20. Project development

I wanted my record player to switch between a speed of 33 rpm and 45 rpm. I also wanted it to have its own built in preamp so that, when simply connected to a speaker via RCA cables, the turntable could easily play records. I have most of my documentation for my final project on my Final project page.

What tasks have been completed?

I’ve done a lot of research this past week. I found a really helpful online, open-source turntable linked to a Github page where the schematics are posted. This schematic is what I have already based my own schematic off of. Zach’s page has also helped me find the bearings that I wanted to use. They’re skateboard bearings and have a center diameter that is very similar to the center diameter of a spindle.

At this point, I have already completed about half of all the 3D prints I need to complete. I’ve designed and printed:

  • Casted foot holders
  • Spindle
  • 1” pulley (top measurements)
  • Large pulley

I’ve also:

  • Designed, created the toolpath for, and milled (on the Shopbot) my platter out of HDPE
  • Ordered and received my components from Newark (see my BOM)
  • Casted my three extra feet (I only casted one during week 10)
  • Ordered the bearings I will use for my tonearm and spindle from Amazon (arriving tomorrow, 9/13/2019)
  • Designed and milled my motor board (in Week 16)
  • Created the schematic and board files in Eagle based off of Zach’s files and am ready to mill and solder
  • Annotated Zach’s schematic so that I understand it better

What tasks remain?

As for 3D prints, I still need to design and print the tonearm mechanisms, which includes the tonearm base and the tonearm stand (where the tonearm will rest). I can only do this when the bearing arrives tomorrow. Similarly, I have to wait until the bearing arrives so that I can figure out the measurements of the bottom of the 1” pulley. The bearing has to fit very snugly into the tonearm base and the 1” pulley bottom, so I need it with me and have calipers to measure. I will also run test prints for the fit around the bearing. I also need to design and mill my base, which will be teardrop shaped. This should not take super long, as I just have to get the dimensions right, design it, throw it in Aspire, and mill it. Once I have my physical parts all organized, I must also assemble everything together. Thankfully, this should not take too long, as I am designing screw holes into all of my 3D parts, so all I have to do is screw stuff into my wooden base.

Most importantly, I still have to get my preamp board to work. This will probably be the part that takes the most time, especially since I don’t understand the components super well. So, I plan on doing research on the components, just to familiarize myself with what I’m working with.

What has worked? What hasn’t?

A lot of what I’ve done so far has worked decently well. I’ve pretty much taken up one of the 3D printers that works best at our lab, so I’ve only had one print fail so far (shoutout to my main 3D printer, da Vinci). I’m hoping that this track record continues. I did, however, struggle with getting the right tolerance and angle for the top of the 1” pulley. I wanted it to fit into the design of the platter (aka fill the empty space that was removed by creating the design on the platter), but it was super difficult getting the proper tolerances. I eventually got it after maybe 3 test prints. I also ran into problems when I design the casted foot holders and the screw holes. Originally, I used Fusion to design little tabs that had screw holes so I could screw the feet onto the wooden base really easily. Unfortunately, the first time that I designed it, I made the rectangle around the screw hole circle too small, and I was scared that the PLA would snap when I would try to screw in the foot holders. So, I went back and designed foot holders so that the screw holes were more stable.

In general, most of the things I’ve done so far have worked out really nicely.

What questions need to be resolved?

I still need to understand the components I’m using (from Zach’s schematic) better and understand the schematic as a whole better. I have a suspicion that I do not need the sections of Zach’s schematics that deal with the motor and the autostop function, but I’m scared that removing whole chunks of the schematic will negatively affect the parts of the schematic that I really need (the preamplification components, power jack, and RCA output).

What will happen when?

Since the bearing will likely arrive tomorrow night, I can work on the designs that need bearing measurements (1” pulley bottom and tonearm base) on Friday 6/14/2019. I may be able to print one of those designs on Friday, or I might have to wait until Sunday 6/16/2019 (I’m not going into the lab on Saturday). I will also remove the tonearm from the existing record player that I have when I design the tonearm base. I will need to see what is actually connected directly to the tonearm in this record player I have and what isn’t then design around what I have.

I will design, create the toolpath for, and mill my base on Monday. It’s really a quick thing that I have to do, and I’d rather get my electronics figured out first before I move onto that.

My main priority for the upcoming days is getting the preamp to work. Even if everything else works but the preamp doesn’t, there’s no point to my record player.

I will assemble everything on Monday 6/17 and Tuesday 6/18. On these days, I will also document, create my slide. and create my video.

What have you learned?

I’ve learned a bunch of random things during the past week, including…

the units of capacitors and how they are interrelated. I found that Farads (the “f” in “uf” or “nf”) were not a super applicable unit when they were discovered, so the more practical micro, nano, and pico farads were more commonly used.

how to use a switch as just on or off. Mr. Rudolph explained to me that using the middle and one end pin of a 3 pin switch enables it to just be on or off. The last leg of the slide switch should be cut and covered with electrical tape or soldered down onto the board, with its pad not connected to any trace.

the RCA cables are color coded as follows: red = right, white = left, and black = GND. It’s quite annoying that they decided to use white as the left color. In the beginning, I had to keep on checking which was ground: white or black.