×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

*
*
*
*

Thanks. We have received your request and will respond promptly.

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

LM386 audio amplifier

thread643-280842

LM386 audio amplifier

LM386 audio amplifier

(OP)
I'm trying to make a small audio amplifier using an LM386N-3 IC from National. 700 mW max output.
I have a small loudspeaker, 4 ohm, 700 mW max power.
I connect the IC like indicated in the datasheet, with a gain of 20. I get lots of distortion, even at low levels.
I'm using the schematic indicated in the datasheet as 'Amplifier with gain 20 minimum parts'.
I found out that with earphones (135 ohm) there is no distortion, so I put a 56 ohm resistor in series with the load and it works ok, but the sound level is dramatically reduced. If I go lower then 56 ohm I get distorsion.
Any idea?  
 

RE: LM386 audio amplifier

How much power is "low level"? Have you measured it?
What are the frequencies that you are trying to reproduce? The 250uF cap with the 4-ohm load creates a high-pass filter with a knee at about 160Hz, so your gain below that is going to drop off rapidly.
Have you scoped the power supply pin to see if it is being pulled down by the load?

Glenn

RE: LM386 audio amplifier

(OP)
Thank you, Glenn. In the meantime I've solved it. It was probably 50 Hz noise coming from power lines. I put a small cap between positive of power supply and ground and everything disappeared. I don't have testing instruments, so it was hard for me to understand where it was coming from. A fact that still I don't understand is that it was doing it also when I was using a battery to power it, probably it was getting the noise from the socket power lines.

RE: LM386 audio amplifier

My guess is still that the power supply pin was getting pulled down by the load.  That would happen whether it was powered by a power supply or a battery. In fact, it might be worse for a battery because the battery might have a higher series impedance.

Anyway, glad to hear you solved the problem.

Glenn

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login

Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now
Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close