Measuring the Input Impedance of a Product, Circuit or System (070a)

There are two kinds of situations where you might want to measure the input impedance of a product, system or circuit: 1. At a Low frequency like an audio amplifier where there is no real concern about the complex aspects of impedance. 2. At Higher frequencies like a receiver pre-amp where we are very much interested in the complex impedance. In this video I will be addressing the first of the two. I will be measuring the input impedance of a small, inexpensive audio amplifier. I will discover how this input impedance is affected by: * The position of the volume control * The level of the input signal * The frequency of the stimulus ======================================= Time Markers for Your Convenience ---------------------------- 00:05 Introductory Comments 00:59 Why not use a DVM to measure Input Z? 01:53 Planning our Measurements 02:52 What is "Line Level?" 03:22 What is the difference between dBv and dBu? 04:20 Planning our Test Voltage 06:12 Three Important Questions ... 06:15 1. How does the Volume Control affect the Input Impedance? 06:43 2. How does the Signal Level affect the Input Impedance? 06:59 3. How does Frequency affect the Input Impedance? 07:36 Setting Up for the Test 07:39 Test Equipment Settings 09:00 Test Equipment Connections 10:00 First Test: How does the volume control affect the Input Impedance? 12:40 Second Test: How does the signal level affect the Input Impedance? 14:20 Third Test: How does Frequency affect the Input Impedance? 15:21 Bringing it all together 15:56 Parting comments and Toodle-Oots