Review and Measurements of Massdrop THX AAA 789 Amp

[Music1969]

Sorry we dont have those curves for 8 Ohms. But like all AAA, distortion remains extremely low even at high current. Peak current is approx 0.9Apk before protection invokes.
Also beware the limitations on driving low impedance like this. See the owners manual.

Thanks Andrew.

Is it safe to say the single ended headphone output can deliver 0.5A easily into 8 ohms planar magnetic headphones, with ultra low distortion (<<<0.1% THD)?

That's 2 Watts but it's the high current output (up to 0.5A) into 8 ohms low impedance I'm interested in, with ultra low distortion (<<<0.1% THD).

 

[Music1969]

24.0 vdc +/- 5% regulated supply, and yes 5.5x2.1mm.

Thanks and what's the maximum power consumption?

 

[AndrewMason]

Thanks Andrew.

Is it safe to say the single ended headphone output can deliver 0.5A easily into 8 ohms planar magnetic headphones, with ultra low distortion (<<<0.1% THD)?

That's 2 Watts but it's the high current output (up to 0.5A) into 8 ohms low impedance I'm interested in, with ultra low distortion (<<<0.1% THD).

Yes should be fine, and yes ultra low distortion.

 

[AndrewMason]

Thanks and what's the maximum power consumption?

2.0 amps at 24 V

 

[mi-fu]

@AndrewMason , just out of curiosity, if I drive two headphones from the SE outputs on the 789 together, will it create any problem? How about the extreme case, driving three headphones together (one balanced output plus two SE outputs)?

 

[AndrewMason]

@AndrewMason , just out of curiosity, if I drive two headphones from the SE outputs on the 789 together, will it create any problem? How about the extreme case, driving three headphones together (one balanced output plus two SE outputs)?

It's ok so long as a) the headphones have combined parallel impedance higher than the minimum impedance that the 789 is rated for, and b) you dont blow up your headphones (ie don't overdrive IEMs by accident while listening to parallel headphones with high voltage .)

 

[mi-fu]

It's ok so long as a) the headphones have combined parallel impedance higher than the minimum impedance that the 789 is rated for, and b) you dont blow up your headphones (ie don't overdrive IEMs by accident while listening to parallel headphones with high voltage .)

Got it! Thanks, @AndrewMason !

 

[jsmiller58]

It's ok so long as a) the headphones have combined parallel impedance higher than the minimum impedance that the 789 is rated for, and b) you dont blow up your headphones (ie don't overdrive IEMs by accident while listening to parallel headphones with high voltage .)

@AndrewMason - combined as in parallel resistance calculations 1/Rt = 1/R1 + 1/R2 + 1/R3, or series Rt = R1 + R2 + R3... makes a big difference, particularly if the impedances involved are low...

 

[elira]

2.0 amps at 24 V

The power supply that comes with it is only 1.8 amps. Should it be 2.0 amps?

 

[Tup3x]

How's the channel crosstalk? I assume it's good, especially when using balanced but I do wonder if that's the weakest point when using single ended output.

Gotta say that I really like the idea of <1x gain options. That makes life much easier with powerful DACs.

 

[AresHarvest]

@AndrewMason - combined as in parallel resistance calculations 1/Rt = 1/R1 + 1/R2 + 1/R3, or series Rt = R1 + R2 + R3... makes a big difference, particularly if the impedances involved are low...

Just want to point out he was explicit in saying parallel. "the headphones have combined parallel impedance higher than..." (emphasis mine)

 

[AndrewMason]

The power supply that comes with it is only 1.8 amps. Should it be 2.0 amps?

1.8 A is fine. I was just giving you some safety margin.

 

[AndrewMason]

@AndrewMason - combined as in parallel resistance calculations 1/Rt = 1/R1 + 1/R2 + 1/R3, or series Rt = R1 + R2 + R3... makes a big difference, particularly if the impedances involved are low...

Yes, all the headphones will load the power amps in parallel. Not series.

 

[jsmiller58]

Just want to point out he was explicit in saying parallel. "the headphones have combined parallel impedance higher than..." (emphasis mine)

Yeah, I saw that. Just not sure if everyone has done the math. Very small effective load will resut in many cases, possibly violating the spec.

 

[Roen]

It's ok so long as a) the headphones have combined parallel impedance higher than the minimum impedance that the 789 is rated for, and b) you dont blow up your headphones (ie don't overdrive IEMs by accident while listening to parallel headphones with high voltage .)

Sorry, what is that minimum impedance that the 789 is rated for?

 

[mi-fu]

Sorry, what is that minimum impedance that the 789 is rated for?

I think the manual says 16 - 600 ohm headphones

 

[mi-fu]

btw, just looked at the massdrop page, there are only 18 units left.

 

[Veri]

btw, just looked at the massdrop page, there are only 18 units left.

Hope that's not true God effin damn it,
I am still post-poning my purchasing it

 

[AresHarvest]

15 left now

 

[L-Train]

Hi all, I just wanted to give an update regarding the crosstalk at the lowest gain. It occurred to me, since I had to put the volume control at 4 o'clock in the test that had the crosstalk issue, perhaps it's the potentiometer that's causing it. So I did another test, this time with gain setting "2", with 20 dBu input and the volume set to 1-2 o'clock to reach 6 dBV output, and I get a similar, albeit lower, increase in crosstalk!

So it looks like the increase in crosstalk is caused by the potentiometer (and varies with the position of the potentiometer), and not the gain setting.