The available range of operational amplifiers is extremely diverse. Usually, the initial selection for a specific purpose is based on technical specifications — for example, on the websites of semiconductor distributors. If several candidates then remain on the shortlist, you may have to carry out further measurements yourself, as it is not always possible to ascertain all the relevant parameters under the planned operating conditions from data sheets. This is exactly what the opamp tester presented here is for. Once you’ve made a selection of possible candidates, you often have no choice but to order samples and then put these opamps through their paces. Harmonic distortion, in particular, depends on the input level, the gain, the output level, the load, and the frequency. In data sheets, these values are often only found for certain parameters that do not cover all applications and are also not always truly comparable between manufacturers. The following small test board was thus...