O2 AMP + ODAC

Hi all,

In all manuals we can see 2 methods to connect O2 and ODAC according to usage of 3.5 input socket: 1) to keep O2 input on it, 2) to change it to ODAC output. 

However, ODAC has two outputs: four pins in the middle of PCB and 3.5 mm socket. Why nobody uses them both? Pins to connect ODAC with O2 and 3.5mm socket to get direct ODAC output. Does such setup affect the output quality with some negative influence of O2 input?

xenophon said:

No, you'd only encounter those conditions using low-impedance headphones at very high (unlistenable) sustained volumes.  At loud volume absorbing a peak without extra distortion but while delivering extra power would be possible.  Wether wise for your ears is a different matter.

Click to expand...

 


The booster board is suppose to increase current output which is needed by low impedance low sensitivity planars. The 35% increase in current at 32 Ohm load translate to around 2 - 3 dB SPL.

For 150+ Ohm load, the booster board has very little to no added benefit.

I'm pretty sure using an HE-6 will easily hit that maximum load of the booster board. A Stock O2 can drive HE-6 at a little below 110 dB . With the booster board it can reach around 112 dB. Which is loud enough for most people but certainly is not painfully loud. Some people listen at around 115 dB.

Just as John mentioned, this is just not acceptable in HE-6 context. ( Which is supposedly what the booster board is about).

OK, owning an HE-6 and odac/o2 combo I'm not going to enter into this pointless discussion again, certainly not with people who don't own the 6 but suffice it to say that even with the booster board I wouldn't ever use let alone recommend this.  There's other gear for the 6.

I'm not trying to argue but rather trying to make sense of the booster board's benefit as add-on for O2.

You need about 50 O2 amps with booster boards to power the HE6 properly.

The O2 also handles playing music into all kinds of loads. If testing is done with sine waves the output amps will overheat eventually. This is with sustained high power sine or square wave testing into low impedance loads. This is also true with lots of high power headphone and speaker amps. These are designed to play real world music not test signals.
 
But testing often involves using signals and sign waves but should be used for long period of times.
 
So its has to be noted that testing into low impedance loads should be limited to a few seconds with the O2 and the booster board as well. Especially below 150 ohms.Also the xfmr should be 15 vac or greater when doing this.
 
I haven't heard of any O2 or booster boards having issues playing for long periods of time with lower impedance loads below 150 ohms. I have used several cans with low level impedance for hours and hours...with no heating issues.
 
If you want HOT just try a Class A amp, one which I had and I don't want to disparage other good amps or companies. The one I had was HOT to handle and to the touch but the chassis was designed to be the heat sink!! It still worked well.
 
A.

I also think it's a question of DIY v production.

If you are producing a product and putting your name on it, it has to meet different standards and some of those are about consistency and being able to stand up to abuse/non designed use.

Yes and no....there are amps both for headphones and speakers that will NOT handle sine waves for very long....there are products in production that will fail in long term 100% duty cycle tests....
 
You would have to define NON-designed use?? That's a BIG open field......whats the standard for non-designed use or Abuse????
 
A.

schmalgausen said:

  Hi all,

In all manuals we can see 2 methods to connect O2 and ODAC according to usage of 3.5 input socket: 1) to keep O2 input on it, 2) to change it to ODAC output. 

However, ODAC has two outputs: four pins in the middle of PCB and 3.5 mm socket. Why nobody uses them both? Pins to connect ODAC with O2 and 3.5mm socket to get direct ODAC output. Does such setup affect the output quality with some negative influence of O2 input?

Click to expand...

I have an O2+ODAC from Mayflower Electronics and it seems to have what you are describing. When the ODAC is plugged in through USB, the "line in" jack actually doubles as a line out for the DAC. This works with the unit turned off or without the AC adapter turned on, since the ODAC is 100% usb powered. When the ODAC is disconnected, it functions as a line in for the O2 amp. This isn't a very well advertised feature to be honest, and I only learned about it when watching a video about the unit by the guy who owns Mayflower electronics. I think the JDSlabs models also have this feature, but I don't know for sure.
 
 
So basically, the O2+ODAC units have the same line out capability as buying the two units separately, but you get them in a much smaller package.

james-uk said:

I converted to the dark side a couple of years back from Microsoft to apple and I haven't looked back. Call them what you like, I admit they have me , I'm in their pocket but my 'digital ' life has never been more carefree and easy . I have a mac / iPad/ I phone / Apple TV and Everything works with continuity and without hassle . I want computers and devices to make my life easier and to just enjoy using them. I never enjoyed using windows it was so high maintenance .

Click to expand...

 
I agree with the goal - if only it worked out that way.  IOS versions of Spotify and Overdrive, my two most used apps, are garbage compared to android.  On the flipside, android phone makers seem incapable of producing a device without audible his when using iem's.  My current combo is a rooted note 2 (which supports airplay), several pc's, an ipad 4, and multiple apple tv's.  The fact that I have to jump through huge hoops to put my existing flac library on my ipad is absurd.  Third party paid apps let me play the files, but there is no supported way of loading them on the device, and folders have to be manually created.  Talk about not making life easier.  Apple is the devil notwithstanding their tasteful asthetics.
 

mcandmar said:

   
I was never a fan of those JRCs either, i highly recommend you look into the Booster Board with OPA827's...

Click to expand...

 
I haven't been keeping up with the booster board thread like I should have been, did you conclude these sound better in the booster than the stock OPA140's?  The 3.0 sounds awesome to me stock, with the lme49990 adaptor in the 02 gain stage.  Frankly, I'm not skilled enough to try desoldering the 140's anyways, but still curious.
 

jseaber said:

 
....In short, the base O2 circuit needs to be abandoned to thermally satisfy LME49600s.

Click to expand...

 
Thanks for sharing the preliminary findings!  So I don't run into issues, I'd be grateful for any further info you can provide as to what sort of load gave rise to the thermal problems.  Was this really just an issue that came up with hifiman and/or audeze's?  I've been running my alpha dogs via my boosted o2 for months with no evident problems (and certainly no shutoffs).  It is an excellent sounding combo and truly remarkable, imo, that a battery driven amp can be engineered to come within a stone's throw of the performance of the wire (at least on paper, pending the results of your testing), and with far less dc offset!
 

headwhacker said:

I'm not trying to argue but rather trying to make sense of the booster board's benefit as add-on for O2.

Click to expand...

 
In a nutshell, by adding the booster board and a dual lme4990 adaptor in the gain stage, you get a drastic improvement in dc offset, as well as improvements in current output for transients, slew rate (up to 20v/us) and presumably distortion over the stock O2, pending jds' lab confirmation.  Eliminating all turn on/off thump is also cool.  Perhaps its just confirmation bias in my head, but I continue to believe that the boosted o2 sounds better and just slightly different from stock.  There was something about my stock build, albeit a diy effort, that sounded slightly thin and piercing on occasion.  With the booster, its the same degree of transparency that we've all come to expect from the o2 but minus what I previously found slightly objectionable.  YMMV as always.

I think the testing done was done with a sine wave for a long period of time, more so that the few seconds warned about by the designer.
 
With real music playing I never had a heating issue.
 
Alex

I just purchased an O2/ODAC Limited Ed from an Australian distributor. I have some technical questions, when I connect the ODAC to my iPad via the CCK and USB Hub,
 
1. I observed that the volume controls on the iPad is adjustable, this psychologically lead me to believe I'm double amping. But this is not possible right? Given it's a digital out connection to the DAC. This does not happen on my Sony PHA-2 DAC/Amp - I am able to connect directly from the iPad to DAC and the iPad detects this and changes to line-out without volume controls.
 
2. If the O2/ODAC is powered via the mains, why is the iPad still throwing the device is consuming too much power error? Is the ODAC still drawing power despite it being connected to the mains?

mjolnir125 said:

 
This isn't a very well advertised feature to be honest, and I only learned about it when watching a video about the unit by the guy who owns Mayflower electronics. I think the JDSlabs models also have this feature, but I don't know for sure.
 
 
So basically, the O2+ODAC units have the same line out capability as buying the two units separately, but you get them in a much smaller package.

Click to expand...

 
Thanks for the feedback. DAC line output is listed in the product "Tech Specs". Additional detail has been added to page 1 of the Instructions:
 

CONNECTIVITY

Analog Output	3.5mm or 6.35mm*​
Analog Input	3.5mm or shared RCA*​
Digital Input	Mini-USB​
DAC Line Output	3.5mm or RCA**​
Power Input	14-20VAC​
	​
* Denotes Limited Edition	​
** See Jack Configurations below

 
 
There are two ways to wire an O2+ODAC. We use Method 1 by default, which provides DAC line output and is safe to use with any consumer level line-input device. This is the most common request. Method 2 mechanically disconnects ODAC's line output from the 3.5mm jack, so that it's only active while an analog input source is disconnected. This method is preferred when using the 3.5mm jack primarily for analog input (no need to disconnect USB cable).
 
O2+ODAC can be assembled in over 20 possible combinations aside form our default offerings, while remaining in accordance with the designer's license. We're working on a site update which will soon make all options easier to understand and request.
 

skeptic said:

 
Thanks for sharing the preliminary findings!  So I don't run into issues, I'd be grateful for any further info you can provide as to what sort of load gave rise to the thermal problems.  Was this really just an issue that came up with hifiman and/or audeze's?  I've been running my alpha dogs via my boosted o2 for months with no evident problems (and certainly no shutoffs).  It is an excellent sounding combo and truly remarkable, imo, that a battery driven amp can be engineered to come within a stone's throw of the performance of the wire (at least on paper, pending the results of your testing), and with far less dc offset!
 
In a nutshell, by adding the booster board and a dual lme4990 adaptor in the gain stage, you get a drastic improvement in dc offset, as well as improvements in current output for transients, slew rate (up to 20v/us) and presumably distortion over the stock O2, pending jds' lab confirmation.  Eliminating all turn on/off thump is also cool.  Perhaps its just confirmation bias in my head, but I continue to believe that the boosted o2 sounds better and just slightly different from stock.  There was something about my stock build, albeit a diy effort, that sounded slightly thin and piercing on occasion.  With the booster, its the same degree of transparency that we've all come to expect from the o2 but minus what I previously found slightly objectionable.  YMMV as always.

Click to expand...

 
We've tested default O2+ODACs in the past for over 8 hours under a full power, 1kHz sine wave at @ 150 ohms. I've also duplicated NwAvGuy's basic measurements of O2 and ODAC under a 32 ohm load. While these tests are far from a real world usage scenario, it proves the amp is thermally stable. 
 
It was my intention to perform equal benchamrks on agdr's O2 booster board using the same tests @ 32 ohms. My usual quick test routines take at least an hour--just for a quick look. It's easy to spend an entire day investigating a device. Anyway, the LME49600s only lasted for a few minutes of testing before the chips overheated and spoiled test results. I'll produce new benchmarks ASAP at reduced power. The point is, the booster board is marginally stable in terms of power dissipation. I doubt it will overheat while listening at reasonable volumes with most dynamic headphones. Give it an inefficient 20-60 ohm headphone playing at high volumes, and there's a strong chance the chips will at least overheat enough to increase THD+N to audibly unacceptable levels, >= 0.5%. agdr has admitted that his enclosure has become warm to the touch under with some listening. By the time my testing configuration was warm to the touch, the chips were either distorting, or seconds from distorting (> 50C). Here are a couple frantic photos taken while testing. Sorry for the shaky angles:
 
 
 
I've also tested the reference LME49600 board from National Semi. / TI. The reference board has around 10x more copper surface area than agdr's booster board, so the LME49600s can handle more power. Thermal dissipation is an important design consideration. 
 

xenophon said:

  The O2's good but it has its limitations, as was recognised at the outset by the designer.  I salute agdr for the work he did but repeat what I said a couple of 100 posts back in the thread:  with his talent I'd opt for revolution and a new design on my own terms rather than incrementalism and respecting the constraints of the existing product.  My hat off to him, I hope he carries this forward.
 

Click to expand...

greenkiwi said:

I also think it's a question of DIY v production.

If you are producing a product and putting your name on it, it has to meet different standards and some of those are about consistency and being able to stand up to abuse/non designed use.

Click to expand...

 
Both well put. I congratulate agdr's DIY contributions. It takes successes, failures, and passion to build remarkable projects. The successor to O2/ODAC logically most not be derived from Objective2, as it's both a legal and engineering dead-end.
 
 

gtan said:

  I just purchased an O2/ODAC Limited Ed from an Australian distributor. I have some technical questions, when I connect the ODAC to my iPad via the CCK and USB Hub,
 
1. I observed that the volume controls on the iPad is adjustable, this psychologically lead me to believe I'm double amping. But this is not possible right? Given it's a digital out connection to the DAC. This does not happen on my Sony PHA-2 DAC/Amp - I am able to connect directly from the iPad to DAC and the iPad detects this and changes to line-out without volume controls.
 
2. If the O2/ODAC is powered via the mains, why is the iPad still throwing the device is consuming too much power error? Is the ODAC still drawing power despite it being connected to the mains?

Click to expand...

 
1) This is a feature of iOS7+. Like desktop operating systems, iOS7 allows the user to control volume digitally for audio output device. For iOS6 and older, digital volume was locked to 100% for external DACs (and UAC1 was limited to iPad then). There's little incentive to digitally force 100% volume. It's actually best for a DAC to operate slightly below 100% volume to prevent overfill errors at 0dB peaks. Consider this a functionality improvement in iOS7. 
 
There's also a hardware flag in some DACs called 'Hardware Volume Control'. The flag is normally enabled to allow an operating system to use its digital volume control as described above. I imagine some DACs have this option disabled, which should prevent iOS7, Windows, etc. from controlling volume. 
 
Last, your Sony is an MFi certified device and therefore does not present itself as a UAC1 device. UAC1 devices are definitely processing a digital signal regardless of the operating system volume; the device drivers in iOS surely have a different feature set for MFi connections.
 
2) O2 is powered by AC. ODAC is powered by USB. You can find more information here.

I haven't been keeping up with the booster board thread like I should have been, did you conclude these sound better in the booster than the stock OPA140's? The 3.0 sounds awesome to me stock, with the lme49990 adaptor in the 02 gain stage. Frankly, I'm not skilled enough to try desoldering the 140's anyways, but still curious.

Click to expand...

Removing surface mount opamps is a lot easier then you may think. All you need is some good desoldering braid and a pin. Use the braid to remove as much solder as you can from the opamp legs being careful not to overheat the chip then use the pin to VERY GENTLY pry each leg up while you heat it with your soldering iron. It only takes a very slight upward pressure on the opamp legs and as soon as the solder melts you will feel the leg pop up from the board. Wether it's worth the effort is different story. I've tried the opa140, lme49990, Ad8610, and ada4627 and didn't hear much if any difference between them so I stuck with the opa140 for the best battery life.

jseaber said:

Thanks for the feedback. DAC line output is listed in the product "Tech Specs". Additional detail has been added to page 1 of the Instructions:

CONNECTIVITY

Analog Output

Analog Input

Digital Input

DAC Line Output

Power Input

* Denotes Limited Edition

** See Jack Configurations below

[TD]3.5mm or 6.35mm*[/TD]​

[TD]3.5mm or shared RCA*[/TD]​

[TD]Mini-USB[/TD]​

[TD]3.5mm or RCA**[/TD]​

[TD]14-20VAC[/TD]​

[TD] [/TD]​

[TD] [/TD]​

There are two ways to wire an O2+ODAC. We use Method 1 by default, which provides DAC line output and is safe to use with any consumer level line-input device. This is the most common request. Method 2 mechanically disconnects ODAC's line output from the 3.5mm jack, so that it's only active while an analog input source is disconnected. This method is preferred when using the 3.5mm jack primarily for analog input (no need to disconnect USB cable).

O2+ODAC can be assembled in over 20 possible combinations aside form our default offerings, while remaining in accordance with the designer's license. We're working on a site update which will soon make all options easier to understand and request.


We've tested default O2+ODACs in the past for over 8 hours under a full power, 1kHz sine wave at @ 150 ohms. I've also duplicated NwAvGuy's basic measurements of O2 and ODAC under a 32 ohm load. While these tests are far from a real world usage scenario, it proves the amp is thermally stable. 

It was my intention to perform equal benchamrks on agdr's O2 booster board using the same tests @ 32 ohms. My usual quick test routines take at least an hour--just for a quick look. It's easy to spend an entire day investigating a device. Anyway, the LME49600s only lasted for a few minutes of testing before the chips overheated and spoiled test results. I'll produce new benchmarks ASAP at reduced power. The point is, the booster board is marginally stable in terms of power dissipation. I doubt it will overheat while listening at reasonable volumes with most dynamic headphones. Give it an inefficient 20-60 ohm headphone playing at high volumes, and there's a strong chance the chips will at least overheat enough to increase THD+N to audibly unacceptable levels, >= 0.5%. agdr has admitted that his enclosure has become warm to the touch under with some listening. By the time my testing configuration was warm to the touch, the chips were either distorting, or seconds from distorting (> 50C). Here are a couple frantic photos taken while testing. Sorry for the shaky angles:


 


I've also tested the reference LME49600 board from National Semi. / TI. The reference board has around 10x more copper surface area than agdr's booster board, so the LME49600s can handle more power. Thermal dissipation is an important design consideration. 


Both well put. I congratulate agdr's DIY contributions. It takes successes, failures, and passion to build remarkable projects. The successor to O2/ODAC logically most not be derived from Objective2, as it's both a legal and engineering dead-end.



1) This is a feature of iOS7+. Like desktop operating systems, iOS7 allows the user to control volume digitally for audio output device. For iOS6 and older, digital volume was locked to 100% for external DACs (and UAC1 was limited to iPad then). There's little incentive to digitally force 100% volume. It's actually best for a DAC to operate slightly below 100% volume to prevent overfill errors at 0dB peaks. Consider this a functionality improvement in iOS7. 

There's also a hardware flag in some DACs called 'Hardware Volume Control'. The flag is normally enabled to allow an operating system to use its digital volume control as described above. I imagine some DACs have this option disabled, which should prevent iOS7, Windows, etc. from controlling volume. 

Last, your Sony is an MFi certified device and therefore does not present itself as a UAC1 device. UAC1 devices are definitely processing a digital signal regardless of the operating system volume; the device drivers in iOS surely have a different feature set for MFi connections.

2) O2 is powered by AC. ODAC is powered by USB. You can find more information here.

Click to expand...

Interesting point about dac volume being at 100% . Correct me if I'm wrong but does this mean it's best to turn the digital volume down a few db in bit perfect/ pure music for mac etc for care free listening at best sound quality?