The Secret Society of Lathe Trolls

tape · Joined: 25 Jan 2007 Posts: 82

I have question about speed instabilty while cutting.
I use a Bell Record o Phone at 33 rpm.

When I play the cuts there are two problems:

1: It's much faster than 33 rpm - not 78 but something like 8 semitiones higher in pitch.

2: There is a lot of 'vibrato' which is very noticeable and annoying!

For question 1 I'm thinking it has something do with the machine running on US power (60hz) Im in europe where we use 50hz. Maybe the motorspeed is somehow dependant on the powerfrequency?

For qustion 2 I have no clue - a mechanical defect on the turntable?

hope sombody have had experiences with these issues...

thanks

mossboss · Joined: 01 Jul 2007 Posts: 19

Hey tape
At 60 HZ the machine would run at it's designed speed However at 50 HZ it would run at 20% SLOWER not faster
I would suggest that you get a paper template to check the speed of the turntable first before you do anything else
They are available from record shops or turntable sellers
At 50 HZ with a standard neon globe you should be able to shine the light on the template to determine speed and see where you are
For the other problem I have no Idea but I would have thought that getting the speed right should be your first stop to get it right
Then see what results you get before going further
Cheers
Chris

cuttercollector · Joined: 11 Jun 2006 Posts: 268 Location: San Jose, CA

OK, it's your turntable drive. That machine uses idler wheels to engage the motor to the turntable. You don't have enough torque transmitted through the old hardeded rubber idler to cause the speed to remain stable. The good news is that that machine uses a fairly common mechanism made by General Industries. It was also used in at least a Masco a Meissner and an Airline (Montgomery Ward). Get the idler rebuilt with new rubber, clean the inside of the turntable drive surface and the motor shaft. Also, really the lathe leadscrew mechanism should be re lubed as well as the motor.
The drag comes from both running the leadscrew driving the arm across the disc and even more so the actual cutting resistance.
Now for the bad news, if it was designed for US 120V 60Hz, if you give it 120V @50Hz it will run slow because the frequency is lower.
Thus when you play your recording on a turntable running at an actual proper 33 1/3 RPM, it will soud fast - higher in pitch because you are playing it back at an actual faster speed than it was recorded at. You are probably cutting at an uneven 22-25 RPM.
If you are getting these results playing it back on the same machine then it is entirely due to slippage during recording. That would also account for the speed instability or wow and flutter. It takes quite a bit more turntable torque to cut a record than to play one!

cuttercollector · Joined: 11 Jun 2006 Posts: 268 Location: San Jose, CA

2 more thoughts, I THINK a machine shop could make a sleeve to fit over the motor shaft to "convert" it to 50Hz operation. The shaft just has to be a litle larger to make everything come out right because motors do lock to the line frequency.
One more experiment you could try beside a strobe disc and neon lamp.
Place a 1/4" by 1" piece of paper so it sticks out just beyond the edge of a record on the turntable and the rest is underneath to hold it in place.
Count how many times it goes around at the 33 1/3 speed in one minute.
Do this with no load, while playing back if you want, and then while cutting. That will give you the actual RPM and I would bet that it's not 33 even with no load and drops quite a bit as you cut.

tape · Joined: 25 Jan 2007 Posts: 82

thank you!

I suspected the power frequency issue.