Even more on the LM-386 http://www.radiowrench.com/sonic/so02144.html
cheers skipp > Kevin Custer <[EMAIL PROTECTED]> wrote: > Steaven Rogers, W4YI wrote: > > > Kevin, > > > > This is perfect. I have only one more question. What is the > > component labeled 386. I would expect it to be an op-amp or something > > along that line. What is the actual part number that I would need to > > look for. > > > Hi Steaven, > The part is a LM-386, available at Radio Shack. > > While this part resembles an op-amp, it's actually a power amplifier > intended to run loads down to 16 ohms. Why do I use it? Several > reasons, including available locally cheap, low support components > count, and highly RF immune because of having a poor slew rate. The > slew rate limitation allows signals below 10,000 cps to be amplified > without distortion/roll-off, and those above that will be attenuated to > a greater degree as frequencies increase. Since most FM communications > we deal with here have bandwidths that are somewhat below 10K, it makes > a great amplifier for many 2-way instances. Also, realize that this > amplifier *does not* need to be loaded to 16 ohms; it's stable into just > about anything, including nothing when the 10 ohm and .05 uF network is > used. > > There are two things I have found that are a must when using this > amplifier IC. You must use a 100 uF or larger filter capacitor on the > power supply rails placed near the IC, and you must use the 10 ohm - .05 > uF network. These components suppress parasitic oscillations, and keep > the amplifier stable. > > Many common op-amps cannot source a load below 2K, the LM-741 and common > TLO series are an example. These op-amps become unstable when loaded > below 2K, and proper design requires a build-out resistor to ensure the > op-amp's stability. The build-out resistor is lossy when driving low > impedance loads and the use of this chip eliminates the need for a > build-out resistor, and is stable down to 16 ohms. > > More on the 386: > http://www.repeater-builder.com/rbtip/audioamp.html > > Hope this helps... > Kevin Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
