Double Bass COVID preamp

[fdeck]

I get an employee discount on preamps, but not on batteries. So I decided to hook up a phantom powered piezo preamp for my audio interface. It looks pretty scary but it works. It's literally a JFET buffer that is powered by the severely limited amount of power available from "phantom power." It lets me plug my piezo pickup directly into the box.

This was brought about by a friend setting up a Jamulus server and inviting some of us to a twice-a-week online jam. Man, it's good to be playing again, even if only into the cloud. I've been learning some things about Jamulus and the upright bass, will hopefully arrange my thoughts into a few coherent paragraphs, and post here.

 

[Happy Steve]

Hi Francis, I made a 'quick 'n' dirty' DI some time ago using your single FET design, but with phantom power. A friend used it with his gypsy guitar and said it was the best sound he had ever got!

I still have a very ugly looking (both circuit board and outside/cosmetically) home-made HPFPre with the 9V battery mounted externally in one of those plastic circuit board battery clips. I always thought it would be great with XLR output and powered by 48V phantom but I lack the time to attack that project, and I have other $$$ gear which does the job now.

Thank you for making your work 'open source' and showing that simple ideas executed well can be so useful.
It is great to see function taking such pride of place over form in this example!
best, Steve

 

[Happy Steve]

Here are some pics.
Phantom powered DI: (2Mohm input)

Hpf Pre:

ugly, but fully functional!

 

[fdeck]

Nice! I'll have to find the links, some folks have posted "tagboard" layouts that look quite well done. The darn thing is the JFETs, which have gone obsolete. If you can tolerate surface mount, the MMBF4416 JFET is still available, made by Philips. I've experimented with putting little squares of copper tape on a proto board, soldering the surface mount JFET to the tape, and then wiring to that. I'll have to dig up some pics. Also, Adafruit sells a tiny breakout board for surface mount transistor packages.

 

[bassically_eli]

I just posted a question in another forum about making a piezo buffer using phantom power, and I now I see it has been done! However, my idea was actually to use low-voltage, unbalanced phantom power, the kind intended for electret condensers. It did also occur to me to ask about powering pedals or the HPF-Pre with 9V phantom power. I don't think it would be enough current for most devices, though.