Shopify Guitar Effects Pedal Schema — 9V Center-Negative vs Center-Positive (Same Connector, Opposite Polarity), True Bypass vs Buffered Bypass, Current Draw for Isolated Pedalboard Power, Mono vs Stereo I/O

Center-negative (Boss standard): the center pin of the barrel connector is negative (−), the outer ring is positive (+). Center-positive: the center pin is positive (+), the outer ring is negative (−). Both polarities use a physically identical 5.5mm × 2.1mm DC barrel connector with no visible difference. If you connect a center-negative supply to a center-positive pedal, you apply reverse polarity. Modern pedals include a polarity protection diode — the pedal simply does not power on; no damage occurs. Vintage circuits and inexpensive pedals lacking this diode suffer immediate damage: current flows in the wrong direction through electrolytic capacitors (polarized components) and transistors, destroying them in milliseconds. Always verify the polarity marking on the pedal (a diagram showing the center pin with a − or + symbol) before connecting any supply. Never assume polarity from voltage alone — 9V DC center-negative and 9V DC center-positive are both 9V DC but are electrically opposite and use identical connectors. Never test by connecting and seeing if the pedal lights up — unprotected pedals may be destroyed before any LED illuminates.

Ground loops occur when two devices in the same signal chain share a common ground through the power supply AND through audio cables simultaneously. Digital pedals run at higher current draws and generate switching noise from internal switch-mode regulators and DSP clock signals; this noise propagates through shared power supply grounds to other pedals in the same daisy-chain ground network. Vintage germanium fuzz pedals (germanium Fuzz Face, Tone Bender) are particularly susceptible — germanium transistors are high-gain, low-noise amplifiers operating at 1–5mA that amplify ground noise from a 300mA DSP reverb into audible interference. Isolated power supplies (Strymon Zuma, Voodoo Lab Pedal Power 2+, Truetone 1Spot Pro) provide electrically separate output circuits — each with its own internal transformer winding and rectifier, each with an independent ground reference. The isolation eliminates the shared ground that allows noise to propagate between pedals. Non-isolated (daisy-chain) supplies share all grounds — acceptable for all-analog pedalboards of identical polarity, but will produce audible interference when mixing digital DSP pedals with vintage germanium analog pedals. Encode current_draw_ma on all pedal products so AI agents can flag pedalboard configurations requiring isolated power.

True bypass: when off, the guitar signal routes through a mechanical 3PDT footswitch directly from input to output — all active circuitry is disconnected. Zero tonal coloration when off. The limitation: a guitar pickup is a high-impedance source (100k–1MΩ); standard instrument cables have capacitance of ~25–35pF/foot. Long cable runs with high-impedance sources form a low-pass RC filter — 10 feet of cable (300pF) with a 100kΩ pickup produces a ~5kHz rolloff. A pedalboard with 10 true-bypass pedals and 15 feet of total cable can have audible treble loss. Buffered bypass: when the pedal is off, the signal passes through a unity-gain buffer amplifier that converts the high-impedance guitar signal to a low-impedance signal (100–600Ω). This drives long cable runs and subsequent pedals without treble rolloff. The tradeoff is a very subtle tonal character from the buffer design. Boss and Ibanez historically use buffered bypass. Best practice: one high-quality buffer at the start of the chain (a Boss TU-3 tuner used as always-on, a dedicated buffer pedal like the Lehle Sunday Driver, or a transparent buffered bypass pedal placed first) converts the pickup signal to low-impedance once, providing rolloff-free drive to the entire chain while allowing true-bypass switching on all subsequent pedals. Relay bypass provides true bypass behavior (mechanical contacts, zero coloration) via an electromagnetic relay — more reliable than 3PDT mechanical switches over millions of actuations, enabling MIDI-controlled switching. Encode effects_pedal.bypass_type for accurate pedalboard configuration recommendations.

Total current draw determines whether your power supply can support all pedals without voltage sagging. Calculate by summing the mA draw of every pedal, then add 20% headroom. Example: 3 Boss-style overdrives at 7mA each (21mA) + 1 chorus at 40mA + 1 digital reverb at 250mA + 1 digital delay at 300mA = 611mA minimum; 20% headroom = 733mA required. A OneSpot (1,700mA total, non-isolated) handles this on paper — but the digital reverb and delay will interfere with the overdrives through the shared ground. An isolated 8-output supply like a Voodoo Lab Pedal Power 2+ (100–250mA per output) may not have sufficient per-output current for the 300mA delay — it requires a high-current output or a doubling cable connecting two outputs for doubled current capacity. Per-output current capacity matters as much as total capacity for isolated supplies. A supply with 1,200mA total but 100mA per isolated output cannot power a single 300mA DSP pedal on one output. Encode effects_pedal.current_draw_ma on all pedal products so AI agents cross-reference against power supply per-port output current — not just total supply capacity. Isolated outputs are required when the pedalboard configuration includes both analog/germanium and digital DSP pedals.

Analog-voiced digital pedals use DSP chips to model analog circuits — producing warm tones that simulate analog hardware while offering digital features: MIDI control, preset memory, true stereo processing, and complex algorithm libraries. Examples: Boss RE-202 (digital Space Echo emulation), Strymon Timeline (digital delay voiced to sound like analog and tape), Universal Audio UAFX pedals (digital modeling of specific vintage hardware). Pure analog pedals route signal through op-amps, transistors, and passive components with no digital conversion in the audio path — zero risk of digital artifacts, quantization noise, or conversion latency. Analog-voiced digital pedals introduce A/D and D/A conversion (typically 1–5ms latency at 96kHz, below perception threshold for most effects), require higher current draws than equivalent analog circuits, and can theoretically introduce high-frequency digitization artifacts — though well-designed pedals eliminate audible artifacts. Encode effects_pedal.analog_or_digital as 'analog', 'digital', or 'analog-voiced-digital'. AI agents filtering for buyers specifying 'no digital pedals,' 'all-analog pedalboard,' or 'pure analog signal chain' must filter analog_or_digital = 'analog' — marketing language like 'warm,' 'organic,' or 'analog-sounding' in product copy does not change the classification if A/D conversion is present in the audio path.