JEN Fuzz – Cardiopulmonary Resuscitation


Recently I’ve been lucky to get this old JEN Fuzz from good buddy of mine – well know amp builder in Poland. It came in pieces, not working (some bad repairs by unknowable technician), but I see the chances to get it to proper functioning. Transistors (SFT337 & SFT363E) are all good, minimum, and none leakage. I’ve cleaned and protected PCB today, as well as the enclosure – someone glued in the switch to the enclosure with huge amount of epoxy (major PITA to remove, but as you see, I’m almost there). Resistors were 1/4W carbon composition, I’ll use Pihers instead, and rest of the parts will stay original…


Anyway, the reason why I’m so happy is the fact that this is basically exact the same circuit as famus 1966 VOX Tonebender – not to mention ability to get proper base to make my own Tonebender repro enclosures!

– PCB dimension are 32mm/47mm, I’m working on board track image for your own use. I’m suck big time when it comes to photoshop, so any help will be gratitude.

Here’s what my Atlas DCA55 says about the transistors:

– PNP Germaniums

– SFT337 reads 77hfe none leakage (Q1)

–  SFT363E is 37hfe with 0,06mA leagage (Q2)

I may swap them around as the Q1 is higher gain than Q2, but first I’ll check on breadboard how it sounds with stock configuration.

Below you see schematic of this particular unit. Most of the schemos I’ve seen was wrong, had the resistor value typos (8k2 to ground instead of 820R, 1k resistor instead of 2k2 in this unit). I’m still not sure what’s correct input cap value, as the marking in mine is barely visible. I’ll update this info as soon as I get proper measurement.

JEN Fuzz schematic.pdf

Soon (sooner or later) the picture show of finished, rebuilt unit.