Electronic – Help me modernize this audio circuit


listen to your capacitors

When I was a kid, I built this circuit. You hook up a small capacitor to the test leads or maybe a couple in parallel and the speaker will output a different pitch based on the test capacitance. I thought it was a fun learning tool and I wanted to show it to my daughter.

The problem is, it seems these kinds of transformers are rarely used any more. I'd like to find a way to modernize the circuit to eliminate it. The one I used was a 4K CT : 2K

I don't understand center tapped transformers well enough, or I guess the circuit in general to do this myself. Hoping to get some pointers.

I'd be fine with using a black-box amplifier IC, the idea is to play with caps, amps can come later.

Best Answer

The circuit is just an audio oscillator and as Ignacio has suggested it could be replaced with a 555. Here's the circuit below.enter image description here

R1 could be varied (or switched) to give a suitable output frequency depending on the value of capacitor being tested. (output frequency about 1/RC )