[mrspeakers]

Many thanks, but the Pro iDSD doesn't have the XBass feature.

Or are you pairing the Pro iDSD with the Pro iCAN?

Thanks again!

iDSD Black Label has it, that's what I have been playing with.

 

[flyte3333]

iDSD Black Label has it, that's what I have been playing with.

Ah no worries. You replied to my question about the new Pro iDSD so that’s probably where the mixup came.

 

[chekrdnickrs]

Just got my AFCs in from the mail today and I just have to say, wow!!!

Granted, these are only my third pair of proper headphones (Momentum 2.0s first, if you count them as 'proper', and HD6XXs second) so I don't have much for comparing, but they sound incredible!

However, am surprised that even with an impedance of 13ohms, my AK70 still can't drive them? As in, with the Momentum 2.0s the volume is usually 100-105 (out of 150), but I'm having to crank it up to 130 thereabouts for the AFCs. Will my DAP be rendered redundant unless I buy it a portable amp that can drive the AFCs? :\

Also, I don't think trawling through 296 pages to look for the answer will be particularly fruitful so I'll ask here: my Schiit stack (Modi 2 + Magni 3) does a great job, but what amp/DAC combo should I aim for next? Something that will really bring the AFCs' power out, if my stack isn't doing so already! Budget-wise, no more than the Mojo?

Thanks!!

 

[441879]

Just got my AFCs in from the mail today and I just have to say, wow!!!

Granted, these are only my third pair of proper headphones (Momentum 2.0s first, if you count them as 'proper', and HD6XXs second) so I don't have much for comparing, but they sound incredible!

However, am surprised that even with an impedance of 13ohms, my AK70 still can't drive them? As in, with the Momentum 2.0s the volume is usually 100-105 (out of 150), but I'm having to crank it up to 130 thereabouts for the AFCs. Will my DAP be rendered redundant unless I buy it a portable amp that can drive the AFCs? :\

Also, I don't think trawling through 296 pages to look for the answer will be particularly fruitful so I'll ask here: my Schiit stack (Modi 2 + Magni 3) does a great job, but what amp/DAC combo should I aim for next? Something that will really bring the AFCs' power out, if my stack isn't doing so already! Budget-wise, no more than the Mojo?

Thanks!!

Congrats on the new cans! Re the AK70- I couldn’t find any output impedance specifications, which leads me to suspect the AK70 is kinda high. The AFCs are not particularly efficient in terms of dB / MW and they are fairly low impedance. That means to get the best out of them, you need an amplifier that can deliver a fair amount of power into a low impedance load, or put another way, low output impedance. The Magni 3 can do that without any problem, but not so sure about the AK70. Also, if you haven’t already, get a balanced cable for your headphones so you can connect them to the balanced out on the AK70- more power available that way.

As far as recommended amp upgrades, I would definitely consider the Schiit Lyr3 as an option for non portable use. I felt it was a definite improvement over the Magni 3 with the AFCs.

Re DAC: My personal choice would be either an Airist R2R DAC currently on sale at Massdrop for 349 or a Topping D30 or D50. That said, IMHO your DAC won’t matter much if you’re streaming music.

 

[chekrdnickrs]

Congrats on the new cans! Re the AK70- I couldn’t find any output impedance specifications, which leads me to suspect the AK70 is kinda high. The AFCs are not particularly efficient in terms of dB / MW and they are fairly low impedance. That means to get the best out of them, you need an amplifier that can deliver a fair amount of power into a low impedance load, or put another way, low output impedance. The Magni 3 can do that without any problem, but not so sure about the AK70. Also, if you haven’t already, get a balanced cable for your headphones so you can connect them to the balanced out on the AK70- more power available that way.

As far as recommended amp upgrades, I would definitely consider the Schiit Lyr3 as an option for non portable use. I felt it was a definite improvement over the Magni 3 with the AFCs.

Re DAC: My personal choice would be either an Airist R2R DAC currently on sale at Massdrop for 349 or a Topping D30 or D50.

Thanks a lot for your reply and insight! Yeah I'm really loving them so far. I bought them for use mostly at the office (home will be my 6XXs) and was thinking the AK70 would be enough to be its source. Its 3.5mm output has 2ohm impedance. Is this why it doesn't drive the AFCs as well, or is it because the AFCs' sensitivity is relatively low? Still trying to wrap my head around all this, thanks for your patience!

Having said that, it looks like I'll need to start saving up for a portable DAC/amp to pair with my AFCs at the office down the line - I initially tried bringing my home setup (Schiit stack and HD6XXs) to work, but after the second day found it too risky and time-consuming to pack, transport, unpack and set up over and over.

I considered the Mojo a strong candidate to fill this vacancy as I am able to buy one locally, which is quite rare (my country is full of people who think running potato-quality mp3/YT streams into $10 earphones is more than enough). However I've read that it doesn't do the AFCs the justice it deserves, so I'm just wondering what other portable options out there will.

I'll check your two suggestions out (reading reviews etc.), but Massdrop doesn't ship to my country! I got my 6XXs on eBay where a smart seller bought the five units they were allowed to buy and then sold them for profit.

 

[441879]

Thanks a lot for your reply and insight! Yeah I'm really loving them so far. I bought them for use mostly at the office (home will be my 6XXs) and was thinking the AK70 would be enough to be its source. Its 3.5mm output has 2ohm impedance. Is this why it doesn't drive the AFCs as well, or is it because the AFCs' sensitivity is relatively low? Still trying to wrap my head around all this, thanks for your patience!

Having said that, it looks like I'll need to start saving up for a portable DAC/amp to pair with my AFCs at the office down the line - I initially tried bringing my home setup (Schiit stack and HD6XXs) to work, but after the second day found it too risky and time-consuming to pack, transport, unpack and set up over and over.

I considered the Mojo a strong candidate to fill this vacancy as I am able to buy one locally, which is quite rare (my country is full of people who think running potato-quality mp3/YT streams into $10 earphones is more than enough). However I've read that it doesn't do the AFCs the justice it deserves, so I'm just wondering what other portable options out there will.

I'll check your two suggestions out (reading reviews etc.), but Massdrop doesn't ship to my country! I got my 6XXs on eBay where a smart seller bought the five units they were allowed to buy and then sold them for profit.

RE AK70 output impedance: the general recommendation I’ve seen is the amp output impedance should be less than 1/10 the headphone impedance. IIRC the AFCs output impedance is around 13 ohms. The HD6XXs have a fairly high impedance and I would simply use them as my office headphones since the AK70 is a very good match for them. I don’t know about your office, but mine is not particularly conducive for careful listening and the AFCs are (IMHO) quite a bit nicer than the 6XXs.

 

[chekrdnickrs]

RE AK70 output impedance: the general recommendation I’ve seen is the amp output impedance should be less than 1/10 the headphone impedance. IIRC the AFCs output impedance is around 13 ohms. The HD6XXs have a fairly high impedance and I would simply use them as my office headphones since the AK70 is a very good match for them. I don’t know about your office, but mine is not particularly conducive for careful listening and the AFCs are (IMHO) quite a bit nicer than the 6XXs.

Nope I can confirm that I have to pump my AK70's volume up to 130+ for my 6XXs just like I do for the AFCs. Definitely hungry headphones, these two!

Yeah like I told you earlier, I have tried bringing the 6XXs to the office which for me is conducive for critical listening - other than the occasional tea break, banter with colleagues or routine meeting, I rarely if ever leave my seat or am in a position not to use headphones. However it's all cubicles there so I get self-conscious depending on what I'm listening to - and that's definitely an unwanted distraction. The AFCs will definitely solve this problem!

I'm really liking the look of the iFi Micro iDSD Black Label DAC/amp. Might be at the top of my wishlist now!

I can't get enough of these AFCs!!

 

[441879]

I'm really liking the look of the iFi Micro iDSD Black Label DAC/amp. Might be at the top of my wishlist now!

I can't get enough of these AFCs!!

I’ve never heard the iDSD, but if it’s good enough for Mr Speakers, I’d guess it’s good.

 

[Zachik]

+1 on the Massdrop RDAC + Schiit Lyr3 combo recommendation!

 

[AdamWill]

The Flows have low impedance but also low sensitivity/efficiency - which is really just a fancy way of saying they need power There's a handy post here which helps you calculate how much power headphones actually need:

https://nwavguy.blogspot.com/2011/09/more-power.html

the AFC and AFO both have nominal 13 ohm impedance, the AFC's efficiency is 92dB/mW, the AFO is 94dB/mW. From the table we can see the AFCs are going to need somewhere around 60mW power to drive them to 110dB peak SPL (which is a very high level, but nwavguy recommends it as a good guide for various reasons, e.g. recordings with high dynamic range where the average volume may be 30dB below the peak). That's not crazy high, but it is higher than IEMs and headphones specifically intended for portable use.

Looking at the AK70's specs, it looks like it ought to be able to do that, though: https://avprogear.com/astellkern-ak70-mk-ii-portable-premium-dap/

There's another handy resource here - https://www.owenduffy.net/calc/voltcnv.htm - which lets you convert between all kinds of different ways of specifying power. The lowest specified power for the AK70 (mark 1, unbalanced) is 2.0Vrms. If you put 13 ohms and 2.0Vrms into the calculator, it'll show 307mW, which is more than enough, in theory. However, that output spec was measured with no load, which is a kinda flattering way of doing it. Amps can't always manage the same amount of output power into different input impedances. Fortunately, the reference-audio-analyzer folks measured the AK70 for us, so we can find out:

https://reference-audio-analyzer.pro/en/report/amp/astell-kern-ak70-unbalance.php

there's a whole buncha scary numbers there, but if you ignore most of 'em and go to the "Maximum voltage output level vs load" table, it gets interesting. Look at the "Optimal or equal class AB" Vrms column (the whole 'class' thing is a bit complicated, see https://reference-audio-analyzer.pro/en/test-amp-class-power.php#ab , but it sorta-kinda means "max power before the audio quality may possibly be measurably compromised"), and we see it can only manage 0.17 Vrms into 16 ohm (close enough to 13 for rough figuring). Hell, even under "Max, before clipping" - which is 'absolutely max power it'll put out, regardless of whether the signal gets a bit noisy' - we can see it can only manage an absolute max of 0.27 Vrms into 16 ohm. It *can* manage 2.0Vrms - AK aren't lying - but it can only really do it into 763ohms, or no load at all.

So, let's go back to the calculator and try plugging in 0.17 Vrms and 13 ohm...and we only get 2.22mW. Even 0.27 Vrms (the 'max, before clipping' number) is only 5.6mW. To put it another way, if we scroll down a bit to the 'math part' of the post, nwavguy gives us this calculation to figure out exactly how loud a given source can drive a given pair of headphones:

dBSPL = Sensitivity in dB/mW + 10 * LOG ( Pmax in mW)

I *think* that's meant to read Sensitivity in dB/mW + (10 * LOG Pmax in mW) , otherwise the calculations come out weird. So if we plug in the numbers there we get 92 + 10 * LOG 5.6 , which if I didn't mess up the ordering, is 99.48dB - the absolute loudest the measured AK70 could make a pair of AFCs play (in fact it may be slightly lower, since the measurement was for 16 ohm not 13 ohm, presumably the real measurement at 13 ohm would be slightly lower). That'd be the *peak* volume on a track; the average volume would be lower (though for highly compressed music, not much lower).

So: yeah, it's not too surprising your AK70 is kinda maxed out driving the AFCs, based on those measurements at least; if you have a different model from the one they measured, or you're using the balanced output, the numbers would be different, but probably not crazy different.

The AK70's output impedance was measured at 3.40 ohm; that's not *very* high, and probably isn't causing a problem, but it is kinda borderline. I think the general guideline is that the output impedance should be max 1/4 of the input impedance, and 13/4 is 3.25, so yeah, right on the line. (edit: seems nwavguy recommends 1/8, so this *could* be a problem. There's more info on the actual problems caused by using an amp with a higher output impedance and headphones with lower input impedance at https://nwavguy.blogspot.com/2011/02/headphone-amp-impedance.html?m=1 . For Aeons the second point - "Headphone impedance changes with frequency" - doesn't matter, as for planars the impedance does *not* in fact change with frequency, but the other two points may be relevant.)

I mean, you say it's loud enough for you at 130/150, so is this *really* a problem? Do you sometimes need to play it louder? Just the fact that you're at a high number doesn't necessarily mean it's a problem. You're likely in the range where the measured THD+noise is kinda above the ideal level (the difference between 'class AB' and 'Max, before clipping' from earlier), but if you're not *hearing* any obvious issues, is there really a problem?

If you are worried, though, yes, you *could* get more power with an amp or a different DAP: look for one that can manage at least 0.9Vrms into 16 ohms, and ideally has <1ohm output impedance just for safety. There are plenty like that. (FWIW I'm currently hanging onto an Opus #1s and an iBasso DX200 and trying to pick which one to keep, both of those can power AFCs easily, but there are many other options too).

 

[nrbatista]

Any recommendation for a mobile amplifier with a balanced output to properly drive the AFCs ?

I’m currently using ALO Audio The International but it doesn’t do the job and the sound gets distorted / clipped on one of the channels when I cranked up the volume. This distortion only happens with the AFCs, being barely listenable with a LCD-XC and not audible at all with a LCD-2. Can this be due to the AFCs extremely low impedance which makes them “incompatible” with some amps?

 

[441879]

The Flows have low impedance but also low sensitivity/efficiency - which is really just a fancy way of saying they need power There's a handy post here which helps you calculate how much power headphones actually need:

https://nwavguy.blogspot.com/2011/09/more-power.html

the AFC and AFO both have nominal 13 ohm impedance, the AFC's efficiency is 92dB/mW, the AFO is 94dB/mW. From the table we can see the AFCs are going to need somewhere around 60mW power to drive them to 110dB peak SPL (which is a very high level, but nwavguy recommends it as a good guide for various reasons, e.g. recordings with high dynamic range where the average volume may be 30dB below the peak). That's not crazy high, but it is higher than IEMs and headphones specifically intended for portable use.

Looking at the AK70's specs, it looks like it ought to be able to do that, though: https://avprogear.com/astellkern-ak70-mk-ii-portable-premium-dap/

There's another handy resource here - https://www.owenduffy.net/calc/voltcnv.htm - which lets you convert between all kinds of different ways of specifying power. The lowest specified power for the AK70 (mark 1, unbalanced) is 2.0Vrms. If you put 13 ohms and 2.0Vrms into the calculator, it'll show 307mW, which is more than enough, in theory. However, that output spec was measured with no load, which is a kinda flattering way of doing it. Amps can't always manage the same amount of output power into different input impedances. Fortunately, the reference-audio-analyzer folks measured the AK70 for us, so we can find out:

https://reference-audio-analyzer.pro/en/report/amp/astell-kern-ak70-unbalance.php

there's a whole buncha scary numbers there, but if you ignore most of 'em and go to the "Maximum voltage output level vs load" table, it gets interesting. Look at the "Optimal or equal class AB" Vrms column (the whole 'class' thing is a bit complicated, see https://reference-audio-analyzer.pro/en/test-amp-class-power.php#ab , but it sorta-kinda means "max power before the audio quality may possibly be measurably compromised"), and we see it can only manage 0.17 Vrms into 16 ohm (close enough to 13 for rough figuring). Hell, even under "Max, before clipping" - which is 'absolutely max power it'll put out, regardless of whether the signal gets a bit noisy' - we can see it can only manage an absolute max of 0.27 Vrms into 16 ohm. It *can* manage 2.0Vrms - AK aren't lying - but it can only really do it into 763ohms, or no load at all.

So, let's go back to the calculator and try plugging in 0.17 Vrms and 13 ohm...and we only get 2.22mW. Even 0.27 Vrms (the 'max, before clipping' number) is only 5.6mW. To put it another way, if we scroll down a bit to the 'math part' of the post, nwavguy gives us this calculation to figure out exactly how loud a given source can drive a given pair of headphones:

dBSPL = Sensitivity in dB/mW + 10 * LOG ( Pmax in mW)

I *think* that's meant to read Sensitivity in dB/mW + (10 * LOG Pmax in mW) , otherwise the calculations come out weird. So if we plug in the numbers there we get 92 + 10 * LOG 5.6 , which if I didn't mess up the ordering, is 99.48dB - the absolute loudest the measured AK70 could make a pair of AFCs play (in fact it may be slightly lower, since the measurement was for 16 ohm not 13 ohm, presumably the real measurement at 13 ohm would be slightly lower). That'd be the *peak* volume on a track; the average volume would be lower (though for highly compressed music, not much lower).

So: yeah, it's not too surprising your AK70 is kinda maxed out driving the AFCs, based on those measurements at least; if you have a different model from the one they measured, or you're using the balanced output, the numbers would be different, but probably not crazy different.

The AK70's output impedance was measured at 3.40 ohm; that's not *very* high, and probably isn't causing a problem, but it is kinda borderline. I think the general guideline is that the output impedance should be max 1/4 of the input impedance, and 13/4 is 3.25, so yeah, right on the line.

I mean, you say it's loud enough for you at 130/150, so is this *really* a problem? Do you sometimes need to play it louder? Just the fact that you're at a high number doesn't necessarily mean it's a problem. You're likely in the range where the measured THD+noise is kinda above the ideal level (the difference between 'class AB' and 'Max, before clipping' from earlier), but if you're not *hearing* any obvious issues, is there really a problem?

If you are worried, though, yes, you *could* get more power with an amp or a different DAP: look for one that can manage at least 0.9Vrms into 16 ohms, and ideally has <1ohm output impedance just for safety. There are plenty like that. (FWIW I'm currently hanging onto an Opus #1s and an iBasso DX200 and trying to pick which one to keep, both of those can power AFCs easily, but there are many other options too).

Some great reference data there and a nice explanation of why the AK70 is underperformingfor the AKC. Using the source you cited, the AK70 max output current is right at 19 ma (hard clipping). At 13 ohms, you’re looking at 4.7 mW or 98.7 dB and clipping hard. At the optimal max out of around 10mA (at 16 ohms), it’s down to 1.3 mW or pretty much 92 dB.

 

[AdamWill]

Some great reference data there and a nice explanation of why the AK70 is underperformingfor the AKC. Using the source you cited, the AK70 max output current is right at 19 ma (hard clipping). At 13 ohms, you’re looking at 4.7 mW or 98.7 dB and clipping hard. At the optimal max out of around 10mA (at 16 ohms), it’s down to 1.3 mW or pretty much 92 dB.

Yeah, I've been using Vrms just because that happened to be what most of the things I've been looking at had specs in, but indeed you can reckon from Vrms or mA and get the same result...thanks, math! Indeed since this DAC seems to have its output current capped, it makes sense to look at where that cap is and reckon from there.

 

[flyte3333]

the AFC and AFO both have nominal 13 ohm impedance, the AFC's efficiency is 92dB/mW, the AFO is 94dB/mW. From the table we can see the AFCs are going to need somewhere around 60mW power to drive them to 110dB peak SPL

Hi Adam

That table doesn't mention impedance though. So when looking at amp specs, they usually specify mW at either 16 ohms or 32 ohms (some 8 ohms).

So are you looking for 60mW at 16 ohms? Or what impedance?

Cheers!

 

[AdamWill]

Hi Adam

That table doesn't mention impedance though. So when looking at amp specs, they usually specify mW at either 16 ohms or 32 ohms (some 8 ohms).

So are you looking for 60mW at 16 ohms? Or what impedance?

Cheers!

That table's basically 'after impedance'. Whatever the impedance of the headphones, the amp needs to be able to output the amount of power shown in the table *into that impedance* in order to drive the headphones to the volume shown in the table. So, since the impedance of the AFCs is 13 ohms, the table tells us we need our amp to output about 60-70mW (I'm too lazy to do the math and get the exact number) *into 13 ohms* in order to drive them to 110dB SPL. That number of mW would be the same whatever the input impedance of the headphones, if they had the same *sensitivity* as the AFCs.

The effect of higher impedance headphones, in the context of the table, is that most amps will be able to output more current (mA) and hence power (in mW) into lower impedances. So effectively, if you have two pairs of headphones with the same sensitivity but one is 16 ohm and the other is 600 ohm, you're aiming for the "same target" but it will be much "harder to hit" for the 600 ohm headphones, with most amps.

Some, though, like the AK70, seem to have their output current capped at some level, so they don't quite behave like this - in the graph will f posted you can see that the line is flat from 0 to about 90 ohms, that's the 'cap' I mean. From 90 ohms to 800 you see a different relationship between current output and impedance - the amount of current the device can put out starts going down as the impedance goes up. (If you look at the graph of *power* output versus impedance, it shows the AK70 actually puts out more power into about 100ohms than into any other impedance, higher or lower).

Possibly the amp technically *could* output more current into lower impedance loads, but this was intentionally restricted by AK. Or else, according to nwavguy, this can actually just be a property of the device design - "The answer is some sources run out of current as the load impedance drops below some value...[they] just [don’t] have the beans to maintain the same voltage into loads much below 100 ohms."

Here's the same graph for the iBasso DX200:

Note how it doesn't level out like the AK70's graph - so this is a device that behaves more 'intuitively', throughout the range, it's able to put out more current the lower the impedance of the headphones. (so don't use it in high gain mode with your IEMs :>)