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Review and Measurements of Massdrop THX AAA 789 Amp

maxxevv

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You meant 20~400hz as opposed to the 789 I think?

It is interesting indeed. It makes me wonder if a live load like say a HD650 and say the HE400i for the same test would bear similar flaws in the recently well measuring amps.

Yes, no need full voltage either 1V as you suggest or 90dB SPL equivalent for each headphone.

Likewise, maybe something similar when it comes to power amps too ??
 

JohnYang1997

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Very interesting indeed, I wonder if you could please include such a test with all future headamps, because it's very relevant. 1V RMS should do, I guess. I would call it "headphones driveability" and one planar + one dynamic headphone should be good enough. I guess such a test will help some of us to better understand if an amp "sounds" better or worse than another amp, with real headphones attached instead of a dummy resistor.

Funny thing, apparently my Objective2 with MUSES8920 used as buffers (mostly because of the lower output DC) seems to be measuring a bit better between 20-4000 Hz than Atom (e.g.: THD @40Hz is 0.05% instead of 0.15%). However, I don't have SR60e, so I used instead the SR60i (I've heard there are the same drivers inside):

View attachment 32191
O2 driving Grado SR60i



Note: At 8 KHz my ASUS U7 ADC is developing an issue, or the drivers used, so the high THD from around 8 KHz may be ignored.
You can reduce the output impedance to reduce distortion with load. At least from what I measured a year ago. Best that I have measured are with opa827 and opa1622 with 0.05ohm/0.1ohm output ballast resistor. Also the cable/splitter has an big impact to the measurements. You should be able to get under 0.01% at resonance frequency.
 

amirm

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Likewise, maybe something similar when it comes to power amps too ??
The issue with this test is that external noise, resonances in the headphone/measurement rig, fit of the headphone, etc. all seem to contribute to this measurement. So it is not just a pure example of a realistic load.

I have thought about testing with a real speaker though when it comes to amplifiers at low volume. Thinking of running a long cable with the speaker in the attic....
 

maxxevv

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The issue with this test is that external noise, resonances in the headphone/measurement rig, fit of the headphone, etc. all seem to contribute to this measurement. So it is not just a pure example of a realistic load.

I have thought about testing with a real speaker though when it comes to amplifiers at low volume. Thinking of running a long cable with the speaker in the attic....
Its a problem indeed due to the sound volume issues. I guess capping things at say a reasonable 50 ~100 Watts might be feasible (if your attic is big enough to dissipate the "noise" ) ?
 
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Thanks! I do notice when running ref of 7dBu (or 1dBu when using XLR) and volume at 0dB it pushes into overdrive in some situations (or very close - level indicators turning yellow etc) so perhaps rocking 7dBu (which is actually 13dBu via XLR, yes?) and reducing volume dB by 4.5 prevents this. As you said, I certainly can't tell a difference, even when it's nearing overdrive. Seems the 7dBu and -4.5dB is the better option and enables room for EQ tweaks etc.
 

trl

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You meant 20~400hz as opposed to the 789 I think?

It is interesting indeed. It makes me wonder if a live load like say a HD650 and say the HE400i for the same test would bear similar flaws in the recently well measuring amps.

Yes, no need full voltage either 1V as you suggest or 90dB SPL equivalent for each headphone.

Likewise, maybe something similar when it comes to power amps too ??
I've attached some more measurements here; don't want to pollute the thread with full image size, as it's off-topic, I guess. It's Conductor V2+ measured at the 6.3mm plug, 1V RMS (checked by scope).
 

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trl

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You can reduce the output impedance to reduce distortion with load. At least from what I measured a year ago. Best that I have measured are with opa827 and opa1622 with 0.05ohm/0.1ohm output ballast resistor. Also the cable/splitter has an big impact to the measurements. You should be able to get under 0.01% at resonance frequency.
Thanks for the info, but O2's output impedance should not have much impact on the >32Ohms cans.
There was no cable splitter, I simply unscrewed the plug and soldered directly the short shielded wires that go to the ADC (used to be a double shielded RCA - 3.5mm jack sometimes).
 
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trl

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The issue with this test is that external noise, resonances in the headphone/measurement rig, fit of the headphone, etc. all seem to contribute to this measurement. So it is not just a pure example of a realistic load.

I have thought about testing with a real speaker though when it comes to amplifiers at low volume. Thinking of running a long cable with the speaker in the attic....
For the headphones the dummy-head should be about perfect I'd say, and the external noises can be easily minimized with the right attitude...or the right shotgun. :)

10V RMS should do fine for 4Ohms speakers and 14V RMS for 8Ohms speakers as well. That would be 25W, probably a bit over 100dB SPL @1m for most common speakers (88-92dB/Wm), so any cheap passive or active noise cancellation headphone will help you staying inside the room to do the measurements.
 

maxxevv

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I've attached some more measurements here; don't want to pollute the thread with full image size, as it's off-topic, I guess. It's Conductor V2+ measured at the 6.3mm plug, 1V RMS (checked by scope).
I think from your measurements, Planars do not alter the THD+N measurements as dramatically as Dynamic driver headphones.

So its probably a good idea to do such measurements with dynamic driver headphones ?

Just to check though, were the headphone cups covered ? As far as I understand, back-pressure does affect coil load on dynamic drivers, so they should vary with an open ended cup or a covered (like worn on head) test protocol.

This does raise the question of whether having static loads on the amps actually depicts performance that's "real world.". So, though slightly off topic, is still relevant for this thread.

Just a suggestion for @amirm , perhaps if possible, a THD+N test for headphone amps using dynamic driver headphones that run 32 Ohm, 300Ohm, 600 Ohm, either at 1V (if the headphone is insensitive enough) or at output set to correspond to 90~100 dB SPL, being the upper limits of what's user applicable levels.
 

trl

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I think from your measurements, Planars do not alter the THD+N measurements as dramatically as Dynamic driver headphones.

So its probably a good idea to do such measurements with dynamic driver headphones ?

Just to check though, were the headphone cups covered ? As far as I understand, back-pressure does affect coil load on dynamic drivers, so they should vary with an open ended cup or a covered (like worn on head) test protocol.

This does raise the question of whether having static loads on the amps actually depicts performance that's "real world.". So, though slightly off topic, is still relevant for this thread.

Just a suggestion for @amirm , perhaps if possible, a THD+N test for headphone amps using dynamic driver headphones that run 32 Ohm, 300Ohm, 600 Ohm, either at 1V (if the headphone is insensitive enough) or at output set to correspond to 90~100 dB SPL, being the upper limits of what's user applicable levels.
Both inner sides of the cups were perfectly covered indeed, I've used my own leg/pulp for that, so perfect sealing.
 

solderdude

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I believe RayDunzl also noticed increased distortion with real loads which turned out to be the speakers picking up sounds when testing some tube amps.
As there seems to be no relation to the impedance swing of the headphones it is unlikely to be back EMF but rather the load acting as a microphone picking up background noise ?
If it were related to back EMF one would expect the impedance rise to pop up.

LF background noise is very hard to get rid of.

Perhaps run a test with the input of the amp shorted (so no signal) and faking a sweep, so no stimulus on the headphone is a possible test for this.
I don't know if this is possible though. If it is background noise from the room being picked up you should still see a rise in distortion ?
 

JohnYang1997

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Thanks for the info, but O2's output impedance should not have much impact on the >32Ohms cans.
There was no cable splitter, I simply unscrewed the plug and soldered directly the short shielded wires that go to the ADC (used to be a double shielded RCA - 3.5mm jack sometimes).
Just try it. Also with different opamps. Two dual opa827 or opa1622 + 0.1ohm balast output resistors. The output resistors are essentially affecting the feedback take off point. So when emf hits, it increases the distortion which isn't going to be fully absorbed by the opamp. PM me if you want some measurements I made.
 

JohnYang1997

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I believe RayDunzl also noticed increased distortion with real loads which turned out to be the speakers picking up sounds when testing some tube amps.
As there seems to be no relation to the impedance swing of the headphones it is unlikely to be back EMF but rather the load acting as a microphone picking up background noise ?
If it were related to back EMF one would expect the impedance rise to pop up.

LF background noise is very hard to get rid of.

Perhaps run a test with the input of the amp shorted (so no signal) and faking a sweep, so no stimulus on the headphone is a possible test for this.
I don't know if this is possible though. If it is background noise from the room being picked up you should still see a rise in distortion ?
If it's the background noise it will be absorbed by the feedback. The previous instance was the amp not turned on. Once he turned on it went away.
I have done tests that output impedance affects distortion with around resonance frequency. 1ohm 0.5ohm is low on paper but when comparing to 0.01% it's very big number.
 

JohnYang1997

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However in the real world situation. It's not that important anymore. The impedance of contacts and cable starts to be prominent when getting into sub 0.1ohm output impedance. But as we can go at least we should get sub 0.2ohm output impedance.
 

Julf

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I wonder about the long term health of this unit. I know that to a lot of people anything under $1K is entry level, but this unit is not cheap to me. In Canada, the landed cost is about $650.00/$660.00, all in. There is basically no warranty. If you have a problem within the first year they will replace (unlikely) or just refund you. Much like department stores do now, there is no warranty, just a one year refund period if you can drag that treadmill, barbecue, etc. back to the store.

What if something breaks after 12 months? For Amir and the experts do all the internals point to a long life span (in a general sense - failures happen), or more to a "built to a price unit" that you will probably get a few years out of?

My LCX cost me $345.00 landed and my Burson Fun-Classic was $335.00 landed, all in. I thought both were great values. The 789 is about double and seems to offer no service after "warranty". Seems risky though...

Shane D

PS: And for those that were paying attention, I am aware that the LCX is in the same boat. But at $345.00, tax in, I am willing to take the risk.
 
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I wonder about the long term health of this unit. I know that to a lot of people anything under $1K is entry level, but this unit is not cheap to me. In Canada, the landed cost is about $650.00/$660.00, all in. There is basically no warranty. If you have a problem within the first year they will replace (unlikely) or just refund you. Much like department stores do now, there is no warranty, just a one year refund period if you can drag that treadmill, barbecue, etc. back to the store.

What if something breaks after 12 months? For Amir and the experts do all the internals point to a long life span (in a general sense - failures happen), or more to a "built to a price unit" that you will probably get a few years out of?

My LCX cost me $345.00 landed and my Burson Fun-Classic was $335.00 landed, all in. I thought both were great values. The 789 is about double and seems to offer no service after "warranty". Seems risky though...

Shane D

PS: And for those that were paying attention, I am aware that the LCX is in the same boat. But at $345.00, tax in, I am willing to take the risk.
The 789 has good quality parts, and generates almost no heat. If it survives 1 year it will most likely last a long time. The power supply looks cheap (and is cheap), it might die in a couple years, if it dies nicely then you can just buy another one, if it dies catastrophically then it might damage something.
 
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The 789 has good quality parts, and generates almost no heat. If it survives 1 year it will most likely last a long time. The power supply looks cheap (and is cheap), it might die in a couple years, if it dies nicely then you can just buy another one, if it dies catastrophically then it might damage something.
With most electronics (TV's, computers,etc.), if you get past that first 6-12 months you are set. I hope this amp is the same. I am debating on just grabbing the Atom for SE duty, but this 789 is staying on Drop forever.

Shane D
 
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trl

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FUN is an OK headamp: low noise, powerful enough, lot of gain, medium sized, not hot to touch, big PCB inside and relatively easy to repair (worth mentioning the 5-years warranty too and you don't pay for the shipping, in most cases). If you want to replace FUN with Atom you will loose some of power (not that you'll ever need so much power anyway) and the lower noise of the Atom will make no difference for your LCD (not even with 16 Ohms IEMs will feel the difference).

If you really think it's time to swap your existing FUN, then THX AAA 789 is indeed an upgrade, not because it measures better (in an A/B test you won't feel any difference between FUN and THX 789 anyway), but mostly because it's single-ended and balanced and it has plenty of power reserve for your future cans.

However, there's an entire thread about THX AAA 789 headamp here https://www.audiosciencereview.com/...n-of-massdrop-thx-aaa-789-headphone-amp.5327/ and you might want to ask the same question in that thread too. In the first post Amir uploaded a large picture with the internals of the THX AAA 798 headamp. There's also @304290 forum member that has some issues with his 789 headamp; not sure he managed to fix it or to get his money back.
 

JohnYang1997

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FUN and CV2 are very noisy. How are they suddenly become low noise?? The only earphone that I can't hear the noise is er4b/s. Even with er4sr will have the noise. Many earphones are very noisy on burson. And FUN is even worse than CV2.
 
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