LM741-Is there an easier or better way? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 13th April 2004, 08:35 PM   #1
Bose(o) is offline Bose(o)  Canada
diyAudio Member
 
Join Date: Dec 2001
Location: Ottawa, Ontario, Canada
Default LM741-Is there an easier or better way?

Hello all.

I have a quick question here. I have built and tested a microphone circuit which connects to an 8W pre-amp and then is further amplified by a car-amp that I have. Everything is fine here, no worries . Though, my question includes taking an audio signal and biasing it as positive. In other words, taking a sine wave and it's negative counterpart then flipping it such that I will have a cusp-type wave. This will be used with my LM339 comparator such that an LED will turn on from the output of such.
__________________
ERTW 4 life!
"the day has 24hours. If that is not enough take the night."-Roemhild
  Reply With Quote
Old 13th April 2004, 08:40 PM   #2
azira is offline azira  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Near Seattle
Use 4 diodes in a bridge-rectifier configuration. The mechanism you're describing is a called "full wave rectification." You might want a large size capacitor and/or a schmidt trigger configured opamp to help smooth out the signal so that your LED doesn't turn on and off constantly.

Rod Elliot's website has a project for a signal detector (for like subwoofers). It's similar to what you want.
--
Danny
  Reply With Quote
Old 13th April 2004, 08:56 PM   #3
Bose(o) is offline Bose(o)  Canada
diyAudio Member
 
Join Date: Dec 2001
Location: Ottawa, Ontario, Canada
I have many LN5408 diodes, would those do? I'm thinking they may be too slow. I really don't mind about quality or anything of the like, I just have to detect whether there is a change in SPL or not. I looke up full-wave rectification, and it is perfect! I knew there was a proper name for this method. The capacitor you mentioned, would I connect that before the LED? Seeing as it would "hold" the power that the LM339 would send.
__________________
ERTW 4 life!
"the day has 24hours. If that is not enough take the night."-Roemhild
  Reply With Quote
Old 14th April 2004, 12:09 AM   #4
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
you're trying to build a VOX -- here are some things to take into consideration:

-- buffer the sound input with an opamp -- then feed into a second opamp configured as a comparator * With Hysterisis * -- thus the opamp will "hang" on while the hysterisis comparator remains charged above the threshold level of the comparator.

i wouldn't be concerned about rectifying since the eye "integrates" anyway.
  Reply With Quote
Old 14th April 2004, 12:40 AM   #5
Bose(o) is offline Bose(o)  Canada
diyAudio Member
 
Join Date: Dec 2001
Location: Ottawa, Ontario, Canada
I hope this isn't too much to ask, but do you have a schematic? (jack)
__________________
ERTW 4 life!
"the day has 24hours. If that is not enough take the night."-Roemhild
  Reply With Quote
Old 14th April 2004, 03:49 AM   #6
azira is offline azira  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Near Seattle
Quote:
Originally posted by Bose(o)
I have many LN5408 diodes, would those do? I'm thinking they may be too slow. I really don't mind about quality or anything of the like, I just have to detect whether there is a change in SPL or not. I looke up full-wave rectification, and it is perfect! I knew there was a proper name for this method. The capacitor you mentioned, would I connect that before the LED? Seeing as it would "hold" the power that the LM339 would send.
Hmm... if you want a SPL meter (or a VU meter), then there is a chip that would do it for you....

Anyway, so it's kind of like building a power supply. What you do is take the input, run it through the 4 diodes (those would be fine i think, no need for fast ones) and then into the cap to gnd. The cap will "hold" the DC level of the signal and reduce ripple. The DC level should change along with the RMS level of the signal... What you do with this signal is up to you..

One more thing, this will only work for signals that are over 1.4V (2 diode drops). So in an 8-ohm environment, it'll only output a signal if there is more than 175mW RMS of power.
--
Danny
  Reply With Quote
Old 21st April 2004, 10:19 AM   #7
diyAudio Member
 
Join Date: Jul 2003
Location: Dona paula, Goa
Default Dot/Bar display

Go to the site www.national.com and search for LM3915
This IC will do a amuch better job with less components and less effort.

Enjoy

Gajanan Phadte
  Reply With Quote
Old 21st April 2004, 10:56 AM   #8
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Some of the application notes have also good examples of fullwave rectifiers and peak detection.

http://www.national.com/an/AN/AN-20.pdf#page=10

page 10 in the pdf

http://www.national.com/ds.cgi/LF/LF155.pdf

page 17, a classic. I have it in my old VU-meter from the stone age. The VU-meter consists of 80 opamps (= 40 dB, 1 dB resolution), home made voltage dividers, totally unprotected CMOS40?? (was it 4010?) from the mid 70's.
__________________
/Per-Anders (my first name) or P-A as my friends call me
Tube Buffered Gainclone in work |Thread ||
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Dipole design made easier rick57 Multi-Way 1 11th April 2007 06:54 PM
Wire frames...is there an easier way? Spasticteapot Planars & Exotics 7 19th January 2007 02:42 AM
Easier AlephX...Can you diy it ? aht Pass Labs 4 14th January 2005 04:04 AM
LM741 and RF NOISE!!! nfway Chip Amps 29 15th January 2004 07:40 PM


New To Site? Need Help?

All times are GMT. The time now is 09:50 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2