Jensamp 51X, a DIY germanium preamp

Origins

RCA BC-7A

This germanium preamp is based on a classic mic preamp: the RCA BA71. These modules came from the film and broadcast consoles of the 60s-70s and are considered as one of the finest of this era.
GroupDIY forum member Jensenman redesigned this old beast adapting it to modern recording environments constraint (48V, DI input, variable gain etc.) and optimizing it a bit for a better bandwidth.
Kubarth and [silent:arts] managed to put everything in a 51X form factor, a kind of big brother of the infamous API500 format. Note that you can plug an API500 module in a 51X rack (and it will even work!).

Build

An easy build

Jensamp kits are available through [silent:arts] white market thread. The kit comes with everything except 2 bits of wire for the LED. The yellow PCBs are really well made, and metal work is as you expect from a german production.
It is really easy to build, I didn't struggle on anything. Start with small things like resistors and solder your way up until the big Haufe transformers.
Plug it...
Enjoy the sound!

I had first a little oscillation problem that I solved by changing some vintage components. I also took care that no metal casing was touching the PCB traces.
Take care to discharge yourself from static as germanium diodes can be sensible to it.

Costs

The kit comes with everything and costs 220€ (excl. VAT and shipping costs). It is a really cheap preamp when you hear such a sound quality. Germanium preamps usually cost 4-5x more...

Sound

Here comes the real deal. The sound of the Jensamp germanium preamp is thick and large. It is not a clean preamp. And you'll love it for its sound. No wonder people are comparing it with Neve mic preamps...

As a test example I plugged a cheap chinese mic in it and it sounded good, full bodied! I then plugged the same mic in a Lindell audio preamp (6X-500) and it sounded harsh and aggressive.

 

Recall sheet

I wrote a little recall sheet for those who are trying like me to document their sessions.
Download it and tell me on what you used it.

Feel free to post any comments or questions about this unit. If you want to try it yourself, contact me at my recording studio in South Germany.