What a speed check can tell you
A record cut for 33 1/3 RPM should be played at 33 1/3 RPM, and a 45 at 45 RPM. A steady error changes pitch and tempo; changing speed during a revolution sounds more like instability than a simple pitch shift. A phone can reveal an obvious, repeatable problem, but its sensors, case, placement and movement on the platter all affect the reading.
CrateCore treats the phone result as an estimate. That distinction matters: the useful question is not whether the last decimal place looks perfect, but whether repeated runs point to the same meaningful deviation.
Prepare the turntable before measuring
Use a stable surface
Place the turntable on a firm, level surface away from footfall and speaker vibration.
Remove the record
Run the test on the mat or bare platter only if the turntable manufacturer permits it. Lock the tonearm in its rest.
Check the selected speed
Set 33 for an LP or 45 for a 45 RPM record. If the deck moves a belt between pulley steps, confirm the belt is on the correct step.
Let the deck settle
Give the platter a short warm-up so the measurement does not consist mainly of startup acceleration.
If the turntable manual gives a specific speed-check procedure, follow that procedure first. Some decks are user-adjustable; others require access to internal controls or service.
Measure speed with the phone
Centre the phone
Place it as close to the spindle as the shape of the phone and platter allow. A small off-centre position is easier to secure than an edge position.
Start the measurement
Start the platter and then begin the CrateCore speed check. Keep hands, cables and loose clothing clear of the rotating platter.
Record a settled interval
Ignore the startup phase. Measure long enough to see whether the displayed average settles rather than chasing each instant value.
Repeat at least three times
Stop safely, reposition the phone if needed and repeat. Test 45 RPM separately if the turntable supports it.
Read the result without overreacting
| Pattern | Likely meaning | Next step |
|---|---|---|
| Repeated averages agree | The estimate is probably stable | Confirm only if the deviation is audible or outside the maker's specification |
| Results change when the phone moves | Placement is influencing the sensor | Improve centring and repeat |
| 33 is wrong but 45 is normal | The speed mechanism may behave differently by setting | Check belt position or the model-specific adjustment |
| Reading wanders during every run | Possible mechanical instability or measurement movement | Confirm with a strobe and inspect belt, pulley and bearing per the manual |
Do not use a generic internet tolerance as permission to adjust every deck. Compare the result with the specification and service instructions for the exact model. A small numerical difference that is not repeatable may be measurement noise; a repeatable error deserves confirmation.
Confirm the result with a strobe disc
A strobe disc provides an independent visual check. Use the ring that matches both the target speed and the local mains frequency. Under the specified type of mains-powered light, the correct ring should appear stationary; apparent movement indicates fast or slow rotation. The Pro-Ject Strobe it instructions also warn that daylight and many DC-powered lights are unsuitable for their disc.
Choose the matching ring
Before starting, check which mains frequency your strobe disc is made for: some discs carry rings for both 50 and 60 Hz, others only one.
Place the disc flat
Put it on the platter with the record removed and the tonearm secured.
Use the specified light
Follow the strobe-disc instructions; a random LED or phone flashlight may not provide the required flicker.
Watch the correct marks
Marks that drift one way indicate one direction of error; reverse drift indicates the other. Use the disc legend rather than guessing.
Adjust only when the method is clear
If both methods show the same persistent error, consult the turntable manual. External pitch controls are meant to be used; hidden trim pots, motor controllers and belt systems may not be. Photograph the original position before any permitted adjustment and make one small change at a time.
A worn or contaminated belt, residue on the pulley, incorrect belt placement, bearing trouble or unstable power can all affect speed. Use only the maintenance steps approved for the model. If access requires opening powered equipment or the instructions are unclear, stop and use a qualified technician.