[SilverEars]

   
What phone is this - the value is amazingly good for a phone if it's true and should be ok for typical IEMs with 16 ohms (headphone impedance divided by 8 or 10 is the usual rue of thumb).
 
If the output impedance is higher than 1/8 or 1/10 of the headphone impedance the frequency response will usually be quite non-linear. This is because headphones are not a purely resistive load and thus the actual impedanc depends on the frequency of the signal.
 
Joachim

Galaxy S4

 

[HaVoC-28]

   

1. · Twice the output current capability and power dissipation - 280mA per channel. Useful for low impedance and low sensitivity headphones.

       Lower DC offset voltage.
 
Alex

 
But it will not improve anything for 99% of the headphones out their

, bah ortho users will be happy

 

[jring]

  Galaxy S4

 
You know this and have the updated firmware?
 
http://www.jensign.com/S4Distortion/
 
Joachim

 

[adydula]

Yup agree there are (2) versions of the ODA...from agdr:
 
"The "standard" build going forward will have +/-12.5Vdc rails, just slightly more than the O2 headamp's 12.0Vdc rails, but 3x more current capability of course. This build works with any headphone impedance values from 16R to 600R or more. This +/-12.5Vdc build will now use a 1K linear volume pot rather than a log pot, since the linear pot has twice the power dissipation rating as it turns out. The 1K pot will work just fine whether the attentuation resistors are used or not. The transformer will probably change to 16Vac at 2.4A (Mouser WAU16-2400) but that is one of the things I'm still testing. Anything in the 16vac - 20Vac range with adequate current for the headphone load will probably work too, and is being evaluated.

The second "optional" build is for folks who specifically have 300 ohm or 600 ohm (or higher) headphones that almost have enough volume with the O2 headamp, but not quite. This build has +/-15Vdc power supply rails and uses a 5K volume pot (linear or log taper, either is fine) again for pot power dissipation reasons. The transformer with this +/-15Vdc build remains that same as up until now, 20Vac - 24Vac. This +/-15Vdc build should only be used with 300R or higher headphones for output chip power dissipation reasons.

Note that if you have 300R or 600R headphones that are nowhere near loud enough with the O2 then the +/-15Vdc rail option here isn't likely to help. You need a lot of additional voltage swing to get adequate dynamic range on music peaks, such as AMB's b22 headamp with +/-30Vdc rails or a tube amp.
 
I have the standard build and will use it with Beyer T90;s. DT1350's, AKG Q701 *until I sell....I don't have any cans that need the higher rail voltages etc..
 
Best new stuff:
 

1. · Up tp +/-16Vdc power rails with adjustable regulators for up to a 11Vpeak swing. Useful for high impedance headphones.
2. · Lower noise voltage regulators, LT1963A and LT3015. Probably won’t make any audible difference, though.
3. · Twice the output current capability and power dissipation - 280mA per channel. Useful for low impedance and low sensitivity headphones.
4. · 4 NJM4556A chips to handle the current and +/-16Vdc dissipation, two per channel. Uses the SIP 8 pin inline version, NJM4556AL.
5. · NJM2068 replaced with OPA627, which is now in a feedback loop with the NJM4556 chips to null out DC offset and reduce distortion even further. DC output offset voltage should be around 0.3mV = 300uV per channel.
6. · Has input RCA jacks and output ¼” Neutrik jack in addition to better (Switchcraft) 3.5mm jacks.
7. · Bass boost circuit – switchable on/off.
8. · Rotary gain switch with 4 gain settings.
9. · Relay-based no-thump circuit that waits 2 seconds to switch in the headphones and then drops them out quickly on power switch-off.
10. · Should have even lower background noise than the O2 headphone amp at high gain settings. 4 layer PCB with full middle ground plane.
11. · Volume pot is on the input now rather than the middle of the circuit, so it can attenuate “hot” sources as much as needed. Still no pot turning noise.
12. · Coupling cap is on the input, 4x as large to work with the 10k pot vs. 40.2k resistor in the O2, to block all incoming DC from the source.

FYI
 
Alex

 

[adydula]

Also note that there is a good chance of this ODA being measured with the same dScope that the O2 was measured with in the near future if and when this happens the results will be posted at DIY.

Alex

 

[r010159]

Also note that there is a good chance of this ODA being measured with the same dScope that the O2 was measured with in the near future if and when this happens the results will be posted at DIY.

Alex

 
If this happens and it test well, I will sign up for one. The ODA may test out good. But still I would be surprised if it is actually noticeability better than the O2. If it does, I am a sure customer (once I save up the dinero). 

 

[Xenophon]

   
If this happens and it test well, I will sign up for one. The ODA may test out good. But still I would be surprised if it is actually noticeability better than the O2. If it does, I am a sure customer (once I save up the dinero). 

 
After extensively reading what agdr did, the components and the way he organised things, my guess is that it will test 'better' in the technical sense.  Wether it will be meaningful in the audible domain is something else.  What's certain is that the new device will drive more headphones and drive them better than the basic ODAC/O2.  Besides, in that last combo, it's the ODAC that's hard to beat imo, the O2's a much softer target.

 

[adydula]

Yes it will be interesting, but again the ODA is meant to be what it might have been etc.....
 
I think AGDR has done a really great job in designing this version of an ODA and sharing with us all what it is and how he came up with his design.
 
He has listened to may headphone folks and take in several ideas to make it a better operational amp.
 
I will have mine here on Saturday and I will start listening etc...
 
There are a few things that I left out and might add or change in the future, ie bass boost etc.
 
Stay tuned.
 
Alex

 

[adydula]

Here's is a picture of the front panel ready for my drill press....Its a red panel, its covered with the drilling template agdr provides at DIY.
 

 
Alex

 

[XIX47]

I have a couple of newbie questions if you do not mind me asking
 
After turning on the O2 amp, should I delay plugging in the headphone cable until the amp "warms up"?
 
Also, should the O2 be placed on top of a cover to prevent damage to the wooden desktop it is on? I have heard that amps can damage wooden desktops due to the amount of heat generated.
 
This is my first headphone amp and I have started using it tonight. So far I have noticed that the sibilance of the DT-990s has been greatly reduced. I like that very much. I wonder if it would be adequate for a pair of AKG k712s or similar models.

 

[Xenophon]

  I have a couple of newbie questions if you do not mind me asking
 
After turning on the O2 amp, should I delay plugging in the headphone cable until the amp "warms up"?
 
Also, should the O2 be placed on top of a cover to prevent damage to the wooden desktop it is on? I have heard that amps can damage wooden desktops due to the amount of heat generated.
 
This is my first headphone amp and I have started using it tonight. So far I have noticed that the sibilance of the DT-990s has been greatly reduced. I like that very much. I wonder if it would be adequate for a pair of AKG k712s or similar models.

No and no.  It's not supposed to run hot and it doesn't, not even at (too high) ambient temperatures.  The warnings are usually about tube amps or some very specific *FET designs running in full class A at low efficiency.  On some of those you could bake an egg.  
 
Enjoy but read up on its capabilities and know that it's not 'the ultimate' in amplification.  No idea about suitability for the K712, don't know them.

 

[Smugsie]

  No and no.  It's not supposed to run hot and it doesn't, not even at (too high) ambient temperatures.  The warnings are usually about tube amps or some very specific *FET designs running in full class A at low efficiency.  On some of those you could bake an egg.  
 
Enjoy but read up on its capabilities and know that it's not 'the ultimate' in amplification.  No idea about suitability for the K712, don't know them.

I took a temperature scan of the bottom of my odac+o2. It runs at 40 degrees celcius (103 farenheit). I think it's a fairly suitable temperature?
Of course, I put this on top of my PC near the front port without fans because I have nowhere else to put it.

 

[XIX47]

  No and no.  It's not supposed to run hot and it doesn't, not even at (too high) ambient temperatures.  The warnings are usually about tube amps or some very specific *FET designs running in full class A at low efficiency.  On some of those you could bake an egg.  
 
Enjoy but read up on its capabilities and know that it's not 'the ultimate' in amplification.  No idea about suitability for the K712, don't know them.

Alright. Wanted to make sure just in-case.
 
Yep, it is a budget amp with a neutral sound signature. I do not have a lot of space on my desktop or a bid budget, so it is fitting in nicely with my setup (especially since it is black like the rest of my computer/peripherals). I have no plans to buying very expensive headphones in the future so I should be good with the O2 for a long time?

 

[Xenophon]

 
I took a temperature scan of the bottom of my odac+o2. It runs at 40 degrees celcius (103 farenheit). I think it's a fairly suitable temperature?
Of course, I put this on top of my PC near the front port without fans because I have nowhere else to put it.

Just for the hell of it I took a reading with my IR-kitchen thermometer.   Device is sitting on my desk, been switched on for 4 hours and the temperature measured at the top of the enclosure is 36.4 centigrade with an ambient temperature in my office of 30 centigrade (not a typo  Fair to say that it doesn't require a massive heatsink although I do believe that the lifespan of some components might be a bit longer at lower temps.  Mine is the epiphany acoustics ODAC/O2 version, btw.  If you want to go wild & crazy:  liquid cooling anyone?

 

[Xenophon]

 
Alright. Wanted to make sure just in-case.
 
Yep, it is a budget amp with a neutral sound signature. I do not have a lot of space on my desktop or a bid budget, so it is fitting in nicely with my setup (especially since it is black like the rest of my computer/peripherals). I have no plans to buying very expensive headphones in the future so I should be good with the O2 for a long time?

In short, yes though there's no 1-1 relationship between price and ease/quality of driving.  I use the device in my office, have a vastly more expensive setup at home that offers different things but if you don't have really insensitive cans it'll do fine (it drives my HE-500 acceptably and those are not the most sensitive cans around).  The DAC is top-class (for practical purposes), the amp's a bit less imo but still hard to beat at the price.