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Confusion regarding JDS Labs Atom power vs THX AAA 789 power

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#1
Hello, I'm new here, although I've been lurking and reading the reviews for a few weeks now. I hope this is the right place to post this question, I saw other posts asking for recommendations, etc, so I thought this was as good a forum as any to ask.

My question relates to the power measurements of the JDS Labs Atom and the THX AAA 789, specifically the unbalanced (SE) headphone outputs in the case of the 789.

I'm still a bit new to a lot of this terminology and not sure if I'm reading all of these graphs correctly in many cases, but I noticed that on the "Distortion vs Power @ 300 Ohm" tests, it appears as if the Atom actually has more power than the 789 does (again, compared to the 789's SE output); is this actually the case or am I not understanding these graphs correctly?

JDS Labs Atom "Distortion vs Power @ 300 Ohm" : 250mw @ 300 Ohm
THX AAA 789 "Distortion vs Power @ 300 Ohm" : 150mw @ 300 Ohm

The reason I ask is because I recently bought a pair of Beyerdynamics DT 990 headphones, they are the 250 Ohm version (here, they look like the massdrop editions, not sure how different they are from normal DT 990s). As could be expected, my old DAC/Amp (Audioengine D1) wasn't able to drive them properly, so I went looking for something better; after a bit of trial and error, I found out about the Topping DX3 Pro on this forum and bought that. It definitely works well at high gain, but there are some situations where I would like to be able to raise the volume a bit higher.

I had my eye on the 789 for awhile, I figured even though it was expensive, I would save up and then the next time it showed up on Massdrop, I'd get one; it seems good enough that I figured I'd probably never have to get anything else, even if I eventually got 600 Ohm cans, but then I took a closer look at those graphs..

Thus far I've mostly seen the Atom discussed as a "budget alternative" to the 789, since the 789 is hard to get a hold of and way more expensive, but these measurements confuse me, is the Atom actually louder in terms of max volume (with no distortion obviously) than the 789?
 

Roen

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#2
The 789 has 3 different gain settings, which is the one you're showing?
 

MZKM

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#3
The 789 has 3 different gain settings, which is the one you're showing?
Gain 3, which is the highest. And looking at 1% THD, it looks like it does meet spec at 200mW. The JDS Labs Atom’s measurement, if we extrapolate, match the advertised specs, as 150ohm is stated as 502mW and 600ohm as 125ohm.
 
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#4
Gain 3, which is the highest. And looking at 1% THD, it looks like it does meet spec at 200mW. The JDS Labs Atom’s measurement, if we extrapolate, match the advertised specs, as 150ohm is stated as 502mW and 600ohm as 125ohm.
I'm not sure how to use the advertised specs of the Atom to calculate what it should be at 300 Ohm though, since they don't list 300 on their official specs in the product page.

So I'm still unclear on which would be louder between the two. (maybe it's because the 'THD' stuff still confuses me a bit.)
 

MZKM

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#5
I'm not sure how to use the advertised specs of the Atom to calculate what it should be at 300 Ohm though, since they don't list 300 on their official specs in the product page.

So I'm still unclear on which would be louder between the two. (maybe it's because the 'THD' stuff still confuses me a bit.)
Wattage at 300ohm would ideally be 2x the wattage at 600ohm (125 -> 250) and ideally 1/2 the wattage at 150ohm (502 -> 251).

So, even if you go to 1% THD, at 300ohm the Atom is still 50W more powerful.
 
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#6
Wattage at 300ohm would ideally be 2x the wattage at 600ohm (125 -> 250) and ideally 1/2 the wattage at 150ohm (502 -> 251).

So, even if you go to 1% THD, at 300ohm the Atom is still 50W more powerful.
So why do people love the 789 so much? is it the balanced output? or does it sound better than the Atom or something?
 

MZKM

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#7
So why do people love the 789 so much? is it the balanced output? or does it sound better than the Atom or something?
Being balanced is a big plus to some people. It came out before the Atom if I recall, and at the time it was for sure the best for the bang headphone amp for those that were originally looking at super high end ones. The THX title is also a draw to some.
 

amirm

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#8
So why do people love the 789 so much? is it the balanced output? or does it sound better than the Atom or something?
First, your observation is correct that using normal "unbalanced" headphone jack, the JDS Atom has more power.

As to your question, there are a few reasons for THX AAA 789:

1. It has balanced (XLR) inputs. If you have a balanced source, this can help eliminate ground loops (hum/buzz).

2. In balanced output mode the THX AAA 789 has much more power. So if you have a really inefficient and/or higher impedance headphone, you can re-wire it for balanced and take advantage of this power.

3. It has a less than 1 gain mode which is handy for IEMs.

4. It is larger, more stable and looks nicer on your desk.

If these factors are not important, the JDS Atom should be your choice as it is also readily available for purchase.
 
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#9
First, your observation is correct that using normal "unbalanced" headphone jack, the JDS Atom has more power.

As to your question, there are a few reasons for THX AAA 789:

1. It has balanced (XLR) inputs. If you have a balanced source, this can help eliminate ground loops (hum/buzz).

2. In balanced output mode the THX AAA 789 has much more power. So if you have a really inefficient and/or higher impedance headphone, you can re-wire it for balanced and take advantage of this power.

3. It has a less than 1 gain mode which is handy for IEMs.

4. It is larger, more stable and looks nicer on your desk.

If these factors are not important, the JDS Atom should be your choice as it is also readily available for purchase.
#4 is definitely nice; I actually do wish the Atom had a metal case. I'm not sure if there's another amp out there (say, $500 or less) that measures as well as the Atom (and same or greater power) but with a metal case, if not then I guess the Atom is my best option until something new shows up on the market.

Thank you very much for the information amirm, I really appreciate it, and I love reading your reviews, even though I don't understand every single thing yet. :)
 
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#10
Doesn't balanced output also improve channel separation?
 

amirm

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#11
Doesn't balanced output also improve channel separation?
It is claimed but I have not seen measurements to back it. But even if there were, channel separation is so good already in electronics that I don't even bother to measure it often.
 

JohnYang1997

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#12
The unbalanced output, yes atom is better. Thx789 uses opa564 which can only be used with +-12V which caused the low output swing.
However thx789 has balanced output which in this case will havr twice the swing/4 times the power of unbalanced. So easily more than atom.
 

GGroch

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#13
Are there any unbalanced headphones that the Atom would not have enough power to drive properly?

This Benchmark article discounts any advantage of balanced headphone amp outputs beyond increased power. They do see an advantage in balanced headphone amp inputs for noise rejection. But, in normal home use the short runs between DAC and amp are not a likely source of audible noise.

I would guess that Amir's reason 4, plus the fact that it has the THX logo (people have long paid more for receivers with that logo) explain much of the popularity. Nothing wrong with that. $400 is quite cheap by audiophile standards.
 
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#14
Are there any unbalanced headphones that the Atom would not have enough power to drive properly?

This Benchmark article discounts any advantage of balanced headphone amp outputs beyond increased power. They do see an advantage in balanced headphone amp inputs for noise rejection. But, in normal home use the short runs between DAC and amp are not a likely source of audible noise.

I would guess that Amir's reason 4, plus the fact that it has the THX logo (people have long paid more for receivers with that logo) explain much of the popularity. Nothing wrong with that. $400 is quite cheap by audiophile standards.
Yeah, although the perceived value of something can change if someone else designs something in the same neighborhood performance-wise, for less money. The Atom doesn't have balanced, but given that it's more powerful than the 789 in unbalanced output, I feel like that makes the 789 more of a niche thing where you have to think about your use cases; when I first heard of the 789, my impression was it was basically the endgame amp for anyone, regardless of whether you were using balanced or unbalanced. Now I realize it's a bit more complicated than that.

As for that Benchmark article, I have read it, and I've also read tomchr's post in another thread where he answers a question about whether balanced headphone cables are useful or not (included the section of the post relevant to headphones, for full post, click the preceding link):
Now for your headphone case: Marketeers have caught onto balanced = good, so now anything "high-end" has to be balanced. "Back in the day" when amplifiers had 1% distortion, you could lower the distortion considerably by converting to a balanced design. I have a few issues with this: 1) You only cancel the even order harmonics (those that many find pleasing to the ear) leaving the odd order harmonics (that many find to sound harsh) in the signal. That doesn't sound like a wise thing to do. 2) Most cancellation circuits, in my experience, end up making the performance worse rather than better. This is especially true at the ultra-low distortion levels of modern opamps. 3) There is really no compelling technical reason to use cancellation schemes to lower the THD as modern parts already deliver THD that's orders of magnitude below audible (OPA1612 0.000015% anyone?)

Now before someone cries, "but THD isn't everything!" ... that's true. THD is not everything. But by improving the THD you usually end up with a lot of other improvements as well (IMD and multi-tone IMD spring to mind).

Where balanced is relevant to the headphone case is for crosstalk or coupling between channels. If you share the ground connection between the two headphone drivers, you will have some of the left channel signal mixing with the right channel signal. Even the shared ground in a 1/4" plug can cause crosstalk. For example, I measure 115 dB channel separation in my HP-1 when using the XLR output and about 95 dB when using the 1/4" output. The difference is due to the shared ground in the 1/4" plug. Now, both are below audible and I've never detected any difference in subjective listening tests, but it is definitely a measurable effect and is backed up by theory (Ohm's Law, to be specific). Both outputs on the HP-1 are single-ended. In the XLR output, I just ground the (-) side of the XLR plug. I see no advantage of a balanced amplifier for reasons outlined above.

So to answer your question: If the only shared ground in the connection from the amp to your headphones is in the 1/4" plug, I doubt you'll notice any difference between 1/4" jack and XLR connections to the headphones.
So yeah, it doesn't look like it does much, apart from getting rid of a bit of crosstalk which doesn't appear to even be audible.

On an unrelated note, I've read from other threads that Tom is working on a Neurochrome HP-1 successor in the range of 500-600 dollars; given the way the first one measured (comparable to 789), and how it delivered a massive amount of power in single-ended, that seems like the ideal "endgame" amp for me, so I'm definitely interested. :D
 

Dro

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#15
It is claimed but I have not seen measurements to back it. But even if there were, channel separation is so good already in electronics that I don't even bother to measure it often.
Most likely just a result of the 4 wire connection that you are guaranteed to get with balanced. A good TRS jack with low output impedance and a 4 wire cable going to the headphone should perform just as well in crosstalk. I know the ADI-2 DAC is excellent.
 
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