LM386 AUDIO AMPLIFIER KIT

Almost every ham radio project needs an audio amplifier. Rather than reinventing the wheel every time I've started making a series of modular kits so I can just pull a generic board off the shelf and use it. I am also trying to encourage more hams to build goodies. It isn't that hard - it is actually easier today than it was when I started in the early 1960's.

The first kit in the series is an LM386 audio amplifier. This nice little chip can run on from 4V to 15V and (certain versions) can produce up to 1 Watt of audio. This is way more than enough to run a pair of headphones or even a small speaker. It was tempting to do the amplifier in surface mount, but I expected that there would be others wanting to use the board and most "junque" boxes have leaded components - so this is a through-hole version. A later version will be surface mount. This version is 1.2 inches by 1.25 inches so it should fit almost any spot. I tried to minimize the space requirements and yet leave future expansion possibilities, so this is intentionally a tightly packed board. I included the bass boast components although they aren't necessary for most ham purposes. I also brought all the wires out to an optional connector. In most cases the connector will only add expense and annoyance so it's not included in the kit. It is easier to just solder the wires in the holes - but the connector could be used if desired. Future audio amplifiers will have the mounting holes and the connector in the same locations so they can be interchanged easily. A 10-Watt version using the TDA-2003 is nearing completion and should fit the same mounting holes and connector, although - I think I may have to stretch the board a little to fit everything in, it should be a near fit. The TDA-2003 will likely be 1.4 by 1.25 inches and will extend to the left past the connector a little. Included on the board are de-coupling (F1, R1, C1, C2) from the power supply to make sure the amplifier remains stable. The circuit can be set for gains of 20 to 200 depending upon selection of components.

Figure 1. Board layout.

Figure 2. Schematic of the LM386 board. Kit instructions will include discussion about each component and ranges of values that may be used and a data sheet.