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  1. #1
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    Default ADA8000 External Mains Power Modification

    I posted this as a follow-up to my SAC rig case build-out, but thought it might be useful as a standalone posting.

    Furman ADA8000 Power Strip Modification

    My initial thought was to add some fan cooling to the ADA8000 along with case ventilation. There have been a number of variations on this to lower the stress and heat on the voltage regulators. The mod shown from the German posting was rather silly, as adding a fan to a sealed case does almost nothing to improve heat dissipation, other than to distribute the heat throughout the inside of the case.

    I figured I would add a case fan to the side and cross ventilate, or add ventilation holes in the case bottom and lid to allow for air flow. This idea rapidly passed, as there is insufficient space on the sides of the case to mount a fan or to allow for proper airflow.

    Adding ventilation top and bottom was also problematic as the holes would need to line up perfectly top to bottom to allow multiple units to stack.

    Instead I decided to go the "lower the mains voltage" route. Instead of creating a separate box for this, I built it into the Furman power strip. Isolating 4 of the strip plugs for ADA8000 use.

    CLICK images for Larger View:



    The transformer cost about $20 and is a 110/220 Primary to Dual 25V Secondary. I was going to get a dual 12V model, but they didn't have any in stock. The transformer is rated at 1.25A on the secondary, which translates to about 140 Watts, which is more than enough to handle 4 ADA8000 with room to spare.

    What I discovered in the first pass however was the voltage dropped too much. With a 118V mains source, I was only getting about 89V to the ADA8000s which proved too low and the power supply fell out of regulation.

    This created a slight 60Hz buzz in the audio path.

    Since the transformer was a dual primary (110 or 220) I modified the circuit adding a switch to allow for full or reduced power, and a second switch to select the voltage reduction (-12.5v or -25V).

    This worked out perfectly. See additional pictures below.



    The end result was at -12.5v the ADA8000s are perfectly clean (no buzz) and definitely run much cooler. I may order a 20V transformer instead and switch it out as the -25V is probably overkill. (although would work where the mains voltage is 120V or higher).

    The Transformer is available through Farnell. They have distributors worldwide through various different website names.

    This is the one I purchased: (110/120 Pri / 2 x 25v Sec)
    http://us.element-14.com/multicomp/m...78?Ntt=38K4878

    For those interested... here is the schematic

    Last edited by cgrafx; 01-24-2013 at 11:20 PM. Reason: Added Schematic

  2. Default Re: ADA8000 External Mains Power Modification

    This one would probably work just as well.

    http://us.element-14.com/multicomp/m...mer/dp/38K4872

    It's the 18 volt model. Since the voltage differential is reduced the current draw is also reduced.

    This one is rated at 50VA and it's only a couple of bucks more.

    http://us.element-14.com/multicomp/m...Ntt=MCTA050/18

    I like how you modified a power strip. That is cleaner than the 120 -100 volt converters.

    A wiring diagram would be nice.
    Last edited by Yogi; 06-21-2010 at 10:17 AM.

  3. #3
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    Default Re: ADA8000 External Mains Power Modification

    Quote Originally Posted by Yogi View Post
    This one would probably work just as well.

    http://us.element-14.com/multicomp/m...mer/dp/38K4872

    It's the 18 volt model. Since the voltage differential is reduced the current draw is also reduced. I like how you modified a power strip. That is cleaner than the 120 -100 volt converters.
    It seemed like a good idea as there is room for the transformer in the case.

    Plugs, grounding, filtering, and case are all already there, and it only adds the weight of the transformer (about 1 lb) to the box.

  4. Default Re: ADA8000 External Mains Power Modification

    pretty slick....
    intel e8400, intel dg41ty mobo, 4gigs Corsair ddr2 800 ram, rme digi9652, 3x ada8000

  5. #5
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    Default Re: ADA8000 External Mains Power Modification

    Very nicely done!
    Richard B. Ingraham
    RBI Sound
    http://www.rbisound.com
    Email Based User List: http://tech.groups.yahoo.com/group/sac_users/

  6. #6

    Default Re: ADA8000 External Mains Power Modification

    I just had to take my ADA8000 to the bench and run some tests. The 15 volt rails fall out of regulation when the input AC drops below about 90 volts. With my converted control transformer in the circuit to drop the voltage, (about equivalent to the 24 volt transformer wired "bucking" as recommended), the line voltage must not drop below about 110 volts. This makes me think I need to look for a smaller voltage drop as a compromise. At the moment I am leaning towards maybe an 18 volt transformer.
    Cary B. Cornett
    aka "Puzzler"
    www.chinesepuzzlerecording.com

  7. #7
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    Default Re: ADA8000 External Mains Power Modification

    Quote Originally Posted by Cary B. Cornett View Post
    I just had to take my ADA8000 to the bench and run some tests. The 15 volt rails fall out of regulation when the input AC drops below about 90 volts. With my converted control transformer in the circuit to drop the voltage, (about equivalent to the 24 volt transformer wired "bucking" as recommended), the line voltage must not drop below about 110 volts. This makes me think I need to look for a smaller voltage drop as a compromise. At the moment I am leaning towards maybe an 18 volt transformer.
    If you get either a dual primary or dual/center tap secondary its easy to wire up with a switchable bucking voltage.

    If you look at the diagram in my original post, you will see I have -12.5V and -25V options.

    If I were going to build a second unit however, I think I would opt for a lower secondary range, probably 18V or 20V instead of the 25V I used.

    And yes, your right the power supply starts to drop out of regulation right around 90V.

    pg

  8. #8

    Default Re: ADA8000 External Mains Power Modification

    Quote Originally Posted by cgrafx View Post
    If I were going to build a second unit however, I think I would opt for a lower secondary range, probably 18V or 20V instead of the 25V I used.

    And yes, your right the power supply starts to drop out of regulation right around 90V.

    pg
    Yep, that's probably the route I will take. Meanwhile, there is at least one published internal mod that replaces the 470 uF filter caps on the 15 volt rails with 1000 uF caps. Looking in my part stock, I have some 3300 uF 35V electrolytics, and I am thinking of upgrading to those. My only concern is whether the initial charge on turn-on will be too much of a current surge for the transformer, rectifiers, or fuse. Any idea whether there is a risk, or am I worrying too much?
    Cary B. Cornett
    aka "Puzzler"
    www.chinesepuzzlerecording.com

  9. #9
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    Default Re: ADA8000 External Mains Power Modification

    Quote Originally Posted by Cary B. Cornett View Post
    Yep, that's probably the route I will take. Meanwhile, there is at least one published internal mod that replaces the 470 uF filter caps on the 15 volt rails with 1000 uF caps. Looking in my part stock, I have some 3300 uF 35V electrolytics, and I am thinking of upgrading to those. My only concern is whether the initial charge on turn-on will be too much of a current surge for the transformer, rectifiers, or fuse. Any idea whether there is a risk, or am I worrying too much?
    I'm not inclined to believe it will be a problem, although the existing caps provide plenty of filtering so don't know that there is a compelling reason to change them.

    The only real issue, is the caps are sandwiched in between the regulators so are subject to heat from those components.

    Its useful to move them off-board just as a means of locating them away from the heat source. Although dropping the mains voltage reduces the heat considerably, so probably isn't a big deal either way.

    pg
    Last edited by cgrafx; 06-25-2010 at 06:39 PM.
    ---------------------------------------
    Philip G.

  10. #10

    Default Re: ADA8000 External Mains Power Modification

    Quote Originally Posted by cgrafx View Post
    I'm not inclined to believe it will be a problem, although the existing caps provide plenty of filtering so don't know that there is a compelling reason to change them.

    The only real issue, is the caps are sandwiched in between the regulators so are subject to heat from those components.

    Its useful to move them off-board just as a means of locating them away from the heat source. Although dropping the mains voltage reduces the heat considerably, so probably isn't a big deal either way.

    pg
    The mod that I saw puts the new, larger filter caps off the main board because they won't fit there, so they are away from the heat source. Wires are run from the board to where the new caps are. I would necessarily have to do the same.
    Cary B. Cornett
    aka "Puzzler"
    www.chinesepuzzlerecording.com

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