Audio electronics development

1. Requirements

First, it is necessary to know well what the expectations / requirements of the client are. Electronics development becomes costly if it becomes a search-process for the right solution. If the requirements are not yet on paper, that is the first step. Both the client and the electronics developer must think carefully about the consequences of adding or omitting a requirement. Both can lead to additional work.
For audio applications, specifications such as distortion and noise are very important. But the characteristic of, for example, the volume control and other settings must also be defined.
Furthermore, it is important for the developer to know for which target group the product is being made.

1.1 Functional requirements

The functional requirements describe on an abstract level what the solution should do.

For example for an amplifier:

• The maximum output power in peak and continuous, at 4 and/or 8 Ohm.
• The expected output power during normal use.
• The desired max. distortion (usually at 1kHz), preferably also for e.g. 10kHz.
• The various source inputs and how they are selected.
• Installation form with possible cooling options.

2. Development Phase

This is the phase of the concepts for electronics development in which the basic schematic is created. The concepts are calculated and tested with a simulator. This allows for optimizations to be implemented and for it to be predicted whether the specifications will be met.
For power amplifiers, the housing design will also be done, due to heat management and possible interference from stray signals.

3. Electronics implementation

Now the ideas from the development phase will be turned into reality. Schematics are drawn and circuit boards are designed. The circuit boards are assembled so that the electronics can be tested.
If there are also digital parts, the firmware is also written and tested for these.

4. Tests and adjustments

Tests are carried out and also any electronics and mechanical adjustments. Especially the mechanical fit for the connection of the connectors and the height of components and also provisions for heat dissipation are implemented.
If the design has already been ‘fitted’ on the computer via 3D drawings, the chance of adjustments is smaller.

5. Qualification phase

Qualification is the process of checking whether all requirements are actually present in the prototype and work within the specifications. Much attention is paid to noise, crosstalk and distortion. All measurements are documented, so that it can be seen later that something was tested, and what the result was.
This is also a moment to show the results to the client.

6. Acceptance tests

The client is now involved in the process again. They must now convince themselves that the product meets the set requirements. For the client, this is the moment to properly assess all functions and behavior. Making changes later is extra costly.

A durability test under varying conditions is also highly desirable.

7. Production preparation

When it has been approved, production can often be started immediately. If changes have been implemented, it is wise to start a pre-production or a 0-series. Such a 0-series is then a limited number, e.g., 10 to 25.
If something serious has gone wrong, these can be easily adjusted. When 1000 or 5000 circuit boards are already produced, the costs for repair, or worse, replacement are very high.

7.1 Production test

With every production, the result must be tested. In production, errors can have been made, such as an incorrect component mounted. But more often it concerns soldering errors. Then a component is not properly soldered, or a solder short has occurred. There are 2 levels of tests:

• Functional test
• Specification test

In many cases, a Functional test is sufficient, but for devices that go to distant countries, and where service and repair are expensive, a test system that also tests the specifications can be cheaper. Testing on specification means, for example, that the frequency characteristic of analog inputs is measured. With only a functional test, a faulty component in this path may not become visible. That increases the damage.

For production with larger numbers, a bed-of-nails tester will often be made. An automatic test is performed with this. Often the test electronics are more extensive and more complicated than the produced product.