The Secret Society of Lathe Trolls

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

How successful 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 leadscrew and a 78 only turntable.
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.

Anybody done a speed conversion and also gotten a microgroove stylus to work, even with the leadscrew limitations mentioned above?
I would also think the response of the crystal or simple really old magnetic cutters, which was only good to 7-10Khz at best at 78 would fall off to well below AM radio quality by the time you get down to 33 RPM.
The lower speed if present at all on some of these machines was designed for lower quality, longer, speach/voice recording.
As I have said here before, just as with analog tape machines, the faster the recording speed, the better the quality. A modern pro stereo machine can be quite incredible at 78 RPM!
Our preceptions have changed because we hear what older lower quality processes did at 78 speed and only relatively modern stuff at the 33 speed.
There is a reason that a lot of those direct to disc and other modern audiophile pressings are issued as 12" 45 RPM discs. Potentially much higher quality in terms of dynamic range and frequency response.

JayDC · Posted: Fri Jul 27, 2007 12:28 am Post subject:

your correct, the faster the rpm the higher the dynamic range of the recording. RPM = SAMPLE RATE...

The problem with 78 RPM, and most likely the reason for the 45 rpm adoption, is that the technics 1200 turntable is not available with 78 RPM. DJs are the primary consumers of vinyl records, and the standard DJ turntable is the technics 1200.

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

I am not suggesting 78 for club use and I know about the 1200 being a 2 speed unit, though there is this:
http://www.kabusa.com/78SL1200.htm
and there are other dj tables with 78 (I owned the Denon with the built in digital converter for a while)
Furthermore I have heard of some drum n bass dubplates being cut at that speed from some people doing that. They did it for just the reasons I was saying, more dynamic range, and headroom, higher overall level etc.
Of course these are the same people using extra cooling on the head coils to cut at higher levels. I am not sure how the club pickups can play this stuff back without serious mistracking. They don't use Shure V15 type V's there for back cuing and scratching, THAT'S for sure.
But the dj world is not really where I live. I love the fact that vinyl has continued to defy odds and hang in there and somehow become cool to new generations. I tend toward audiophile though you will find some 12" dance singles and punk 7" in my collection as well as accoustic 78s and everything in between.
Odd to think of speed = sample rate but it does equate. I remember thinking of that the other way around having learned about analog before digital audio. Analog is a continuous sample rate, but there is always some sort of storage media. That media has a finite structure. The more material you try to pack into a smaller amount of that structure (lower speed) the more the actual material structure causes issues with noise and/or not being able to fully represent the analog signal properly - somewhat in the same manor as a lower digital sample rate,
but also there is ite aditional issue of speed stability. The process is not running under some stable clock and error correction process. The very stability of the speed of the media determines pitch stability of the music.
It is much harder to make a mechanical system be perfectly stable at lower speeds.

JayDC · Posted: Fri Jul 27, 2007 8:36 pm Post subject:

oh crap... and I just sold my 78 idler to gib.. Sad

I'm very interested in the technics modification.. never heard of that.. Cool!..

grooveguy · Joined: 22 Jun 2006 Posts: 40

Getting back to your original question, a Recordio or other General Industries-based machine can be converted to microgroove, providing that you have some elementary mechanical skills.

The first part of the procedure involves disconnecting the leadscrew drive from the turntable shaft. If you remove the leadscrew, you can grind off the spur gear that's part of it. When you reassemble the turntable bearing the leadscrew is free-wheeling.

Next is to fit the far end of the leadscrew with a pulley of some sort. I made one from quarter-inch-thick plexiglass.

First you cut a circle (I used a 2-inch hole saw for wood), then run a quarter-inch bolt through it with a nut so you can grab the bolt in the chuck of a drill press. With the plexiglass 'blank' spinning in the drill press, hold a coarse file on the outside to get a flat surface. Then you hold a rat-tail file against it to form a groove.

I recall that the diameter of the GI leadscrew is about 3/8 inch. Bore a hole in the pulley to fit tightly on the leadscrew (a good selection of drills is mandatory for this kind of experimentation... they don't have to be expensive ones), so that the pulley can be forced onto the leadscrew and fixed with 'superglue' or epoxy.

This 2-inch pulley is then driven by a smaller pulley on a separate motor using an O-ring as a belt. I believe that the original GI gear reduction was 10:1, and the leadscrew was about 12 threads to the inch, giving a groove pitch of 120 lpi. This means that at 33rpm, the leadscrew was turning at about 3.3rpm. There are gearmotors available on the surplus market that turn at various speeds; what you do is make a driving pulley to give the approximate pitch you want. You might be able to use a Variac to fine-tune the pitch; my motor was a 12V motor and I used my old Lionel train transformer for a power supply.

A shortcoming of the GI deck is that the largest blank you can cut is 10 inches... perhaps a bit less when the pulley is fixed on the end of the leadscrew. I was cutting '45s for car phonos (yes, I'm old).

A similar trick might be possible with the Presto K-series 'swingarm' cutters, though there won't be enough clearance between the turntable and the leadscrew for much of a pulley.

Hope this gives you some ideas.

tape · Joined: 25 Jan 2007 Posts: 78

I am going to try this with my Wilcox Gay Sr Recordette.

QUTE FROM CUTTERCOLLECTOR: "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"

Could it really be as simple as decreasing the size of the motor shaft?

Im not so keen on destroying my machine.....
Assuming that decreasing the size will only lower the speed, and not mess up the position of the cutting arm, will it then only be a matter of changing the needle with a microgrooveneedle?