I don't know if Radio Shack still even sells them, but over the years I've run into a store and bought an LM 386 audio op-amp and a pre-etched prototyping board to throw together an audio "buffer" for applications such as this. The chip draws just 4 ma at idle, is optimized for audio use with low parts count (just add two capacitors,) works with high-Z inputs and 8-ohm outputs, and can provide all the gain you need if configred properly. When used to drive a speaker, the output is coupled through a large electrolytic cap. If you're driving a 600-ohm load, you can reduce this to .5 uF or less. Be careful of "sample circuits" published using this chip. I've seen lots of applications in which the amp was powered off a "12 volt" rail that could actually be 14 volts; the chip is specified, I believe, for an absolute max of 12 VDC. If you have a regulated DC stage at 8, 9 or 10 volts, that's perfect. 73, Paul, AE4KR
_____ From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Eric Lemmon Sent: Sunday, April 27, 2008 5:02 PM To: [email protected] Subject: RE: [Repeater-Builder] Re: ADI 247 for a link radio Robert, Impedance matching is usually a problem when a low-impedance load is connected to a high-impedance source, which sounds like what you describe. When you use an impedance matching transformer, the audio level will be reduced as well as the impedance, and you may not have enough audio. I am thinking along the lines of an emitter follower amplifier, which transforms a high input impedance to a low output impedance, but implemented with an operational amplifier (opamp). 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com [mailto:Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com] On Behalf Of georgiaskywarn Sent: Sunday, April 27, 2008 3:14 PM To: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com Subject: [Repeater-Builder] Re: ADI 247 for a link radio Eric, I was actually thinking of some 600 to 1 transformer. Your thinking a opamp / preamp would work? Really didn't think about giving it more audio level. Now I am speaking of the TX audio, not RX. So it is really what the RC210 is offering...not what the ADI is offering. Eric...you still think it needs an opamp?? Thanks for the reply, Robert KD4YDC --- In Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> , "Eric Lemmon" <[EMAIL PROTECTED]> wrote: > > Robert, > > I agree- and the audio level needed by the RC210 is probably much greater > than what the radio has to offer. An opamp should work for you. > > 73, Eric Lemmon WB6FLY > > > -----Original Message----- > From: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > [mailto:Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of georgiaskywarn > Sent: Sunday, April 27, 2008 10:29 AM > To: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > Subject: [Repeater-Builder] ADI 247 for a link radio > > Started a project at the end of LAST summer and never got finished. > Using a ADI247 as a 220mhz link radio. Blew something up in it (in > looking for cos), sent it off, got fixed, now just getting back to the > project. *I Thought* I had decent tx audio out of it into the RC210 > controller hooked to it. However now I barely get a whisper out of my > tx audio. I can hook a mic to it...no problem with the audio, works > fine. Almost sounds like an impedance mismatch. > > Ideas? > Thanks, > Robert > KD4YDC
