O2 AMP + ODAC
Mar 17, 2021 at 4:40 PM Post #5,656 of 5,663

Starbound

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Everything is related to basic math here: AKG K240 has a sensitivity of 104 dB SPL/V @ 1 kHz and according to Digizoid we have this:


Listening LoudnessVoltage NeededCurrent NeededPower Needed
Safe85 dB SPL0.11 Vrms0.18 mA0.02 mW
Moderate100 dB SPL0.63 Vrms1.05 mA0.66 mW
Fairly Loud110 dB SPL2 Vrms3.33 mA6.67 mW
Very Loud115 dB SPL3.55 Vrms5.92 mA21 mW
Painful120 dB SPL6.31 Vrms10.52 mA66.36 mW

Given that O2 has a max. output power of about 7.3 V RMS, I see no problems driving K240.

My DT880 has a lower sensitivity and O2 will not drive them to full power, but I can still get acceptable dB levels to my ears.


Probably folks thinking that a simple resistors added to speakers output will make 600-Ohms headphones sound "better". I would ignore them and use a dedicated headamp with a low output impedance (even if the 1/8-rule will not matter to our 600-Ohms headset, you never know when you'll pair a 16-Ohms headset with that amp).
That Digizoid tool is awesome, thanks. I ran the calculation again at 600 ohms, 92dB/mW (the sensitivity of the vintage K240 Monitor is reported to be between 92 and 95 dB/mW) and the results are still good enough, as I tend to listen to music at a very moderate volume.

SR4S8Z7.png


I don't plan on getting low impedance headphones and I don't like IEMs, but one of the many things I like about the O2 is its low output impedance.

BTW, doesn't having a source with low output impedance also result in better performance with cans that have very non-linear impedances with respect to frequency?

For whatever reason, I have noticed quite an improvement with my MDR7506 through my O2/ODAC vs through other sources. That could be in part to the ODAC being cleaner, but I think there might be something else going on, maybe the low output impedance in the O2 making the headphone more controlled?
 
Mar 20, 2021 at 2:22 PM Post #5,657 of 5,663

raoultrifan

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BTW, doesn't having a source with low output impedance also result in better performance with cans that have very non-linear impedances with respect to frequency?
I don't see a correlation between source's output impedance and headamp's output impedance. However, a low output impedance is usually providing a cleaner signal and with a lower noise & interference (well, at least theoretically and only if using long interconnects).
 
Mar 23, 2021 at 9:10 PM Post #5,658 of 5,663

Starbound

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I don't see a correlation between source's output impedance and headamp's output impedance. However, a low output impedance is usually providing a cleaner signal and with a lower noise & interference (well, at least theoretically and only if using long interconnects).
I see, thanks. I was under the impression that it was the O2's low output impedance which made it a good match for headphones of very different impedances (and I assume, would also make it a better amp for headphones with very nonlinear impedance vs frequency graphs).
 
Mar 26, 2021 at 12:05 AM Post #5,660 of 5,663

Starbound

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Bu "source" I meant ODAC, not O2. Indeed, O2's low output impedance will make it compatible with most headphones, even with 8-Ohms ones.
I see where the misunderstanding was. And just for a final clarification, this is why in theory the O2 would be a more neutral amp with headphones that have impedance/frequency curves which are non linear, is this correct?
 
Mar 26, 2021 at 11:45 AM Post #5,661 of 5,663

raoultrifan

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Usually headphones do not vary much their impedance while playing music, as speakers do, so I don't think neutrality of a headamp is much related to this. Instead, frequency response tested with several impedances across audibile bandwidth will be more helpful here.

More probably, the O2 is neutral because it has a rather low output impedance and is able to drive, with +/- 0.1 dB freq. linearity, all headsets between 16 to 600 Ohms.
 
Mar 26, 2021 at 11:59 AM Post #5,662 of 5,663

Starbound

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Usually headphones do not vary much their impedance while playing music, as speakers do, so I don't think neutrality of a headamp is much related to this. Instead, frequency response tested with several impedances across audibile bandwidth will be more helpful here.

More probably, the O2 is neutral because it has a rather low output impedance and is able to drive, with +/- 0.1 dB freq. linearity, all headsets between 16 to 600 Ohms.
I think I was misunderstanding. Every headphone has a non-linear impedance to frequency curve, but some move than others. My understanding was that because of this, if a headphone has an output impedance that is relatively high, it can cause frequencies where a specific headphone has a peak in the impedance/frequency curve to not be represented correctly. But now that I think about it it I see this doesn't make sense, because in these sense higher impedance actually is not a problem. It's more a matter of the amp being able to produce enough power even at frequencies where there is a peak in the impedance.

So yeah, I get what you are saying there, thanks.
 
Mar 26, 2021 at 1:16 PM Post #5,663 of 5,663

raoultrifan

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On speakers the impedance across audible bandwidth is usually between 3...5 Ohms to 20...25 Ohms, depending on the frequency, so it's varying with at least 500% between min. and max. On headsets the differences are usually below 10% between min. and max., but of course, it depends from one headphone to another.

Not sure this is related to your question, but low impedance headphones might not have the best bass response under some circumstances, especially when the output impedance of the headamp is higher than 1/8 of headphone's impedance.

In case of O2, people and measurements are calling it neutral due to its ability of driving headphones of different impedances with an almost perfect frequency response. Well, electronic engineering advanced a lot in the past years, so most of today headamps are neutral and trying to not alter the input signal at all. So, best bet when buying a headamp is mostly related to THD+N, output noise (in uV RMS), price and warranty (period and who's paying the shipping back and forth).
 
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