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Review and Measurements of Massdrop THX AAA 789 Amp

rajapruk

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Maybe also you can test single-ended output in 16ohm? That would be nice.
 
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amirm

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Here is balanced at 16.7 ohm (closest I could come to 16 ohm):

Massdrop THX AAA 789 Headphone Amplifier Power at 16r7 ohm balanced Measurement.png


Power output is identical to 25 ohm load. So the protection circuit kicks in based on both voltage and current.

Note that the analyzer output is in discrete steps. So there may be tiny amount of extra power that can be had if the steps were smaller.
 
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amirm

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Maybe also you can test single-ended output in 16ohm? That would be nice.
That is a different fixture unfortunately and one that I hesitate to try to modify. The balanced one is not in a case and much simpler so it was easier to make the change there.
 
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amirm

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I should report one quirk I have found with this amp which is the power switch. It seems to have some strange logic in that it doesn't like being powered on or off quickly. If you turn it off and then immediately try to turn it on, you can push the switch half a dozen times and nothing happens. But if you wait a few seconds, then a single activation turns it on. Same is true in reverse.

I see reports of bad power switch in massdrop. I wonder if this is what they are seeing.

I don't know if this is a bug or they meant to have such long delay. Either way it is going to results in some number of people returning it thinking the power switch is bad. Impacts my work more because I am frequently turning it on and off for testing.
 

rajapruk

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I should report one quirk I have found with this amp which is the power switch. It seems to have some strange logic in that it doesn't like being powered on or off quickly. If you turn it off and then immediately try to turn it on, you can push the switch half a dozen times and nothing happens. But if you wait a few seconds, then a single activation turns it on. Same is true in reverse.

I see reports of bad power switch in massdrop. I wonder if this is what they are seeing.

I don't know if this is a bug or they meant to have such long delay. Either way it is going to results in some number of people returning it thinking the power switch is bad. Impacts my work more because I am frequently turning it on and off for testing.

Is it running Windows 3.11 under the hood? :)
 

pos

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Thank you Amir!
That is 0.58Arms. Still shy of 0.63rms, and shy of the 6W rating, but we are getting closer.

Interestingly distortion between 2W and 5.6W appears to be lower on that 16.7 ohm load than on the 25 ohm one, which is counter intuitive...

25 ohm:
index.php


Looking at the 16 and 24 ohm measurement it looks like there is a protection for anything above (err, approaching...) 6VA, and another one for the 0.63A limit?
 

pos

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Amir, do you think this amp is compatible with mono/summed operation on the SE output? (ie using a mono jack)
In theory that would allow to double the current limit...
 
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Sythrix

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I should report one quirk I have found with this amp which is the power switch. It seems to have some strange logic in that it doesn't like being powered on or off quickly. If you turn it off and then immediately try to turn it on, you can push the switch half a dozen times and nothing happens. But if you wait a few seconds, then a single activation turns it on. Same is true in reverse.

I see reports of bad power switch in massdrop. I wonder if this is what they are seeing.

I don't know if this is a bug or they meant to have such long delay. Either way it is going to results in some number of people returning it thinking the power switch is bad. Impacts my work more because I am frequently turning it on and off for testing.

Perhaps the circuit design means it would damage itself under certain conditions if it were to be turned on and off quickly.

I'm guessing this isn't an on/off specific position switch, but rather a toggle, which means something else is handling when power is actually delivered?
 

rajapruk

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Yes it is a toggle. The button returns to the same extruded position for both on and off.
 
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amirm

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I'm guessing this isn't an on/off specific position switch, but rather a toggle, which means something else is handling when power is actually delivered?
Correct. It is a very long travel momentary switch.
 

Shadow12347

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Oh nice! I wish there was some explanations with the measurements... maybe Amir can take a look for us :) It looks good for sure but context and explanations would be helpful for those of us that are still learning how to read measurements.

From what I can tell (which is basically just from comparison to what Amir's other graphs show), they seem to be quite good, with the exception of the frequency response graphs, which aren't quite ruler flat (this being the best of the bunch which is into the XLR and at 300 ohms):

FR 300R XLR4.JPG


However, the FFT graphs don't show the measurements below 1khz, which seems a little funny... (this being at 100mW into 300 ohm in the balanced XLR):

FFT 1kHz 100mW 300R XLR4.jpg


That said they did perform the tests with what appears to be multiple output impedances which seems to show A LOT of clean power output. The graphs are a little different from Amir's however because they say they are THD, rather than THD+Noise. That said, some are quite good (this one being one of the best into the balanced XLR with 300 ohms):

THD v Power 300R XLR4.JPG


Seems promising! However, feel free to correct me if I drew any incorrect conclusions here :)
 

Jimster480

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I'm using my AAA 789 with a 24ohm and 14ohm headphone at the same time basically day every day.
For reference the two headphones are mrspeakers Aeon Flow Closed and Oppo PM-2
 

Sythrix

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My August order (due to deliver in February) just shipped. Way ahead of schedule, which is unusual for Massdrop.

Pretty pumped, should arrive at the same time as my ADI-2 Pro Fs and Hifiman HE-6se.

Please let me know how it goes with the HE-6SE. :D
 

BurritoJustice

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Please let me know how it goes with the HE-6SE. :D

I got a balanced cable adaptor made for the RME to see if it can power it alone. The official word is that it should work with the HE-6 given that it is rated at 20v RMS and 3w maximum but hey; it's the HE-6. It's rated at 83dB but Tyll measured his pair at 77dB, which is just absurdly low sensitivity.

I'm excited to actually turn an amp past about 8 o'clock lol, I'm a low volume listener.
 

SchwarzeWolke

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My August order (due to deliver in February) just shipped. Way ahead of schedule, which is unusual for Massdrop.
[...]
Same here too! My experience with the HD-6xx and the HE-4xx is a little different. Both were shipped ahead of the schedule, the HD-6xx a whole month!
 

mi-fu

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My August order (due to deliver in February) just shipped. Way ahead of schedule, which is unusual for Massdrop.

Pretty pumped, should arrive at the same time as my ADI-2 Pro Fs and Hifiman HE-6se.

Good to hear that. Hope they will have the next drop soon!!
 

Veri

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Just made a preorder of Monoprice AK/THX dac-amp https://www.monoprice.com/product?c_id=120&cp_id=12008&cs_id=1200801&p_id=24459&seq=1&format=2&res=1
Hope that they will deliver to Finland, Europe....

I'm sad to tell you that monoprice asks exorbitant shipping prices to EU. Try to check out the little liquid spark amp to your home for reference... and that's for a tiny/low-weight product.

You'd do much better to ask a buddy in the US to buy and ship it for you.
 
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I'm sad to tell you that monoprice asks exorbitant shipping prices to EU. Try to check out the little liquid spark amp to your home for reference... and that's for a tiny/low-weight product.

You'd do much better to ask a buddy in the US to buy and ship it for you.

You're right, just got the shipping cost for the Monolith by Monoprice Portable Headphone Amplifier and DAC with THX AAA Technology to Sweden, guess shipping to Finland is in the same ballpark - 72.48 USD
 
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