my first amp based on lme49830 - diyAudio
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 27th September 2012, 01:37 PM #1 diyAudio Member   Join Date: Aug 2011 my first amp based on lme49830 hello, this is my first post here so i introduce myself. i'm study EE in uni. i'm now on my last year and maybe this will be my graduate project! before i'm starting my project, i wanted to ask a question about the transformer. i know it's better to use a toroide type transformer because of the low noise high effictioncy and the small profile but i'd like to know which one i need. i'm planning to build 100w x 5 amp @ 8ohm . so based on ohm's power law: P=I * V = V^2 / R = I^2 * R so if i need P=100W and R=8ohm V=28.28VDC (after the rectifing , smothing and regulation) A= 3.5A. is it correct? or i need a safe margine? based on this i need a transformer rated on about 500VA (or more??) ?? thanks Ido
 27th September 2012, 02:26 PM #2 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders if you build one channel (two channels won't get you any higher grade) then expect a 100VA to 200VA transformer to successfully power a 100W amplifier. If you want that 100W into 8ohms speaker the use a 35+35Vac transformer to get the PSU voltage right. But here's me giving you the answers. __________________ regards Andrew T. Sent from my desktop computer using a keyboard
 27th September 2012, 11:28 PM #3 diyAudio Member   Join Date: Aug 2011 so if i want 500W amp i need 500VA transformer ? what about the current calc. that i made, is it correct? or do i need to take higher current rating for spikes or whatever (i calculated about 3.5A per channel so if i take 4A per channel is it enough or i need more?)
 27th September 2012, 11:43 PM #4 diyAudio Moderator     Join Date: May 2003 Location: Palatiw, Pasig City ^if you are just playing music, then that should do..... __________________ planet10 needs your help: Let's help Ruth and Dave...http://www.diyaudio.com/forums/plane...ml#post5010547[B
 27th September 2012, 11:54 PM #5 diyAudio Member   Join Date: Aug 2011 what you mean by "just playing music" and if i watch DIVX movies it won't be enough?? can you explain yourself...?
 28th September 2012, 10:57 AM #6 diyAudio Member   Join Date: Feb 2010 Location: England How do you not know this stuff if your at uni? It's very basic, just do a little reading. If you knew basically how an amplifier works its very easy to make a psu for it. __________________ Audio projects and more: gswdh.co.uk
diyAudio Member

Join Date: Feb 2010
Location: England
Quote:
 Originally Posted by snakebite what you mean by "just playing music" and if i watch DIVX movies it won't be enough?? can you explain yourself...?
Doesn't matter.
__________________
Audio projects and more: gswdh.co.uk

 28th September 2012, 02:52 PM #8 diyAudio Member   Join Date: Aug 2012 Location: Völkermarkt I wonder if anyone have used LME49830 at unity gain, inverting, compensated.
 28th September 2012, 02:53 PM #9 diyAudio Member RIP   Join Date: Nov 2003 Location: Brighton UK Hi, Unfortunately EE courses don't teach most of the basics of sensible cost effective analogue audio design, or teach you any common sense regarding properly selecting and properly dimensioning components and hardware for higher power audio amplifiers, and that ends up being a matter of opinion as well as design. The decision process for a power supply is far more complicated than outlined in the initial post but with experience designers settle on "rules of thumb" that simply won't do in a project write-up. Different designers can have different "rules of thumb". Different rules can apply if cost is the major issue compared to performance (at higher cost) being the major issue. There are no simple answers. Good design is balancing these factors. rgds, sreten. Generally I don't like Mosfet outputs with simple supplies as you lose too much voltage swing at the output for me.
diyAudio Member

Join Date: Feb 2009
Location: Brisbane, Australia
Quote:
 Originally Posted by Headbanger I wonder if anyone have used LME49830 at unity gain, inverting, compensated.
From memory LME49830 stipulates min gain of 26dB for stability.

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