Hello! It's been a long time since I've visited this forum. I started getting busy with other hobbies instead of audio. But, it's great to be back! I see not much has changed with the layout and color scheme. 
Enough reminiscing. Here's the background... I'm an engineer at a company in LA where we build bizarre projects. The latest project that landed in my lap is to build "The World's Largest Record." According to Guinness, that record is a normal sized 78. Our client is a charity (musack.org) so the budget isn't huge. Right now I'm deciding between a 6' and a 4' diameter record. The decision will come down to whether we can get a big enough piece of plastic to cut.
Here's how I'm approaching this:
Here's where I need help.
Any ideas on how to cheaply improve the design? Anyone have a record lathe that they don't mind us ripping apart a bit (hopefully non-destructively)? We're in LA and we're looking for help. This could be an awesome project, and as a pseudo-audiophile I want it to sound as good as possible.
The event where it will make it's debut is in August.
Thanks in advance...
Enough reminiscing. Here's the background... I'm an engineer at a company in LA where we build bizarre projects. The latest project that landed in my lap is to build "The World's Largest Record." According to Guinness, that record is a normal sized 78. Our client is a charity (musack.org) so the budget isn't huge. Right now I'm deciding between a 6' and a 4' diameter record. The decision will come down to whether we can get a big enough piece of plastic to cut.
Here's how I'm approaching this:
- Build a big turntable with a belt driven motor. Large, quiet bushings instead of ball bearings. The RPM will be controllable so we can achieve the correct needle-speed.
- Cut a big disc out of an appropriate plastic. It might be hard to get vinyl that big, but other plastics seem to work well in the DIY world. The black color would be a huge aesthetic win for the project.
- Either modify an existing record lathe (if we can find one!), or create our own lathe cutting head, DIY style.
- Control the head's path across the record with a dc stepper motor and an acme screw.
- Cut a largish groove in the record. We'll need stability for tracking for our large tone-arm.
- Use a normal needle for playback on a long, light tonearm.
- Hopefully succeed with decent sounding music on playback.
Here's where I need help.
Any ideas on how to cheaply improve the design? Anyone have a record lathe that they don't mind us ripping apart a bit (hopefully non-destructively)? We're in LA and we're looking for help. This could be an awesome project, and as a pseudo-audiophile I want it to sound as good as possible.
The event where it will make it's debut is in August.
Thanks in advance...
for test discs "laquers" or "acetates" were often cut for immediate playback: Acetate disc - Wikipedia, the free encyclopedia
whether any working/restorable cutting heads are affordable with all the recent interest in boutique vinyl is another question
whether any working/restorable cutting heads are affordable with all the recent interest in boutique vinyl is another question
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The record groove has to be the same size as on an LP, or the stylus won't be able to function.
Have you seen the Vestigial arm? Maybe something like it, or else a straight-line tracking arm
would be better for this.
http://www.vinylengine.com/library/transcriptors/vestigial.shtml
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Record companies cut into the lacquer coating on a metal plate (not the metal itself), and make a make a mold from that, in order to press thousands of records. That's not our workflow here. We just need to cut the same record we'll be playing. Only one side of one record needs to work for everyone to be happy. Cutting vinyl is indeed what people do. In fact they sell vinyl blanks to people for exactly this purpose. Here's a German company for example: Information
We won't be cutting a crazy deep groove, just on the deeper side of normal. I managed to get a record cutting pro on the phone (he's too busy now, it seems) and he was suggesting to do this. Usually groove depth is a function of volume, recording length, bass levels, etc. We've got a lot of area to play with on this big record, so we can afford to go deepish throughout.
I'm wondering if a linear tracking arm might ruin the aesthetic just a bit. The client isn't crazy picky or anything, but it would bother me just a bit. The more recognizable the device is as just like the one from grandma's place, just bigger, the happier I will be. It's gotta hit just a bit of a nostalgia button for people. If a linear tracking arm solves some major problems, though, that might be worth doing.
I think you'll have more than a bit of trouble getting such a long tone arm to work at all with any available cartridge.
Cartridges are designed for arms with parameters not in a much longer arm.
The long tone arm will have higher "mass" (actually moment of inertia referred to the stylus tip) than a standard one,
even if the long tone arm could have zero weight. This is because of the cartridge's own mass being so far from the pivots.
The LF resonance will be much lower than usual, and there will be a lot of subsonic output due to warps, etc.
This is why I suggested that you look at the Vestigial arm design, with the vertical pivot near the head shell,
which raises the vertical LF resonance instead of lowering it. Or, a straight-tracking arm, which would be shorter.
Also, if you don't have an offset angle for the cartridge at the head shell, the distortion will be much higher.
Scale up the standard Baerwald alignment according to the large record size if you can use a pivoted arm with offset.
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Rayma,
Great suggestions! I had to look through google images of the Vestigial arm, but I see what you're talking about. The vertical pivot point is right at the cartridge... I see how that could help. My original idea was to use counterweights to bring the needle pressure down, but I can see what you're saying about that decreasing the resonant frequency. Wouldn't that make it easier just to filter out the extreme low end?
I'll have to figure out the right angle for the cartridge to be cocked at to get the right Baerwald alignment.
Thanks, you've given me a lot to think about.
Great suggestions! I had to look through google images of the Vestigial arm, but I see what you're talking about. The vertical pivot point is right at the cartridge... I see how that could help. My original idea was to use counterweights to bring the needle pressure down, but I can see what you're saying about that decreasing the resonant frequency. Wouldn't that make it easier just to filter out the extreme low end?
I'll have to figure out the right angle for the cartridge to be cocked at to get the right Baerwald alignment.
Thanks, you've given me a lot to think about.
Yes, it would be easier to filter, but the stylus would be working mechanically too hard.
Counterweights would actually make the situation much worse.
The Vestigial arm could track almost anything at a very low VTF. Shures ran at 3/4 gram just fine.
Unless, of course, the bearings seized up, which they sometimes did.
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If Edison could do it, he can. Too bad Doug Sax isn't around any more, he would have liked this project.
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How big the record player and record would be ? One can 3d print a music record. Here is the link. I don't know if one can equalize to improve the sound quality. I read somewhere in the forum itself of making a DIY phono cartridge. So if one can make a big cartridge a larger groove can be modulated with 3D printing.
Regards.
Regards.
The high frequency response of a scaled up player like that would be very poor, and stereo would likely
be out of the question.
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