Monthly Archives: March 2012

Altoids piezo pre-amp

Update: Fully built and tested Altoids Piezo Preamps are available for sale in the shop here. I’ve been taking my Altoids piezo DI box to open mic nights and have had some interest and feedback.  People seem to like the concept but are less impressed with the balanced output and phantom power – which is… Read More »

Low-battery monitor with TC54 voltage detector

Update: Adding an output transistor – see below. So you’d kind of like to know when the battery in your stompbox  is getting a bit flat but you’re not sure how to proceed. The first problem is that you don’t want your low-battery monitoring circuit to make a significant contribution to battery drain – which… Read More »

Altoids piezo DI box

There is an update to this article here. As I mentioned in my post on the vagaries of phantom power, I have been looking at designs for a compact self-contained box to connect an upright bass to the PA.  The bass pick-up in question is a piezo jobbie integrated into the bridge like the Fishman… Read More »

Phantom power – it’s spooky!

I’ve been looking at the design of direct injection (DI) boxes with a view to making a phantom-powered piezo preamp for a friend who has acquired an acoustic bass with a passive piezo pickup but doesn’t have a preamp for it.  He’s tried plugging it straight into the mixer – but has experienced major tone-suckage… Read More »

Testing and Matching JFETS

Update: Matching JFETs – Revisited here. Update: Kits available in the shop here. Update: Matched sets of JFETs available for sale here. We’re talking here about N-channel depletion-mode junction field-effect transistors. “Field effect” because the current flowing between source and drain is controlled by the electric field strength at the gate.  Impedance at the gate… Read More »