Belt Drive Turntable Is Running Fast or Slow, HELP! Could it be a bad belt? 

A DC motor's speed is directly proportional to the input voltage. The higher the input voltage, the faster the output speed. The lower the input voltage, the slower the output speed. Thank you for the video. I have contemplated buying a direct drive turntable, but I want one that's definitely autostop, but maybe full auto (start too)

Thanks for the video. You confirmed what I long suspected that belt fitment affects platter speed. Here is my input on motor speed variations. DC motor speed is controlled by input voltage. AC motor speed is controlled by input frequency. Turntables which use DC motors usually have a circuit that varies the input voltage to control the platter speed, either with a manual adjustment or a quartz lock circuit to automatically maintain the speed. Turntables with AC motors can control the platter speed either with a mechanical adjustment (Dual) or by a circuit which changes the frequency on the AC input voltage (Thorens TD-125). I also have seen some variation in platter speeds on AC motor turntables over time but I usually chalk this up to environmental conditions other than voltage like temperature, humidity, lubrication status, etc. Very large variations in voltage can affect AC motor speed but not the small variations in line voltage. I control the speed of my Leslie unit with a variac.

Just looking at the motor of this t table, it appears to be an AC Four-Pole Synchronous motor. Synchronous motors maintain accurate speed from the AC's line frequency which is 60Hz in the US. I suppose subtle variations in the line frequency will alter the speed. More of an issue with lighter platters than the flywheel effects of platters with more mass. Some turntable motors have tapered spindles to allow speed adjustment by moving the belt up or down on them. You know, if you're going to be doing videos on this subject, dump the phone app, (real rookie stuff, plus you're using it incorrectly) and get something more accurate with a quartz locked illuminator that doesn't rely on the power line frequency like an AT AT6181DL Stroboscope Disc and Quartz Strobe, or my personal fave, The KAB SpeedStrobe where the strobe features the actual speed numbers instead of "Instead of hypnotic bars". There are pricier devices but these are very accurate. On another subject, the emphasis on making sure the speed is exact, on a lot of cheaper turntables, vintage stuff, DC motors and almost all direct drive models that were not made in the last few years, you're more likely only getting speed accuracy centered around your target speed; 33.33, 45 RPM. There is a saying about DC motors; "They go right by going wrong". A turntable that might be off a smidge too fast or too slow can sound fine if there is little or close to no variation in speed compared to something that you think measures well with a phone plopped on the platter but varies enough to be audible. Many people don't listen very well, not noticing the speed variations. I've said this on other websites: play some piano music that has long sustained notes, notes where the key is held down for a long period and listen if you hear any variation, wavering of the note. You would be surprised at how many turntables fail at this simple test. Also damage to these forty, fifty year old turntables bearing or motor induced noise. A decent stethoscope placed at various points on a table's base is always a good way of checking. It's amazing how much of this noise goes unnoticed.

ive often wondered if the weight of the phone and its battery affects the true speed adjustment, it may read a bit different without the weight of the phone-??

Grazie mille per il video, mi hai salvato (e mi hai fatto risparmiare parecchi soldi)😉… Ho un DENON DP29F e su internet non c’è quasi nulla su come regolare la velocità e sono 3 anni che mi ascoltavo i vinili come se stessero cantando i Chimpmunks… Grazie mille ancora

My Lab 300 turntable was running fast. I ordered a new belt, still running fast, then I saw there was a little bit of old belt residue stuck on the motor pulley. I scraped it off and now it runs perfectly! I tested it with a paper stroboscope disc and then again by playing an album on vinyl and streaming at the same time and the speed matched. I wonder if the weight of a phone could affect those rpm apps

I have a ps2350 and just put a new belt that fits tight, like the 3rd example and my speed was 34.2, a little fast.

Hey Andy. I have that same Sony 2700. What size belt did you use for the correct speed?

when measuring the belt, do you measure it in diameter or radius? sorry for the daft question, I'm really new at the whole replacing belt thing

my motor of my turntable goes always in top speed (very very fast) what i do? thespeed adjusts don work.

What app are you using?

your method seems flawed , depends how far away the motor is from the sub platter , if i did that method with my thorens the belt would be far to tight and damge the bearings in both the centre bearing anfd the motor