Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: LM386 amplifier assist  (Read 1341 times)
W6AOA
Member

Posts: 36




Ignore
« on: July 28, 2011, 02:25:40 PM »

Can anyone assist me with the LM386 circuit.  All examples I see for this circuit only address an output of 8 ohms for a small speaker. I would like to use this ckt to addapt an electrovoice 638 mic to about 1300 Ohms my Icom 730 requires as a mic input.. wondering if a xfmr would do it. If so  what would it be.


Logged
W5FYI
Member

Posts: 1046




Ignore
« Reply #1 on: July 28, 2011, 06:33:39 PM »

You could use a Radio Shack 273-1380, a 1000-ohm CT to 8-ohm secondary audio transformer, but unless you have a compelling urge to use the LM386, a simpler single-transistor circuit might prove better performance. Remember, the LM386 will draw a lot of current, even when you're not talking, and if your mic-to-rig interface is battery powered, if might go dead midway into a QSO. Also, LM386s come in different flavors, and the LM386N, the most common of the group, is the one most prone to give poor performance. One characteristic of '386Ns is to oscillate or "motorboat" when the battery voltage gets low. However, they are common and cheap, and generally do a pretty good job in most applications. GL
Logged
KE3WD
Member

Posts: 5689




Ignore
« Reply #2 on: July 28, 2011, 07:16:25 PM »

Can anyone assist me with the LM386 circuit.  All examples I see for this circuit only address an output of 8 ohms for a small speaker. I would like to use this ckt to addapt an electrovoice 638 mic to about 1300 Ohms my Icom 730 requires as a mic input.. wondering if a xfmr would do it. If so  what would it be.




Not a problem, this is audio, not RF.  Just tack a 1K resistor across the output of the '386 and then attach to the radio. 

In audio applications, we can always apply a lower impedance into a higher impedance.  It won't work like that the other way around, though as trying to drive a low impedance input with a high impedance output will load down the signal. 

The opamp is high impedance at input, but low impedance output. 

No transformer needed at all here. 


73
Logged
W6AOA
Member

Posts: 36




Ignore
« Reply #3 on: July 28, 2011, 07:23:23 PM »

Thanks to all..  I do have the 386N, But its gonna be socketed and easy to swap out... I can have the mic open the 9v ckt when not talking..  TNX  Ed W6AOA Pensacola, FL
Logged
WB6DGN
Member

Posts: 619




Ignore
« Reply #4 on: August 01, 2011, 12:13:36 AM »

Why not use a transistor emitter follower?  Or a Darlington, also hiZ in, Med/Lo Z out.  Fewer parts, simpler and less room.
« Last Edit: August 01, 2011, 12:38:53 AM by WB6DGN » Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!