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O2 AMP + ODAC - Page 46

post #676 of 3245

The ODA's relay circuit would be a welcome addition however. So would a triple gain or variable gain switch, clearly marked to simplify adjustments based on source (i.e. 2V position would be 2V source, and so on).

 

How about bass and treble adjustments? Would that be wrong?

 

Should accept, at minimum, 3.5mm input, RCA, USB, and a digital in.

 

Also, I'd like to see it do a solid power upgrade - 1-2 watt max.

 

I'd pay about $100-$200.

post #677 of 3245

Bass and treble would be wrong to me IMO....

 

This is a purist design..to be flat, transparent, simple straight wire with gain design...etc all specs that matter are well beyond what the human ear can discern...

 

Adding bass boost, or tone controls would very foreign to this amp....not that it couldnt be done etc....

 

You can always muck with a software EQ in most players if you like, DSP etc...but not for me.

 

All the best

Alex

post #678 of 3245
Is this the latest ultra low-end head amp? How does it compare with Glite?
post #679 of 3245
Quote:
Originally Posted by chesebert View Post

Is this the latest ultra low-end head amp? How does it compare with Glite?

I'm not sure about the Glite, but the $150 O2 sounds very similar to the new $100 Schiit Audio Magni headphone amplifier from what I've read.

post #680 of 3245

This amp has been around now for several months.....do a search and you will find the designers site.....

 

Alex

post #681 of 3245

Gilmore Lite is quite a different design.

 

Not sure how to parse "ultra low-end".  Ultra performance at low-end cost?  Or ultra low-end... what?  Grammatically I think it's the latter, but I'm not sure what would be considered low-end here.  It doesn't have the best performance, certainly not the lowest, and it's not the cheapest or most expensive.

 

At $150 the cost is not that low.  It's just about ~$23 for parts (based on single-unit quantities) on the PCB other than the battery before shipping.  i.e. does not include PCB (I suppose $4-10), enclosure / panels ($25 ish?), rechargeable batteries ($10), AC/AC wallwart ($5-10).  The $23-30 figure would be pretty low.  Silicon costs are very minimal here.

 

Also check out The Wire on diyaudio, for what you get if you use higher-end ICs.

post #682 of 3245

Ok, I've finally found the bookmark I've been looking for: Measurements of the O2 under real loads, ie: with multiple driver IEMs plugged in.  This is why you pay your money for good amps: Linearity when playing music with headphones plugged in, not just a scope or a computer/ADC which has a flat impedance curve.

 

http://scientistsaudio.blogspot.jp/2012/06/leckerton-uha-6smkii-part-2.html

 

Before anyone complains to me about posting this, I have two O2s here I built for evaluating headphones, as well the Leckerton. 

post #683 of 3245
Quote:
Originally Posted by Currawong View Post

Ok, I've finally found the bookmark I've been looking for: Measurements of the O2 under real loads, ie: with multiple driver IEMs plugged in.  This is why you pay your money for good amps: Linearity when playing music with headphones plugged in, not just a scope or a computer/ADC which has a flat impedance curve.

 

http://scientistsaudio.blogspot.jp/2012/06/leckerton-uha-6smkii-part-2.html

 

Before anyone complains to me about posting this, I have two O2s here I built for evaluating headphones, as well the Leckerton. 

 

Thanks for digging up the link.  It was my request, after all.

 

 

I can't remember precisely what the context was or which thread it was, but paraphrasing from weeks back, I think it was roughly:

(1) Me — any evidence that shows that an amp with good performance into all sorts of test tones / loads will do poorly or significantly less well with headphones + music?

(2) Currawong — yeah, but I hesitate to post because it's an anonymous source; also forgot what the link was so would need to find it

(3) Me — please post anyway if you ever remember, thanks

 

Unfortunately for me, I'd seen that before and that's not what I'm talking about.

 

What is exposed there is how the O2 / other amp output impedance will interact with an IEM with crazy impedance variations, a very well-known and boring result.  Also, we're looking at resulting FR variations of less than 1 dB from max to min:  perhaps audible and a valid point of contention, but largely not much of a big deal at all.  Or is somebody going to suggest that mostly flat EQs with a max 0.7 dB variation ruin the sound quality?

 

So still no measurement-based evidence, or at least I haven't seen it yet.  Which of course doesn't necessarily prove anything in of itself.

post #684 of 3245
Quote:
Originally Posted by Currawong View Post

Ok, I've finally found the bookmark I've been looking for: Measurements of the O2 under real loads, ie: with multiple driver IEMs plugged in.  This is why you pay your money for good amps: Linearity when playing music with headphones plugged in, not just a scope or a computer/ADC which has a flat impedance curve.

 

http://scientistsaudio.blogspot.jp/2012/06/leckerton-uha-6smkii-part-2.html

 

Before anyone complains to me about posting this, I have two O2s here I built for evaluating headphones, as well the Leckerton. 

I don't get it. How do I read these graphs? Can someone explain for me!redface.gif

post #685 of 3245
Quote:
Originally Posted by Currawong View Post

Ok, I've finally found the bookmark I've been looking for: Measurements of the O2 under real loads, ie: with multiple driver IEMs plugged in.  This is why you pay your money for good amps: Linearity when playing music with headphones plugged in, not just a scope or a computer/ADC which has a flat impedance curve.

 

http://scientistsaudio.blogspot.jp/2012/06/leckerton-uha-6smkii-part-2.html

 

Before anyone complains to me about posting this, I have two O2s here I built for evaluating headphones, as well the Leckerton. 

From that website, for those particular loads:

Quote:
Not as good as from the Leckerton, but as we are well in 1 dB the result is still very good.

So really it's not a big problem for the O2? Is a 1 dB difference really going to make an amp purchase a make-it/break-it decision?

 

I'm still fairly new to DACs and amps, so I'm not quite understanding what you're trying to say. Are you saying that with higher impedance headphones the O2 might not give a linear output and have an output that's outside of the 1 dB tolerance?

 

 

 

Also, since there are now 2 active O2 threads, I think you may have confused this thread from the other one:

Quote:
Originally Posted by Currawong View Post

Quote:
Originally Posted by adydula View Post

There are many happy LCD-2 users using the O2. It has power to spare to drive the LCD-2 to hearing damaging levels and beyond.


The LCD-2 hits 110 dB with about 1 volt of input. Peaks of 110 dB are considered plenty loud by most people (hearing damage starts past 85 dB). 110 dB is standing on a sidewalk next to a jack hammer tearing up concrete.

Even if you plan for 115 dB peaks, which is extremely loud, you only need about 1.7 Vrms which is 0.048 watts. The O2 can provide 5+ Vrms which is good for 124 dB SPL with the LCD-2. And that's running from battery power.

So just on batteries alone the O2 will dirve the LCD2's to their limits and ear damaging levels.

 

There is not shortage of bass with the O2....if its there in the recording it will get amplified and if your cans can reproduce these low frequencies you will hear them!

 

Alex

 

When you listen to complex music with the LCD-2s, do you get compression? Whether or not an amp can drive a pair of headphones capably isn't just about the numbers, it has to be able to maintain a linear flow of power to the circuit despite the widely fluctuating voltage it has to deliver.


Edited by miceblue - 1/13/13 at 9:05pm
post #686 of 3245
Quote:
Originally Posted by wolfetan44 View Post

I don't get it. How do I read these graphs? Can someone explain for me!redface.gif

 

Those are frequency response graphs, for what is seen across the load (the IEMs / headphones).  Thus any changes here from the amp is going to affect the balance of what you hear.  O2 and Leckerton UHA-6S MKII are tested with three different IEMs.

 

More or less for these purposes, one can consider that the amp is an ideal voltage source, and it is driving its own output impedance in series with the headphones.  Thus you have a simple voltage divider:

http://en.wikipedia.org/wiki/Voltage_divider

 

Note that if the impedance of the load (Z2) varies widely by frequency and the amp output impedance (Z1) is relatively large compared to Z2, then the voltage the load sees (Vout) will be altered compared to the voltage the amp is trying to send (Vin).  The ratio of Vout/Vin is shown in those frequency response graphs.  To see what is what, check the first diagram in the above link.  Note that it's a function of frequency because the load impedance can vary with frequency—output impedance can also vary, but here it's mostly resistive and flat across the audio frequency range.  What you see here is that even though the O2 has a flat FR (less than 0.04 dB variation from 20 Hz to 20 kHz), the response of the output into some IEMs will be a little less flat because the O2's output impedance is somewhere around 0.5 ohms and not 0 ohms.

 

 

Again, < 1dB is pretty small.  Also, for most headphones, impedance is fairly flat with frequency or generally a lot greater than for some of those IEMs, so the lines will look more like the green one in most cases.  Many amps have much higher output impedance than the O2, so you'll see much more wild swings for the few IEMs like the Westone 4 and UERM listed.


Edited by mikeaj - 1/13/13 at 9:09pm
post #687 of 3245
Quote:
Originally Posted by mikeaj View Post

Quote:
Originally Posted by wolfetan44 View Post

I don't get it. How do I read these graphs? Can someone explain for me!redface.gif

 

Those are frequency response graphs, for what is seen across the load (the IEMs / headphones).  Thus any changes here from the amp is going to affect the balance of what you hear.  O2 and Leckerton UHA-6S MKII are tested with three different IEMs.

 

More or less for these purposes, one can consider that the amp is an ideal voltage source, and it is driving its own output impedance in series with the headphones.  Thus you have a simple voltage divider:

http://en.wikipedia.org/wiki/Voltage_divider

 

Note that if the impedance of the load (Z2) varies widely by frequency and the amp output impedance (Z1) is relatively large compared to Z2, then the voltage the load sees (Vout) will be altered compared to the voltage the amp is trying to send (Vin).  The ratio of Vout/Vin is shown in those frequency response graphs.  To see what is what, check the first diagram in the above link.  Note that it's a function of frequency because the load impedance can vary with frequency—output impedance can also vary, but here it's mostly resistive and flat across the audio frequency range.

Gotcha! Thanks a bunch!

post #688 of 3245
Quote:
Originally Posted by mikeaj View Post

Quote:
Originally Posted by wolfetan44 View Post

I don't get it. How do I read these graphs? Can someone explain for me!redface.gif

 

Those are frequency response graphs, for what is seen across the load (the IEMs / headphones).  Thus any changes here from the amp is going to affect the balance of what you hear.  O2 and Leckerton UHA-6S MKII are tested with three different IEMs.

 

More or less for these purposes, one can consider that the amp is an ideal voltage source, and it is driving its own output impedance in series with the headphones.  Thus you have a simple voltage divider:

http://en.wikipedia.org/wiki/Voltage_divider

 

Note that if the impedance of the load (Z2) varies widely by frequency and the amp output impedance (Z1) is relatively large compared to Z2, then the voltage the load sees (Vout) will be altered compared to the voltage the amp is trying to send (Vin).  The ratio of Vout/Vin is shown in those frequency response graphs.  To see what is what, check the first diagram in the above link.  Note that it's a function of frequency because the load impedance can vary with frequency—output impedance can also vary, but here it's mostly resistive and flat across the audio frequency range.  What you see here is that even though the O2 has a flat FR (less than 0.04 dB variation from 20 Hz to 20 kHz), the response of the output into some IEMs will be a little less flat because the O2's output impedance is somewhere around 0.5 ohms and not 0 ohms.

 

 

Again, < 1dB is pretty small.  Also, for most headphones, impedance is fairly flat with frequency or generally a lot greater than for some of those IEMs, so the lines will look more like the green one in most cases.  Many amps have much higher output impedance than the O2, so you'll see much more wild swings for the few IEMs like the Westone 4 and UERM listed.

Thanks for the explanation.

I noticed that the K 701 has a rising impedance for frequencies 2 kHz and above (Innerfidelity's measurements seem to go from ~67 ohms at 2 kHz to ~110 ohms at 20 kHz). Could this be a reason why the K 701 is known to be picky with amps?


Edited by miceblue - 1/13/13 at 9:26pm
post #689 of 3245
Quote:
Originally Posted by miceblue View Post

Thanks for the explanation.

I noticed that the K 701 has a rising impedance for frequencies 2 kHz and above (Innerfidelity's measurements seem to go from ~67 ohms at 2 kHz to ~110 ohms at 20 kHz). Could this be a reason why the K 701 is known to be picky with amps?

 

Not really.  That rise is fairly smooth and mostly in the upper octave anyway.  The ~60 ohms baseline level is already reasonably high relative to most amps' output impedance.  With an amp with a very high 100 ohms output impedance, that's just a 2.32 dB difference between the level at 2 kHz and 20 kHz then.  People aren't sensitive to small changes in 10 kHz+.  With a 0.5 ohms output impedance, that's a 0.025 dB difference.

 

 

My guess would be more like

  • Relatively low impedance
  • Relatively low sensitivity
  • Reputation for being good for jazz and classical; most jazz and classical recordings actually have wide dynamic range so listeners will use larger peak volume
  • All of the above mean relatively large current required, particularly if listening loudly
  • Some amps misbehaving when being asked for large currents (e.g. many popular OTL tube amps)
  • Word of mouth and confirmation bias giving an issue more mindshare than it should otherwise have
post #690 of 3245
Quote:
Originally Posted by mikeaj View Post

Quote:
Originally Posted by miceblue View Post

Thanks for the explanation.

I noticed that the K 701 has a rising impedance for frequencies 2 kHz and above (Innerfidelity's measurements seem to go from ~67 ohms at 2 kHz to ~110 ohms at 20 kHz). Could this be a reason why the K 701 is known to be picky with amps?

 

Not really.  That rise is fairly smooth and mostly in the upper octave anyway.  The ~60 ohms baseline level is already reasonably high relative to most amps' output impedance.  With an amp with a very high 100 ohms output impedance, that's just a 2.32 dB difference between the level at 2 kHz and 20 kHz then.  People aren't sensitive to small changes in 10 kHz+.  With a 0.5 ohms output impedance, that's a 0.025 dB difference.

 

 

My guess would be more like

  • Relatively low impedance
  • Relatively low sensitivity
  • Reputation for being good for jazz and classical; most jazz and classical recordings actually have wide dynamic range so listeners will use larger peak volume
  • All of the above mean relatively large current required, particularly if listening loudly
  • Some amps misbehaving when being asked for large currents (e.g. many popular OTL tube amps)
  • Word of mouth and confirmation bias giving an issue more mindshare than it should otherwise have

Hm you do have a point there.

I know this is probably going to sound stupid, but with all of the posts of how picky the K 701 is with amps, I was honestly expecting a night and day difference with a good amp. People are always like "oh without a good amp the K 701's sound like garbage" or things of the sort. I hardly find that to be the case. Straight out of an iPhone 4S yes the bass seems leaner than with a good amp and yes the treble is a bit grainy and fatiguing, but amping doesn't make a HUGE difference in sound quality like what I was expecting from people's posts.

 

That being said, I do really like how the K 701 sounds with the O2.

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