[miceblue]

On the topic of power:
 
Quote:

  O2 gets 353 mW @ 15 ohms, 534 mW @ 33 ohms, (interpolated by me) 272 mW or so @ 100 ohms, 94 mW or so @ 300 ohms, on a mid-high charge on battery

What exactly do these numbers mean? I know the creator of the O2 mentions Vrms, and JDS Labs is using that measurement for their C5 (600Ω: 4.146 VRMS), but what do the above measurements measure? Those above measurements are pretty commonly found in amplifiers from what I've seen (all the news of the FiiO E12 pumping 800+ mW @ 32 ohms). On Tyll's measurements from Innerfidelity, there is the "Power Needed for 90d BSPL" measurement, but it's on the order of 0.0X mW, not a few hundred.

 

[shadow419]

Those power numbers would be max power into a load before distortion gets too high.  Different companies use different thresholds for distortion when reporting max power into a load, but generally somewhere between 1% and 10% distortion.  Tyll's measurements for power needed to reach 90dB SPL let's you extrapolate how much power you'll need to reach a desired SPL.  For every 3dB you increase the SPL you need double the power.  So for example if you need 0.05mW for 90dB spl, 93 dB would need 0.1mW and so on.

 

[mikeaj]

Those are max possible power levels.  For the O2, they're the point at which if you draw any more power, the total harmonic distortion will exceed 1%.  That's a common reference point for power amp specs.  Commonly, for consistency, this is done using a resistor as a load, with a single-tone sine wave test.  For a sine wave, the root-mean-square voltage is 1/sqrt(2) of the peak voltage.  Power is rms voltage squared, divided by the resistance:  P = V^2 / R.
 
The power that can be delivered is different depending on the load impedance, hence the multiple figures.
 
 
InnerFidelity measurements for headphones indicate how much power is required to make the device output a certain sound pressure level (90 dB SPL, a fairly loud level), using a 1 kHz test tone.  There's quite a wide range.  e.g. 0.004 mW for Shure SE535, 19.69 mW for HiFiMAN HE-6.  That's 37 dB difference between the two.
 
The more power you deliver, the louder they sound.  Deliver 2x the power, and you get 3 dB SPL higher.  Deliver X mW into a headphone quoted at 90 dB SPL / Y mW, and you get [10*log(X / Y) + 90] dB SPL out.  That's base-10 log, not natural log.
 
For the SE535, deliver say 500 mW into the 36 ohms or so, and that would be [10*log(500 / 0.004) + 90] = 141 dB SPL.  heh j/k, not really—they would burn out / explode well before 500 mW, and distort horribly before that point. But that's how it works up until the point where they're distorting really badly.
 
The point I usually make still stands that few people are using these astronomically high levels consistently.  Sure, you need some margin for that really loud peak in that one part of a (classical) recording, but most people get nowhere close to the limits of their amps unless they're using some power monster like HE-6 or whatever, or maybe a 600 ohms Beyer, etc. and are listening loudly.
 
 
edit: whoops shadow419 got it first

 

[shadow419]

I got it first but you broke down the math way better.  

 

[miceblue]

Quote:

Those are max possible power levels.  For the O2, they're the point at which if you draw any more power, the total harmonic distortion will exceed 1%.  That's a common reference point for power amp specs.  Commonly, for consistency, this is done using a resistor as a load, with a single-tone sine wave test.  For a sine wave, the root-mean-square voltage is 1/sqrt(2) of the peak voltage.  Power is rms voltage squared, divided by the resistance:  P = V^2 / R.
 
The power that can be delivered is different depending on the load impedance, hence the multiple figures.
 
 
InnerFidelity measurements for headphones indicate how much power is required to make the device output a certain sound pressure level (90 dB SPL, a fairly loud level), using a 1 kHz test tone.  There's quite a wide range.  e.g. 0.004 mW for Shure SE535, 19.69 mW for HiFiMAN HE-6.  That's 37 dB difference between the two.
 
The more power you deliver, the louder they sound.  Deliver 2x the power, and you get 3 dB SPL higher.  Deliver X mW into a headphone quoted at 90 dB SPL / Y mW, and you get [10*log(X / Y) + 90] dB SPL out.  That's base-10 log, not natural log.
 
For the SE535, deliver say 500 mW into the 36 ohms or so, and that would be [10*log(500 / 0.004) + 90] = 141 dB SPL.  heh j/k, not really—they would burn out / explode well before 500 mW, and distort horribly before that point. But that's how it works up until the point where they're distorting really badly.
 
The point I usually make still stands that few people are using these astronomically high levels consistently.  Sure, you need some margin for that really loud peak in that one part of a (classical) recording, but most people get nowhere close to the limits of their amps unless they're using some power monster like HE-6 or whatever, or maybe a 600 ohms Beyer, etc. and are listening loudly.
 
 
edit: whoops shadow419 got it first

 
Quote:

Those power numbers would be max power into a load before distortion gets too high.  Different companies use different thresholds for distortion when reporting max power into a load, but generally somewhere between 1% and 10% distortion.  Tyll's measurements for power needed to reach 90dB SPL let's you extrapolate how much power you'll need to reach a desired SPL.  For every 3dB you increase the SPL you need double the power.  So for example if you need 0.05mW for 90dB spl, 93 dB would need 0.1mW and so on.

Ah, now things make more sense. Thank you for clearing that up!
JDS Labs uses the DT880 (they don't list the ohm value) for their benchmarking tests.
 
A few more questions:

1. The SE535 is rated at 119 dB SPL/mW, whereas the K 702 is rated at 105 dB[/mW?]. These numbers correspond to a headphones SPL at 1 mW, so the higher the value the more "sensitive" it is? If this is the case, Sennheiser's website says the HD650 is rated at 103 SPL[/mW?], which is less sensitive than the K 702 yet the K 702 seems to get pinged a lot for being insensitive, not so much for the HD650 from what I read.
2. With the O2's gain at 2.5x, I can hear the background hiss through my sensitive headphones/earphones; the designer of the O2 designed the O2 to have a very "black background", so why is it that with a higher gain I can hear the background hiss?

 

[shadow419]

Take sensitivity ratings from some manufacturers with a grain of salt.  Some of them may fudge the numbers a little or maybe it's just they're testing environment.  Some companies also list sensitivity in dB/mV and not dB/mW.  If you want to compare apples to apples, you need to make sure that the same units are being used since you'll have a higher number if the sensitivity is in dB/mV.  
 
As far as the amp goes, remember that you want to use as little gain as necessary since the amp will also amplify any noise that's already in the signal.  The less gain you use the lower the noise floor will be.  Sometimes hiss can also come from a ground issue.  Try to track down the source off the hiss.  With in ears and no music playing, I start to hear hiss with x3 gain at about 1 o'clock on the pot.  With unity gain hiss doesn't get audible till 3 o'clock, but my ears are begging for mercy at about 1 o'clock on unity.

 

[adamlr]

deep breath....
Quote:

 
Oh, I totally misread you then.  My first reply is what's relevant then.
 
In the real world, if you're connecting headphones (speakers) to an amp and asking that amp to drive them, the amp will not do a perfect job.  There will be some deviation from the original (the input to the amp).  The deviation depends on the electronics design of the amp, the headphones, the output level, and the nature of the input.  A so-called high-fidelity amp will make the signal the headphones receives look very much like the input to the amp, no matter what the other factors are.  Other amps may behave differently.  They may try and fail to maintain an output that looks like the input.
 
Some people spend megabucks to try to get amps that deviate in certain specific ways, hence a different sound.
 
By using an amp with 1x gain, you are still using that amp's electronics to run the headphones, so it's not pointless.  You need some kind of amp, or else you don't get sound.  Some are just better than others.  If you use some device not designed to drive headphones at all, you could get some terrible garbled junk out.
 
So internally, there is some step where you are multiplying by 1, but that's not all that's going on.
 
 

 
 
Frequency response is about the relative amplitudes of signals at the output of the device, at different frequencies (technically it probably should include phase as well as amplitude, but...).  That's unrelated.  Be careful if you talk about reducing volume by a certain amount in software.  Reducing by 60% is turning down 8 dB in foobar.  If you set computer volume to 40 / 100, it's probably reducing it by more than 60%.  Those things rarely scale linearly.
 
Fidelity would suffer in the sense that you might reduce the SNR, but the noise is probably still inaudible.
 
 
 
 

 
You might need some more-sensitive headphones or IEMs and reduce the volume even more in software, maybe more than 6.5x gain too.  Also, play some music or test track that doesn't have noise in the recording itself.  Then you might hear the noise from the DAC without totally blasting your ears off when the actual sounds start playing.  DT 770 250 ohms is too insensitive for this stuff to be a big deal.

about unity gain: im starting to feel like the village idiot, repeatedly asking a question, getting answers, but still not grasping them. in my knowledge, when turning the volume knob, your adding power, which in turn makes for higher volume. if the added power is multiplied by 1, whats going on?
nevermind. im sure that in time, through my own research (based mostly around ethen winers book) i'll find the answer myself. its just that with my day job, social life, and listening time, my own "research" is moving at a very low pace, so i sometimes ask in the forums. it looks like i asked a question too complex to understand with the small amount of knowledge i have, so im mostly just confusing myself further, and wasting your time. thank you for your patience =]
 
about the 250 ohm impedance, could this be the advantage to having high impedance headphones that no one seems to know? does insensitivity translate into insensitivity to noise?
most of this conversation (atleast the bits i contributed) was started in order too asses whether or not using the O2 with sensitive headphones was a good idea or not, as im soon going to get new headphones and am currently trying to decide between the m-100 and the ws 99, both of which are rather sensitive.
Quote:

The 6.5x gain on my O2 is a joke. It's like an  "add massive amounts of distortion" button. Is this normal?

what source are you using? if your using the odac, note that the following: playback devices > odac. is not enough. you must also set: volume control options > odac. atleast thats what i did, cause i got alot of noise even at *2.5 gain.
Quote:

Those power numbers would be max power into a load before distortion gets too high.  Different companies use different thresholds for distortion when reporting max power into a load, but generally somewhere between 1% and 10% distortion.  Tyll's measurements for power needed to reach 90dB SPL let's you extrapolate how much power you'll need to reach a desired SPL.  For every 3dB you increase the SPL you need double the power.  So for example if you need 0.05mW for 90dB spl, 93 dB would need 0.1mW and so on.

that sounds pretty high actually... i think i may have misunderstood something, but doesn't 10% translate into -20 dBu, and 1% = -40 dBu? i imagine this would be quite audible no? the O2 for example has the following listed in the jds labs spec: "THD 1 Khz 150 Ohms: 0.0016%" which translates (very roughly) into -80 dBu, which i think would be virtually impossible to hear.
any chance you know what happens to these numbers when the impedance rating is higher/lower? id be very interested to know =]
Quote:

Those are max possible power levels.  For the O2, they're the point at which if you draw any more power, the total harmonic distortion will exceed 1%.  That's a common reference point for power amp specs.  Commonly, for consistency, this is done using a resistor as a load, with a single-tone sine wave test.  For a sine wave, the root-mean-square voltage is 1/sqrt(2) of the peak voltage.  Power is rms voltage squared, divided by the resistance:  P = V^2 / R.
 
The power that can be delivered is different depending on the load impedance, hence the multiple figures.
 
 
InnerFidelity measurements for headphones indicate how much power is required to make the device output a certain sound pressure level (90 dB SPL, a fairly loud level), using a 1 kHz test tone.  There's quite a wide range.  e.g. 0.004 mW for Shure SE535, 19.69 mW for HiFiMAN HE-6.  That's 37 dB difference between the two.
 
The more power you deliver, the louder they sound.  Deliver 2x the power, and you get 3 dB SPL higher.  Deliver X mW into a headphone quoted at 90 dB SPL / Y mW, and you get [10*log(X / Y) + 90] dB SPL out.  That's base-10 log, not natural log.
 
For the SE535, deliver say 500 mW into the 36 ohms or so, and that would be [10*log(500 / 0.004) + 90] = 141 dB SPL.  heh j/k, not really—they would burn out / explode well before 500 mW, and distort horribly before that point. But that's how it works up until the point where they're distorting really badly.
 
The point I usually make still stands that few people are using these astronomically high levels consistently.  Sure, you need some margin for that really loud peak in that one part of a (classical) recording, but most people get nowhere close to the limits of their amps unless they're using some power monster like HE-6 or whatever, or maybe a 600 ohms Beyer, etc. and are listening loudly.

but as i said before, 1% is quite a loud bit of noise no? (honest question) shouldnt the standard be set at say 0.1% (-60 dBu) to be certain you wont hear any noise?

 

[shadow419]

Quote:

deep breath....
about unity gain: im starting to feel like the village idiot, repeatedly asking a question, getting answers, but still not grasping them. in my knowledge, when turning the volume knob, your adding power, which in turn makes for higher volume. if the added power is multiplied by 1, whats going on?
nevermind. im sure that in time, through my own research (based mostly around ethen winers book) i'll find the answer myself. its just that with my day job, social life, and listening time, my own "research" is moving at a very low pace, so i sometimes ask in the forums. it looks like i asked a question too complex to understand with the small amount of knowledge i have, so im mostly just confusing myself further, and wasting your time. thank you for your patience =]
 
about the 250 ohm impedance, could this be the advantage to having high impedance headphones that no one seems to know? does insensitivity translate into insensitivity to noise?
most of this conversation (atleast the bits i contributed) was started in order too asses whether or not using the O2 with sensitive headphones was a good idea or not, as im soon going to get new headphones and am currently trying to decide between the m-100 and the ws 99, both of which are rather sensitive.
what source are you using? if your using the odac, note that the following: playback devices > odac. is not enough. you must also set: volume control options > odac. atleast thats what i did, cause i got alot of noise even at *2.5 gain.
that sounds pretty high actually... i think i may have misunderstood something, but doesn't 10% translate into -20 dBu, and 1% = -40 dBu? i imagine this would be quite audible no? the O2 for example has the following listed in the jds labs spec: "THD 1 Khz 150 Ohms: 0.0016%" which translates (very roughly) into -80 dBu, which i think would be virtually impossible to hear.
any chance you know what happens to these numbers when the impedance rating is higher/lower? id be very interested to know =]
but as i said before, 1% is quite a loud bit of noise no? (honest question) shouldnt the standard be set at say 0.1% (-60 dBu) to be certain you wont hear any noise?

Most companies use the 1%(or even lower) distortion for max power rating.  Some companies will use a higher distortion point to inflate the usable power number.  Not really an issue with most reputable companies.
 
Think of the amplifier as having two power increasing sections.  The gain stage increases the voltage, and the output stage increasing the current available.  The volume pot on the O2 sits between the two stages and controls how much output from the gain stage is fed into the output stage.  On most amps the volume pot sits before the gain stage and controls how much input is fed into the gain stage.  It's more of a volume attenuator.  Even if the gain stage isn't increasing the signal, turning the volume increases the amount of signal being passed to the output stage of the amp.

 

[adamlr]

Quote:

Most companies use the 1%(or even lower) distortion for max power rating.  Some companies will use a higher distortion point to inflate the usable power number.  Not really an issue with most reputable companies.
 
Think of the amplifier as having two power increasing sections.  The gain stage increases the voltage, and the output stage increasing the current available.  The volume pot on the O2 sits between the two stages and controls how much output from the gain stage is fed into the output stage.  On most amps the volume pot sits before the gain stage and controls how much input is fed into the gain stage.  It's more of a volume attenuator.  Even if the gain stage isn't increasing the signal, turning the volume increases the amount of signal being passed to the output stage of the amp.

so lets see if i understand:
most amps: signal coming from the source recieves voltage at the gain stage, and current at the output stage with the volume pot controlling how much of the signal from the source comes through.
 
O2 with unity gain: signal coming from the source recives no added value, but recieves more current before the output stage, with the volume pot controlling how much of the signal from the gain stage reaches the output stage.
 
is that right?

 

[shadow419]

The output stage op-amps provide the extra current, but yes think you have the gist.

 

[adamlr]

Quote:

The output stage op-amps provide the extra current, but yes think you have the gist.

thank you so much =] 

 

[JakeJack_2008]

Many interesting posts.   - For me, this thread is like a 24-bit Encyclopedia. Ha, ha, ...
I'm glad that I found it.
 
 
Anyway, why the ODAC doesn't handle 88.2 kHz files? I've read that it cleanly downsamples 88.2 kHz files to 44.1 kHz files?
At the same time, the Dragonfly  handles 88.2 kHz files correctly.
(It does not downsample 88.2 kHz files to 44.1 kHz files). - Any comments?

 

[mikeaj]

Quote:

Many interesting posts.   - For me, this thread is like a 24-bit Encyclopedia. Ha, ha, ...
I'm glad that I found it.
 
 
Anyway, why the ODAC doesn't handle 88.2 kHz files? I've read that it cleanly downsamples 88.2 kHz files to 44.1 kHz files?
At the same time, the Dragonfly  does not downsample 88.2 kHz files. - Any comments?

 
 
Either the USB receiver chip (TE7022) or the DAC (ES9023) doesn't support 88.2 kHz.  I forget which.  Some other devices do, as you've seen.
 
The ODAC isn't responsible for sample rate conversion.  That's in whatever software you're using.  Usually, at least with a reasonable algorithm, sample rate conversion shouldn't really be an issue.

 

[JakeJack_2008]

Quote:

 
 
Either the USB receiver chip (TE7022) or the DAC (ES9023) doesn't support 88.2 kHz.  I forget which.  Some other devices do, as you've seen.
 
The ODAC isn't responsible for sample rate conversion.  That's in whatever software you're using.  Usually, at least with a reasonable algorithm, sample rate conversion shouldn't really be an issue.

 
Yeah, You're right, I vaguely remember reading  that it's the receiver.
 
Nevertheles, there are many   88.2 kHz tracks (on HDTracks.com) by The Rolling Stones.
So, the ODAC will deprive me of listening to The Rollings Stones on 88.2 kHz tracks.
It will downgrade - ha, ha, .. -  The Rolling Stones to the Red Book 44.1 Khz.

 

[HamilcarBarca]

Quote:

Anyway, why the ODAC doesn't handle 88.2 kHz files? I've read that it cleanly downsamples 88.2 kHz files to 44.1 kHz files?
At the same time, the Dragonfly  handles 88.2 kHz files correctly.
(It does not downsample 88.2 kHz files to 44.1 kHz files). - Any comments?

 
Not many people can hear frequencies as high as 22,050 Hz which is the theoretical limit -- vaguely speaking -- of a 44.1kHz signal. Increasing the sampling rate to 88.2kHz means, again in theory, the DAC can reproduce frequences up to 44.1kHz. However, humans can't hear those frequencies. There's essentially no benefit to the listener.
 
Why might another manufacturer support 88.1kHz or even 192kHz (which has zero benefit to humans)? Ask them why. Don't forget to mention Nyquist rates. I predict the response, if any, will be "science doesn't apply to our products."