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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. AndrewM888
    Unfortunately you can't take XLR bal out from DAC and reduce to RCA because it will short one of your DAC bal outputs.
    Just use XLR DAC out to AMP XLR in. For a given headphone jack e.g. 1/4", the 789 gain is same whether using RCA or XLR input. It has a diff input stage.
    Last edited: Jul 30, 2019
    trellus and flyte3333 like this.
  2. flyte3333
    Ooops. Good thing i checked first :)

    Ok cheers
  3. adeadcrab
    Is there any point getting a balanced DAC for this amp if I'm not running super long interconnects? Does a balanced source just provide more power??
  4. phthora
    trellus likes this.
  5. PopZeus
    None of the lengthy reviews I've read have mentioned the balanced XLR input being significantly better or louder than the single-ended RCA.
  6. Fatdoi
    But has anyone here done an AB between RCA and XLR input to settle this issue?
  7. hakuzen
    if signals are true balanced when reaching XLR inputs, you should get +6dB (double power) and much less crosstalk than single-ended RCA.
    if you carry a non true balanced signals (i.e., single-ended) into XLR inputs, there shouldn't be noticeable difference with single-ended RCA (the only difference would consist of plugs and jacks quality and conductivity: small one)
  8. PopZeus
    But this amp isn't fully balanced. Before it gets to the amplification stage, it takes half of the balanced input (ditching the other half) and then doubles it, just like it does with the single-ended RCA inputs. I have yet to hear it for myself, but I think that brings both input types closer together in terms of power and quality.
  9. hakuzen
    humm.. didn't know this. then, guess it creates its own balanced signal when doubling, instead of getting and amplifying the balanced input signal.
    but doubling is adding negative signal for XLR-4 balanced output, which is different than adding ground for RCA single-end output. that's why you get double power and much lower crosstalk in balanced XLR-4 output (check the specs).
    if it works this way, you could get balanced output from a single-ended input signal. so the 3.5TRS cable to 2*XLR (single ended) gets sense. this is not usual, i'll search for further info.

    EDIT: yes, it generates its own balanced signal from single-end signal, coming from either single-ended (RCA/XLR) or balanced (XLR) inputs.
    using single-ended signal via XLR input, gets the benefit of removing possible ground loops (hum) and decreasing the chance of RF noise (XLR cables use to be full shielded), like if it was a balanced input signal. so it's much preferred than RCA input.
    i like this very much.
    Last edited: Jul 31, 2019
  10. hf6576
    I can do it recently.
    adeadcrab likes this.
  11. escalibur
    Still not 'sold out' at Drop. Either the interest has dropped (thanks to Atom?:)) or they finally managed to have bigger stock than before. :)
  12. PaganDL

    More stock definitely, @escalibur.

    Otherwise they wouldn't have it available to order for a month.

    Hope you have a great day !
    escalibur likes this.
  13. AndrewM888
    You can achieve max output on all HP outputs with 2V unbal or 2V bal. Gain is same.
  14. AndrewM888
    No, we don't just use half the input signal. We use it all, through an instrumentation opamp differential input stage.
    Both 789 input types are extremely high quality with impeccable measurements. For most setups, indistinguishable.
    Choose the DAC you like best, and if you must use RCA use short cables 1-2ft. It'll be awesome. Cheers!
    ayang02, jsmiller58 and trellus like this.
  15. jsmiller58
    I think that technically it isn’t that they have more stock (if it were in stock they could ship it right away at the end of the drop rather than waiting till mid November). They probably have secured more production capacity at their contract manufacturer and/or they have secured more of the scarce components from their supply chain, allowing them to build many more units than before,

    In either case, a great development indeed.
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