Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Chip Amps Amplifiers based on integrated circuits

Max voltage input lm3886
Max voltage input lm3886
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
Thread Tools Search this Thread
Old 5th February 2010, 10:07 PM   #1
baene123 is offline baene123  Italy
diyAudio Member
Join Date: Nov 2009
Default Max voltage input lm3886

hi, one mouth ago i finished to built my power amp based on LM3886s in parallel configuration (100W on 4Ohm load),LM3886 power supply is +30V and -30V.... now , i've just started to built a new preamp but i can't understad what is the maximus voltage input of each lm3886... preamp power supply is +30 - 0 V, not dual. how can i determinate preamp gain, my signal input is from my guitar (about 5mV rms, i think)?
  Reply With Quote
Old 5th February 2010, 11:26 PM   #2
tomchr is offline tomchr  Canada
diyAudio Member
tomchr's Avatar
Join Date: Feb 2009
Location: Calgary
Gain is defined as the output voltage (versus frequency) divided by the input voltage (versus frequency). Measure those two and calculate the gain.

...or post a schematic of your circuits then it's possible for others to calculate the gains for you.

  Reply With Quote
Old 9th February 2010, 03:51 AM   #3
ryan750 is offline ryan750  Philippines
diyAudio Member
Join Date: Oct 2007

plug it in your components value then you'll see how sensitive your LM3886, from there you can calculate the needed gain by your preamp,

by the way, how's your parallel LM3886? planning to build one soon,
  Reply With Quote
Old 9th February 2010, 07:08 AM   #4
ratza is offline ratza  Romania
diyAudio Member
ratza's Avatar
Join Date: Dec 2007
Location: Sibiu, Romania
Taking the LM3886 datasheet, the maximum voltage swing at the output is in the limits (V+ - 3V) to (V- + 3V). In your case the maximum voltage swing is +/-27V or 54Vpp. I will assume that you use a gain of 23 for your amp (22k and 1k feedback resistors). So, Aamp = 23.

Knowing your gain of the amplifier so the maximum peak to peak input voltage for maximum output voltage will be Uout / Aamp. The gain and has the following expression:
Aamp = 1 + (Rf1/Ri) = 1 +22/1 = 23 (27dB)

Using the first equation will result that the input voltage is:
Uin = Uout / Aamp = 54Vpp / 23 = 2.348Vpp

Now, for the preamplifier is just the same, except you need to calculate the gain instead of voltage, and afterwards choose the values for the feedback resistors. You know that the input voltage is 5mVrms, which means that you have:
Uin1 = 5mVrms * 2 *sqrt(2) = 14.14mVpp

Gain of the preamp will be:
Apre = Uin / Uin1 = 2.348Vpp / 14.14mVpp = 166
The above is the hard way The easy way is like this -> know input voltage, know output voltage, calculate total gain:
Aglobal = Uout / Uin = 54Vpp / 14.14mVpp = 3818.9

But Aglobal = Apre * Aamp, so the gain of the preamplifier will therefore be:
Apre = Aglobal / Aamp = 3818.9 / 23 = 166

The minimum preamplifier voltage supply must be chosen bigger than Uin (voltage at preamplifier output) with the values shown in the opamp datasheet. Your preamp is powered at 30V single rail, which is more than enough, even 6V might do the job. I hope I cleared up the things a little bit.
Any solution is a compromise.
  Reply With Quote
Old 10th February 2010, 01:04 PM   #5
AndrewT is offline AndrewT  Scotland
Join Date: Jul 2004
Location: Scottish Borders
the maximum input to your power amp, assuming the same as Ratza showed, is 2.35Vpp.
I like to see 10 to 20dB of signal overhead capability in the preceding stages.
10dB requires 3.2 times as much voltage and 20dB requires 10 times as much voltage. Since we will never need to use this for a valid audio frequency signal, it does not matter if the signal is becoming grossly distorted at this artificially high value.
So, let's settle for 10dB of overhead giving the maximum output requirement for you pre-amp of about 3*2.35 = 7.4Vpp. This is just about achievable from a 9Vdc supply.
Now, we'll look at 20dB of overhead. 10 * 2.35 = 23.5Vpp.
This should be achievable from a 26Vdc supply.
A supply of 30Vdc would be ideal for a 20dB overhead on a maximum output audio signal of 2.35Vpp
regards Andrew T.
  Reply to this post


Max voltage input lm3886Hide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Where to measure max. input voltage to woofer MCPete Multi-Way 0 9th December 2009 07:41 PM
Max voltage of 2SK170? revintage Solid State 4 29th November 2009 05:37 PM
LM317 max input voltage?? imperfectcircle Parts 11 10th March 2007 12:09 PM
Max supply voltage for LM3886 @ 4 Ohms madscience Chip Amps 8 4th October 2005 06:00 PM
LM3886 Max Current thomasfw Chip Amps 1 24th May 2005 07:03 AM

New To Site? Need Help?

All times are GMT. The time now is 09:14 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio