Is marking A on a potentiometer linear or logarithmic

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Direct answer to the question - In most modern parts USAsia and most current global suppliers, marking “A” denotes a logarithmic audio taper; “B” denotes linear. - Important exception: some legacyJIS-era parts common in vintage JapaneseEuropean gear use the opposite convention A = linear, B = log. When in doubt, verify by datasheet or measurement. Detailed problem analysis - Potentiometer taper defines how resistance vs. rotation behaves: - Linear typ. “B” modern: resistance is proportional to shaft angle; 50% rotation ≈ 50% total resistance. - Logarithmicaudio typ. “A” modern: resistance follows a log-like law to match human loudness perception; at 50% rotation you typically see ~10–30% sometimes ~15–20% of total resistance from one end to the wiper. - Why the confusion: historic standards notably older JISDIN usage labeled A = linear and B = log. Many vintage ALPSPanasonicNoble parts and some European stocks follow that scheme. Modern catalogs from BournsVishayTTetc. overwhelmingly use A = log, B = linear. - Practical consequence: using the wrong taper mainly affects user feel: - Volume control with linear feels “bunched up” near minimum. - Adjustment control with log can feel overly coarse at one end and fine at the other. Current information and trends - Current industry practice from major distributors and datasheets largely standardizes on A = log audio, B = linear, C = reverse log. Nevertheless, legacy stock and some niche suppliers still reflect the older convention. Always confirm for replacement parts in vintage equipment. Supporting explanations and details - Quick multimeter check works regardless of markings: - Measure total resistance across the two outer terminals Rt. - Set the shaft to mid-rotation and measure from wiper to one end Rw. - If Rw ≈ 0.5·Rt → linear. If Rw ≈ 0.1–0.3·Rt or 0.7–0.9·Rt from the other end → log. - Many “log” pots are actually multi-segment approximations; the exact midpoint percentage depends on the manufacturer’s “law” e.g., 10A, 15A, 20A curves. Ethical and legal aspects - No specific legalethical concerns, but mislabeling or misinterpretation can degrade user experience or service restorations. For safety-critical controls, verify taper to prevent unexpected behavior. Practical guidelines - Replacements: - Modern gear: order “A” for audio volume, “B” for general adjustments. - Vintage JapaneseEuropean gear: check the original datasheetservice manual; if unavailable, measure the original pot’s taper as above. - If you must substitute: - To mimic a log response with a linear pot, add a seriesshunt “law-faking” resistor ≈10–22% of pot value from wiper to ground for typical audio direction. Test and tune by ear or curve. - Documentation: - Prefer parts with explicit “taper law” graphs in the datasheet rather than relying solely on ABC codes. Possible disclaimers or additional notes - Mark codes can be incomplete e.g., “A10K” without a brand or worn. Mechanical center detents do not imply linear taper. - Reverse log “C” exists and is used for balance or specialized controls—do not confuse it with standard log. Suggestions for further research - Check the specific manufacturer’s datasheet for the exact taper curve look for R vs. angle plots. - For vintage restorations, consult service manuals or community databases for the original part numbers and taper conventions. - Explore “law faking” resistor calculators to derive a desired response from a linear pot. Brief summary - Usually, “A” = logarithmic audio, “B” = linear—except in some older JapaneseEuropean conventions where it’s reversed. Don’t rely on the letter alone; confirm via datasheet or a quick midpoint resistance measurement.

Potentiometer Marking A: Linear or Logarithmic? Bourns, Alpha, Piher, Vishay Taper Codes Explained

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