AC motor noise & heat

[60goldtop]

First off, I’m new to the diy audio hobby and to be perfectly honest I’m not really all that knowledgeable when it comes to these things beyond a very basic understanding. I’m not trying to build a better mouse trap or best a $5k turntable and I could be totally “out to lunch” with this idea. I just like to tinker with things in my spare time.

I’m trying to build an outboard idler drive for a Rek-O-Kut B-12. The drive consists of a 7 watt Hurst LYD55 300rpm motor driving a live idler shaft, which runs in what is basically a miniature version of a platter bearing. The idler shaft is driven via mxl timing pulleys. The timing pulleys generate some noise, but a few globs of lithium grease minimized belt noise and since there’s no slippage they produce accurate speed. The outside edge of platter is driven by an o-ring drive roller. The final version of the drive would likely use custom round belt pulleys and a different motor to further minimize noise. The LYD series motor and the mxl pulleys were just a cheap and easy way to mock up and test the drive using off the shelf parts. Mechanically speaking the drive actually works pretty well. It spins the platter to 33.3 rpm almost immediately and maintains stable speed. I have yet to attach a tonearm, so as a crude way of testing the noise transmitted to the platter I put a small rta meter at the five o’clock position on the platter as close as I could without touching it. The measured difference between running and not running was .6 db. I don’t really know if that’s good or bad.

I’ve never used an ac synchronous motor for anything, so I have absolutely no experience. This particular motor seems to be fairly noisy and it gets quite hot. The motor noise seems to be primarily electrical, not mechanical. I don’t have any accurate way to test the temperature of the motor, but after running for 30 minutes it’s hot enough that you can’t comfortably hold a finger on it for longer than about five seconds. However, it never seems to get any hotter. I thought that it could be undersized, but it seems to get just as hot running alone as it does when driving the platter. Is this noise and heat normal for this type of motor?