Review and Measurements of Massdrop THX AAA 789 Amp

[Veri]

Is there any difference in impedance measurable between outputs? The 1/4 and 1/8 SE outputs seem to have the same gain, so I’m assuming there’s not something weird going on with impedance like there is with the topping a30, for example.
View attachment 33944

No, same impedance. No worries.

 

[greatmagician]

hello guys i receive my THX 789 after using the gain Switch its work at the first time but after using the switch now not working at all no deferent when i try to change i have Akg 702 HD6XX Fostex TH-X00 HE4XX any advice ?

 

[Dana reed]

hello guys i receive my THX 789 after using the gain Switch its work at the first time but after using the switch now not working at all no deferent when i try to change i have Akg 702 HD6XX Fostex TH-X00 HE4XX any advice ?

???
You mean that you get no sound at all, or that the level sounds the same no matter the gain setting?

 

[greatmagician]

View attachment 34176 ???
You mean that you get no sound at all, or that the level sounds the same no matter the gain setting?

No i mean when i try to switch the gain nothing change .

 

[Sythrix]

I just got the HE6SEs from Hifiman and I am using them on this amp. However, I am unsure what would be the best gain setting to use. I have tested all 3 gain settings and they are all able to drive the headphones to painfully loud settings. I am wondering however, because of the uniquely low sensitivity of these headphones, 83.5 dB (somewhat lower in actual tests) (50 ohm). So would it be better to just keep it at 3? Or should I keep it at 1 for the longer throw of the volume knob?

I know gain =/= volume, but I also don't quite know how that's going to work out with these headphones in regards to how much power they require and how they will sound optimally. I also don't want to enter clipping territory... if that's possible.

EDIT: I’ve discovered that clipping occurs on gain level 3, being fed with XLR from RME DAC-2. This really surprised me, but I guess I just don’t understand it enough. Keeping it at gain 1 for now. Source was Amazon-HD audio, so maybe that had something to do with it. Either that or my settings.

 

[AnalogDE]

Looks like the latest drop closed... Does anybody know if you can cancel your order? I wanted to explore the other options (SMSL, Monolith, etc)... if not I guess I'm stuck with this amp

 

[Sythrix]

Looks like the latest drop closed... Does anybody know if you can cancel your order? I wanted to explore the other options (SMSL, Monolith, etc)... if not I guess I'm stuck with this amp

As far as I know, you cannot once the drop is submitted. However, that’s also the assumption they’re submitting a mass order to a different company. Since this is a Massdrop-made product, you might try looking... being that they fulfill the orders. If there isn’t an option on your order page, I highly doubt it, but you could try contacting support.

Honestly, I don’t know why you would want to though. Anything that’s "better" isn’t worth the hassle since it won’t be audibly different with such high performance numbers. I would only do it if your use-case has expanded or changed... or you simply hate the aesthetics.

 

[AnalogDE]

As far as I know, you cannot once the drop is submitted. However, that’s also the assumption they’re submitting a mass order to a different company. Since this is a Massdrop-made product, you might try looking... being that they fulfill the orders. If there isn’t an option on your order page, I highly doubt it, but you could try contacting support.

Honestly, I don’t know why you would want to though. Anything that’s "better" isn’t worth the hassle since it won’t be audibly different with such high performance numbers. I would only do it if your use-case has expanded or changed... or you simply hate the aesthetics.

The Monolith amp looks a bit better to me.. Not sure it's worth the hassle because it's coming out late-Nov.

 

[Sythrix]

The Monolith amp looks a bit better to me.. Not sure it's worth the hassle because it's coming out late-Nov.

The measurement are close, although I think they were actually measured at different gain and voltages so... yeah. Things get hazy. Also, Since I sent Amir the original 789, we know that’s the performance from a common unit. This one is an advance unit, sent by Monoprice or someone with direct access to early hardware. Something... something... "cherry picking"... we just don’t know this early on. I really wouldn’t worry about it.

 

[Dana reed]

I just got the HE6SEs from Hifiman and I am using them on this amp. However, I am unsure what would be the best gain setting to use. I have tested all 3 gain settings and they are all able to drive the headphones to painfully loud settings. I am wondering however, because of the uniquely low sensitivity of these headphones, 83.5 dB (somewhat lower in actual tests) (50 ohm). So would it be better to just keep it at 3? Or should I keep it at 1 for the longer throw of the volume knob?

I know gain =/= volume, but I also don't quite know how that's going to work out with these headphones in regards to how much power they require and how they will sound optimally. I also don't want to enter clipping territory... if that's possible.

EDIT: I’ve discovered that clipping occurs on gain level 3, being fed with XLR from RME DAC-2. This really surprised me, but I guess I just don’t understand it enough. Keeping it at gain 1 for now. Source was Amazon-HD audio, so maybe that had something to do with it. Either that or my settings.

if you feed it from RCA on the RME DAC, does it still clip on gain 3? I haven't tried feeding mine via the balanced inputs yet, since I read somewhere that there's really no advantage on this amp (converts XLR to SE and back again for XLR output.
I only have to push HE560 as my most insenstive cans, but on gain 3 I can push them to ear-bleeding without noting any clipping

 

[MC_RME]

A balanced connection always has advantages against unbalanced, mainly hum suppression and much lower ground loop sensitivity. And for these it doesn't matter what the unit does inside ( I would say more than 90% of units with a balanced XLR input go unbalanced inside at some point).

 

[Sythrix]

if you feed it from RCA on the RME DAC, does it still clip on gain 3? I haven't tried feeding mine via the balanced inputs yet, since I read somewhere that there's really no advantage on this amp (converts XLR to SE and back again for XLR output.
I only have to push HE560 as my most insenstive cans, but on gain 3 I can push them to ear-bleeding without noting any clipping

Interestingly, it does not clip with the RCAs. Signal level is too high...? I don't understand it. Everything should be better with the XLR, but here we are.

 

[Dana reed]

Interestingly, it does not clip with the RCAs. Signal level is too high...? I don't understand it. Everything should be better with the XLR, but here we are.

I'm just wondering if it's a 2V vs 4V input thing. When I get a chance to bring my DX7s home from work, I can try it with the 789 both with XLR and RCA to see if I get the same results. For now, it's either the Modi 3 or my iPhone headphone port directly as the source.
Have been itching to the try the HE6 SE, but haven't pulled the trigger. Between the HE560, LCD2 and Aeons, I probably have enough invested in planars.

 

[Sythrix]

I'm just wondering if it's a 2V vs 4V input thing. When I get a chance to bring my DX7s home from work, I can try it with the 789 both with XLR and RCA to see if I get the same results. For now, it's either the Modi 3 or my iPhone headphone port directly as the source.
Have been itching to the try the HE6 SE, but haven't pulled the trigger. Between the HE560, LCD2 and Aeons, I probably have enough invested in planars.

Playing around with "Reference Level" on the ADI-2 DAC and lowering that eliminates the clipping. It was at +13 dB. The options are +13, +7, +1, -5.

I'm not sure as to the relevance here. Is it an artificial manipulation of the signal? Why isn't straight up "0" an option if so? +1 seems the closest. I don't want to lower it below normal levels, but I also don't want overzealous pre-amplification going on. I'm not sure what the best option would be for signal integrity.

EDIT: Also, the HE6SE seems a lot easier to drive than I was lead to believe, although I think the full potential is where people see all that wattage being used. Gets pretty damn loud on all of my amps (WHAMMY, ADI-2 DAC's HP out and Pete Millett's Nuhybrid Headphone amp... and the 789 of course.)

 

[Sythrix]

I'm just wondering if it's a 2V vs 4V input thing.

Found the answer in the discussions on Drop.

INPUT Maximums: The 789 can tolerate the following rms input voltage from your DAC without clipping:

-10dB Mode: 7 V
0 dB Mode: 7 V
+10 dB Mode: 2.1 V

On the 789, the RCA unbal and XLR-3 bal have same input voltage tolerance.

Here are two good options for you that will avoid clipping at any volume level with a 4.5V DAC:
1) Use 789 in 0dB or -10dB mode all the time and you'll never clip even at full volume. You'll achieve 4.5V for your TRS headphones, and 9V for your XLR-4 balanced headphones. or
2) To access the maximum voltage swing... attenuate 7dB in your player (e.g. Foobar) or DAC, and then use the 789 in +10dB mode. That'll achieve 7V at your TRS or 14V at your XLR-4, and never clip at any volume level.

You should avoid the max gain position unless your DAC is guaranteed (e.g. with attenuation) to not be putting out more than 2.1V. Else you'll clip the preamp inside the 789.

So yeah, you're right. That explains what you said and why the RCAs are holding steady at max gain.

EDIT: Followed advice #2 and set +7 for Reference and set it to gain 3. No clipping and I have a hell of a lot of headroom to go. However, I could get more travel with the knob and still a hefty voltage curve, one I'm unlikely to go past, if I follow advice #1. The impedance isn't terribly high on these, so I don't think I need the max voltage swing, at least not to get to any sane (or even semi-insane) volume.

 

[ReAlien]

Hi All! I'm considering to replace my THX with some DIY head-amp from a local engineer but encountered some particular problem. This DIY amp has no pre-amp output, this means that I will not be able to listen to the headphone amp and a speaker amp simultaneously unless I use some Y-adapter or another pre-amp in the chain.
When I started to look into the matter I have found a piece of information on a "golden" rule of impedance, that output impedance from DAC should be 10-20 times less than the input impedance of an amp. While THX has 50 KOhm input impedance, this DIY amp has only 2 KOhm input impedance which is a big difference. My DAC has 600 Ohm output impedance so 600 is not 10 times less than 2000. And if I use Y-adapter the resulting ratio would be even less.

What should I do to avoid this problem? Is there a cheap way to increase this ratio with some additional device? Or should I ask the engineer to increase the input impedance of his DIY amp? He says that it would require a lot of film resistors and might be detrimental to sound quality.

Also, how does this problem with mismatched impedance manifest itself? I've heard about reduced bass response and lack of clarity, is that so?

 

[JohnYang1997]

I just got the HE6SEs from Hifiman and I am using them on this amp. However, I am unsure what would be the best gain setting to use. I have tested all 3 gain settings and they are all able to drive the headphones to painfully loud settings. I am wondering however, because of the uniquely low sensitivity of these headphones, 83.5 dB (somewhat lower in actual tests) (50 ohm). So would it be better to just keep it at 3? Or should I keep it at 1 for the longer throw of the volume knob?

I know gain =/= volume, but I also don't quite know how that's going to work out with these headphones in regards to how much power they require and how they will sound optimally. I also don't want to enter clipping territory... if that's possible.

EDIT: I’ve discovered that clipping occurs on gain level 3, being fed with XLR from RME DAC-2. This really surprised me, but I guess I just don’t understand it enough. Keeping it at gain 1 for now. Source was Amazon-HD audio, so maybe that had something to do with it. Either that or my settings.

Gain = Volume but doesn't = power or headroom. And less gain(or close to unity gain) = better until it's not loud enough at maximum volume control setting.

 

[JohnYang1997]

Hi All! I'm considering to replace my THX with some DIY head-amp from a local engineer but encountered some particular problem. This DIY amp has no pre-amp output, this means that I will not be able to listen to the headphone amp and a speaker amp simultaneously unless I use some Y-adapter or another pre-amp in the chain.
When I started to look into the matter I have found a piece of information on a "golden" rule of impedance, that output impedance from DAC should be 10-20 times less than the input impedance of an amp. While THX has 50 KOhm input impedance, this DIY amp has only 2 KOhm input impedance which is a big difference. My DAC has 600 Ohm output impedance so 600 is not 10 times less than 2000. And if I use Y-adapter the resulting ratio would be even less.

What should I do to avoid this problem? Is there a cheap way to increase this ratio with some additional device? Or should I ask the engineer to increase the input impedance of his DIY amp? He says that it would require a lot of film resistors and might be detrimental to sound quality.

Also, how does this problem with mismatched impedance manifest itself? I've heard about reduced bass response and lack of clarity, is that so?

Biggest issue with low input impedance is decreased volume. As it's still 2k so no concern about distortion or such. My own diy headphone amplifier only has 1k input impedance. Just for the record. And low input impedance also drastically reduces the possibility of interference.

So.
As long as you don't experience volume decrease you are fine. No issue.
But if you experience some issue what i can say is why bother.....
Solutions if you really want to use it:
1 connect input of the new amp to the output of thx.
2 accept it as a attenuator which isn't necessarily a bad thing allowing you better low volume operation range
3 reduce the dac output impedance. 600ohm is indeed really rare, most are 100-200ohm. That depends on how its output is implemented. If it's just resistor you may just change it to 100ohm. Ask people who can help you to do the modification if you like.

 

[lator]

Been doing some back and forth comparisons between this and the JDS Atom. It seem that when considering just the single ended output, the Atom is clearly superior. The only substantial advantage this amp has is when it is run through the balanced out. So for those like me who are not interested in running balanced to headphones, the Atom seems the clear winner here.

I have similar experience. The biggest differences are Atom's better instrument separation and more articulate bass when both are using SE. THX wins with better horizontal imaging. Need to order better than stock XLR headphone cable to make final decision which one has to go.

 

[Veri]

I have similar experience. The biggest differences are Atom's better instrument separation and more articulate bass when both are using SE. THX wins with better horizontal imaging. Need to order better than stock XLR headphone cable to make final decision which one has to go.

Better than stock XLR cable? That won't make a difference mate