The Secret Society of Lathe Trolls

tape · Joined: 25 Jan 2007 Posts: 78

I have recently aquired a Wilcox Gay SR.
It cuts at 78 rpm.

Now I am interested in cutting records that can be played on a normal modern recordplayer at either 33 or 45 rpm.

To do that I guess I will have to pitch up the music I am cutting, in a manner so that the pitch will be normal when the record is played back at 33 or 45 rpm.

My question is: how to dertermine how many tones the music has to be pitched up?

I guess that there must be some simple math, that converts pitchrange from 78 rpm to 33 or 45.....

blight · Joined: 19 Jul 2006 Posts: 48

You would have to cut at 78/33.3 times the speed.
That means 2.34 times faster. So 10 kHz would have to be cut as 23.4 kHz which is well beyond the limit of your head I guess - you would probably get a response from 5-7000Hz so I dont think you really want to cut 33RPM records at 78RPM unless all you want to record is human voice Wink

cuttercollector · Joined: 11 Jun 2006 Posts: 265 Location: San Jose, CA

7Khz is about it for those crystal cutters so you are quite correct. Doing that would yield a net response when played back at 33 only out to about 3Khz - telephone quality.
Not to mention these things were never meant to cut microgroove records. You could probably make a microgroove stylus work but the leadscrew was designed for coarser pitch, wider grooves. So you end up with shorter recording time and lots of land between the grooves.

This brings up a point. How successfull has anybody on here been with converting any of the 78 home or semi pro recorders to cut something beside 78s? Specifically the Wilcox Gay recordios and recordettes, the Presto K8s etc that have pivoted arms, non- replaceable or adjustable coarse lines per inch and a 78 only turntable. Perhaps I will post this as a new topic.

cuttercollector · Joined: 11 Jun 2006 Posts: 265 Location: San Jose, CA

I guess this was covered but for us mathematically challenged, the relationship between speed and pitch is a direct one. That is the note "A" - 440 hz recorded at say, 33 rpm, becomes one octave higher - 880Hz at 66 rpm.

Jesus H Chrysler · Joined: 26 Nov 2006 Posts: 36 Location: Charleston, SC

seems like you could just slow down the motor by adding a resistor inline. And wasn't the k-8 a 2 speed cutter? I know the k-6 is 78 only, but I thought the 8 cut both speeds like th k-10. If I'm wrong then I inadvertently gave some misinformation in another thread.

cuttercollector · Joined: 11 Jun 2006 Posts: 265 Location: San Jose, CA

According to the Presto history site you are correct. K-8 and forward were 2 speed (my K11 is 3).
The problem with a simple resistor on an AC motor is that for one it wants to lock onto the power line frequency (though not as much as an actual synchronous motor) and stay at speed because of that, and you also loose torque as you lowwer voltage with a series resistor. Same issue with a variable transformer (variac). Loss of torque is loss of speed stability when cutting. You might be able to do it with a variable frequency motor power amplifier - keep the voltage the same and lower the frequency, but the best way is to alter the mechanical drive ratio - typically by decreasing the size of the motor shaft.