Back in 2005 I was suddenly (and inexplicably) struck by the urge to see if I could modify a gramophone (or phonograph, as I believe it’s referred to in the US) to be compatible with devices like my mp3 player or anything else that takes a 3.5mm jack. On investigating, I found a reproduction gramophone for sale on Ebay for £30 (about $50), and in a fit of ‘what-the-hell’ ended up ordering one. With the delivery of one extremely large box I had my gramophone.

Fortunately, I found I was able to produce an excellent result with far less effort or complexity than I had anticipated: if you have a few basic tools, simple components and soldering skills (oh, and a gramophone) you should have no trouble with this build. See below for my reasons and experiences, a summary of how it was built, and an analysis of the final product.

Why?

There are various ways to rationalise it - for instance, since it makes use of mechanical amplification rather than electrical, it doesn’t need batteries or a plug and saves power. In reality, though, I made it because it was fun, and because I liked the idea of adapting an archaic tool to a similar, modern problem. Plus, a gramophone horn has a certain character and style that impersonal speakers lack.

First Attempt

Unfortunately, graduation combined with my usual procrastination to mean I put off the project and eventually led to me doing a fairly shoddy job, which I was never happy with. The initial build was considerably simpler than the final version presented here; while I was thinking about how to construct it, a friend pointed out that the size of a headphone speaker that I’d dissected was roughly equal to the size of the opening to which the soundbox is normally attached. The quick application of some copper tape, araldite and silver paint later and I had a very basic working system. The problem was, it looked pretty ugly (I’d done my bets to sculpt the araldite, but it still looked remarkably like a blob), and the volume left a lot to be desired.

Not being particually proud of the result, it was only a matter of time before I decided to try again. Step one involved several hours with a heavy file to remove the araldite and everything else I’d added, which put me back at the starting point determined to do a better job.

Design and Build

For my proper design, I decided to focus on modifying the soundbox. The way the model of gramophone I have works is that the the record turns, causing a needle held in a groove to vibrate. These vibrations pass up the needle to the soundbox. Inside the soundbox, the end of the needle’s holder is connected to a thin metallic membrane about 4cm across; this is the first stage of amplification, as the vibrating needle causes the membrane to vibrate as well, producing faint sound waves which are amplified by the resonant quality of the small metal casing around the vibrating membrane. The soundbox is connected to the brass horn of the gramophone, which further resonates and amplifies the sound into what is that is then projected into the room.

My gramophone came with an HMV soundbox, the top plate of which is held on by three small screws. Removing these gave access to the inside, which I proceeded to gut, removing the tympanic membrane and snapping off the needle holder by wiggling it back and forth until the metal fatigued and broke, which left me with a hollow metallic container with a somewhat jagged hole at the bottom. At this stage I did some initial tests, confirming that a speaker inside the now-empty soundbox would give me sufficient volume without any additional amplification.

Obviously, I needed something to create sound, replacing the tympanic membrane. Fortunately, Maplin sell some nice thin mylar speakers, and I found the 55mm one suited me nicely; it’s be larger than the original foil disc because it has a solid frame and sits snugly inside the soundbox (whereas the foil could only be held in place by the needle holder, not touching the sides to avoid damping any vibrations), about 5mm closer to the front than the original membrane.

The next step was to smooth and enlarge the hole through which the needle-holder had entered; it was already quite large, so it didn’t take too much work with a small file to smooth it off. I also filed down the thread on the 3.5mm mono jack I planned to use as the input, so that it fitted snugly into the soundbox, leaving the connector poking out nicely.

Since the soundbox had some fretwork at the back and I didn’t particually want the wiring to be visible, I glued a circle of kitchen foil to a larger circle of paper, and glued it to the bottom so that the metallic foil was visible through the metal fretwork. A couple of pieces of carboard glued together provided a platform on which to rest the speaker (which otherwise had a tendency to rattle inside the box when closed up).

I recommend soldering a pair of wires to the jack before soldering/glueing the jack in place (you can push them through the hole as you slide the jack in); I didn’t, which required a degree of dexterity with a hot soldering iron (and some swearing) when it came to attaching said wires. I held the jack in place with the liberal use of superglue before slotting it in, bending the arms outwards so that they would resist any force pulling the jack outwards, and adding a couple of dabs of solder to make sure it wouldn’t budge. The only thing left was to solder the wires to the speaker, screw the top back onto the soundbox, and christen the project by digging out some Elgar for the occasion.

Volume: The volume is mostly good, though not quite perfect: if you plug in an iPod you were previously listening on headphones, then the volume from a meter or so away is a little less loud than when you had the earbuds in - you need to increase the volume a couple of notches to get it back to the same level. It’s only noticeable if you’re doing a direct comparison, though; the gramophone is perfectly able to fill a room at medium volume setting, and maxing out the volume on your portable player produces a suitably impressive racket. The loss is probably due to a decrease in the resonant properties of the soundbox caused by swapping out the tympanic membrane for a speaker. Without adding electronic amplification (which would pretty much ruin the whole point), the only way to increase the volume for a given input is to change the gramophone itself - my one is a cheap reproduction; a different horn might give more volume.

Sound quality: There is a notable difference between the sound produced by the gramophone and a normal speaker; while it’s hard to characterise the exact difference the music from the gramophone does seem slightly ‘flatter’, perhaps because the horn is amplifying the midrange more than the extremes. It’s not unpleasant, though, and definitely gives the output its own tone.

Looks: The final product looks very fine indeed - one advantage I hadn’t anticipated is that when not plugged in the protruding jack rests on the turntable rather like the needle would in a real gramophone (though to play it it has to be turned sideways to make room to plug in a device or extension cable). The only downside is that I’ve found the jack has a tendency to scuff the felt on the turntable, which has left a small but noticeable bare patch; I’ll probably add a discreet piece of plastic to rest it on at some point.

Extensions

Since I’m happy with the result I probably won’t make any modifications beyond this (though I can’t quite rule out a completely new project including a music player build into the base with some sort of archaic display and controls). There were a couple of ideas I had during the build that I discarded as unnecessary that others might want to incorporate:

Active Amplification: When I first started, I was concerned that I might not be able to get the volume I needed for a practical build (particularly with my original setup, where a portable music player needed to be turned up to its maximum volume to get a respectable sound out of the thing). If this had proved to be the case I anticipated adding a small amplifier inside the case, pulling the recharging component from a cheap wind-up torch or radio to power the amplifier (since the turntable is wound up with a detachable crank slotting in through the side). Fortunately it wasn’t necessary, so I didn’t have to dismantle the beautiful clockwork turntable drive.

Volume Control: Until quite a late stage I toyed with including a simple volume control sticking out of the back out the soundbox using a potentiometer. While it would have been a simple addition in the end I decided it was unnecessary since I’d just keep it turned to maximum (and none of the potentiometers I had on hand had a narrow enough knob to fit through the grill).

Conclusion

Overall I’m very pleased with the piece - it looks great, works well and was a very simple build, all things considered. One advantage this design has is that because only the soundbox has been modified it can be used with any gramophone sized to take an HMV soundbox without any need for modification or damage. The only problem now is that it’s pretty big, and takes up rather a lot of space in my flat.

via  http://www.r-hansen.com/tech/gram.html