Pedals, especially analog ones, are more than just boxes that take voltage and spit out signal. They are nonlinear, frequency-sensitive, and impedance-dependent. The power supply isn’t just providing energy; it’s part of the signal circuit.
In a well-designed pedal, especially modern ones, you'll often find a power rail filtering capacitor (typically 47μF to 470μF) right at the DC input. This capacitor shunts high-frequency noise to ground, effectively isolating the signal from the power source's AC characteristics.
But many vintage designs, including classics like the Fuzz Face and Tone Bender, lack this filtering or include only minimal decoupling. In these circuits, the audio path finds its ground return not only through signal ground but also through the power supply impedance. This means the internal impedance of a battery—especially as it changes dynamically with signal draw—does influence tone.
The internal impedance acts as a frequency-dependent resistor, modifying the power rail's behavior. For example:
Without the capacitor, the impedance is directly in the AC signal return path.
While LTSpice is a powerful tool for modeling basic circuit behavior, simulating the nuanced effects of real-world battery behavior is a challenge. LTSpice primarily allows for series resistance modeling, which does not account for the reactive components (capacitance and inductance) present in real batteries.
This means that subtleties like frequency-dependent impedance or dynamic sag under load are difficult to represent accurately in simulation. So while basic filtering interactions can be observed, the deeper tonal changes claimed by some musicians must be tested empirically.
Ultimately, if you're curious about the tonal impact of batteries vs. power supplies, the best approach is real-world testing with your own rig. Just know: using a battery won’t magically turn you into Jeff Beck. But it might be the missing piece of the puzzle for your tone—or at the very least, a fun experiment worth trying.
There are rare but fascinating examples of pedal circuits designed around battery impedance. These rely on resonance peaks or nonlinear behavior to produce unique distortion or bias interaction effects. Some vintage units even fail to operate correctly with regulated power due to lack of impedance in the rail.
In these cases, the battery is effectively a dynamic filter + sag component + nonlinear resistor, and its contribution is integral to the circuit's behavior.
Is the difference real? Absolutely. Is it always audible? No. Is it always desirable? Depends on your aesthetic goals.
The key takeaway: power supplies are part of the audio signal chain in certain designs. Treating them as purely functional "on/off" devices is a misunderstanding of circuit behavior, especially in high-gain, minimally filtered designs.
So yes, those players who swear they hear a difference? They're not crazy. But they're also often responding to nuanced, circuit-specific behavior.
As always: listen critically, measure obsessively, and never settle for marketing hype when you can model it yourself.
If you'd like, check out my YouTube video on this topic:
