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O2 AMP + ODAC - Page 199

post #2971 of 3233
I can try tonight. Given that it's a standard class 1 USB audio device any modern Linux system should have support right out of the box.
post #2972 of 3233

Tube amps are great at voltage and hence at higher impedance loads.  For optimal theoretical damping with dynamic headphones you'd need a 7-8 factor difference between the output of the amp and the cans' nominal impedance (which might be < 50% of max impedance at certain frequencies), if it's much less then you  get a typical 'loose' bass due to lack of control over the diaphragm.  Planars are reasonably insensitive to this phenomenon though.  My 38 ohm HE-500 plays very nice with tube amps.

post #2973 of 3233
Quote:
Originally Posted by Xenophon View Post
 

Tube amps are great at voltage and hence at higher impedance loads.  For optimal theoretical damping with dynamic headphones you'd need a 7-8 factor difference between the output of the amp and the cans' nominal impedance (which might be < 50% of max impedance at certain frequencies), if it's much less then you  get a typical 'loose' bass due to lack of control over the diaphragm.  Planars are reasonably insensitive to this phenomenon though.  My 38 ohm HE-500 plays very nice with tube amps.

Is that because planars end up being a simpler purely resistive load?

post #2974 of 3233
Quote:
Originally Posted by CADCAM View Post
 

Does anyone have the ODAC and run Linux as an OS? I run PCLinuxOS 64 and want to verify that the ODAC works and is recognized with the OS before purchasing.

thanks for any help

 

Works fine here with different Ubuntu and Debian flavours. As has been said before - it should work with just about anything capable of using a USB audio class 1 device...

 

Joachim

post #2975 of 3233

I have a Maverick D2 and my system ignores the DAC when I plug it in...

Do you happen to know if I need to install something from the Package Manger? BTW using Clementine to play tunes but tried Pandora and get the same:triportsad:

post #2976 of 3233
Quote:
Originally Posted by James-uk View Post

At its best, the ODAC sound expansive, detailed, and precise in imaging. At its worst, the ODAC sounds closed-in, flat, dull, uninteresting, and with wooly bass (Class S). It depends upon the USB connection. Overall the ODAC is not as precise in rendering of sounds. This is where the comparable Modi exceeds its performance.

^(Quote from said shoot out)

^^^^^This is hilarious . It depends on the USB connection!
Quote:
Originally Posted by miceblue View Post

Well my older MacBook's USB connection is kind of lame and yeah, I can agree with that observation.
Quote:
Originally Posted by James-uk View Post

Bring some double blind examples to the table and I'm all ears.

Here's an example of a bad USB port. I think even a mostly deaf person can tell it's bad.
Foobar2000 + WASAPI output -> ODAC -> USB audio recorder with line out connection from ODAC to a different computer -> Audacity
https://dl.dropboxusercontent.com/u/2816447/BadUSB.wav
Edited by miceblue - 5/27/14 at 11:03pm
post #2977 of 3233
Quote:
Originally Posted by greenkiwi View Post
 

Is that because planars end up being a simpler purely resistive load?

There are a couple of issues with high output impedance for the amp and low impedance headphones:

 

- The higher the output impedance, the higher the voltage drop with a low impedance load--> This can cause insufficient 'drive' of headphones (insufficient volume, distortion...) if your amp is not up to it.

 

- With dynamic cans, impedance fluctuates across the frequency band, this may or may not exacerbate the previous problem, planars are not subject to this fluctuation as they indeed behave like a resistive load even though (long explanation which I'll skip) they're really not.

 

- Damping:  Also plays with planars, I frankly don't understand all aspects so what follows is speculation:  if a headphone is underdamped it'll start showing signs such as 'loose' bass.  Fact is, none of my planars show this, even though they're low impedance loads connected to a high impedance output sources.  Electrical damping is negligible due to this.  I suspect the all things considered good damping is related to mechanical damping due to the different structure with the membrane and the metal conductive tracers.

 

The above -especially about damping- is speculation, there are a number of interrelated factors at play and I lack the knowledge to really give a founded opinion.  But in the end, who cares, the sound is good. I did extensive comparisons with my planars connected to a tube amp vs to my (close to zero output resistance) V200 and the bass on the V200 is a bit tighter but not a big deal.   If your tube amp is sufficiently powerful and you use planars I don't think you need to worry.  With dynamic cans that have a low impedance it's best to try before you buy.  Imo really low impedance headphones and tubes are a no-no.

 

Or if you have either the time, knowledge and skills, develop a custom tube amp that ensures a decent impedance match (can be done but tends to become expensive) or lacking those skills but possessing money, the great equalizer, hire someone to do it for you.

post #2978 of 3233
Quote:
Originally Posted by Xenophon View Post

There are a couple of issues with high output impedance for the amp and low impedance headphones:

- The higher the output impedance, the higher the voltage drop with a low impedance load--> This can cause insufficient 'drive' of headphones (insufficient volume, distortion...) if your amp is not up to it.

- With dynamic cans, impedance fluctuates across the frequency band, this may or may not exacerbate the previous problem, planars are not subject to this fluctuation as they indeed behave like a resistive load even though (long explanation which I'll skip) they're really not.

- Damping:  Also plays with planars, I frankly don't understand all aspects so what follows is speculation:  if a headphone is underdamped it'll start showing signs such as 'loose' bass.  Fact is, none of my planars show this, even though they're low impedance loads connected to a high impedance output sources.  Electrical damping is negligible due to this.  I suspect the all things considered good damping is related to mechanical damping due to the different structure with the membrane and the metal conductive tracers.

The above -especially about damping- is speculation, there are a number of interrelated factors at play and I lack the knowledge to really give a founded opinion.  But in the end, who cares, the sound is good. I did extensive comparisons with my planars connected to a tube amp vs to my (close to zero output resistance) V200 and the bass on the V200 is a bit tighter but not a big deal.   If your tube amp is sufficiently powerful and you use planars I don't think you need to worry.  With dynamic cans that have a low impedance it's best to try before you buy.  Imo really low impedance headphones and tubes are a no-no.

Or if you have either the time, knowledge and skills, develop a custom tube amp that ensures a decent impedance match (can be done but tends to become expensive) or lacking those skills but possessing money, the great equalizer, hire someone to do it for you.

I have a similar experience with a higher output impedance amp. My HDVD800 amp has a supposed 47 ohm output and therefore using the hd800s with it I expect bass to have a bit more 'bloom' and the upper mids and treble to be slightly quieter due to its impedance curve ( 600ohm across mid bass and less than 300ohm across upper mids into treble ) but when I switch between the hdvd800 and O2 it's very difficult to hear any difference . I would put money on me failing a blind test between them.
post #2979 of 3233
Quote:
Originally Posted by James-uk View Post

I have a similar experience with a higher output impedance amp. My HDVD800 amp has a supposed 47 ohm output and therefore using the hd800s with it I expect bass to have a bit more 'bloom' and the upper mids and treble to be slightly quieter due to its impedance curve ( 600ohm across mid bass and less than 300ohm across upper mids into treble ) but when I switch between the hdvd800 and O2 it's very difficult to hear any difference . I would put money on me failing a blind test between them.

The HD800 may have a nominal impedance of 300Ohms but like other dynamic driver phones it's load impedance can fluctuate wildy at different frequencies, Most of the time the wild flunctuation is at the mid bass. HD800 could easily go up to 600ohms at the mid bass, which could explain why you don't hear much difference against O2.
post #2980 of 3233
Quote:
Originally Posted by headwhacker View Post

The HD800 may have a nominal impedance of 300Ohms but like other dynamic driver phones it's load impedance can fluctuate wildy at different frequencies, Most of the time the wild flunctuation is at the mid bass. HD800 could easily go up to 600ohms at the mid bass, which could explain why you don't hear much difference against O2.

That's my point, the fluctuating impedance should mean that with a higher output amp such as the hdvd800 the damping factor means it should effect the sound compared to the O2. If I'm right in thinking a high output impedance amp won't act like the O2 and won't give equal voltage across the fluctuating impedance curve because the damping factor is poor. Basically high output amps would supply more voltage at the highest part of the impedance curve and less at the lowest and therefore alters the headphone frequency response. I don't hear this with the hdvd800 however , it sounds the same as the O2 yet it's damping factor is much worse . Why is that do you think? Maybe the damping factor is still high enough that is not having a noticeable effect?
post #2981 of 3233

Can anyone compare the 02 and Vali with HD800?

post #2982 of 3233
Quote:
Originally Posted by James-uk View Post

That's my point, the fluctuating impedance should mean that with a higher output amp such as the hdvd800 the damping factor means it should effect the sound compared to the O2. If I'm right in thinking a high output impedance amp won't act like the O2 and won't give equal voltage across the fluctuating impedance curve because the damping factor is poor. Basically high output amps would supply more voltage at the highest part of the impedance curve and less at the lowest and therefore alters the headphone frequency response. I don't hear this with the hdvd800 however , it sounds the same as the O2 yet it's damping factor is much worse . Why is that do you think? Maybe the damping factor is still high enough that is not having a noticeable effect?

Assuming the worst impedance swing at 600 ohms, Damping factor is between 6 - 12. So it's possible HD800 is still adequately damped.
post #2983 of 3233
Quote:
Originally Posted by headwhacker View Post

Assuming the worst impedance swing at 600 ohms, Damping factor is between 6 - 12. So it's possible HD800 is still adequately damped.
Good point. I can't help but wonder why the HDvd800 engineers decided on a 47 ohm output. It's a well designed amp otherwise. Granted its expensive and has snake oil balanced connections but I do like running multi headphones from it. The O2 /odac sounds the same at 1/5 the cost though and probably measures better. Gotta love the O2!
post #2984 of 3233
Quote:
Originally Posted by James-uk View Post


Good point. I can't help but wonder why the HDvd800 engineers decided on a 47 ohm output. It's a well designed amp otherwise. Granted its expensive and has snake oil balanced connections but I do like running multi headphones from it. The O2 /odac sounds the same at 1/5 the cost though and probably measures better. Gotta love the O2!

It's extremely pricey for what it is.  But ok, it's Sennheiser so there's the name premium (just take a look at their new cables...)+ the case that must cost a pretty penny to fabricate and the connectivity options.  Beats me too why they settled on the 47 Ohm output impedance (I'd guess some of their measurements were 'helped' by selecting that value although generally lower = better) but let's not forget that the 1996 IEC 61938 standard still specifies an insane 120 Ohm.

 

And admit it, guys, it looks more impressive sitting there than an ODAC/O2.  I'd say the components would be higher specced too but after my last shocking look under the hood of a tube amp that retails for >3 kUSD I'm no longer convinced of the positive correlation between price and quality.

post #2985 of 3233

FYI....thought I would share the thoughts of AGDR in his ODA designand damping for headphones and amps:

 

Output damping factor resistors. This version of an ODA has PC board holes for a series resistor on each channels output (R88 & R89) that changes the damping factor. This resistor can simply be omitted and the PC holes shorted out with a jumper wire to get the lowest output impedance and highest damping factor, about 0.083 ohms. That is the default in the BOM. Some headphones may sound better to the user with a lower damping factor (adding in the series resistors), especially adding more bass. In an email exchange with AKG (Harman International) they said that the recommended amplifier output impedance for my AKG K550 headphones is the same as the phones, 32 ohms, +/-20 ohms in either direction. Not zero ohms. These two R88 & R89 resistor pads have three holes to accommodate different sized resistors. Just run the jumper between the two outer holes, and it doesn’t matter if the (bare) jumper wire touches the middle hole.

An external 6 position rotary switch can be mounted on the front panel with wires running to these PCB holes to give more damping factor selections. I’ve included a suitable optional panel mount rotary switch in the BOM.

So in most cases the two damping factor resistor positions on the PC board will simply be jumpered across (not used) to obtain the lowest amplifier output impedance of 0.083 ohms per channel. But if you want to experiment with different damping factors the holes are there to insert resistors and give it a try! I would suggest trying the following:

• 10 ohms, which is a common resistor value used on many amps that don’t have output short circuit protection like this amp does. The resistor helps limit current spikes in those amps.

• A resistor equal to the impedance of your headphones if under 80 ohms or so. In the case of my AKG-K550s, 30 ohms. That will result in a 50/50 voltage divider and cut the maximum output voltage swing to the headphones in half.

• 120 ohms. A very old standard for headphone amp output impedance was 120 ohms, but that had more to do with the use of tubes at the time. Some older headphones may have been designed with that standard in mind though! Unless the headphones being used are 300R or 600R, a significant amount of the voltage swing would be dropped across the 120R resistor though.

 

Alex

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