At 01:19 PM 07/23/10, you wrote: >Hey Guys. I was looking at the schematic for the above mentioned >speaker (thank you repeater builder site) and I had a few questions.
If anybody's interested it's here: <http://www.repeater-builder.com/motorola/genesis/pdfs/nsn6054a-68p81108c39-o.pdf> >First, does anyone know where to find a replacement for the >5184320A99 dual op-amp labeled U1? I'd look in the National Semiconductor products manual that covers automotive audio products. That schematic resembles what I saw in an early 1980s app note for a car stereo receiver. LM187something. >Secondly, Is this op-amp basically being used as a buffer, preamp, >and inverter? Both halves are being used strictly as an inverting buffer for out-of-phase audio. Look carefully at the schematic and remember that nothing in the input circuit is ground referenced - the audio input (from the radio) is balanced audio (both are sides hot, 180 degrees out of phase with each other, and there's an implied / virtual audio ground) in the middle. Each side of the circuitry driving the speaker is a mirror image of the other, just like the incoming audio is a mirror image compared to the virtual ground. >Thirdly, what on earth are pins 3, 4, 5 and pins 10, 11, 12 doing? >I have never seen so many pins on an op-amp tied together. If that chip is the one I'm thinking of its capable of about 2 watts per channel on it's own. That takes some heat sinking. Probably a heat sink for the final transistors inside the opamp. And if you look closely, pin 1 is audio ground, and pins 3,4,5, 10, 11 and 12 are power ground - and those are switched to ground by Q3, which is driven by the squelch circuit in the radio. >Thanks! >Albert Mike WA6ILQ
