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Massdrop x THX AAA™ 789 Linear Amplifier - Impressions Thread

Discussion in 'Headphone Amps (full-size)' started by XERO1, Mar 1, 2018.
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  1. stimuz
    except neither of them are made by massdrop or monoprice, they both outsource.
    Ken G likes this.
  2. Roll
    THX did design the 789



    " I dont know about this. THX didn't design the two Monoprice products. We just supplied IP for some key analog stages."
  3. maxxevv
    If you have a problem with ASR regarding your disdain for their non-praise of something that seems to be highly prized by you, why don't you raise it up over there ?
    And have you actually read the complete proceedings of that particular thread for that matter ? If you haven't then perhaps you should, it puts in proper perspective why the review was shelved. And what has transpired since your 'disappointment' at a non-positive review there. s

    There is no need to repeat and lament about it over and over on this thread that has almost no direct correlation with the so said Monoprice product.
  4. stimuz
    No, I have a problem with them claiming a preview for a review of a unit sent to them by a member where they didn't even review it and instead **** on them for shipping woes. Btw, I bought my unit AFTER his review expecting to have to return it, so you could imagine my surprise.
    Last edited: Apr 11, 2019
  5. flyte3333
    Hi Andrew, do these noise currents only originate from AC mains connected power supplies?

    So if using a battery powered source & DAC (not connected to mains power) then these CM noise currents through RCA to RCA interconnects are not an issue?

    For example a Chord Hugo2 (which only has RCA outputs) running on battery power fed by a battery powered DAP.
  6. AndrewM888
    - Yes AC mains-connection transformers, whether 50/60 Hz linear toroid or SMPS, are often the source of this common mode noise injection. Battery-powering everything upstream (e.g. source + DAC) is a great way to prevent that CM injection.
    - Keep Source-DAC and DAC-amp cabling short to prevent CM pickup from RF fields nearby. <1ft if possible.
    flyte3333 likes this.
  7. flyte3333
    Thanks Andrew.

    So if source + DAC are both battery powered (disconnected from mains) then RCA interconnects can be 3 meter in length with no RF pickup issues to worry about?
  8. AndrewM888
    I'd be concerned. 3m RCA is pretty long and can pickup RF fields. Instead consider two of these from amazon.com. Any CM current from RF pick up will be restricted to the shield, and the inner signal pair will remain clean:
    Monoprice 10ft Premier Series XLR Male to RCA Male Cable, 16AWG (Gold Plated)
    flyte3333 likes this.
  9. alpovs
    Are these cables properly wired? I think it would be better not to connect XLR pin 1 to the shield and leave the shield floating connected only to the RCA shield. The schematic from monoprice.com:
  10. AndrewM888
    Yes this is proper wiring.
    CM currents are often current sources and will flow on the lowest impedance path. In this case we want them to flow from RCA sleeve to pin 1, leaving wires 2,3 unadulterated.
    If you float wire 1, then the CM currents will try to push through wire 2/3 in parallel and cause massive common mode noise voltage on wire 2/3, which the 789 will have to reject.
    alpovs likes this.
  11. BrotherKathos
    8AAB51E6-E983-4655-BFA9-F1CEC867F830.jpeg I finally found my perfect sound. Thx 789, mimby, and some nighthawks. Unbeatable for the price!
    Jearly410 and BobSmith8901 like this.
  12. BananaOoyoo
    maxxevv likes this.
  13. domho7
  14. BananaOoyoo
    I’m guessing it’ll be up in 7-8 hours. I think that’s when it usually updates.
  15. domho7
    Ok tks I probably whack 1 to try out fully balance features.
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