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Use DAC unbalanced RCA output to Headphones directly?

L5730

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As the title, is this even possible?

Take any consumer CD Player or DAC with unbalanced outputs.
We'll assume 2 Volt RMS output @ 0 dBFS and an output impedance of 100 ohm (Khadas ToneBoard / Topping D10).

If we took some cheapish headphones which "don't require a dedicated headphone amp", say something like 32 ohm with sensitivity of 96 dB SPL/mW, I gather that even a really low output current from such a DAC might be enough to drive such headphones to an acceptable loudness level?

I get the point that line output is meant to send voltage and the current is just negligible. Headphones typically require an amount of current to drive them, just like loudspeakers, and there we see the reasoning for an amplifier.

So I guess, things like laptop line/headphone outputs have enough current to drive easy-to-drive (is "sensitive" the right term?) headphones, whilst also putting out enough voltage to feed other line-level gear down the chain, if required. In my limited experience, the line output voltage from laptops is well under 2 volts and is rather quiet going into a regular integrated amplifier, compared to say, a CD player.

Output impedance seems to be something too. The lower the better? Maybe I should find the material and read, Amir's comparison chart certainly plots/ranks different headphone amps based on output impedance. 100 ohm might be a bit much for less sensitive headphone,s but some easy to drive IEMs or over-ears would be fine, no? Even if the tonal characteristic changes a bit?

I am not being cheap here, I have plans to get a headphone amp as soon as, or even before I settle on what headphones I want. That's me, but I am just interested in this idea, and it might help out someone else on a very tight budget.

So, yeah, is it possible? Would it sound OK?

As always, thanks for your input and discussion.
 

solderdude

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Probably not O.K. unless the output circuit is specifically designed for low impedance headphones.
Even when the output resistance is close to 0 Ohm chances are the output circuit may not drive low impedance headphones.
300 Ohm and 600 Ohm headphones could well be driven but won't play loud enough.

100 Ohm output resistance may be a bit too high for most low impedance headphones and due to voltage division the output power would be very low for 32 Ohm headphones.

So, not recommended but you won't kill devices operating it this way and if one likes to experiment, go ahead. Maybe some headphones benefit from a higher output resistance.
 

sergeauckland

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In principle, it should work. As an example, if the output if the DAC is an opamp like the ubiquitous 5532, that can drive headphones directly. My Meridian preamp and my older Hafler preamps both had 5532s as headphone drivers. They may have a 75ohm resistor in series with the output to protect the opamp from excessive capacitance, but that generally just reduces level. It could affect the headphone's frequency response, but measuring my various headphones, they all have a pretty flat impedance characteristic, to something within 1dB on voltage frequency response or so from 20-20kHz with a slight rise at hf due to inductance so of little consequence.

It depends what the outputs stage of the DAC actually is, but I would be surprised if most didn't work fine.

S
 
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L5730

L5730

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Ah, I think I need brush up on Ohms law stuff again.
I came away from reading something where someone was connecting some high impedance headphones to the balanced line outputs of a DAC. Of course, there was a lot more voltage from the DAC (5v+ vs. 2v.)

It's funny but my PC motherboard has a TI Ne5532 OpAmp onboard which apparently supports up to 600 ohm headphones!, and this is linked to the front panel headphone jack.
The Realtek chip disables the rear Line Out jack when some earbuds are put in the front panel.

I found my short-cabled Sony CD Walkman (D-EJ725) earbuds (MDR-E805 ?) from years ago, added some janky cable extensions (you don't wanna see that, it's as ugly as sin), and then shoved 'em in the front panel. Oh, jeeze these are harsh in upper mid!
Well, one thing at least the "Headphone Power" drop down does do something. I have other options of "Dynamic" and "Ultimate", of which they just make the bass muddier on these ear buds.
That Headphone Virtualisation check box is supposed to simulate Home Theatre sound, whatever that is supposed to be. Well, it certainly sucks out the middle of whatever stereo image there is! :D

Haha, I'm reliving that annoying jaw ache feeling I got in high school when I last wore these earbuds. NOT comfy at all !!!
Finding a spot where they fit in my ear and sound decently full but don't immediately cause physical ear pain is tough. At least there is plenty of volume coming off of my PC jack, even if the balance sounds slightly off to the right :p

Enough listening to these, I have a headache already!

1572974804072.png
 

garbulky

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Ah, I think I need brush up on Ohms law stuff again.
I came away from reading something where someone was connecting some high impedance headphones to the balanced line outputs of a DAC. Of course, there was a lot more voltage from the DAC (5v+ vs. 2v.)

It's funny but my PC motherboard has a TI Ne5532 OpAmp onboard which apparently supports up to 600 ohm headphones!, and this is linked to the front panel headphone jack.
The Realtek chip disables the rear Line Out jack when some earbuds are put in the front panel.

I found my short-cabled Sony CD Walkman (D-EJ725) earbuds (MDR-E805 ?) from years ago, added some janky cable extensions (you don't wanna see that, it's as ugly as sin), and then shoved 'em in the front panel. Oh, jeeze these are harsh in upper mid!
Well, one thing at least the "Headphone Power" drop down does do something. I have other options of "Dynamic" and "Ultimate", of which they just make the bass muddier on these ear buds.
That Headphone Virtualisation check box is supposed to simulate Home Theatre sound, whatever that is supposed to be. Well, it certainly sucks out the middle of whatever stereo image there is! :D

Haha, I'm reliving that annoying jaw ache feeling I got in high school when I last wore these earbuds. NOT comfy at all !!!
Finding a spot where they fit in my ear and sound decently full but don't immediately cause physical ear pain is tough. At least there is plenty of volume coming off of my PC jack, even if the balance sounds slightly off to the right :p

Enough listening to these, I have a headache already!

View attachment 37946
What do they mean by "balanced" headphone power. Aren't those 3.5mm unbalanced jacks?
 

garbulky

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As the title, is this even possible?

Take any consumer CD Player or DAC with unbalanced outputs.
We'll assume 2 Volt RMS output @ 0 dBFS and an output impedance of 100 ohm (Khadas ToneBoard / Topping D10).

If we took some cheapish headphones which "don't require a dedicated headphone amp", say something like 32 ohm with sensitivity of 96 dB SPL/mW, I gather that even a really low output current from such a DAC might be enough to drive such headphones to an acceptable loudness level?

I get the point that line output is meant to send voltage and the current is just negligible. Headphones typically require an amount of current to drive them, just like loudspeakers, and there we see the reasoning for an amplifier.

So I guess, things like laptop line/headphone outputs have enough current to drive easy-to-drive (is "sensitive" the right term?) headphones, whilst also putting out enough voltage to feed other line-level gear down the chain, if required. In my limited experience, the line output voltage from laptops is well under 2 volts and is rather quiet going into a regular integrated amplifier, compared to say, a CD player.

Output impedance seems to be something too. The lower the better? Maybe I should find the material and read, Amir's comparison chart certainly plots/ranks different headphone amps based on output impedance. 100 ohm might be a bit much for less sensitive headphone,s but some easy to drive IEMs or over-ears would be fine, no? Even if the tonal characteristic changes a bit?

I am not being cheap here, I have plans to get a headphone amp as soon as, or even before I settle on what headphones I want. That's me, but I am just interested in this idea, and it might help out someone else on a very tight budget.

So, yeah, is it possible? Would it sound OK?

As always, thanks for your input and discussion.
I once used adapters to connect the XLR output of an Emotiva XDA-1 directly to sennheiser HD600's. Now it used XLR->RCA adapters as I didn't have an XLR cable. Anyway long story short there was some sound differences and it did sound fun and very detailed in certain ways but not necessarily accurate. I also encountered a hum which may have had to do with the connectors I used.
 

Vincent Kars

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It works.
At least I tried it once.
Sound horrible
What you want is a low impedance of the output, substantially lower that the impedance of the headphone.
Using a line out as a source, the opposite is the case.
 

sergeauckland

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It works.
At least I tried it once.
Sound horrible
What you want is a low impedance of the output, substantially lower that the impedance of the headphone.
Using a line out as a source, the opposite is the case.

Why? If the headphone has a flat impedance characteristic, then the output impedance of the driver amplifier is, within reason, irrelevant. A high output impedance will just result in a lower voltage level, not a change in sound quality. I accept that a low output impedance is desirable, as then it matters much less what the headphone's impedance variations are, and it will maximise available output level, but if sound quality is affected, then there are other parameters operating than just output impedance.

Most headphones consist of a single driven element, no crossover or similar, so the headphone presents a largely resistive load, with some inductance causing the impedance to rise at HF. I have three headphones, and all three (AKG, Koss, Sony) measure within 1dB on their voltage frequency response when driven from a 600 ohm source, so less variation with lower impedances like the more typical 75 ohms.

S.
 
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L5730

L5730

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What do they mean by "balanced" headphone power. Aren't those 3.5mm unbalanced jacks?
Their term "Balance" in the power setting has nothing to do with electrical type. Nah, just a name to append to some setting internal to the DSP I think, or maybe something to do with current drive. It just adds mud to whatever shoddy earbuds or headphones I have lying around. Doesn't even increase the volume.

I think it's safe to say that there won't be enough volume from using the low current output unbalanced line outs from a DAC.
Headphone amps exist for good reason.

For fun, I read that the NE5532 OpAmp powered front jack on my PC may deliver 1.5-2v RMS with 15-20mA. Might power DT770 250ohms to a listenable level, but the onboard sound, although better than ever, is still what it is.
 

Purpl3n3ss

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Some DACs have very low output impedance. Chord DACs, for example. My Qutest has an output impedance < 1 ohm. I'm running a pair of Focal Utopias (80 ohm impedance, high sensitivity) directly from the RCA outputs. There is more than enough volume.

Still figuring out the sound characteristics compared to using an amp, but the differences don't seem to be glaring at all. If anything, simplifying the chain by completely removing the amp seemed to be beneficial to transparency.
 

DVDdoug

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Some DACs have very low output impedance. Chord DACs, for example. My Qutest has an output impedance < 1 ohm. I'm running a pair of Focal Utopias (80 ohm impedance, high sensitivity) directly from the RCA outputs. There is more than enough volume.
It's not always that simple.

You can have low effective source impedance but the circuit may not be designed to supply the current into a low impedance load. Resistance and impedance is "the resistance to current flow" and the lower the impedance the higher the current (with the same voltage). (Ohm's Law describes he relationship between voltage, resistance & current.)

Solid state electronics "naturally" have relatively-low output impedance but there is no direct correlation with current capability. Techniques such as negative feedback (or just the design of the chip and/or circuit) can lower the effective output impedance without increasing current capability and you can over-stress the chip or transistors. You probably aren't going to fry the electronics with a headphone load but you also might not get the expected performance..

With power amplifiers there is sometimes a spec for damping factor which is the ratio between speaker impedance and output impedance. You can calculate output impedance from the damping factor but that doesn't tell you if the amp can safely drive 4-Ohm speakers or lower. Even with a very-low damping factor (spec'd with 4 or 8-Ohm speakers) you might burn-up the amp or send it into thermal-overload shutdown if you connect a 1 or 2 Ohm load.
 
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