What happens if you heat up a Germanium fuzz pedal?
The classic fuzz face sine wave at 330HZ.
Getting hot at 330HZ high E on guitar
Getting hotter at 330HZ high E on guitar
Way too hot at 330HZ high E on guitar
Increased leakage current is the main problem when the Germanium transistor heats up: Heat on Germanium transistors will increase leakage current, which significantly shifts the circuit's bias points. Shown on the oscilloscope, the entire bottom waveform shifts vertically relative to the ground. See the increased leakage current and loss of gain in video below.
Reduced Output/Sputtering: When the bias point shifts too far due to heat, the transistors no longer operate in their optimal range, leading to a reduction in overall output volume. You can hear this happen by turning the bias knob on your guitar pedal, the volume decreases. If the bias drifts enough to push the transistor into saturation the output signal flattens out completely and appear heavily "gated".
Increased Noise/Hiss: An increase in background hiss can result from the high gain nature of a Fuzz pedal combined with increased leakage current in a hot Germanium transistor.
Less "Warmth" or More "Farty" Tone: The optimal "warm" and "smooth" sound of a Germanium fuzz is often achieved at a specific bias point (around -4.5V on the collector of Q2). When the transistor gets hot and the bias point shifts away from this ideal voltage, the sound, and thus the waveform's shape on the oscilloscope, can become less desirable, often described as "farty" or "dying".
The FreezeZone pedal has eliminated the shortcomings of the germanium transistor, by introducing a refrigeration unit inside the pedal.
The video shows the germanium transistor at room temperature with the current gain of 183, the leakage current at 851 milliamps. At 120°F the current gain is 28, and the leakage current is 1569 mA almost double the previous leakage current of 851 mA. When the germanium transistor is cooled, the current gain is 159 and the leakage current is 38 milliamps.