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Review and Measurements of Massdrop THX AAA 789 Amp

greyscale

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Don’t look now but the Drop THX 789 is back up for sale, again:eek:
 

Music1969

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Don’t look now but the Drop THX 789 is back up for sale, again:eek:

It's been up for a month, for pre-order. And it's just been extended for another month.

Great opportunity to have one before end of the year.
 

ZeDestructor

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It's been up for a month, for pre-order. And it's just been extended for another month.

Great opportunity to have one before end of the year.

Hopefully it ships on time on 15 Nov. I preordered t (and the SDAC-B) in July when it last reopened, and the impatience is strong :p
 

greyscale

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I preordered one then canceled on Friday. 3 hours before closeout, Last night(Sat) it is once again available for preorder with as of now, 29 days left.
 

Tks

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Hopefully it ships on time on 15 Nov. I preordered t (and the SDAC-B) in July when it last reopened, and the impatience is strong :p


Well in a case of exceptional surprise, mine was shipped two weeks before it was set for the Aug 30th ship date (I ordered mine in the April drop). So there is hope I suppose.
 

Ty89m

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Hey all, wondering if anyones running a 789 and RME ADI-2 DAC? As this is my first higher end DAC, I'm curious what kind of settings I should be targeting? Running Arya via balanced out on the 789, and paper to have Volume line out on auto, and am able to control volume via DAC and 789. Honestly not even sure what gain setting on 789 is ideal in my case ha. Up until now I've used fixed output voltage DACs, so this is all new to me.
 

JohnYang1997

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Hey all, wondering if anyones running a 789 and RME ADI-2 DAC? As this is my first higher end DAC, I'm curious what kind of settings I should be targeting? Running Arya via balanced out on the 789, and paper to have Volume line out on auto, and am able to control volume via DAC and 789. Honestly not even sure what gain setting on 789 is ideal in my case ha. Up until now I've used fixed output voltage DACs, so this is all new to me.
Set to minimum gain on 789, as long it's still loud enough. And you can either control volume using 789 and dac. Both reserve SNR.
 

Ty89m

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Appreciate you getting back to me, so no particular volume setting on DAC on should shoot for? The 2 bars below the PEQ visualizer seem to show clipping if volume on DAC is set too high, yes? I need to dig through the manual and figure out what all this is referencing.

Yes, a bit silly to jump into the RME when I have no idea what I'm doing, but will ultimately use is as an AMP/DAC combo and use different DAC for THX for my office setup - just wanted to play around a bit :)
 

JohnYang1997

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Appreciate you getting back to me, so no particular volume setting on DAC on should shoot for? The 2 bars below the PEQ visualizer seem to show clipping if volume on DAC is set too high, yes? I need to dig through the manual and figure out what all this is referencing.

Yes, a bit silly to jump into the RME when I have no idea what I'm doing, but will ultimately use is as an AMP/DAC combo and use different DAC for THX for my office setup - just wanted to play around a bit :)
No need to worry about the volume on dac. It's all basically optimal thanks to hybrid volume control of adi2dac.
In regarding eq, as long as you only cut instead of boost, you will be fine, meaning maximum needs to be <=0db. It's not 100% tho, you can mostly have a bit higher settings without experiencing clipping but 0db maximum is safe.
And yes you can definitely use adi2dac as amp/dac combo without having degradation from 789. In some cases could be even better than 789.
 

Ty89m

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All good info - stupid question, but what are the two bars below EQ representing? the L and R bars which have values to the right. I get it's referring to the left and right channel, but what do the values represent? Digging through the manual but not finding this info. I notice if I raise the volume on the DAC too far, it'll start turning from green to yellow then to red, signifying clipping perhaps?
 

Ty89m

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Alright, referencing levels for L and R, up to a maximum of 0db it seems. Making more sense now. I see I could set +7dbu and 0db on volume to mimic the typical 2v output of typical DACs. Whats the benefit of using the Auto Ref Level, being able to control volume via DAC/Remote etc? Wondering where having the ability to to adjust output voltage would be beneficial, perhaps on equipment that requires more than the typical 2v output?

Regardless, this RME is pretty darned slick.

Also, manual mentions when using XLR out to a non balanced device, that the 3rd pin not be connected, as connection to ground might caused decreased THD and more power consumption. As the 789 isn't truly balanced, is this something I should concern myself with? I don't need balanced regardless, as I'm not running long lengths of interconnects - but curious none the less, as I DO have short XLR cables to toy with.

Sorry for the bombardment of questions - but very much appreciate you guys giving me some input/help! Great forum!
 

Veri

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Also, manual mentions when using XLR out to a non balanced device, that the 3rd pin not be connected, as connection to ground might caused decreased THD and more power consumption. As the 789 isn't truly balanced, is this something I should concern myself with? I don't need balanced regardless, as I'm not running long lengths of interconnects - but curious none the less, as I DO have short XLR cables to toy with.

No they mean using the XLRs with unbalanced conversion cables, shorting one of the XLR connector pins.

The THX AAA is not 'truly balanced' as in a independent dual mono set-up per channel, but it is balanced differential which is absolutely fine when you look at its performance, they couldn't possibly do dual mono at its asking price. More 'concerning' is that the volume pot is unbalanced so it goes balanced>unbalanced>balanced when using the XLR output. Still, when you look at performance, no issue but purists might frown at this.

But as for your question, there is no problem, all 3 XLR pins are fed via the inputs on the THX AAA without any 'decreased THD' concerns. The inputs are balanced proper.
 
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AresHarvest

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No they mean using the XLRs with unbalanced conversion cables, shorting one of the XLR connector pins.

The ADI-2 DAC manual specifies that pin 3 should be floated when connecting to an unbalanced input, I'm guessing because it's impedance balanced instead of servo balanced. So referring to Rane Note 110, fig 3b shows the wiring.
 

Veri

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Ty89m

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Ah, gotcha - I'll not concern myself with that then. Now, how can one tell if I'm clipping the input stage of the 789 itself? Would the level meters show that? The 789 appears to handle up to 7v input on the middle gain setting without clipping, but if using max gain (+10db) input voltage must not be higher than 2.1v rms. Not that I anticipate needing highest gain, but if I did, how would I ensure I don't output for that 2.1v to the amp?

Manual mentions Auto Ref setting of +7dBu is equivalent to 1.73v, so I just need to not raise DACs volume too higher to prevent auto switching to the +13 setting?

Seems there's some wiggle room when adjusting volume up and down before it'll switch to the next higher ref setting
 

AresHarvest

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Manual mentions Auto Ref setting of +7dBu is equivalent to 1.73v, so I just need to not raise DACs volume too higher to prevent auto switching to the +13 setting?

If you're using the 13 dBu ref level, then use the pot to set volume to -4.5 dBr and that'll give you nearly the maximum voltage swing (8.5 dBu = 2.06 V). With this voltage, you will not clip the 789 in any of the three gain modes.
 

Ty89m

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Very good info, curious, how does one calculate the voltage based on ref level and volume knob level?

What’s the benefit of using auto ref with the typical consumer equipment vs running fixed?
 

AresHarvest

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Very good info, curious, how does one calculate the voltage based on ref level and volume knob level?

What’s the benefit of using auto ref with the typical consumer equipment vs running fixed?

The advantage to auto ref level is so that you don't need to change gain modes to get the full range of output levels with the pot. It's not useful in this case.

As for calculating the voltage:
  • Volume is shown in dBr is somewhat of an open scale, where the reference value is implied. In this case, we can assume the reference value is the user-set Ref Level. So with ref level of 13 dBu, and a volume of -4.5 dBr, we have an output of 8.5 dBu (13 - 4.5 = 8.5).
  • dBu uses a reference value of 0.775 Vrms
  • Calculation for converting voltage to decibels is 20 * log(V2/V1) where our desired voltage is V2 and our ref voltage can replace V1
  • Plug our values in with a desired voltage of 2.1 V... 20 * log(2.1/0.775) we get a gain of 8.658 dB, and I rounded down to the nearest 0.5 dB to account for the increments of the RME's volume control
 
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