Opamp power supply

Looks like a great noise generator.

I'm not surprised to hear a negative critique. I built the amp he designed, and when I had a question, I got all kinds of remarks about what was wrong with it and that it didn't meet his specs.

Ok, so what would you do different for the detector? All I want to do is drive a meter to compare ferrite L/C antennas. Since I have a high impedance amp with 50 ohms out, I could use a low input impedance detector. But either way.

The audio part is a useful bonus.

Mikek

Opamp driving a transformer... very 70s. IC used to generate -ve rail when the input could just have been divided or rectified both ways... why?

NT

I'd hook your antenna directly to an oscilloscope. Maybe with a jfet follower if you care much about capacitive loading.

I plan on using the Radio Shack 1000 ohm to 8 ohm transformer, I think I have one around here.

I don't know, post a quick schematic so I can see what you mean.

Thanks, Mikek

Is that from the opamp or the circuit design?

I want it battery operated, so I can setup in the backyard away from noise sources and read an analog meter. I'd like as little loading as possible which I think I have, with the Kleijer amp I previously built. This can be my impedance converter very high input to 50 ohms output.

Thanks, Mikek

the former: o----------Reg------o +out | | dc in +-------o 0v | | o----------Reg------o -out

the latter, from ac in:

But if you're running from battery, why not just tap the battery? It's a fair few cells, but they'll last longer due to lower current draw.

NT

A front-end diode rectifier, a crystal set, will be a very nonlinear detector, with a bad temperature coefficient. You might amplify up to some decent signal level, and then rectify. Pop in attenuators as needed.

Several people make really cool integrated, wide-range, log-output RF detector chips, with all the hard work done. ADI, LTC, maybe TI. Talk someone out of an eval board.

That can't work, of course; the third pin of a regulator (the ones connected and labeled "0v") is not driven to any particular voltage level. It's a power supply and voltage SENSE pin, not a driven output. You might get by with a resistor and two zener diodes, if you really NEED regulation. Op amps work fine on filtered, unregulated power.

Interesting little IC - TO92, complete TRF AM radio:

The opamp and the megohm input resistors.

Oh, cause I think he's using a wall wart. Which limited his thinking.

I think it is +12V and -4.4V supplies, he had 12V from the wall wart, then just developed the -4.4V. Just a guess.

You put reservoir caps on the output, and zeners on each rail to take care of too much imbalance. Crude but effective. It works.

NT