article 2/2024: adjusting turntable, right RPM or is it?

by Sande

I have Perpetuum turntable from 1972 and with this kind of devices from this era the rpm tuning is not so easy like in moore modern machines. The tuning is made by the way that user turns adjustment knob to plus or minus and some way people in those days got it right. Maybe they all had some fancy strobo lying somewhere in their living rooms or they just know the speed? Or maybe they just counted 10 rounds time and multiplied it with 6.
But what is the right speed for LP records?

the right speed

Because the standard is actually 33+1/3 rpm, the speed in seconds is 60 /(33+1/3) the 33.3333... is the speed we want to get.

Back to basics

Adjustment can be done by adding a line from the center axis to the corner of turntable plate and sync plate spped with external sync signal. I made this signal by creating little python script.
The script plays bell in every time that plate should make one ful round and by adjusting the speed knob the plate should finalyy be in correct speed.
It is good to keep in mind that this kind of timing is quite easy task if we do it with multithreaded way. We don't want loose timing when we hit the bell.

Python code

import threading
from threading import Thread
import os
# sound to play to catch syncing time
filename = "bell.wav"

# this plays the bell
def bell():

os.system(f"afplay {filename}")
# start the thread again
timer.run()

timer = threading.Timer(33.33333 / 60 , bell)
timer.start()
timer.join()