I'm an experienced electronics tinkerer with many gaps in my knowledge of the subject, and am currently trying to educate myself properly. Part of this involves experimenting with actual circuits. I'm hoping to get some help here from folks more knowledgeable than I.
Current project involves fooling around with a simple noise generator. I'm using a reverse-biased NPN transistor, as shown in lots of circuits I've seen. I'm trying to use an op amp to amplify the output. At this point, I'm just trying to get the damn thing to work at all; I've constructed the circuit shown below, with the output connected to a small audio amplifier, in order to hear if it works.
**broken link removed**
Well, it ain't working. The noise generator seems to generate nothing. When I remove the wire connecting it to the op amp noninverting input, I hear no difference in the sound. The op amp definitely works; if I touch the input lead, I get very loud hum. Very frustrating; I've tried a bunch of stuff to no avail. Tried a bunch of different transistors, all tested good. Put in a coupling capacitor between the noise generator and the op amp input. Removed the feedback resistors from the op amp. Put in a load resistor across the op amp input. The only noise I get out of this is the noise of the op amp itself.
So apart from the actual application here (I have some fun things involving random noise generation in mind here), I'm trying to teach myself how to use op amps, and also just basic circuit design principles: computing op amp gain, different op amp configurations and feedback, impedance matching, etc.
My assumption (which could be wrong, of course!) is that since the noise generator produces such a small signal (in the millivolt range), I need a fairly high-impedance input so as not to overload it. But now I'm wondering if there's not enough of a load; should I use a load resistor? Part of my problem, it seems, is an impedance mismatch somewhere.
Also, it seems that the circuit here should give me plenty enough gain to at least hear something through a regular line-level audio input.
Any help will be very much appreciated! Ask me about anything I may have neglected to mention that may be relevant.
Current project involves fooling around with a simple noise generator. I'm using a reverse-biased NPN transistor, as shown in lots of circuits I've seen. I'm trying to use an op amp to amplify the output. At this point, I'm just trying to get the damn thing to work at all; I've constructed the circuit shown below, with the output connected to a small audio amplifier, in order to hear if it works.
**broken link removed**
Well, it ain't working. The noise generator seems to generate nothing. When I remove the wire connecting it to the op amp noninverting input, I hear no difference in the sound. The op amp definitely works; if I touch the input lead, I get very loud hum. Very frustrating; I've tried a bunch of stuff to no avail. Tried a bunch of different transistors, all tested good. Put in a coupling capacitor between the noise generator and the op amp input. Removed the feedback resistors from the op amp. Put in a load resistor across the op amp input. The only noise I get out of this is the noise of the op amp itself.
So apart from the actual application here (I have some fun things involving random noise generation in mind here), I'm trying to teach myself how to use op amps, and also just basic circuit design principles: computing op amp gain, different op amp configurations and feedback, impedance matching, etc.
My assumption (which could be wrong, of course!) is that since the noise generator produces such a small signal (in the millivolt range), I need a fairly high-impedance input so as not to overload it. But now I'm wondering if there's not enough of a load; should I use a load resistor? Part of my problem, it seems, is an impedance mismatch somewhere.
Also, it seems that the circuit here should give me plenty enough gain to at least hear something through a regular line-level audio input.
Any help will be very much appreciated! Ask me about anything I may have neglected to mention that may be relevant.