Piezo pickup with tone and volume8/7/2023 ![]() the effect of the control is going to be treble-cut only. The tone control is similar to that on an electric guitar – i.e. We can add a tone control as well as volume. The track between the cut lines should come off cleanly in one piece. Then take your soldering iron and use it as a chisel to remove the cut section. ![]() ![]() If you have not cut a PCB track before, the best way is to get a sharp knife (such as a small craft knife, Exacto or scalpel) and make two cuts perpendicular to the alignment of the track. Then we need to wire the potentiometer in place of R4 and connect the wiper to the output jack: To add a potentiometer, we need to remove R4 and cut the PCB track between the C3/R4 junction and the output jack. The pot value should be 47k (or 50k depending on manufacturer). This is because the potentiometer affects the output impedance of the circuit (which we want to keep low). We are going to put a potentiometer with lower resistance than the value of R4. The best way to add a volume control is to remove R4 and replace it with a potentiometer: The value of R4 is not too important although we generally make it high because it forms a high-pass filter with C3. The purpose of R4 in the design is to discharge C3 when the output is disconnected. Here’s the schematic for the design as it stands: The PCB was not designed for the addition of these controls, so this article represents something of a hack. We have had enquiries about adding volume and tone controls to the Unbalanced Piezo Preamp (available in the shop here). ![]() Updated – see below for information on improving the design to lower the output impedance. ![]()
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