Tone arms, cones and re-plinthing.

November 13th, 2010

Work continues on the steam gramophone record player thing. It takes a while since 1, I have never made one before and 2, I am totally making it all up on the fly as I go along.

I started trying to work out how to do they tone arm and audio pickup. My first idea was a totally manual old style gramophone. I came up with the idea of using copper water pipe and fittings to make a traditional mechanical pick up. First I took an old wooden baluster left over from another project and chopped a piece out to make a tone arm plinth. Then I machined up a piece of scrap plastic I had to make a bearing carrier for yet another skateboard bearing. Into this fits a piece of brass tube to which I had soldered a copper water pipe fitting.  I assembled a collection of copper parts to mock up the arm on the plinth.

IMG_9002_1 IMG_9004_1 IMG_9008_2 Copper tone arm and original plinth.

The copper arm and pickup head (made from left over boiler tube copper) I liked but the plinth wasn’t right so it had to go. I made a new plinth from some scraps of wood I had.

IMG_9013_1 After re-plinting.

I went ahead and soldered together the copper tone arm and pickup. The pickup is a section of pipe with a brass bottom soldered to one side and a brass ring to allow me to stretch a paper diaphragm over the  other, open end. To this I would attach the needle to run on the record.

IMG_9019_1_1 Pick-up and ring.

The pickup head has a 90 degree pipe fitting soldered into the side of it for the sound to pass from the pickup. Since the pipe fittings are all designed to slide into each other I was able to cut a slot in the pickup tube and create a pin from a screw in the end of the tone arm. This held the pickup to the arm and also allows it to rotate partially.

IMG_9018_1_1 Copper pick up arm pieces.

IMG_9021_1_1 IMG_9023_1_1 IMG_9026_1_1 IMG_9027_2 Pickup.

When it was all done it was a really lovely looking thing. Pity it didn’t bloody work! I tested it with some paper as a diaphragm and tried it on the platter. Unfortunately it is so heavy it creates too much drag on the record and I actually ended up killing part of my $1 test record (bought from the local charity shop) with it. I thought the needle was picking up a lot of fluff until I realised no, that was shavings of vinyl being cut from the LP! This should all have been obvious to me since I know how to set up a normal turntable arm and balance it. I think I was so pleased with how it looked and worked I just wanted to try it anyway.

So, back to the drawing board. Instead of a heavy metal arm I decided to see how things would work with a light weight paper cone. I removed the heavy copper arm and replaced it with a metal ring in a kind of gimbal arrangement. Into this I could insert a paper cone, with a sewing needle in the pointy end, that would then follow the grooves in the LP. This actually works reasonably well.

IMG_9031_1_1 Gimbal mount for paper cone.

I don’t have a picture of the actual cone but I did film the result and put that up on YouTube as usual.

The sound, although there, is not very loud. Certainly not loud enough to be clearly heard over a noisy steam engine rattling away right next to it. I did some experiments with a small electret microphone hooked to a small amplifier. I put the mic right in the end of the cone and that would amplify the sound quite a bit but the quality was rubbish and if I put the speaker anywhere near the cone or mic I would get acoustic feedback. I also tried different needles and even a piece of sharpened bamboo (as used in the Gakken gramophone kit). None of it really helped.

The other problem is the sewing needle does horrible, horrible things to the records! I do have an old ABBA LP and the soundtrack to Saturday Night Fever in my record collection that probably deserve it but I just can’t bring myself to destroy vinyl with a sewing needle like that.

So, another rethink was in order!

Today I wandered along to my favourite junk shop (for those in Auckland it’s on Upper Queen Street just over the hill from Surplustronics – it’s the place that looks like a bomb has gone off in it) and had a hunt about there in their boxes of old tone arms. I was looking for an old stylus and cartridge to test out. The helpful but completely bonkers chap there helped me out and, from a secret stash, found me an old Philips head-shell/cartridge and stylus.  It’s an old GP204 if that means anything to anyone. I came home and soldered on some wires that I then plugged into my existing phono pre-amp and stereo. I then just hand held the head-shell over a record and turned the platter by hand. And that works! Worked very well in fact. Basically just the same as any other record player.

So, I needed to redesign my tone arm to take a normal turntable cartridge. I removed the cone ring and reused the brass axle. I cut a smaller ring from some scrap brass to make a new gimbal. The actual arm is a length of brass tube I found in the junk box. The gimbal ring rotates in the skateboard bearing in the top of the plinth. I soldered a brass tube through the tone arm and used two brass interconnects and a length of threaded rod cut from a machine screw to make the vertical pivot that allows the arm to move up and down.

IMG_9053_1 IMG_9058_1 IMG_9052_1 Brass tone arm.

The counterweight was an amazing find. I was looking though my junk for something suitable to use as the weight on the end of the tone arm. My original though was to melt down some of the brass tyre weights I have collected over the years (I can’t not pick those up off the road when I see them I am afraid) and machine a little cylinder to slide over the end of the arm. Rummaging about though I came up with something better. It is a part of a machine found in a lot of workshops. This one was faulty so I had removed it and thrown it in the junk box. I just cut off the end and found it was perfect for the job. Here are some picture of it after I modified it.

IMG_9016_1 IMG_9054_1 Counterweight.

Know what it is yet? It’s an air compressor hose quick disconnect. They are used on the compressor and on air hoses to allow you to quickly connect things up and disconnect them again. There is a ring of ball bearings inside the connector that usually clip into the matching fitting on the air tool. By sliding back the other ring you release the balls which spring back allowing the connector to pop off. It turns out the hole in the middle of the connector is the exact same diameter as my tone arm. So the connector slides nicely over the end of the arm. The ball bearings also grip the arm so the weight won’t move on the arm unless you slide the outer housing back to release the balls. It is also almost the exact right weight. You change the balance by sliding the weight closer or further away from the pivot.  Without a cartridge on the end of the arm it balances perfectly.

Now, the stylus. This is where I have stopped for now while I decide what to do. My old cartridge and stylus from the junk shop (cost $10) do work so I should probably use them. But I also like the idea of getting a more modern and standard cartridge. Unfortunately these aren’t cheap and this project is meant to be made from junk where possible. I think what I will do is compromise and spend a few dollars to get a piece of brass tube to slide inside the arm. Then I can make a removable head-shell for it. I can start by attaching my junk parts then later, if I feel the need, I can make a new head-shell for a modern replacement cartridge/stylus.

There have a been a few other things done. I have tested driving the platter from the engine on air and I worked out the proper drive ratios needed. And I am working on enhancing the wooden base of the whole thing to make it look better and be more practical. I have also fitted 6 magnets around the rim of the platter and worked on the speed detection. I don’t yet have photos of all that so that will all be in the next update. Lots to do this weekend!

One Response to “Tone arms, cones and re-plinthing.”

  1. Asciimation » Blog Archives » A steampunk record player. Says:

    […] original plan was to use an old fashioned gramophone style pickup and horn. Unfortunately this didn’t work! So I went instead for a more conventional tone arm and pickup arrangement with the sound played […]