PD3 Preamp Prototype

While waiting for FV2 boards to come back, I did a major redesign of the PD preamp. Electronically, it is nearly the same as the PD2, but the layout and mechanical design are very different:

1. New potentiometer/switch connectors. These are a modern surface mount design and use much less space on the board (which is.smaller). They are keyed so they can't be assembled incorrectly. The new cables and connectors will be just as reliable and robust as the old style, but are much less expensive to make. The labor involved in making the current connectors is huge, and the parts are more expensive as well. I haven't worked it all out yet, but the price of the preamp and filter modules will drop, maybe as much as 25-30%, so that's good news. It will also allow me to provide a number of cable lengths as stock items.

2. I changed the input buffer op-amp to a JFET type that is just as quiet, uses less power, and should allow me to eliminate two electrolytic capacitors, which wear out over time (albeit many years).

3. The filter connection is completely changed to allow three filters to be used (neck, bridge, and mixed signal) at the same time. Down the road this will be useful for modules like a headphone amp, DI, or traditional eq to be applied after the LPF filter tuning. Heck, I could add a distortion module, or anything else; a mini onboard pedal board! The preamp profile will also be thinner, and the filters are now locked down with a screw, making the whole assembly more or less solid. The new connections will also make it cheaper and easier to use extension cables to place the filters away from the PD, for installing in really tight spaces. The filter boards will have a lot more space for new designs, and can be smaller. Lastly, the jumper selectors for the position of the second filter go away; it is much easier to understand and set up the preamp for a single filter or single pickup installation.

4. There are now markings on the board for all the connections, so it can be hooked up without referring to a manual or schematic.

5. I am increasing the default input impedance to 330k, though I can set it to whatever you prefer when you order a PD1/2, just let me know. I decided on 220k for the warm sound of a passive when the filters are bypassed, but after customer comments on a wide variety of pickups I think I'll bump it up.

Stay tuned for initial testing and tweaking results. There are a lot of new features to dial in, and new filter boards to design

!

-Tim