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Topping DX7 - DAC and balanced headphone amplifier

Discussion in 'Dedicated Source Components' started by faber65, Mar 16, 2017.
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  1. mabuk
    You can also get soft sticky thermal pads.
     
  2. Voxata
    Correct. I used thermal pads, the same that are used on memory chips for videocards. Easy to purchase on Amazon for quite cheap.
     
    audioadvocate likes this.
  3. audioadvocate
    Will be cracking open my unit to check on the thermal paste issue. Thanks to Voxata for discovering this issue. With the new Innovation Cooling or Panasonic graphite pads that have great thermal performance, I might try these instead of thermal paste. My earlier positive impression of sound quality still stands, but it's disappointing that this QC issue has come up.

    While I'm not schooled in audio amplifier circuit topology, a friend of mine is. He's telling me that many of the current designs coming from China are as a result of successful reverse engineering of American high end audio components...tantamount to thievery of US patented designs. And it's apparently quite aggressive. I wonder if that's why this stuff sounds pretty good. The poor cooling implementation found by Voxata leads me to be concerned China-based motives...a discussion for another forum on another day.
     
  4. Voxata
    I'm not sure about the thermal requirements of these chips but this fix may help the longevity of the DX7s. When a manufacturer puts a heatsink on something I assume it's to help keep it running cool and a no brainier is using a thermal pad to improve heat transfer dramatically.

    This fix only takes 10 minutes, two allen wrenches, a Phillips head screwdriver and some thin thermal pads cut to size. Take the front off first from the 4 side mounted screws and gently disconnect the two ribbon cables to pull the faceplate off. Then remove all of the bottom screws and slide the board out from the back and you're ready to remount the heatsinks.
     
    Last edited: Nov 2, 2018
  5. audioadvocate
    Thank you VERY MUCH!
     
  6. audioadvocate
    I had some free time tonight and some extra Noctua thermal paste from a previous CPU I just assembled. So I said what the heck and dissembled my DX7.
    First the good news. The job is done, the unit reassembled, and it powers on and sounds fine.

    The bad news...
    I discovered that:
    The heat sinks were so loose...the Philips head screws were not tight and the heat sinks were movable and made very poor contact.
    There was no sign of any thermal paste or pad on either the 2 ICs or the 2 transistors.

    [​IMG]

    I applied the thermal paste in an extremely thin layer. I photographed the job before making the paste thickness and amount uniform and ultra-thin, as I always fear the possibility that with the heat generated in an energized unit, this paste will flow a bit. Be super careful if using a paste to avoid using too much, and certainly don't get any on the component pins. I took this photo before making it uniform so you could see the paste on the chips.

    [​IMG]

    I carefully replaced the heat-sinks without sliding them around.

    [​IMG]

    The chassis side screws were difficult to re-align on the bottom and sides. Upon removing them, I discovered that the rear panel was ever so slightly warped, so I wondered whether getting the holes to line up on job completion would be a challenge. It was a challenge, and these side screws in particular, were easily prone to cross-threading, so be careful.
    After reassembly, everything worked well.

    It took me an hour overall. A few minutes to apply the paste and screw down the heat sinks, and about 45-minutes struggling with the chassis holes not lining up because they just couldn't have been laser-aligned upon manufacture.
    If some of these units suffered from thermal runaway and died, I am not at all surprised given the behavior of the person who screwed the heat-sinks down. This degree of looseness simply could not be blamed on shipping vibration.
    Don't rush through the job. Try replacing different screws if at first things don't line up. Your build quality and alignment may be better than mine. And be careful with the tiny screws on the floor of the unit. They may seem like they are tight, but then get a flashlight and look at each standoff to make sure they not only partially tightened, and that the PB board is not "tenting" as partial screw purchase can cause. You do NOT want to stress the PC board tracings.
    Enjoy!
     
    Last edited: Nov 2, 2018
    06S2k07Si, Kuh-Fi, Toshu and 2 others like this.
  7. Voxata
    Looks good. No need to worry about excess paste though as you are using Noctua. Their most common paste is non conductive so if you did indeed use a little extra you'll be fine.

    Your board/case mounting is odd. Both of my units are perfectly aligned and were easy to take apart and put back together. Oh well, so long as it works and keeps working.. I am glad you were able to maybe improve your DX7s's lifespan.
     
    Last edited: Nov 2, 2018
  8. Toshu
    Thanks for the pictures with the arrows. @Voxata did a great job identifying the problem, but you both were speaking in a foreign language to me....I am better at the visual.

    I plan on ordering my DX7s from Massdrop today. Is this the paste I should use ??
    Noctua NT-H1 Pro-Grade Thermal Compound Paste (Gray)
     
  9. Voxata
    06S2k07Si and Toshu like this.
  10. Toshu
  11. Voxata
    That'd be adhesive themal tape - you can use that as well but the pad may transfer heat better and is more mount wiggle friendly.

    The DX7s sinks are held with screws so using a pad is ideal. If you were to be adding extra heatsinks adhesive thermal tape is the way to go.
     
    Last edited: Nov 5, 2018
  12. Toshu
    I am curious if you have shared this info with Topping?


    I will probably pull the trigger today but have a few questions..

    In DAC mode only does the signal still come out of the balanced and analog outputs?? Bypassing the amp?

    Would I need to run in DAC mode only if I am feeding an AV system amp like a Krell or B&K??
     
  13. Voxata
    DAC mode is RCA and balanced simultaneously, fixed. DAC/AMP uses the DX7s as a pre with volume control. These outputs are in the rear and does bypass the amp.

    I'm sure topping is aware, they designed and built the entire thing.
     
  14. Alcophone
    Yes, in DAC mode the single ended RCA outs in the back and the balanced XLR outs work and send a line level signal (equivalent to volume at 100%, volume knob is ineffective), while the front outs are disabled. That's what I'd use with a separate preamp or integrated amp like your AVR, while the DAC+HP mode is good for connecting to a power amp. You can also use this mode with your AVR if you want to reduce the Topping's volume to level match some other device hooked up your AVR.
     
  15. audioadvocate
    I was pretty surprised when I discovered just how loose those heat sinks were. Voxata must be credited with that find, and should be credited with helping us to avoid thermal runaway on these chips. The sink overlying the output transistors in my unit were so loose as to be completely ineffective. I bought mine directly from China, having missed the Massdrop deadline. I'm curious whether Massdrop has gotten any heat over this potential problem.
     
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