A quick update from me, since my last post i've not noticed any buzzing or noise at all so it seems to be gone. Maybe the amp just needed a few hours of burn in. 
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Review and Measurements of Massdrop THX AAA 789 Amp
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Veri
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I'd normally cringe but I do think these circuits need some time of power flow to start running properlyA quick update from me, since my last post i've not noticed any buzzing or noise at all so it seems to be gone. Maybe the amp just needed a few hours of burn in.
only once though, don't want to get people any ideas of running them 24:7 
I think that the power is a “soft start”, so the unit is in low power mode when shutting off. I will try to remove the power supply and wait for the caps to discharge.I'd normally cringe but I do think these circuits need some time of power flow to start running properly
Had paired THX 789 with my new HD6XX. So far have been underwhelm with what I've heard compared to a different setup running HD650.
I've tried running in the headphone for 4 days, so far still not too impressed. Wanted to check how's everyone's experience running on HD6XX
I've tried running in the headphone for 4 days, so far still not too impressed. Wanted to check how's everyone's experience running on HD6XX
I've tried it with both Sennheiser HD650 and Audeze LCD-2C and it beats all my other headphone amplifiers, including my own design. I'm a happy puppy.
maxxevv
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For starters, why were you underwhelmed ? What were you expecting out of it ?
It bested (subjectively) a TEAC head amp, a modded Matrix HPA 3B, and a direct connection to the output of two DACs I have on hand using HE560, HD650 and a balanced connection.
Veri
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Well. All my headphones (AD2000, AKG Q701 and others/IEMs) sound at their best with the massdrop THX.
The HD650 sounded quite good with my iFi black label (bass boost and 3D/crossfeed on), which has much lower SINAD but did have some analog sound processing. I think I did quite like the iFi's sound which is different from the super clean THX sound. If you're used to non-reference/flat sound I can see why you can be underwhelmed, but I believe that's just how you're used to hearing the HD650. YMMV. Tubes and stones may break my bones
I also think that's where the whole "HD650 scales so well" meme stems from. It responds really well to distortion, as in rendering a still attractive sound. Other headphones will sound piercing/inaccurate while the 650 will simply sound a varying degree of "romantic".
I have used the 789 with all of my headphones and a number of other borrowed sets, and the Massdrop amp simply does its job, and pushes clean signal to the whatever you plug into it. I have the HD6xx and it sounds magnificent with the 789, better than I've ever heard it sound. I would go so far as to say the same for all the other headphones, but that is just subjective. However, my subjective experience is borne out by the objective measurements and not littered with audiophile buzzwords.
When you use words like 'intimacy and dynamics' you are trotting out terms that make me cringe a bit. Headphones can either reproduce the signal they get faithfully or they can distort. The HD6xx is renowned for having (after compensation) a remarkably linear frequency response and very low distortion for their price range. With the 300 ohm impedance, mating them with the 789 is truly a excellent-sounding setup. I have just spent over a week with the HD6xx and HD650 side-by-side and the new model HD650 sounds, to my ear, exactly like the HD6xx.
wadec22
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This^
If you are having any actual trouble with the pairing - it probably has more to do with the issue that pops up occasionally with MD headphones/gear - build quality & QC.
That will be sad. I'll try to find a way to verify if it's a equipment issue.
I'm happy with my THX 789 + HD 6xx setup. What other different setups have you been using with the HD650?
If I were to listen to the HD6xx + THX 789 at gain 2 and 70% volume, I'd be deaf in short order. I run gain 1 and about 30-40%, but that is likely the difference between single-ended and balanced. My setup is balanced.
I was listening to via analog out from iphone XS -> RCA of HDVD800 -> HD650 via unbalance
I believe Sennheiser HDVD 800 has high output impedance? If so, it may create distortion, though it could be desirable.
D
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Yes, it is quite high according to HDVD 800's manual:
I too have an HDVD 800 on the desk, but at least to the HD 800 driver the higher output impedance is not supposed to make a discernible difference (see output resistance section of this review). The same site didn't run this test on the HD 650.
Well that is likely your problem, using the DAC of the iPhone to a splitter. Why not feed the HDVD 800 a digital signal from the iPhone?
Just in case your impedance nervosa is getting the better of you, quick, read this and you'll feel right as rain.
Wait, I'm confused. You were asking about the 789 and now you say it was the HDVD 800? Maybe I misread something...
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The previous poster was asking reference what was I initially listening to on the HD650 compared to my current 789+HD6XX combo.
Ah, OK, well then that article I linked to should help inform you. tl:dr= The HDVD 800 has a 16 ohm impedance which does not factor into the frequency response of a 300 ohm headphone as compared to the sub-ohm impedance of the 789.
If you're hearing displeasing sounds from the HD6xx + THX 789, my guess is something is busted. I've got hours on both the HD650 and HD6xx with that amp and they pair marvelously.
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