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Tear down of Massdrop THX AAA 789 Headphone Amp

rajapruk

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#41
@AndrewMason The AAA patents are all named something like "low dissipation amplifier...".
Is this a major feature of this technology, or maybe even the driver of it emerging: that it dissipates very low heat? I thought low distortion was the major feature of AAA.
So was the low distortion like a lucky byproduct of trying to do a good sounding low dissipating amp?
Maybe the language barrier is messing with me here.
 
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trl

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#42
Thanks!

Do you see any dc-protection caps on the input? Might it be C12 and C13 that eventually got emitted at some later stage of the product development?
@AndrewMason said in a Massdrop comment a long time ago there would be dc-protection caps on the input that could be shorted/bypassed, and then maybe giving even lower LF distortion. Warranty-voiding of course.

Interesting to see how tight all SMD-components sits together. This is probably one of the keys to get this level of performance, avoiding unwanted parasitic capacitance etc.

Regarding reverse engineering, is that easy to do on a pcb like this with several layers? I'm just guessing we have 4 layers, or more, of connections. But maybe it is enough to see which SMD-components are used to copy it conceptually?

I am glad there are so few electrolytic capacitators in there that can go bad/old. Looks like this one will live forever :)
It's probably a similar schematic with this one here: http://www.ti.com/lit/ug/snaa052a/snaa052a.pdf. I'm pretty sue it's DC-servo there, but perhaps Amir can trace this out somehow. :)

L.E.: However, they really nailed it with the http://www.ti.com/lit/ug/snaa052a/snaa052a.pdf opamps, very good job indeed.
 

AndrewMason

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#43
@AndrewMason The AAA patents are all named something like "low dissipation amplifier...".
Is this a major feature of this technology, or maybe even the driver of it emerging: that it dissipates very low heat? I thought low distortion was the major feature of AAA.
So was the low distortion like a lucky byproduct of trying to do a good sounding low dissipating amp?
Maybe the language barrier is messing with me here.
THX AAA unlocks several benefits, depending on how one adjusts the system. It can be optimized for insanely low distortion, or for low distortion at insanely low bias current, or somewhere in between.
And although ours is pretty accurate here, as general rule you should never put any trust in Patent titles. They're often a bad indicator and I've seen many that are in fact misleading.
 

amirm

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#45
Are there any informations about the upcoming measurements of the Loxjie P20? I own one myself and I think it is a really cool amp.

best regards
I have purchased one but it is not in front of queue due to large backlog of gear to test.
 
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#47
I have purchased one but it is not in front of queue due to large backlog of gear to test.
Thanks for the answer. I enjoy the device so far and I really want to know how the Loxjie compares to the Massdrop CTH and normal AMPs. I could not test the balanced output yet, because I do not own any balanced cables so far.

By the way: The JDL Support told me that their Cyber Monday promotion will be different than last year. There was a free global shipping promotion last year but this time it is pretty likely to be limited to the US :(
 

Sythrix

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#48

pos

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#49
Unless it won't work for your setup, just get a smart power strip. The control will automatically turn on the dependent outlets.
Thanks for the suggestion, but powering the outlet on is not the problem here: the problem is that the unit wont turn on unless you manually press the power button on the unit.
 

restorer-john

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#50
Thanks for the suggestion, but powering the outlet on is not the problem here: the problem is that the unit wont turn on unless you manually press the power button on the unit.
Looks like a flip/flop with initial delay arrangement. It would very be easy to modify.

So it has an auto-off but no auto-on? Are you serious?
 
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#51
@AndrewMason Would there be any potentially measurable benefit in replacing the standard power brick with a linear power supply? Not that it would be audible of course.
 

Sythrix

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#52
Thanks for the suggestion, but powering the outlet on is not the problem here: the problem is that the unit wont turn on unless you manually press the power button on the unit.
I remember now, yes. You're right, it wouldn't help you. I'm trying to think of a way to make it happen, but I'm coming up blank for now.
 

tomchr

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#53
So it has an auto-off but no auto-on? Are you serious?
It has a signal detect IC in it, so it turns on automatically when music is applied and off when the music goes away (after a delay). There's an always-on override. You can see the block diagram of the signal detect IC (and its part number) in the first post.

Tom
 

restorer-john

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#54
It has a signal detect IC in it, so it turns on automatically when music is applied and off when the music goes away (after a delay). There's an always-on override. You can see the block diagram of the signal detect IC (and its part number) in the first post.
I saw that, but the owner is saying you have to press the power button to turn it on. If a line signal trips it (which it should) I can't see what his issue is...
 

rajapruk

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#55
I never tested the auto-on/auto-off function. I just tested pulling the power while on, and then putting power back on, and it did not start (with auto-off turned off). I might have mislead @pos that auto-on does not work. :facepalm:
I must test this auto-on later today.
 

rajapruk

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#56
I saw that, but the owner is saying you have to press the power button to turn it on. If a line signal trips it (which it should) I can't see what his issue is...
If it works like that there is no issue. It's really good actually because then the amp will probably start last in the sequence of apparatuses automatically.
 

pos

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#57
As per @AndrewMason in the main THX789 massdrop thread:
To turn back on requires pushing the Power button. We decided to not have "auto-on" feature since to do so without impacting fidelity, it would have required more relays and circuitry, driving the cost too high. Of course if you prefer, set the switch to "bypass" mode and the amp will remain on forever.
I can understand this is not an issue for headphone users, but it is for me as my amplifiers are sitting behind my speakers, powering compression drivers (and doing so extremely well, I must say :))
 
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rajapruk

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#58

tomchr

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#59
I saw that, but the owner is saying you have to press the power button to turn it on. If a line signal trips it (which it should) I can't see what his issue is...
As noted by POS above, apparently they designed it differently. Now that I think about it, I kinda like the manual-on/auto-off. As long as it doesn't turn off during quiet passages in the music, that is. It's not the most intuitive, but it does prevent the amp from staying on all night after the user has gone to bed, which is neat.

Tom
 

pos

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#60
I would love to be able to modify it to automatically turn on with power in though, or maybe with an external trigger.
Anybody got an idea on how this could be done, beside @rajapruk proposal? :p
 
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