switchable notch filter after DJ6HP (first published 1974)

thingiverse

This is a description of making an adjustable audio notch filter for use on ham radios. The design was originally published by ham operator DJ6HP in cqDL emission back in 1974. Ham operator DL6HAH later modified the filter's component values. Unfortunately, his article lacked some crucial information, which I had to figure out through trial and error - a classic example of the ham spirit at work! After that, I improved the PCB layout to make it compatible with the toner transfer method. The files are available for viewing; I've reworked the original article to make it more user-friendly. The pdf file contains the revised content in a logical order. If you don't have LM1458 op-amps, don't worry - there are equivalent types that can be used instead. Most uA741 followers will work just fine, as long as they only require a single power source and are internally frequency-compensated. Just check their electrical specs and pin assignments to ensure compatibility. As one of the moderators from the audio forum pointed out, you can find more information on equivalent op-amps here: https://www.diyaudio.com/forums/chip-amps/327361-mc1458cp1-tl071cp-equivalents.html#post5544763 Status update: I've got several other projects in progress, so there's no activity on this one at the moment. However, I have created a PCB based on the design. If you want to create your own PCB using a 3D printer, check out these resources: https://3druck.com/drucker-und-produkte/open-source-eigenbau/3d-drucker-als-aetz-vorlage-bei-platinen-0822703/ https://www.instructables.com/id/Make-Flexible-Circuit-Boards-Using-A-3D-Printer/ You'll need to attach a cutter, such as a Schneideplotter or Folienplotter, like the Cameo or Roland. Here's how: https://www.instructables.com/id/Use-3D-Printer-As-a-Plottercutter/ Alternatively, you can make a PCB using a 3D printer by applying a spray-painted layer to the copper foil and then using a needle to create the tracks. Check out this YouTube video for more information: sNh0ubRcTYU. Go ahead and get creative!