An Outboard Speaker Module for the QCX Mini CW QRP Transceiver

Описание: I recently built a 20m CW, QRP kit from QRP Labs. It is a wonderful piece of equipment and works very well. Hans Summers, G0UPL, of QRP Labs designed the kit. Details are available at https://www.qrp-labs.com/qcxmini.html . The output of my unit is 5W. Incredibly, the entire unit is about the size of a pack of cards.

Understandably, for its compact size, earphones or headphones are required for listening, as no speaker is fitted. For most purposes, this is fine. However, as an avid homebrewer, I decided to design and build an outboard audio amplifier module to drive a small speaker.

Initially, I tried using an LM386N audio chip on its own. This worked but was a little bit tempremental. Either the audio was too low or else distorted. It was difficult to obtain the right balance. I therefore built a preamplifier using a single 2N3904 NPN. transistor.

I now had three level adjustments to make, the volume control on the QCX, a 4K7 potentiometer on the input of the preamplifier and a 10K potentiometer on the LM386 PCB. It was tricky setting up these three inter-dependent controls. By trial and error, I arrived at a satisfactory result. In use, the audio output level is controlled solely by the QCX's own volume control.

Following testing, I installed the two PCBs in a small plastic enclosure. I fitted a small SPST toggle switch, an LED indicator, speaker, headphone socket and the required power and audio connectors. The toggle switch also switches the QCX on and off. A reverse polarity protection diode was also fitted.

The video describes my construction of the audio module and also demonstrates it in action on the air.

Your feedback is always welcome and can be posted on YouTube or emailed to me [email protected] . If you like the presentation then please LIKE and SUBSCRIBE.