The prototype FP1 filter PCB is out for fabrication. I am uber excited about this filter. It's a parametric midrange control, very...

Since the connecting cables are fairly expensive, I changed the filter and control modules to have options for no cables, 50mm, or 100mm...

The PS3 is out for fabrication, soon to be tested and released. It will be about 19mm x 29mm, and use around .75mA of battery power. It...

We now have a Volume push-pull switch for filter bypass. It is available in push-for bypass or pull-for bypass variants. It has a...

Here's a nutty example of what you can do with just a single filter (like the PD3 Jazz Style system).

This video by JWC Bronski is a great demo of the fundamentals of filter preamps. The preamp in the video is a switched resonant type,...

All of the modules and connections have been reworked, and there are now four filter modules to choose from. Boards are at the fabricator...

It was a tight fit, but I got a PD1 preamp and a battery in this PJ cavity. I removed the pickup switch and tone pot, and went with...

I've added a guide for configuring the jumpers on the PD1/2 preamps, to select where the second filter is applied in the signal chain....

The FV1 test boards are out to the fabricator. There is a lot of interest in this filter module, so most of my efforts now are going into...

I built the first PD2 Preamp and everything tests out great. It's essentially the same as the PD1, but has gain trimmers for both...

The website is now in a usable state, with lots of information on the Underhill Preamp. Preamp modules, potentiometers, and switches are...

This is cool. All I had to do was make up a quick cable, and I can plug an EMG BTC into the PD1 Preamp. Here I plugged it into the...

The PD1 and FS1 boards are built and tested. The modular layout is really nice, I can pull out and swap individual pieces, and the system...

The PD1 Preamp board is out for fabrication. This version has connectors for two filter/eq boards, and moves the potentiometers off of...