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DOD Mixer Power (34 V)

Discussion in 'Power Electronics' started by Joby Wilhite, Feb 26, 2018.

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  1. Joby Wilhite

    Joby Wilhite

    8
    0
    Feb 26, 2018
    Hello all,

    I inherited a old DOD mixer from my Dad and I'm trying to revive it. It is missing the power supply and I am having a real hard time locating something that would work. The power requirements on the back say (34 Volt ~ CT 50/60 Hz 1 Amp). It is also a 5 pin DIN connector. I have attached the schematic from DOD here. Any ideas on a replacement? Or will I have to build one?


    Any help would be greatly appreciated.


    Thanks - Joby
     

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,816
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    Nov 17, 2011
    You'll need a transformer with 2 secondary windings, 15 V each or one secondary winding 30 V with a center tap.
    The center tap or the common connection of the 2 windings goes to H2B/HDR3. The two remaining transformer outputs go to H2A/HDR3 and H2C/HDR3 respectively.
    Unless you get hold of an original power supply it i is unlikely you find a matching off the shelf unit. You can easily build your own, provided you fear not dealing with mains.

    We have a thread with almost identical content (regarding the power supply) here. You should find all the information you need in that thread. Feel free to ask if something's missing.
     
  3. Joby Wilhite

    Joby Wilhite

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    0
    Feb 26, 2018
    Last edited: Feb 26, 2018
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    11,816
    2,755
    Nov 17, 2011
    #1 is no match, it is rated at 1.2 VA only.
    #2 is much better, but at 25 VA still not adequate.
    Your specs (24 V, 1 A) call for at least a 34 VA transformer. I can't find a perfect much quickly. This transformer is rated 50 VA, a bit oversized but well up to the job.
    Digikey has better fitting transformers but obviously not on stock :(

    Search your favorite dealers using teh following specs:
    input voltage 115 V
    output voltage 2 * 15 V or 30 V with a center tap
    rated power 35 W (VA) or more
    mains frequency 60 Hz.
     
  5. WHONOES

    WHONOES

    1,181
    319
    May 20, 2017
    Don't forget that you will have to rectify, smooth and regulate the result otherwise you will blow the nuts out of it if you will pardon the expression.
    If you need any more info, ask.
     
  6. Joby Wilhite

    Joby Wilhite

    8
    0
    Feb 26, 2018
    Thanks guys. I am lost with all of this. I found a crimp terminal DIN plug that will work and I am working on finding the right transformer, but as far as smoothing, rectifying or regulating... I am at a loss. This is all new to me. I am afraid that I will need a step by step idiots guide to putting this together. Even the thread shared above left out too much for my feeble mind to comprehend. I may have to take it to someone to build for me.
     
    Last edited: Feb 26, 2018
  7. dave9

    dave9

    1,147
    311
    Mar 5, 2017
    Not in this case. Take a look at the linked schematic. The original power supply "might" have fuse and AC line filtering on the input before the transformer, but as far as smoothing the output goes, it is just taking a center tapped transformer and sending the AC to the mixer which has its own bridge rectifier, smoothing capacitors, then LM7815/LM7915 for the +/- power rails.

    Considering that these rails are regulated, there is flexibility here, a lot of it. It could be as cost effective as anything to just put two identical 15VAC 1A transformers in series and center tap between the two.

    Given a lot of time I could probably find the best value online, but another glance at the circuit tells me that it's probably not even necessary to shoot for 1A current capacity as it's just outputting to line level and driving (a single pair of) headphones.
     
    Last edited: Feb 27, 2018
  8. dave9

    dave9

    1,147
    311
    Mar 5, 2017
    It seems the world has moved on to SMPS and not so many deals left to be had for good ole E-core transformers. A ~dozen years ago I bought some that would have worked for $2.49 each as new surplus, but those days are gone.

    Today the main two options I'm seeing that are most cost effective are buying two 16VAC wall plugs and tearing them open for their transformers and wiring their outputs in series, but that's fiddly and then you need to make frames to mount the transformers, or the following $20 + S/H toroidal:

    http://www.surplussales.com/item/_tp/62073-p2s02.html

    For that, see the PDF linked below it on the page for specs and wiring.
    http://www.surplussales.com/Transformers/Pdfs/Actuant_Amveco_25.pdf

    Briefly it reads "To connect the secondaries in series, the red and brown wires are connected together. Take the output across the green and
    blue wires".

    That means you would do that, connect the red and brown together, then connect either the green or blue wire to H2A on your schematic, then connect the other of the two (green or blue wire) to H2C, then you would connect the red-brown connected wires to one wire going to H2B on the schematic.

    ... or here's another similar transformer at $27:
    https://www.parts-express.com/avel-lindberg-y236103-30va-15v-15v-toroidal-transformer--122-605

    ... or MPJA has some 20VAC for $7 each and you could put two of those in series but the extra work for not much money saved, meh.
     
    Last edited: Feb 27, 2018
  9. Harald Kapp

    Harald Kapp Moderator Moderator

    11,816
    2,755
    Nov 17, 2011
    That's all part of the mixer, see lower left corner of the schematic in post #1.
     
  10. WHONOES

    WHONOES

    1,181
    319
    May 20, 2017
    Yeah you're right. Must confess I only took a quick glance at the schematic and clearly missed the supply circuit.
     
  11. Joby Wilhite

    Joby Wilhite

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    Feb 26, 2018
    Wow, great info here. Thanks guys. I had someone tell me to take it apart and look at the regulators to see if they are mounted on heat sinks. Apparently that would help determine what VA the transformer should be? Is that something I should worry about? Also, just so i'm clear... All I need for this is the transformer, a fuse, a DIN connector and a power cord?
     
  12. Harald Kapp

    Harald Kapp Moderator Moderator

    11,816
    2,755
    Nov 17, 2011
    Not at all.
    is the parameter you're looking for. 34 V * 1 A = 34 VA, Easy as pie.

    Not to forget a suitable case, preferably an insulated one (plastic).
    Power inlet, fuse and filter can be bought as an assembled unit, cf. my link in post #2.
     
  13. Joby Wilhite

    Joby Wilhite

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    0
    Feb 26, 2018
    10-4. Thanks again. I will post some pics when i get it done.
     
  14. JWHassler

    JWHassler

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    17
    Dec 22, 2014
    The attached schematic is called 'Mixer Power Supply'
    Seems to me that the entire circuit- headphone amp, tape out out and rectification/filtering - is what is missing.
    The mixer itself is probably a crapton of opamps and slide-pots, all connected to header H1 with a flat cable
     
  15. Harald Kapp

    Harald Kapp Moderator Moderator

    11,816
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    Nov 17, 2011
    Attachment is missing :(
     
  16. Joby Wilhite

    Joby Wilhite

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    0
    Feb 26, 2018
    So, the secondaries will be in series. Is that going to work with the primaries since they have to be in parallel for 115 volt operation?
     
  17. Harald Kapp

    Harald Kapp Moderator Moderator

    11,816
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    Nov 17, 2011
    It will. Primary and secondary are electrically isolated from each other.
     
  18. Joby Wilhite

    Joby Wilhite

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    Feb 26, 2018
    10-4. Will be wiring it up tonight. I am attaching a sketch I made based on what we've discussed. Last chance to save a possible house fire. If you see something wrong here, please let me know. The square represents the fused power inlet.
     

    Attached Files:

  19. Harald Kapp

    Harald Kapp Moderator Moderator

    11,816
    2,755
    Nov 17, 2011
    According to the avel-lindberg datasheet you linked in post #8 the wiring should be:
    upload_2018-3-3_15-56-14.png

    I'm not sure which transformer you use.
     
  20. Joby Wilhite

    Joby Wilhite

    8
    0
    Feb 26, 2018
    Thank you all for the help. The wire colors are not the same as the diagram, but i was able to figure it out. She is alive!
     

    Attached Files:

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