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Tear down of Massdrop THX AAA 789 Headphone Amp

Veri

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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.
 

Jimmy

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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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#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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#86
Hi! I'm new to the ASR forums and I'm sorry if this is a bit off-topic but...

I ordered this amp on the latest drop (Shipping in May) and was wondering if there is a benefit to purchasing a linear PSU? Someone commented on the Z Reviews video of this amp and said a low ripple linear power supply will make it last longer... He was referring to the capacitors without knowing they were made by Rubycon. Is it worth looking into or am I overreacting?

Also, what is the alleged 12 Ohms headphone impedance limit about? In the documentation (on previous drops) it states you void the warranty if you use headphones with less than 12 Ohms of impedance with this amplifier. Which if true, is a big issue for me and my soon to be Verum 1 headphones (8 Ohms).
I know you can use an iEMatch impedance adapter from iFi (among others) with single-ended cables but what about a balanced cable? Does one simply add 8 or 16 Ohms to the pins carrying the signal?

Any and all replies are appreciated. Thank you.
 
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amirm

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#87
Hi! I'm new to the ASR forums and I'm sorry if this is a bit off-topic but...

I ordered this amp on the last drop (Shipping in May) and was wondering if there is a benefit to purchasing a linear PSU?
Welcome to the forum. For sure don't bother with any other power supply. The Internet is full of folklore with no basis in facts. I measured the superlative performance of this amp with the stock power supply. Any reliability issue will manifest itself in the external power supply, not the internal components.
 

amirm

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#88
Also, what is the alleged 12 Ohms headphone impedance limit about?
The lower the impedance, the more current is drawn from the unit. There are no heatsinks in the this amp so likely running it with too low of an impedance may cause thermal failures.
 

Music1969

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#89
In the documentation (on previous drops) it states you void the warranty if you use headphones with less than 12 Ohms of impedance with this amplifier. Which if true, is a big issue for me and my soon to be Verum 1 headphones (8 Ohms).
Maybe @AndrewMason can give some advice on using 8 ohms headphones?
 
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#90
Welcome to the forum. For sure don't bother with any other power supply. The Internet is full of folklore with no basis in facts. I measured the superlative performance of this amp with the stock power supply. Any reliability issue will manifest itself in the external power supply, not the internal components.
Thank you, Amir. The reviews and the amount of knowledgeable people on here is insane. I'm glad, I will stick with the stock PSU.
The lower the impedance, the more current is drawn from the unit. There are no heatsinks in the this amp so likely running it with too low of an impedance may cause thermal failures.
I see. I figured it was heat related. Do you still have this amplifier and its documentation stating this would void the warranty?
Maybe @AndrewMason can give some advice on using 8 ohms headphones?
Yeah, he'd be the one to ask. I suspect he's too busy to answer all questions people have, especially with the huge discussion section on Massdrop.
 
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amirm

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#91
Do you still have this amplifier and its documentation stating this would void the warranty?
I do and the warning is there and was posted/discussed in the review thread for amp including comment from Andrew Mason.
 

solderdude

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#92
Maybe @AndrewMason can give some advice on using 8 ohms headphones?
The verum has a flat impedance so the simplest solution is to add a series resistance in a small extension cord. This way the amp 'sees' a higher resistance load and won't overheat (which is what would void the warranty) and has no influence on the sound of the Verum.
As the manufacturer (Roman) states it can even be driven by a phone so the THX amp won't run out of steam either with added resistance.
I suggest a resistor between 12 and 22 Ohm.
Don't worry about 'damping factor' its a strawman for planar headphones, there is virtually no electrical damping, most of the damping (large membrane) is 'mechanical'.
 
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#93
The verum has a flat impedance so the simplest solution is to add a series resistance in a small extension cord. This way the amp 'sees' a higher resistance load and won't overheat (which is what would void the warranty) and has no influence on the sound of the Verum.
As the manufacturer (Roman) states it can even be driven by a phone so the THX amp won't run out of steam either with added resistance.
I suggest a resistor between 12 and 22 Ohm.
Don't worry about 'damping factor' its a strawman for planar headphones, there is virtually no electrical damping, most of the damping (large membrane) is 'mechanical'.
That’s what I thought when I read up on this.
What about balanced though? Does one simply open up the XLR connector and add 16 Ohm to the signal leads? Or can you use an XLR extension with added resistance as well? I will probably be getting a Periapt cable before the AAA arrives.
 
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#95
Maybe @AndrewMason can give some advice on using 8 ohms headphones?
Andrew responded to me on Massdrop saying he does not recommend adding resistance manually or by using an extension/adapter while referring to what's already in the manual.

Technically, adding resistance on/in the cable should make the load (Ohms) bigger, right? And in turn won't void the warranty but it's not recommended? :confused:
 
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#96
Andrew responded to me on Massdrop saying he does not recommend adding resistance manually or by using an extension/adapter while referring to what's already in the manual.

Technically, adding resistance on/in the cable should make the load (Ohms) bigger, right? And in turn won't void the warranty but it's not recommended? :confused:
I saw his response, I think the issue will happen if you turn the volume way up and demand too much current. If you are conservative with the volume there shouldn't be any problems. He refers to 4V maximum for load between 8 and 12 ohm, at 12 ohm it translates to 1.3W, and 2W at 8 ohm. I think you don't need to worry as long as you don't listen at crazy loud volume.
 

solderdude

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#97
That’s what I thought when I read up on this.
What about balanced though? Does one simply open up the XLR connector and add 16 Ohm to the signal leads? Or can you use an XLR extension with added resistance as well? I will probably be getting a Periapt cable before the AAA arrives.
For balanced it works the same. All headphones are 'balanced' in principle. It is the cable connection that makes the difference. 4pin with 4 wires or 3 pin where 2 of the wires are connected.

elira is correct as well. As long as you don't play loud or use 8 Ohm speakers you won't overheat/damage the amp. I think the warning is there to discourage people using it as a small speaker amp.

Andrew Mason's concerns are based on the fact that most very low impedance head/ear-phones have wildly varying impedances where adding resistance will alter the sound. Not so with 8 and 12 Ohm planars.
 

JohnYang1997

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I don't know why you can't just use the lower impedance headphones. It's not speakers meaning you don't crank it up. That will be well within the capability of the amp.
 
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