Although we do most of our audio processing in the digital domain these days, there are still places in the audio chain that require low noise analogue circuits. These are primarily at the beginning where transducers such as microphones, magnetic pick up cartridges, tape heads, etc. provide analogue signals that must be amplified prior to digitisation, and also at the converters (analogue to digital and digital to analogue) which often have challenging dynamic ranges to deal with. This requires low noise circuitry in order to handle the dynamic range of these systems.

 

Unfortunately many of the texts on noise in analogue systems assume the presence of a resistive source impedance for the transducer or signal.  In audio this is seldom true because capacitor microphones, tape heads, and magnetic pick up cartridges have a significant, and often high reactive component in their impedances, plus the traditional resistive based noise analysis is insufficient.

 

The purpose of this tutorial is to provide both an introduction to noise in audio circuits and a framework for analysing noise in valve/tube, transistor, FET/MOSFET, and Op-Amp circuits. 

 

The tutorial will be in two parts with question and answer sessions, and a break between them.  Each part will be around 45minutes, with a Q&A session after each one.

 

The first session will cover what sorts of noise occur in analogue circuits and devices.  It will also develop a framework for identifying which components would work best in different situations and look at basic approaches to achieving low noise operation for a variety of transducers. It also will provide some “rules of thumb” for good practice for low noise circuit design. 

 

The second session will look at some more advanced circuit topologies and strategies for achieving low noise circuits, particularly where a very wide dynamic range might be required. It will include conventional circuits, as well as some speculative ideas on how this might be achieved.

 

Both sessions will have space for discussions and questions. The presenter will also endeavour to minimise the amount of mathematics involved. 

 

The sessions should be suitable for people who have never looked at low noise circuit design as well as, hopefully, having content that will appeal to people with some expertise in the subject.