Darrel: There's no need to worry about 'matching' a hi Z input impedance with the 'virtual ground' low source impedance of an op amp. It'll love it. The only real issue is what peak voltage the stage needs to provide. For solid state rigs, it'll be fine, since they're expecting low voltages as well. For most single ended tube line input stages, like a 12AX7, etc., the +/- 15v or so a typical op amp is capable of will also be just fine. Depends on the gain structure thru the modulator. Certainly for a mic preamp input you'll have plenty of steam, in fact you might consider eliminating the mic preamp stage and going into the next gain stage in the rig.
As for isolation into tube stages, you should only need a coupling cap to keep the bias voltage off the opamp output. You could also use transformers, of course, but that's not really necessary. The only problem that might arise by feeding all these different radios like this is potential ground loops. Besides transformers, there are balanced line driver stages that you could use, like the Analog Devices SSM2142, ( http://www.analog.com/Analog_Root/productPage/productHome/0%2C2121%2CSSM2142%2C00.html ), tying one leg of the balanced output to chassis ground of each xmtr. But if all your chassis are ground bonded together, it probably won't be a problem. I wish I had a quick schematic for you. I'll look around to see if I can come up with something. 73, g Darrel Nichols wrote: > Of course I'll build it. I guess I could rephrase the question further. > I'm trying > to figure out how to feed the vintage gear (Viking II, S-Line, HT-44, etc.) > with > something like an OP Amp. I had hoped someone had tried this. Getting the > output up into the megohm range needed might get a little dicey. If someone > has gone here before, I'd like to hear about it and if you did a schematic > that > is Emailable, that would really be great. > > N0DBX
