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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. Yviena
    I actually came from a monitor mini (said to have the same SQ as phonitor 2 just with less functions), and i find this amp to be somewhat better in transients(faster etc) while soundstage/imaging/layering feels the same or so close that I can't distinguish between it.

    Bass/sub I found to be also a little bit better with the 789 while the phonitor is a little more leaner there, or it could be because 789 has balanced output while phonitor mini is unbalanced.
  2. AxelCloris Administrator
  3. Marlowe
    To follow up on Andrew of THX's post a couple of days about an imminent drop, Cee_Tee of Massdrop posted yesterday that additional stock is coming in and should be in store in about a week. I"m still trying to decide between this now or saving up for a Monoprice Liquid Platinum in February or March. (I'm retired on a fixed income, so have to plan my purchases carefully.) The LP is almost certainly a better overall amp, but I don't have a really good SS amp, and I do have a good tube hybrid (CTH) and OTL tubes (Valhalla 2).
  4. MacMan31
    I'm still very much undecided about joining the next drop for this amp. Unless I were to spend over $1,000 I can't see an amp being noticeably better than the Aune X7S. I paid $220 Canadian for that used.
  5. Zbell
    That's a good amp. I would only consider getting this amp if you're driving low impedence cans.
  6. MacMan31
    For now I'm only driving the Sennheiser HD6XX and 58X. I'm only on low gain and never go past 12 o'clock on the volume dial. It's paired with the MD Grace SDAC. But I'm looking into possibly getting these: https://www.massdrop.com/buy/massdrop-fostex-tr-x00-mahogany-headphones
  7. Zbell
    While I think the Aune and Fostex will sound good together, it technically doesn't adhear to the 8 to 1 rule. I can also vouch that the purple hearts and hd600s sound absolutely fantastic on the 789.
  8. MacMan31
    Hmm okay. Well I'm not yet running balanced on my X7S. Just using SE. I'm hoping to get a balanced cable in the future and an XLR to 1/4" adapter just in case I need it. I have never listened to any of the Fostex headphones but I've heard that the Purplehearts have more bass than the Mahogany.
  9. Por_Tu_Guy
    Ladies and gentlemen I present to you the: whateveryoucallthisstack stack!!!!
    Massdrop Stack ? Minus the Ares of course :blush:

    trellus, Fatdoi, spacequeen7 and 5 others like this.
  10. MacMan31
    How would you describe the THX 789 compared to the Aune X7S? I have the latter and I'm considering the former.
  11. Em2016
    Hi @AndrewM888

    With the properly made RCA to XLR cable - how do we know the CM noise current will flow from the RCA sleeve connection to XLR Pin #1?

    i.e. how do we know this current won't actually flow through the RCA shield (signal -ve) to XLR Pin #3?

    Is it assuming the path from RCA shield to XLR Pin #1 is the lowest impedance path?

    And a separate question:

    If you use star-quad cable for an RCA to RCA cable - if the cable has a shield which is connected at both ends of the cable, to the RCA sleeve at each end - does this then provide a separate path for CM noise current to flow along the length of the cable? The star-quad shielded cable then has separate signal, return and shield?
  12. AndrewM888
    Hi @Em2016.

    XLR pin 1 Zin is < 1 ohms to ground, and XLR pin 3 Zin is much higher around 1 meg ohms to ground. CM current can be modeled as a current source. According to Kirchoff's Current Law and the ratio of these impedance pathways, a proper RCA to XLR-3 cable will force the vast majority of CM current to flow into pin 1. The pin 3 wire carries negligible CM current, so incurs no hum-inducing voltage drop.

    However with shielded star quad RCA to RCA, your signal return wires are in parallel with the shield. These impedances are in same ballpark as each other, so the CM current flowing in your signal- wire can generate non-negligible voltage across it per V=IZ, causing some hum. You can mitigate this by throwing lots of copper at it and keeping the length short. e.g. heavy braid shield, heavy gauge signal wire, and length 1 ft or less.
    Em2016 likes this.
  13. Em2016
    Thanks! Makes lots of good sense.
  14. Alcophone
    Between the H20 and the THX, the H20 with Sparkos SS3602s wins, then the THX, then the H20 with stock opamps.

    In terms of tonality and sound stage, the H20+Sparkos combo and the THX amp are on par, I would say, but the THX blurs transients compared to the H20+Sparkos combo, sounding quite sterile in comparison as a result. There's more sparkle, slam, punch, heft - whatever you want to call it - to the H20+Sparkos. It's a more engaging, exciting presentation, putting me more in touch with the artist if that makes any sense. It feels more like I'm listening to someone playing an instrument than to a recording of someone playing an instrument. It's hard to identify what's going on when listening to just the THX amp, as there's nothing obviously objectionable, but going back and forth between the two with primarily recorded music (from 24/192 FLAC down to Spotify Premium), the difference becomes quite apparent.

    Soften the transients a bit further, add a bit of noise and distortion, and you get close to the sound of the H20 with stock opamps. This also doesn't sound bad by itself, but as so often in audio, the deficiencies become clearer once they are gone. Both the THX amp and the H20 with Sparkos opamps sound more clear, clean and refined than the H20 with stock opamps.

    All of the above is using the Yggdrasil's balanced out, with a Y-splitter cable into both amps balanced inputs at the same time, and using the MrSpeakers Ether Flow 1.0 with stock DUM cable out of the amps' 4-pin XLR jacks.
    alpovs and ReAlien like this.
  15. ReAlien
    Very interesting. Is there an easy way (w/o soldering) to upgrade THX 789 with these Sparkos SS3602s, I wonder? If yes, how many of those would I need?

    Checked the pictures of THX's internals on the other site and it seems like there is no easy way to upgrade. But, if I find the specialist to do the soldering, which op amps should be changed for Sparkos ones?
    Last edited: Dec 18, 2018
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