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jsmiller58
573
Nov 28, 2018
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@AndrewMason Question - (sorry if this is asked ad answered but searching through nearly 2000 messages would be painful!!)... I am driving my MD x THX AAA 789 with a Topping DX7S amp through the XLR outputs of the DX7S. As I understand it, there is a max voltage swing that the 789 can tolerate before it begins to clip in at least the highest gain setting... My question is what output level should I set the D7XS so it dos not cause a problem for the 789 in high gain when I am feeding the 789 with XLR inputs? Somewhere I read that was about -6dbfs... A related question... I really don't want to have to remember to reset the output level of the DAC when I switch gain on the 789... If I set the DX7S to the appropriate level to not clip at 789 in high gain mode and just leave it there for the other gain settings, will that result in any quality loss for the output of the 789 when I run the 789 at low or medium gain? I understand that I will lose some volume headroom, but I am OK with that (and if I ever have a problem with volume at the lower settings I can always raise the output level on the DX7S...)
Nov 28, 2018
Hi @jsmiller58 . With Topping DX7S and XLR connection to 789 here are 2 options: 1) Keep 789 in gain 1 or 2 only. Use DX7S all the way to 0dBFS. 789 output will produce 4Vrms SE or 8Vrms BAL. If this is loud enough for you, then you're done. It gives the best SNR. or 2) If wanting to get the full 7/14 Vrms swing from the 789 in Gain 3 and have freedom to use any gain setting 1,2,3 , you need to limit the DX7S to max -6 dBFS output. Do this either manually with DX7S front volume knob (best), or in your PC media player add a 6 dB digital attenuator (in which case you can go up to 0dBFS on the DX7S). As always the THD is pretty much unaffected by gain position, but noise will be - choose the lowest gain setting for desired SPL in order to minimize amplification of upstream DAC noise. Happy listening!
Nov 28, 2018
jsmiller58
573
Nov 29, 2018
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Awesome. Thank you for responding. And thank you for a great product, I am thoroughly enjoying my MD x THX 789. I wish all of you at THX much success in bringing your technology to many, many products. As the song (mostly) says - the future's so bright, you have to wear shades!
Nov 29, 2018
jantonie
2
Dec 2, 2018
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Question for either of you two. Is there a reason or an advantage in using the HP+DAC vs just the DAC output from the DX7S to the THX AAA 789? (Talking the XLR outs here.) Thanks!
Dec 2, 2018
jsmiller58
573
Dec 2, 2018
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The purpose of setting the DX7S to the HP+DAC setting is that you are able to control not only the headphone outputs but also the rear outputs to your amp with the front DX7S knob. When the DX7S is in DAC mode the outputs are fixed at 0dbfs. In HP+DAC you can set that lower - say, to -6dbfs which results in the recommended input voltage level for the 789 inputs in high gain mode, or keep to 0dbfs in low and medium gains for the 789, as per @AndrewMason recommendation. BUT, whatever level that you set the HP+DAC setting to is also coming out the headphone outputs on the front... for example, I usually listen to my headphone output on the DX7s at -23dbfs or so when DX7S is in HP mode,. If I plug in my headphones to the DX7S when in DAC+HP mode and it is set to 0dbfs or -6dbfs, it may well kill my hearing or headphones...! Anyway, this is my understanding.
Dec 2, 2018
jantonie
2
Dec 2, 2018
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Ok. First off, thanks for the detailed reply. Think I got it. I’m only a week in or so with THX AAA 789. I use EQ program from the computer for my HP, that dropped it -6 dB going into the DX7S to begin with. Was fiddling with the different gain settings on the THX looking for my preference. Had always used the DAC out setting only from the DX7S. Was confused why people where using the DAC +HP instead. I never had any distortion or issue of any sort. Seeing how my signal was already attunated, think I understand. Thanks again!
Dec 2, 2018
jsmiller58
573
Dec 2, 2018
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Excellent question. Not sure that changing the input level to the DAC changes the ouptut level of the DAC, though...
Dec 2, 2018
jsmiller58
573
Dec 3, 2018
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@AndrewMason forgot to ask one more clarifying question... I have read on ASR that there is some (most likely not audible) crosstalk on lowest gain on the 789, but not when using the middle gain... Is there any loss in performance (such as noise) if I use the 789 at the middle gain, even if that power level is not required by my headphones (I would just set to a lower volume setting)?
Dec 3, 2018
Crosstalk is a tiny bit higher on lowest gain. But it's still -93 dB at 1kHz. That's ridiculously good for a TRS jack. I wouldn't worry about it and choose the gain that gives you most satisfying range of volume pot usage.
Dec 3, 2018
jsmiller58
573
Dec 3, 2018
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Thanks!
Dec 3, 2018
verifonix
712
Dec 4, 2018
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Hey Andrew. Some user measured the crosstalk https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-massdrop-thx-aaa-789-amp.5001/page-25#post-122619 It might be a little higher than -93dB, but still no real audible concern right?
Dec 4, 2018
-93dB at 1kHz the benchmark frequency, and only on gain "1". That's still super super low. I'd venture its inaudible.
Dec 4, 2018
verifonix
712
Dec 4, 2018
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Excellent, thanks. Bought one of the last units today :) very excited It's very cool btw @AndrewMason that you are so active in the community!!
Dec 4, 2018
jsmiller58
573
Oct 7, 2019
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@AndrewMason - sorry to bring this input level topic back up... One quick question. If instead of XLR inputs the 789 is fed by single ended RCA inputs, is it still necessary to set the DX7s output to -6 dbfs or is 0 ok?
Oct 7, 2019
Hi @jsmiller58, no problem. I see DX7s RCA output is 2V, so it's a perfect match to 789. You can set DX7s to 0 dBFS and use any of the 789 gain settings without fear of clipping. And 2V will give you max output power at Gain 3.
Oct 7, 2019
jsmiller58
573
Oct 8, 2019
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Awesome!! I am thinking of putting a Schiit Loki in the path between the DX7S and the THX 789, so would have to go SE since the Loki is single ended... But I've got RCA to XLR cables so while the DX7S is coming out from it's RCA outputs to Loki RCA I puts, I will go from the Loki RCA to the 789 XLR... Now, the Loki is powered... Hmmm. I wonder what that will do to voltage levels...
(Edited)
Oct 8, 2019
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