[FiiO BTR17/BTR7] True Lossless Bluetooth, Portable Bluetooth DAC and Headphone Amplifier BTR17 Is Officially Released!

[Stu Paddasso]

I've always been told to put the source at max volume, then your last device is used to control the listening level. Also, someone a lot smarter than me explained it's better to use the lowest gain to avoid amp feedback noise. Only increasing gain if your iem's truly need more power.

 

[varunkumar]

I've always been told to put the source at max volume, then your last device is used to control the listening level. Also, someone a lot smarter than me explained it's better to use the lowest gain to avoid amp feedback noise. Only increasing gain if your iem's truly need more power.

Understood.

 

[BS5711]

Oh, am I not supposed to enable high gain mode? Oops, I was thinking I should for 2 ohms. I control volume from the phone and leave Fiio at 40 always.

As we discussed in another thread a while back:

Contrary to what many believe low impedance doesn't mean easy to drive, in fact the opposite is true if the low impedance is coupled with relatively low sensitivity and 2 ohms is crazy low impedance.

Strictly speaking no amplifier is going to be designed to accommodate an impedance of only 2 ohms, that is close to a dead short across the amplifier. Many portable headphone amps are rated at minimum 16 ohms but, again, the sensitivity matters a lot also so very low impedance but very high sensitivity will work OK while very low impedance AND low sensitivity will not.

With the low impedance the BTR17 is almost certainly running out of current resulting in the clipping you experienced.

That is just simple electrical properties, it has nothing to do with bit perfect or UAPP and won't change regardless of what answers you get to asking the same question in a number of different threads.

Also, taking the desktop power from the phone may not be provide sufficient current to function the desktop mode properly or possibly not at all which would not help driving the low 2 ohm impedance.

 

[varunkumar]

As we discussed in another thread a while back:

Contrary to what many believe low impedance doesn't mean easy to drive, in fact the opposite is true if the low impedance is coupled with relatively low sensitivity and 2 ohms is crazy low impedance.

Strictly speaking no amplifier is going to be designed to accommodate an impedance of only 2 ohms, that is close to a dead short across the amplifier. Many portable headphone amps are rated at minimum 16 ohms but, again, the sensitivity matters a lot also so very low impedance but very high sensitivity will work OK while very low impedance AND low sensitivity will not.

With the low impedance the BTR17 is almost certainly running out of current resulting in the clipping you experienced.

That is just simple electrical properties, it has nothing to do with bit perfect or UAPP and won't change regardless of what answers you get to asking the same question in a number of different threads.

Also, taking the desktop power from the phone may not be provide sufficient current to function the desktop mode properly or possibly not at all which would not help driving the low 2 ohm impedance.

Ok.
Just curious, how are some folks able to use ibasso DC Elite and questyle m18i which less powerful sources to drive the Ravens.

 

[BS5711]

Ok.
Just curious, how are some folks able to use ibasso DC Elite and questyle m18i which less powerful sources to drive the Ravens.

Maximum power isn't the only measure of the amplifiers performance.

The power available will vary at different impedances and it might be that those other devices simple handle the very low impedance better than the BTR17 even though they are almost certainly not actually designed to be run as low as 2 ohms.

 

[varunkumar]

Maximum power isn't the only measure of the amplifiers performance.

The power available will vary at different impedances and it might be that those other devices simple handle the very low impedance better than the BTR17 even though they are almost certainly not actually designed to be run as low as 2 ohms.

Got you.

 

[PixelSquish]

Why would anyone use 3.5 unbalanced if 4.4 bal is available, defeats the whole purpose of getting fully balanced source in the first place.
But it's your equipment, use it as you wish and for what works for you personally.

This makes zero sense. Balanced is not needed for lots of reasons with lots of IEMs. So what if the product offers both options. You do not have to use one over the other.

 

[Andrew_WOT]

@BS5711 good info, wondering if there is some more deterministic and less vague way to identify these characteristics.
May be some formula, as traditional way is less impedance = more power.
https://geoffthegreygeek.com/speaker-impedance-changes-amplifier-power/
Most amps have non linear output that change depending on impedance but that main trend still applies. When what you are stating is exactly opposite.

 

[XaFFi]

Understood.

Hi, connecting 2Ω IEMs to the BTR17 could be problematic because the btr17 is designed to handle impedances above 16Ω.
It is not recommended to connect below 16Ω because you could overload the amplifier. Extremely low impedance would cause the output power to go out of control, causing distortion or even damaging the IEMs. Be careful!

 

[BS5711]

@BS5711 good info, wondering if there is some more deterministic and less vague way to identify these characteristics.
May be some formula, as traditional way is less impedance = more power.
https://geoffthegreygeek.com/speaker-impedance-changes-amplifier-power/
Most amps have non linear output that change depending on impedance but that main trend still applies. When what you are stating is exactly opposite.

Speaker amplifiers are a little different because they only need to operate over a somewhat narrow range of impedances, the article you linked shows output power at 2, 4 and 8 ohms for example. I don’t have much of a frame of reference with speaker amps.

Headphone amplifiers need to operate over a huge range of load impedances, typically say perhaps 16 to 600 ohms, and they have a limit at how low the impedance can be with the power output still increasing.

Often you see power output at different impedances and typically the lowest impedance shown relates to the maximum power. At impedances below that the power output drops and sometimes dramatically as the ability of the amplifier to output current reduces.

The below is a screenshot from the BTR17 power specs, you can see that the power at 16 ohms is around 2/3 that of at 32 ohms. That is a halving of impedance.

The example our chap asked about was power at 2 ohms, that is 1/8 of 16 ohms at which power has already dramatically reduced, it doesn’t take much imagination to predict what is going to happen to the power output if dropping the impedance all the way to only 2 ohms, it will likely drop like a stone.

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@XaFFi …. at 2 ohms the power won’t be out of control it will be very low, the amplifier will not be able to output the current needed to drive such a low impedance load. Yes it will distort but that isn’t because it has a lot of power. It will likely clip as the power simply cannot cope with the current demand. It might even trigger a high current protection which will shut down the device or result in it cutting in and out.

 

[Andrew_WOT]

So that spec is even more confusing, why would it be opposite to less impedance more power. Is it high/low gain, switchable impedance based circuit?
This is BTR7 spec, and outlier same as with BTR17 is only BAL output for 16ohm impedance, with the rest following more impedance less power trend.
Wondering what is that and why only this specific mode is different.

 

[BS5711]

So that spec is even more confusing, why would it be opposite to less impedance more power. Is it high/low gain, switchable impedance based circuit?
This is BTR7 spec, and outlier same as with BTR17 is only BAL output for 16ohm impedance, with the rest following more impedance MORE power trend.
Wondering what is that and why only this specific mode is different.

I took the liberty of making a small correction in bold to your comment, seems apparent that is what you meant.

The 16 ohm figure isn't an outlier, it just looks like that because you are only getting a few numbers in isolation. If they provided a power versus impedance plot it would be a curve and you would see where the maximum power is and see that it falls either side of that maximum value. That is completely normal.

The specs show a different trend for the single ended output with the power increasing, as you suggest is usual, as the impedance drops. That is almost certainly different to the balanced output simply because the single ended output is only running two of the four amplifiers and the power supply will maintain adequate current into the lower impedance when the current is only required for two amplifiers not four. What I said will still hold true only the numbers, trends and plot are different, it will still fall below a certain point, be that 16 ohms or 32 ohms or someplace in between perhaps, it will most definitely have fallen significantly at 2 ohms.

Slight correction - In fact I just checked the BTR17 specs and single ended it has 130 mw at 16 ohms and 140 mw at 32 ohms so the drop in power is already happening just much more gently than balanced because the power supply is closer to keep up with the current requirements versus those of the balanced output.

I think you are overthinking it, the simple answer is in imagining it as a plot not as individual values in isolation as is usually provided for marketing material.

 

[Andrew_WOT]

I took the liberty of making a small correction in bold to your comment, seems apparent that is what you meant.

Not sure.
Power = Voltage x Current
Current = Voltage / Resistance (impedance)
So all things being equal, higher Resistance result in lower Current and therefore lower output Power.

You can also use this calculator to verify.

Same as in linked earlier article to speaker amplifiers impedance

 

[BS5711]

Not sure.
Power = Voltage x Current
Current = Voltage / Resistance (impedance)
So all things being equal, higher Resistance result in lower Current and therefore lower output Power.

You can also use this calculator to verify.

Sorry, I misread your comment, I read what I thought you were going to say not what you did say.

Apologies again.

Below is a graph I managed to find online for a Bartok headphone amplifier that demonstrates what I am meaning better then I can explain. You see the peaking power and fall off either side, dramatically on the low impedance side of the graph, and the lower impedance for maximum power of the single ended output due to the better ability of the power supply to maintain adequate current.

Obviously different amplifiers will have different graphs but the trend will remain the same in general, at least for voltage amplification.

I have no idea what a current amplification graph looks like but they are far less common and only serve to muddy the waters for this discussion.

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Edit to add - your speaker amplifier reference is oversimplistic (as you actually said earlier - it isn't proportional at all) and not representative of headphone application. Speakers cover an impedance range of maybe 4 x , say 2 to 8 ohms, in our case we are talking about a headphone amplifier that would be fine running 600 ohm headphones trying to run 2 ohms IEM, a range of 300 x.

 

[Andrew_WOT]

Now that makes total sense. Same as Auralic Taurus MKII that I happen to own, notice how much better single ended fares for lower impedance vs BAL.
Thanks for explanation and bearing with me.