A dying battery simulator allows the voltage of an analog pedal to be reduced to a suboptimal level in order to mimic a dying battery effect. At lower voltages, distortion/overdrive/fuzz pedals are said to produce different sonic textures. For example, fuzz pedals may become gated, and high gain distortion pedals may take on a more subtle overdriven sound.
While the design is presented in pedal form, the schematic can be minimized to fit into another pedal in order to allow a user the ability to vary voltage within a pedal. Furthermore, pedal builders can also place the design into their test boxes in order to provide a wide range of voltages. In the lattermost case, building a 35V charge pump with a LM317 would allow a builder to have a wide breadth of voltages from ~32V to 1.25V - although I personally believe, 25V, 18V, 9V, and 4.5V would be satisfactory for many pedal designs.
The LM317 is a 3-terminal adjustable regulator that is capable of outputting a voltage range of 1.25 V to 37 V depending on input voltage. The regulator has three terminals: Input, Output, and Adjust.
Source: Wikipedia
When the JHS Volture first came out, I immediately knew it wasn't simply a potentiometer in series with a power supply. As soon as gut shots for the Volture became available, it was pretty clear the circuit was based on RG Keen's original concept, which in turn is probably from the actual datasheet for the LM317.
For my version, I utilized a video from Volos Projects to corroborate/refine the design. I then added in a LED voltmeter from Amazon and an internal Age control. New batteries differ from old batteries in that, “while new batteries can put out a lot of current, old ones can't - they develop a high internal resistance.” The Age knobs acts a rheostat. Putting “a resistor on the output of our regulator…will fake the internal resistance of the battery" (source). Voltmeter addition was inspired by MAS Effects’ UV Meter Drive and Silktone Fuzz. I did attempt to have a rotary switch for a Battery Simulator (carbon zinc, alkaline, “wall wort”) to play off the JHS April Fool’s joke, but the idea was too ambitious and overly complicated to implement. I also would've loved the Age control to be an actual potentiometer, but I could not find a reasonably priced and appropriately sized 100 ohm potentiometer.
This circuit allows you to go from ~7.5VDC to 1.25VDC which is similar to the Voluture specs on the JHS website ("...adjustable voltage from 7.5VDC down to 1.25VDC..."). The basic circuit is 5-6 different components and takes a matter of minutes to piece together.
Schematic.
Two changes I would've liked to implement were:
Reverse polarity protection.
100uF to 1000uF electrolytic output capacitor for stability.
Files:
(Pending)