The aim of this project is to design & build a compact rotary DJ mixer using predominantly surface mount components. There are many "boutique" rotary mixers now on the market, they are often advertised as using discrete components - which are generally known to be higher quality for use in audio applications. Unfortunately they have the downside of being more expensive, harder to obtain and physically larger. One other goal of this project will be to build alternate circuit boards using discrete components - so that an A/B tests can be performed - and a direct comparison made using the analytical test instrument of the human ear.
Surface mount components have the advantage of being significantly cheaper than discrete components. They are also much smaller allowing for smaller PCBs to be designed. They are more readily available as they are used in most modern electronic devices. For these reasons it seems compelling to attempt to build a budget rotary mixer using such components and subjectively testing as to whether the audio quality is significantly deteriorated. We would certainly expect a difference but whether is it enough to negate the advantages of surface mount components will be the aim of this project. Like any good piece of engineering hopefully a compromise can be reached using a combination of surface mount and discrete components with the result of a high quality and affordable mixer.
Below is the enclosure that will house the mixer in which we will be attempting to fit the following:
- Mains transformer
- Power supply board
- Dual phono amp board
- Mixer board
- 3 band master isolator board
- Spatial master effects board
The first board to build is the power supply. The design borrows significantly from the Bozure schematic. The aim will be to create positive and negative 12V DC rails from the mains supply whilst hopefully avoiding electrocution. There is alot of important information to understand regarding ground loops/safety earthing both of which are crucial to ensure that audio is hum-free and the device remains safe in the case of malfunction.
The PCB was made using the toner transfer method (using a customised laminator) and etched in ammonium persulphate. There was some pitting that possibly could be avoided by applying a layer of TRF prior to etching.
Here is the completed power supply board whilst measuring inside the case along with the mains transformer.
to be continued...