LME49720 preamp for F5

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
hi
i start to bouild the F5 amplifier by nelson. the input impedance of the amp is 100K and the gain is 15db, so i feel that is need preamp.

my audio surce is sound card so in the output it have ~400mv.

i want to bay this preamp(the LME49720 is very quality specsification)
http://www.ebay.com/sch/i.html?_trksid=p2047675.m570.l1313.TR0.TRC0.XTone+Control+3-Way+Audio+preamplifier+KIT%2C+Lowest+THD%2BN+Bass%2F+Mid%2F+Treble&_nkw=Tone+Control+3-Way+Audio+preamplifier+KIT%2C+Lowest+THD%2BN+Bass%2F+Mid%2F+Treble&_sacat=0&_from=R40

do you think its 20db gain is enough ? maybe i need less gain?

thanks
 
thanks, its good article.
now im sure that if i want 25w on the F5 output, i have to amplified the computer signal.
but how much? i thins 20 db its ok, im worng? 0.3v *30 (F5)=9=>10W
so what i need is 0.8v in the entrance of the F5 to get 25w on the speaker !?
if so, the preamp in need to amplified by ~2 ! ?
i just want to be sure before i buy this preamp
thanks
 
Member
Joined 2004
Paid Member
With the F5's voltage gain of 15.3dB=20*log(x) and a maximum output voltage of +/-20V (from manual), the amplification factor x=10^(15.3/20)=5.82 and therefore the input voltage required to drive it to full output should be 20V/5.82=3.42V. Compare this to what your source can deliver, and decide on how much gain you'll need in the preamp stage.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.