Strobe Disc Generator
Turntable speed drifts. Belts age, motors settle, and a platter that ran true a year ago can run slightly fast or slow today, shifting the pitch of everything it plays.
A strobe disc makes that visible. Generate one below for your speed and mains frequency, print it at full size, and under a mains-powered lamp its marks stand still only when the platter runs true. The check takes seconds.
How to use it
- Choose your platter speed and your mains frequency: 50 Hz in Europe and most of Asia, 60 Hz in the Americas. Print at 100% or “actual size”; scaling does not change the reading, but full size is easiest to read.
- Place the disc on the platter, start playback, and light it with a neon or incandescent lamp driven directly by the mains.
- Marks standing still: speed is exact. Drifting forward: fast. Drifting backward: slow. Adjust pitch until they stand still.
FAQ – Strobe discs and turntable speed
- Why do the marks show nothing under my LED desk lamp?
- Is a printed disc accurate enough?
- Does speed really matter audibly?
- Why does the 45 rpm ring drift at 50 Hz even when the speed is correct?
Most LED lamps rectify and smooth the mains supply, so they do not flicker at line rate and the marks show no pattern. Use a neon pilot lamp, an incandescent bulb, or any lamp you know flickers at mains frequency.
Yes for speed checking. The disc’s accuracy comes from the mains frequency, which utilities hold very close to nominal over any short observation. Print scaling does not affect the reading, only legibility.
A speed error shifts pitch: about 0.6% is a tenth of a semitone, which trained ears notice on sustained piano notes. Speed drift and wow are separate matters; the strobe shows average speed and visible short-term instability.
At 50 Hz, no whole number of marks fits 45 rpm exactly. The disc uses the nearest count, 133 bars, and prints the rule on the ring: at correct speed, the 45 rpm ring must drift counter-clockwise by five bars every 20 seconds. The 33 1/3 rpm ring, and both rings on the 60 Hz disc, stand still in the usual way.
While you are at the turntable
Speed is one of three quick mechanical checks. Alignment is the second: print a custom arc protractor with our protractor generator. Arm and cartridge matching is the third: the tonearm resonance calculator tells you where the combination resonates.
L’Or du Son
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About this tool
What it does. Prints a strobe disc to check that your turntable runs at the right speed, at 33⅓ and 45 rpm, for 50 Hz or 60 Hz mains lighting, or for a number of bars you choose.
How it works. Mains lighting flickers at twice the mains frequency. When the number of bars on a ring matches that flicker at the correct speed, the bars appear to stand still: 180 bars at 33⅓ rpm under 50 Hz, 216 bars under 60 Hz. The disc is drawn as a vector PDF, with scale marks to check the print.
Limits. It needs a light that flickers with the mains, such as an incandescent or neon lamp. Many LED lamps do not flicker, so use the timing mark instead. At 50 Hz the 45 rpm ring cannot be exact: at the correct speed it drifts by 5 bars every 20 seconds.
Example. On a 50 Hz supply, a platter turning at exactly 33⅓ rpm holds the 180-bar ring still. With the timing mark, 100 revolutions take exactly 180 seconds.
Made by. Le Son, Shanghai. Built in July 2026, updated in August 2026.
How to cite. Le Son, Strobe Disc Generator, leson.org/strobe-disc-generator/