Thursday, 10 May 2012

The Motor Spins and a New Layout

So, as mentioned last time, I had my Franken-prototype working again and I wanted to connect it up to a turntable motor to see if it will do as promised.  I made a simple connection of just one sine output to drive the motor's AC cord as per normal capacitor configuration (single supply, cap generated shift).  I connected it to a stock Ariston RD11 turntable.  It worked! the single channel could drive the motor no problem.  I left it connected for awhile to see how my small heat sink would do, it got kind of hot, so as I thought, a better heat sink will be needed.

New PCB Layout
Feeling happy and confident that the unit is working, I set out to re-design the PCB to include the added components and changes needed to fix my noise problems with the original PCB.  The new PCB is slightly larger and I took care to layout the sections differently.  The power supply is closer to the op-amp sections, the transformer hookups are all along the back.  I think this layout is better but the PCB is larger, now measuring 5x5 inches.  I also took care to increase the size of all traces carrying the power rails and the outputs from the op-amps.  You can see a picture of the 3D mock up of the PCB included here.  Also designed a small PCB for the front panel buttons and the RPM indicator LEDs (the fab house had a really good sale price for 5cmx5cm boards).

Button / LED Panel
So designing this new PCB was fun, it took some time as I tried being very careful with all traces, layout and hole sizes.  Now I just have to wait for them to come back from the fab house, and that is the hard part.



  1. I am watching, I am trying a TT build at the moment and motor speed is an issue. I am using a motor from a Dual 1228 (4 pole asynchronous, model SM400) that runs well, silent and smooth. I am going (read trying) to implement the idler drive on the outer rim of an old, heavy brass platter. Due to the differing diameters of the original and proposed drive I have issues with speed and as you state in the brief a motor controller will overcome these issues. However I live in a 240v 50hz country and wonder if your controller is adaptable to the differing international voltage? Once out of prototype will you be sharing details?
    Here is a link to my biuld so far:

  2. Hello Papa Hemi;

    Thanks for viewing the blog. I too am considering a Dual motor for some future turntable project. They are nice motors but do have a higher current draw than the Premotec types used by other manufacturers.

    One of the main goals of this project is exactly to be able to adjust rotation speed to compensate for idler/platter diameter differences in reaching exact speed. Thus for the DIYer, reducing the issues with critical sizing of platters and drive pulleys. So yes, the controller addresses these issues by allowing precise adjustment of the frequency to a precision of 0.01Hz. The effective range is currently between 32Hz to 140Hz. This should easily allow adjustment for the 33.3 and 45 RPM settings and to compensate for minor pulley ratios. As for voltage, I am currently working with 120V 60Hz design parameters, however it should be able to work easily with 220V 50Hz by using different value transformers. The design centres around L165 power op amps and these go to +-18V (this voltage is then stepped up by the output transformers to line level or can be used directly for low voltage AC motors), if more drive voltage is necessary perhaps using LM675 op amps may be substituted to increase voltages up to +-30V. There are two pots to adjust the output voltage levels in the design). I do have a 110V-220V step up transformer for some testing, and the 50Hz should be a non issue as the sine wave gets regenerated by the microcontroller. I have added software that allows the user to calibrate the frequency and store it in memory so that the system can default to the calibrated sine frequency. The design is meant to drive motors with about 3-5 watts or so at 110V, I am not sure what the wattage is on the Dual motors, that would have to be checked, they are considerably large motors. I also have a very nice motor from a reel-to-reel tape deck that is very nice and silent, big too.

    Once I am done the project (I sent out latest files to the PCB fab house the other day) I may make it available to anyone who is interested, maybe in a partial kit form. I will definitely end up with more PCBs than I can ever use. So if you follow along, just keep in touch and we can see how it works out.

  3. Papa;

    Just saw your blog, looks like a nice platter. I recently bought a platter&bearing from an older Pioneer turntable off of eBay, nice heavy platter and robust bearing for cheap - future project.

    I also happened to notice that the Dual motor schematic shows that it can be easily wired for 110V operation. That could be an option too, run it at 110V, coils in parallel as per schematic (which in my opinion would be better than running them in series, more independent of each other). So that would only require one transformed substitution from my design, the input transformer would be a 220V-20V unit or similar.

  4. Ok, I understand that.
    Have you seen the speed controller thrads on Lenco Heaven?
    I had been considering this butthey seem to have had some issues with the build, seemingly sorted now. I would prefer a foolproof build as while I am reasonably competent with a soldering bolt, I have had no experience with chips, and the idea of programming leaves me somewhat bewildered.
    The Dual manual states that the power consumption is >10w, but this will include the strobe, the cureent requirements are 64mA @ 220v 50hz, 115 mA @ 110v 60hz.
    Likely to be a starter?

  5. Papa Hemi, I have not seen the controller on the Lenco site before. I took a quick look at it. A bit different design philosophy for the generation of the sine waves. I chose to use a digital microcontroller to avoid potentiometers and analog parts generating the waveform, as well I wanted it to generate both sine waves, so no capacitor is needed on the motor for phase shift between coils (although it would be possible to just have a single output like the Lenco one if desired). So it is a bit different design from that point. The use of an output transformer to boost voltage is the same.

    I do have a Dual 1229 turntable here, so when I get the new boards in and running I can plug it in and see how it handles the current demands of the Dual TT.

    I am confident it should work, the op-amps I am using can handle up to 3A so it will be more a question of the the transformers and power supply section than anything else.

    In any case, if I make it available I would provide the microcontroller unit already programmed (and it is already mounted on it's own board, plugs into my PCB) so it would just be a case of assembly and put it in a suitable case.

  6. One other thing, Papa, I noticed on the Lenco unit that they us an LM3886 audio amp chip to drive the motor. I have decided to use L165 (or possibly LM675) power op amps, which are designed to drive motors.

  7. Cool - I'm all in favour of getting rid of capacitors (;-) - Thats why I prefer a full range speaker.
    This is looking good - my concern now may be cost.
    My project is definitley low budget. Teachers do not get paid that much in Aotearoa.
    I have been trying to solve the issue of idler wheel engagement for quite a while now, it is time I bit the bullet and made some prototypes - you can only think so much.