A later (post-communist) Russian overdrive stompbox. The full name of the effect (according to the manual) is "Overdrive Electronika PE-12". That means it was made at the same place as Electronika PE-11 Flanger (the name suggests these two should be close relatives), and Electronika FL-01 Flanger - an earlier example of the same flanger. Sadly, we don't have the schematics scanned.
The pedal was spotted on ebay.de a couple of times. Here are a couple of words from one of the sellers (we did not correct the language):
Prefix electronic "Overdrive" @VENTA @"Electronica PE-12" to musical instruments. The prefix is intended for work with an electric guitar and allows to receive two effects:
1. Effect "Overdrive" - soft distortion of a signal
2. Effect "Distortion" - rigid distortion of a signal
At change of a resonance of the controlled filter by handle "Brightness" it is possible to change a level of distortion of a signal and thus to pass from effect "Overdrive" up to effect "Distortion".
- Sensitivity an input - 250 mV
- Nonlinear distortions - 1,5 %
- A strip of reproduced frequencies 30 - 16000 hertz
In general class inexpensive rare! Soviet distortion for your collection.
Prefix is not a brand name, it's probably something like "preamp fx" translated from German (?). The idea of having two effects instead of one is something very nice - the only question is where exactly is the point that overdrive becomes distortion.
Owner's Manual for Elektronika Venta-Overdrive PE-12: