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Tear down of Massdrop THX AAA 789 Headphone Amp

Veri

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Feb 6, 2018
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#81
I think that if this is just a licensed THX's design it would be beneficial to distribute it under another brand, maybe adding an internal connector for a DAC board like f.e. the Moon 430, Jotunheim, ..., and maybe include a better potentiometer too (Alps blue velvet, Vishay pro, ...), selling it as they are doing now is seriously limiting its potential user base.
That is exactly what the THX AAA technology is though. A design that is distributed to other manufacturers
https://www.thx.com/mobile/aaa/

It is licensed to monoprice, massdrop and benchmark right now. more will surely follow.
 
Joined
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#82
I know, but that's not what I meant, what I understand is that THX licenses to Benchmark and maybe Monoprice is mainly their amplifier topology (feed forward), but in Massdrop case from what I've read the entire amp's design has been done by THX, so that's the interesting point, and distributing it under Massdrop's drop model seriously limits its sales

There are many good headphone amps out there, what makes this one special is what it offers for the price, but I also understand that if it was sold under a different distribution model the story could be different.

That is exactly what the THX AAA technology is though. A design that is distributed to other manufacturers
https://www.thx.com/mobile/aaa/

It is licensed to monoprice, massdrop and benchmark right now. more will surely follow.
 

Another Bob

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#83
Was just wondering @amirm or anyone who has the amp, whether it has ventilation holes underneath the case ? I can't seem to spot anything on the few Youtube videos or online photos.

Much appreciate if anyone can snap a photo if there are any vent holes on the underside of it.

Thanks in advance! :)
The bottom is solid (no holes).
 

jackenhack

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Oct 25, 2018
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#84
One thing I've noticed when looking at the PCB is the chosen resistor values used for the feedback loop. I've been designing and measuring a lot with the OPA1612 opamp and tried to optimize the resistor values. If one does the calculations for the OPA1602 and OPA1612, the values on the THX 789 matches the OPA1612 better.

643BB316-671F-462C-91FB-B360249BEDB9.jpeg


Here's the calculated value for OPA1612. A closer match to the resistors on the board. I have a sneaking suspicion that the amp was originally designed with OPA1612 and they cut some cost by replacing them with the cheaper OPA1602. This could explain the discrepancy between their advertised specs vs @amirm.

453CD0D1-644C-48A4-834C-D5772170F420.jpeg


But let's be honest, there's no need for better performance. But I will try to see if I can even eke out enough out of my poor QA-401 to be able to measure the THX 789 and then replace the opamps. I have four OPA1612, so I need to order one more. Could I then have the best THX 789 of all? :)
 
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