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An Improved Op-Amp Mixer


While designing some op-amp mixers I started to get irritated by some of their fundamental shortcomings. So I had a bit of a think and came up with this "new" idea and wrote it up. As tradition dictates it soon became apparent that actually this was an old idea, but hopefully this paper presents it in a new light.

Abstract
Almost every analogue synthesizer contains several signal mixers, both for audio signals and for control voltages. The traditional inverting summing mixer has several drawbacks relating to circuit noise, input impedance and DC offsets. This paper presents a new view of an old technique that solves several of these issues. It analyses the theoretical performance of the old and new circuits, and presents both a theoretical example, and experimental results that confirm the theory.

Download paper (PDF, 324kB).


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