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AM2470 Module - Eµ Dual LFO
Overview This module is a clone of the LFO section of the Eµ Modular 2451 Potpourri module. It has two identical LFO's, each with square and triangle waveforms, a frequency control
and two level controls. Whilst this is not the most exciting LFO, with just two waveforms, it is simple and effective.
Original Circuit
The Eµ modular originally used wide ranging VCO's which could be set as sub-sonic LFO's, just like Moog and ARP. However in March 1976 Dave Rossum created a multi-purpose module - the Potpourri (2451), which included a LFO as well as analog and digital inverters.
The circuit is quite traditional, and uses a 741 Op Amp, 556 and 558 Op amps. The frequency range is from 0.02Hz to 50Hz.
New Circuit
The clone uses the same schematic as the original, but has NE5532 Op Amps instead of the impossible to get 556/558. I have added a simple LED drive circuit from the square wave. The frequency range from the prototype is 0.06 Hz to 32Hz, and the waveforms are clean.
Panel
The front panel is a standard AM design, 90mm wide and 4U high, with black lettering. Controls knobs are standard Eµ Modular designs. The 5mm LED's are high intensity versions in blue and ocean green, mounted in LED clips.
Build History
The schematic and board were laided out with Eagle CAD, and the PCB manufactured by PCB-Pool. Whilst rather more expensive than Olimex, the PCB is of a very high quality. I ordered 3 at once to keep the unit costs down. The board was populated and worked first time, the only adjustment was to sort out the LED resistors to give an even and low level brightness. The ocean green LED is so efficient that it uses a 100k resistor and pulls just 0.15mA.
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Resources
* Schaeffer Front Panel .fpd file 
* Project Build Notes
