Re: Guy's Turntable
Posted: August 1st, 2013, 11:42 am
Drive System and Motor Enclosure, Part 2
Online forums also had a lot of suggestions for motor power supplies. Mark Kelly from Australia wrote a great article in an on-line publication from BasAudio.Net called DIYMAG. (Go to http://basaudio.net/blog/diymag/ and look for “early 2006.”) In the back of the publication was 10-page article about AC and DC turntable motors and how to drive them. Mark’s article impressed me, and he certainly understood more about platter drive than I, so I used his design for a DC motor driver with error correction.
There used to be a kit marketed by diyAudio.com for the controller, but it was no longer listed. Instead I laid out a PC board using Kelly’s circuit (see Figure 23). I still have a couple PC boards left from my first run.
Figure 24 shows the controller board mostly loaded with components. The op amps (U3, U4) and voltage reference (U2) have not been plugged in, and the resistors that set platter speed as also missing. The pots (R7, R27) that adjust platter speed were actually mounted on a piece of perforated board and suspended below the top of the motor enclosure so platter speed could be adjusted while the enclosure was assembled (see Figure 22).
John Parker of Choir Audio indicated that I needed a belt material that addressed two major points:
John preferred round belts because they addressed both points. He also suggested that I try 3/16”- and 1/8”-diameter belts, which he was able to provide once I used a piece of string to determine the length of belt I needed, which turned out to be 45”.
Now for a pulley: There is nothing like friends. One of mine made a bronze ¾ ” diameter pulley with a ½”-diameter groove for the pulley (see Figure 25). The groove had a 1/8” radius (so my round belts would fit nicely and maximize contact) that was located 3/8” from the bottom of the pulley, and the edges were flared at 45° so the belt wouldn’t get pinched. The pulley had a 3mm hole drilled ¼“ into the bottom, and was glued to the Maxon motor shaft to drive the platter using a round-cross-section rubber belt.
Copyright 2012 Guy W. Riffle. All rights reserved.
Online forums also had a lot of suggestions for motor power supplies. Mark Kelly from Australia wrote a great article in an on-line publication from BasAudio.Net called DIYMAG. (Go to http://basaudio.net/blog/diymag/ and look for “early 2006.”) In the back of the publication was 10-page article about AC and DC turntable motors and how to drive them. Mark’s article impressed me, and he certainly understood more about platter drive than I, so I used his design for a DC motor driver with error correction.
There used to be a kit marketed by diyAudio.com for the controller, but it was no longer listed. Instead I laid out a PC board using Kelly’s circuit (see Figure 23). I still have a couple PC boards left from my first run.
Figure 24 shows the controller board mostly loaded with components. The op amps (U3, U4) and voltage reference (U2) have not been plugged in, and the resistors that set platter speed as also missing. The pots (R7, R27) that adjust platter speed were actually mounted on a piece of perforated board and suspended below the top of the motor enclosure so platter speed could be adjusted while the enclosure was assembled (see Figure 22).
John Parker of Choir Audio indicated that I needed a belt material that addressed two major points:
- 1. Properly transfer energy from the drive pulley to the platter without slippage or expansion (stretch).
2. Low-Noise Operation: Surface area causes friction, and friction causes noise and unwanted energy (vibration).
John preferred round belts because they addressed both points. He also suggested that I try 3/16”- and 1/8”-diameter belts, which he was able to provide once I used a piece of string to determine the length of belt I needed, which turned out to be 45”.
Now for a pulley: There is nothing like friends. One of mine made a bronze ¾ ” diameter pulley with a ½”-diameter groove for the pulley (see Figure 25). The groove had a 1/8” radius (so my round belts would fit nicely and maximize contact) that was located 3/8” from the bottom of the pulley, and the edges were flared at 45° so the belt wouldn’t get pinched. The pulley had a 3mm hole drilled ¼“ into the bottom, and was glued to the Maxon motor shaft to drive the platter using a round-cross-section rubber belt.
Copyright 2012 Guy W. Riffle. All rights reserved.