This is a fairly simple design for a preamp suitable for dynamic (or other non-powered) XLR or balanced microphones, to work with a mic input that has phantom power.


It can be built on stripboard, or I now have a miniature surface mount PCB version that has all the passive components, just leaving the transistors as conventional through-hole parts to allow a choice of known good types.

This is the schematic for it:

This video shows the design and the tests of the first prototype:


If you would like to build one of these, I've done an example on stripboard below, and also a tiny surface mount PCB which can be fitted in an inline XLR housing, a casing of your choice or possibly inside a mic body.

Details of that are here:


I've done a video showing the stripboard construction as illustrated below, here:


Stripboard assembly top (through board) view:

Assembly notes - also see the photos below:


The resistor power rating can be anything from 0.1W to 0.5 - 0.6W; none have any significant power dissipation. The only consideration really is what can fit well in the stripboard or PCB. The input coupling capacitors can be eg. 10V, 16V or 25V types.


The white spaces are track cuts. R1 has its right-hand lead through a cut track hole and bent down on the underside, so it can be soldered to output connection 2 track.

The black ellipses indicate tracks joined by solder bridges; this can be assisted by bending & cutting component leads so they overlap the appropriate tracks.

The capacitors are fitted with positive to the RIGHT. RT1 is the R11 1K preset. The transistor base leads are bent out & fitted one track out from the emitter and collector leads; 1 is emitter & 3 is collector.

Two wire links are needed, joining the circled crosses - one fitted and soldered from each input capacitor track to a hole adjacent to the transistor base, with the wire end bent over the base tracks and soldered.


Track cutting points, stripboard underside view:


Fully assembled stripboard version:


Underside, assembled:


 I've also done a small surface mount PCB version of these, the article on those is here: Dynamic preamp kit parts