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Tear down of Massdrop THX AAA 789 Headphone Amp

miero

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Killingbeans

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I've been drooling over the Neurochrome amps for a long time. I'm aware that they take advantage of a somewhat similar principle(?), but I'm thinking that the measly LM3886 could be taken to an even higher level using the circuit topology of THX AAA?

The Benchmark amp is (very, very) cool and all, but it could use some competition :D
 
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JohnYang1997

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Sorry for reviving an old thread, but this has puzzled me lately :)

I'm thinking it might be possible to utilize the design around the LM3886 (?) and thereby jump into the realm of speaker amplification.

But maybe it's not that easy?
It's very possible. But single 3886 is much less power relatively in power amp than opa564 in headphone amp. For small power option it's good.
For higher power output you need more in parallel and in bridge configuration. Then we are talking about the power supply. It's a much worse situation you need 300W+ power supply that's cheap enough, reliable enough, and has dual rail. 789 can get away with virtual ground but that's not how that works in speaker amps. The price obviously can be brought down but there are certainly limitations and difficulties from real world.
Modulus-86 286 boards worked very well, but what about the complete amp? It's quite good but no where near the actual board itself.
 

Killingbeans

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It's very possible. But single 3886 is much less power relatively in power amp than opa564 in headphone amp. For small power option it's good.

True. I'm mostly toying with the idea of a 3886 based amp with THX AAA topology as a dedicated tweeter amplifier in an active speaker.
 

Tks

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It's very possible. But single 3886 is much less power relatively in power amp than opa564 in headphone amp. For small power option it's good.
For higher power output you need more in parallel and in bridge configuration. Then we are talking about the power supply. It's a much worse situation you need 300W+ power supply that's cheap enough, reliable enough, and has dual rail. 789 can get away with virtual ground but that's not how that works in speaker amps. The price obviously can be brought down but there are certainly limitations and difficulties from real world.
Modulus-86 286 boards worked very well, but what about the complete amp? It's quite good but no where near the actual board itself.

Any desktop PC PSU's work for this sort of application? There is no problem getting 300W+ PSU's for less than $100, and for like $100-$200, you basically have the best on offer..
 

JohnYang1997

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Any desktop PC PSU's work for this sort of application? There is no problem getting 300W+ PSU's for less than $100, and for like $100-$200, you basically have the best on offer..
+-40V? or +-35V so no. Also if the price is 100 dollars there's no deal to make. It's already too expensive.
 

ZeDestructor

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I've been drooling over the Neurochrome amps for a long time. I'm aware that they take advantage of a somewhat similar principle(?), but I'm thinking that the measly LM3886 could be taken to an even higher level using the circuit topology of THX AAA?

The Benchmark amp is (very, very) cool and all, but it could use some competition :D

I think the real competition already exists from the Class D amps from Purifi, Hypex and friends. While the sheer audio output performance of the AHB2 is top notch, it's becomes a lot less top notch once you add the power and cooling costs of running class AB over class D. Then you add the difference in power output capability, difference in weight (important for those of us paying a lot for international shipping) and difference in price (more relevant than everything else for those of us running multi-channel).

+-40V? or +-35V so no. Also if the price is 100 dollars there's no deal to make. It's already too expensive.

The Hypex SMPS1200 is quite well-regarded and seems to sell for around $180 (I found em for €180 at DIYclassd.com and assumed the usual 1USD = 1EUR conversion). I can see why it wouldn't be acceptable for some companies (like Topping so far), but it's clearly perfectly acceptable for others like Nord or Audiophonics.

Besides, we already have multi-thousand dollar DACs and headphone amps. Paying 1000-2000 USD for speaker power amps is not too terrible in comparison, if you think about it. Assuming you have the room and speakers for it.

PS: Personally I'm on the Dante/AES67 directly to the PoE-powered active speaker train myself, so I've managed to successfully get completely away from the world of power amplifiers :D
 

JohnYang1997

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I think the real competition already exists from the Class D amps from Purifi, Hypex and friends. While the sheer audio output performance of the AHB2 is top notch, it's becomes a lot less top notch once you add the power and cooling costs of running class AB over class D. Then you add the difference in power output capability, difference in weight (important for those of us paying a lot for international shipping) and difference in price (more relevant than everything else for those of us running multi-channel).



The Hypex SMPS1200 is quite well-regarded and seems to sell for around $180 (I found em for €180 at DIYclassd.com and assumed the usual 1USD = 1EUR conversion). I can see why it wouldn't be acceptable for some companies (like Topping so far), but it's clearly perfectly acceptable for others like Nord or Audiophonics.

Besides, we already have multi-thousand dollar DACs and headphone amps. Paying 1000-2000 USD for speaker power amps is not too terrible in comparison, if you think about it. Assuming you have the room and speakers for it.

PS: Personally I'm on the Dante/AES67 directly to the PoE-powered active speaker train myself, so I've managed to successfully get completely away from the world of power amplifiers :D
Power supply has to be under 50 dollars for it to make any sense. BOM needs to be 1/5 or less than the retail price. Otherwise the whole thing won't make sense.
On the bright side somethings cooking.
 

Killingbeans

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I think the real competition already exists from the Class D amps from Purifi, Hypex and friends.

Absolutely. If I was in the market for a power amp, I'd go for Purifi or Hypex and never look back.

It's mostly the technician in me that's curious to see how far the combo could be pushed for low power applications.

PS: Personally I'm on the Dante/AES67 directly to the PoE-powered active speaker train myself, so I've managed to successfully get completely away from the world of power amplifiers :D

I'd like to jump on a similar train. Maybe not PoE-powered, but active speakers for sure. Won't shed a single tear, if passive speakers becomes a thing of the past.
 

ZeDestructor

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Power supply has to be under 50 dollars for it to make any sense. BOM needs to be 1/5 or less than the retail price. Otherwise the whole thing won't make sense.
On the bright side somethings cooking.

Wouldn't a higher retail price raise the "allowable" BOM to match?

Good to hear that something is cooking though. Looking forward to seeing it put on the bench.

Absolutely. If I was in the market for a power amp, I'd go for Purifi or Hypex and never look back.

It's mostly the technician in me that's curious to see how far the combo could be pushed for low power applications.

I'd like to jump on a similar train. Maybe not PoE-powered, but active speakers for sure. Won't shed a single tear, if passive speakers becomes a thing of the past.

There's plenty of excellent active speakers with analog inputs. Digital inputs are somewhat rarer, but not impossible to find. Dante/AES67/AVB input is quite a bit rarer though, but Genelec has such a line, and it takes power and Dante/AES67 via PoE which makes it *very* convenient for my multichannel application. Expensive though...

That's hardly THX 789 talk though, so we should end here or move to a new thread.

Talking of the 789, the 789's Sanni (iirc, from what's been posted in this very thread) is a much nicer volume pot than the Alps in my Fostex HP-A4 - it's both a lot less stiff on starting the movement, and it doesn't crackle horribly when turned.
 

Rottmannash

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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...
I can assure you it will not power on by itself, even when being fed a signal. Not even sure it will power off when a signal is absent either.
 

Rottmannash

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DrCWO

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More info about THX AAA circuit is in the patent:
- https://patents.google.com/patent/US9071201B2
Source: https://www.thx.com/patents/aaa/
I wonder about this patent because the idea of this kind of amplifier is quite old. In my youth the current dumping amplifier Quad 405 was an unfulfilled wish. Here you see a technical paper http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1975/Current Dumping Audio Amplifer DCD.pdf describing the idea of Peter Walker which is in my eyes the same as THX AAA. Please correct me if I a‘m not right. Really nice that good ideas return, for our luck today in fidelity realization. But an excellent engineering should not be enough for a patent on vintage ideas!
 

338h10

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@AndrewMason

I typically use my DAC's volume control to adjust volume. Given that I will have no use for the amp's volume control and the circuitry around the pot involves balanced-SE-balanced conversion, is there a way to bypass all the circuity around the volume control (and the converting opamps)? The signal path could be cleaner and shorter this way. Thanks!
 

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Jimster480

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It is a Chinese volume pot branded as "SANNI"
I don't think it really matters though, this amp is just great. I've had it since the day it came out basically and I still use it today and I love it. I drive it with a Topping DX7 first gen which is fed by an SMSL xUSB2 after I burned out the USB interface on my DX7...
 
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