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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. tamleo
    Soft bass is really an irritating thing. That was what I found when using a tube amp called Vali 2. Sold the amp after a few weeks
  2. Snitte77
    Anyone knows if the bakanced SDAC from MD will come back? Would be a good match to the 789.

    Anyone joined to first drop?
  3. MikeW
    Considering the 789 is not a balanced amplifier. And actually loses performance with balanced input, (technically for sure, audibly? not likely) It seems like needless feature, if your goal is a dac for 789.
    spacequeen7 likes this.
  4. Snitte77
    How does it loose performance when using balanced inputs?
  5. MikeW
    The 789 is a single ended amplfier, and the balanced portion on the input is there for convenience only. When a balanced signal enters the 789 it go's though a special circuit called "summing" circuit that reduces the balanced signal to single ended before amplification. This circuit introduces various parts and OP-AMPS, that are otherwise bypassed in single ended input. The 789's amplification section is actually discrete and uses no op-amp in signal path, however if you use the summing circuit your now introducing op-amps. The summing circuit is well-implemented, and likely adds no significant loss in sound quality. But it's certainly not superior, and you gain nothing.

    All this said, the OUTPUT section is different, and indeed the balanced headphone out is the best output method.
    Last edited: Feb 23, 2019
    music joe, boxster233 and omniweltall like this.
  6. Snitte77
    What signal will than be outputed by the XLR?
  7. MikeW
    The balanced output is superior to single ended in this implementation. Ideal use case for 789 is Single ended input and balanced output. If you want a balanced DAC go for it, but realize there will be zero performance gain when used with the 789. Also realize that cheap balanced dac's are often times Summed as well, and one must pay attention to make sure the product is truly balanced, aka differential, or your just spinning your wheels. For example, balanced sections of cheap pro-audio gear, sub 200$ products rarely are balanced. The presence of XLR connector's alone does not mean balanced. Though they will work for their intended purpose of cancelling noise on long 100+ ft runs of wire.

    The truth is the balanced input and output of the 789 is of great convenience, and is a nice feature to have, and the amp is so well designed that the performance compromise is likely inaudible. The issue arises when someone believe's there is benefit to balanced input and spends extra money on it.

    There are products that are in fact balanced, that are merely competitive and don't exceed or even meet the technical performance of the 789. The Jotunheim is a truly balanced device and falls into this category. The Monoprice liquid platinum is also a properly balanced device.
    Last edited: Feb 23, 2019
  8. Snitte77
    DAC = RME ADI-2 > balanced into 789 > balanced into > Ether C Flow
  9. MikeW
    The 789 outputs balanced XLR headphone out, regardless of input method. SE to balanced out is functional.
    boxster233 likes this.
  10. MikeW
    The ideal would be RME SE > 789 > balanced out to phones.

    Though, honestly if you've got an ADI-2 the entire 789 is mostly redundant piece of gear as it does not significantly outperform the ADI-2 headamp. Unless you actually need the additional power provided by the 789. I'd give the ADI-2 headamp a serious listen, don't know if you've got a Balanced to SE adapter for your Ether C. You may be able to reduce your gear down a bit. While 1.5 Watts into 32 ohms is modest, it's quite adequate for 90% of today's phones, and would have been Summit-fi 15 years ago.

    Interestingly enough the exact same OP-AMP's used in THX 789's summing circuit are used in a 3 per channel implementation to drive the head-amp of the RME-ADI-2 DAC. OPA1602.
    Last edited: Feb 23, 2019
    music joe, syn959 and Jearly410 like this.
  11. Snitte77
    THX for your thoughts Mike!
  12. audiobean
    It may have been covered but didn’t happen to spot it, does anyone have any idea how the JDS Labs performs against the 789?
    Are they very similar and it comes down to xlr vs rca increasing output)? Or are the treble/mids/bass affected by the amps?
  13. MikeW
    Which one? Atom or el amp, the atom is probably the best sounding 100$ amp right now compared to magni and spark, it also measures extremely well. However with “only” 1 watt into 32 ohms it’s really not in the same ball park as THX 789. And the element is only 1.5 watt, respectively, which is enough for most, but the 789 is 6 watts.

    Not sure how they compare sonically when driving appropriate loads.
    Last edited: Feb 25, 2019
  14. audiobean
    The Atom. I understand now. So the potential of the 300 ohm headphones wouldn’t be realized because of the 1 watt?
    Sonic differences would be based on the impedance of a headphone? That puts the 789 above because it can cover a wide variety of headphones. But should perform sonically about the same assuming impedance matching.
    Amplifying without distortion and getting outta the way so the heaphodone can do it’s thing is the goal...it seems these two can do it well.
  15. escalibur
    Any sings of the upcoming drop? :/
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