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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. natto lover
  2. Baten
    this is not the product we are talking about, the dual AKM4493 dac+amp is the desktop monolith amplifier costing $479.99 excl tax....

    also, the portable amp has 104dB SINAD. disregarding the usb noise for a moment, that is not bad really as far as I know, the really flawed products measure orders of magnitude worse
    natto lover likes this.
  3. Roen
    MY bad, I got them mixed up. I actually did not know about the desktop version, let me take a look.
    Jearly410, natto lover and Baten like this.
  4. Em2016
    Thanks again! The photo has confused me though (I’m a little slow). Is the THX 789 in the loop at all?

    It’s the THX 789 gain settings vs volume knob positions with AEON closed I was interested in.

    Thanks again. And that’s a stellar collection of gear you have there!
    alphanumerix1 likes this.
  5. alphanumerix1
    Differences with nfb1 vs 789?
    tim0chan likes this.
  6. areek
    I am getting this amp and will receive at the end of December. My DAC is an audio gd r2r11. I am planning to use rca to xlr interconnect with it so that I can run my headphones(lcd2) balanced. Will it work? Will there be any issues?
  7. Baten
    You can't simply convert rca to xlr, that won't work.

    Use RCA>RCA, the amp will convert it to balanced to the xlr output for your lcd2. It will not be "true" balanced in a way since your source is single-ended, but it will be converted and it will work just fine. I think most people in this thread are using single-ended/RCA input. it's not a problem!

    Again, RCA>XLR interconnect, impossible. You can't simply use a cable to go balanced lol. DON'T do it.
    Last edited: Nov 26, 2018
  8. AndrewM888
    Not impossible. With 789 it is possible to use RCA>XLR cable with this situation so long as cable is built properly (XLR pin 1 and pin 3 connect to RCA plug by separate wires). However, the R2R11 has XLR output - why not just use XLR cables?
    cardeli22 likes this.
  9. Baten
    What's the benefit to doing this rather than using RCA? I've always been told this is a terrible idea, thanks for clarifying though.
  10. AndrewM888
    First principles approach is there will always be some common mode ground noise currents flowing in your audio cables shield, due to low freq magnetic fields, RF from SMPS and cell phones, and from direct injection by the various products' AC/DC power supplies.
    And your audio cables all have non-zero ground impedance. So if this CM noise current flows in part of the cable that's used for signal (e.g. RCA's shield is also the signal negative wire) then it'll corrupt the signal as hum, machine noise, hiss, etc according to V=I*R where R is the RCA shield impedance.
    But if this CM current is given a preferred pathway (e.g. separate shield wire in XLR cable) then it won't corrupt the audio. Similarly if given a lower impedance path (e.g. very short RCA, or more-copper in the RCA shield) then it'll corrupt less because the "R" term is smaller in V=I*R.
    An RCA>XLR cable, if built properly, will provide a *mostly* separate pathway for CM noise current to flow. It's a half-way house.
    Now the question is whether or not an amp can handle an unbalanced signal on its balanced input... if the amp is designed right as a "differential" input stage, then no problem (as is the case with most product).
    Rule of thumb for users is
    a) use 3-wire balanced cabling where possible (e.g. XLR)
    b) if forced to use RCA, use the lowest impedance shield, and keep the length short
  11. Baten
    Very, very interesting. Thanks man.
  12. MacMan31
    I still have yet to pull the trigger on the THX 789. With my Aune X7S I'm on low gain and never feel the need to go past 12 o'clock on the volume dial with my 58X or 6XX. I'm only using the SE headphone jack at the moment but I do want to get a balanced cable at some point.
  13. humblesquad
    Does anyone else feel that this amp needs a long warm-up (8 to 9 hours) to shine? Without the warm-up it sounds dull, too much smooth, congested and far less dynamic. After that, mid and bass become powerful, lean, clear and realistic by a large margin. When I shut the power off and rest it overnight, it becomes dull again.
  14. oqvist
    Never nnoticed that tbh I seldom listen 10h straight though
    cardeli22 likes this.
  15. BrotherKathos
    I leave all my audio stuff on all the time unless it’s something like tubes that wear out ridiculous fast. All of my components seem to spund better after being on for a while. Could just be a placebo but ymmv
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