Jozef Bogin

Crystal tinkering

by Jozef Bogin, 2023

 

Vinyl revival, anyone? Yes indeed! Nothing beats the sound of a dust-filled groove, pressed into a biscuit of PVC, mastered from ones and zeros and released today. Plastic disks not your cuppa? Substitute them for wax cylinders! Recorded and played back with a big old horn for that overall analog experience. Oh wait… As a foreword, you might have observed that I’m more a tinkerer than a collector, so the following article might be a blasphemy for all the hardcore antique afficionados. This particular piece is by no means a rare model; the 2-minute model B Standard was one of the most common cylinder phonographs. My estimation of the year of manufacture is around 1908, as this is still a single-gearing machine: owing to the high serial number and the fact that the 4-minute cylinders appeared in around 1908. From there on, machines could be then retrofitted with a 2/4-minute gear kit, whereas the models introduced later (such as D) had the 2/4-minute option straight from the factory. It came along with some parts, including mounting hardware for a crane horn, and two incomplete Recorders, one of them being an early Automatic (that I have sold off since), and one of a later model that I tried to make it working (below). The machine itself required just some lubrication and adjustments to the half-nut and bearings on top, to make it spin freely and quietly. I did not bother doing a strip down-to-the-nub, since it runs good, it’s over a century old and especially pot metal can go from happy to snappy when least expected. Machining new replacement parts or rethreading some weird inch pattern in this metric part of the world, is something I wanted to avoid doing. You don’t fix what isn’t broken, in short. Experiment 1: Electronic reproduction of 2-minute wax cylinders The very first thing was to record and digitize the cylinders I had in my collection. Of course, the simplest approach would be placing a microphone next to the reproducer horn, but this would also record the ambient noises and it would sound just as “tinny”, if not more, as the horn itself. A better approach is to use a crystal (ceramic) pickup, also known as a piezoelectric transducer or “contact microphone”; these are commonly found as thin brass disks that convert vibration into an electric signal, and vice versa. Crystal transducers are found inside electronic buzzers, old phono pickups, some people use them to amplify acoustic instruments, and a piezo crystal is also used in lighters to provide a high-voltage spark when struck with enough force. While at it, I have also put in new gaskets sandwiched in-between the copper diaphragm, as the old rubber ones were reduced to pieces. Remarkably though, the rubber legs on the bottom of the phonograph are still in good condition. Crystal pickup mounted on the diaphragm of an Edison Model C reproducer In the picture above, I have drilled a hole into the pickup for it to be able to fit onto the diaphragm, and sealed it around with epoxy to prevent cracking. The signal wire was passed through the “fishtail” of the reproducer’s weight, and the body was used as ground. The output of a crystal pickup is high impedance, in megohms, so in order to connect this to a normal line level input, there needs to be some impedance matching involved. A sound input designed for instruments, such as a guitar pedal effect on a dry setting, or an old amplifier or tape recorder with ceramic phono input, or even a simple NPN emitter follower (or JFET buffer) circut will do the trick. Connecting a pickup like this straight to a line level input will yield a weak signal, stripped off bass and treble – it will sound more “tinny” than the phonograph itself. Now, touching the reproducer’s stylus with fingers on a setup like this, yields a similar, “bassy” BRRRRAP as if the same attempt were done with the stylus of a record player. This also means that it will amplify all imperfections of the cylinder (and resonances of the reproducer), that would otherwise be “drowned” if an acoustic playback were used. The worst problem with this approach are the resonances, having the rigid pickup glued onto the vibrating diaphragm, especially during loud passages it sounds like clothes being torn in the most distorted, “metallic” way possible. Since this also affected the acoustic playback, this idea was scrapped. Perhaps if I had more than 1 reproducer, I’d put a bigger pickup between the gaskets, instead of the original diaphragm, and use it for electronic playback only. An alternative, which I use today, does not modify the diaphragm of the reproducer, so the quality of the acoustic playback is unchanged. It involves putting a smaller diameter crystal pickup into one side of a tube, made from thin copper sheet metal, rolled to the same diameter for the horn adapter of the reproducer, for a snug fit. The connections are the same, with one signal wire only, and the body is used for ground. This approach would not provide such a frequency response as in the solution above, however, the usable sound range of a wax cylinder is still between 300 to 3000 Hz, give or take. Also, more gain has to be used, amplifying any external loud noises close to the crystal pickup, but it is still far better (and less tinny) than using a horn and microphone. In my wax cylinder recordings, I also apply a 4 kHz lowpass to filter out resonance of the thin C-linkage between diaphragm and the stylus rocker arm.

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