input capacitors.
( If your source has DC-offset, you need an input capacitor ~1uF )

The output will be at 50% of 12 Volt = 6 Volt,
so you NEED an output cap, to protect loudspeaker from this voltage.

In my attached, normal circuit with minimum components, I would use a 1000uF in place of 250uF output capacitor.

Eva 29th January 2006 11:02 AM

I think that triden is actually talking about the LM3886, but he missed one eight :)

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