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DDS turntable power supply: how to power the motor

Discussion in 'd.i.y.' started by hi-fi132, May 23, 2021.

  1. hi-fi132

    hi-fi132 pfm Member

    I'm thinking of building a turntable power supply based on readily available AD9833 breakout modules. The AD9833 is a DDS waveform synthesiser that is easy to control with a microcontroller such as the Arduino. I was planning to use 2 of them, 1 per phase.

    The motor to be driven will be either the 12V or 24V Premotec 9904 series ac synchronous motor as used in countless belt drive decks. The AD9833 modules output about 600MV peak to peak. Is n ordinary chip amp the optimal solution to boost the output to drive the motor or is there a better way? If I went with an amplifier, can somebody advise how I would calculate the power requirements to work out the optimal solution where price, performance and power are all considerations?

    I have looked at other projects including the Sincos and Meldano but I want to build something that better suits my requirements than either. Software is however my forte, not hardware. Any advice, and links to other designs greatly appreciated.
     
  2. chartz

    chartz If it’s broke fix it!

    Perhaps you should go DC ?
    AC motors are now part of turntable history.
     
  3. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    A chip amp should work just fine yes. The main decision then is 12V or 24V motor... Whilst the motor will not need more than a few Watts the RMS voltages mean that for 24V motor a 100W amp would be appropriate whilst for the 12V motor a 25W amp would do it. As not much actual current is needed the power supplies do not need to be rated for anything like that which you would use if actually driving 25 or 100W into a speaker and can be "cheap and weedy" . I would tend to sway towards the 24V motor for reasons of lower current involved and higher resistance load etc. IIRC ST Microelectronics do a 100W chip amp.
     
  4. Vinny

    Vinny pfm Member

    Take care - 600 mega-volts is going to need quite some guarding/insulation ;):)
     
  5. radelius

    radelius pfm Member

    Good idea to use AD9833 I think. Is it 90 degrees face difference between the windings on the motor?
    /S
     
  6. hi-fi132

    hi-fi132 pfm Member

    In theory yes, but no two motors are identical. Adjusting the phase angle can drastically reduce vibration to almost imperceptible levels.
     
  7. hi-fi132

    hi-fi132 pfm Member

    Thanks for your input. Can you give me an idea of what I would need, or how I would calculate the PSU requirements to run a 100W chip amp in this scenario and do you feel that a linear PSU would be a benefit over an SMPS?
     
  8. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Any old power supply that can give +50V and -50V will do fine. Quality doesn't matter. The smallest mains transformer you can get should be adequate and as as low as 2200uF smoothing caps will be fine. You would be using a 100W IC to get sufficient voltage swing for the 24V motor but will only be using maybe 3-8W or so from the amplifier. It will be like driving a 100 Ohm speaker!
    A 35 - 0 - 35V or 2 x 35V transformer is what you need and the smallest rating that will be really commonly available will be 160VA, which will be enough to power 10 TT motors!
     
  9. sq225917

    sq225917 Bit of this, bit of that

    Google meldano motor controller, all you need on one pcb, USB controlled, rpm to 0.001rpm, phase to 0.01 degree, voltage via trim pot. Records total run time and has adjustable start and stop ramping.
     
  10. geoturbo

    geoturbo pfm Member

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