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O2 AMP + ODAC - Page 144

post #2146 of 5287
Quote:
Originally Posted by JacobLee89 View Post
 
Quote:
Originally Posted by tomb View Post
 

 

Someone has developed an O2 booster board?  And you notice "better clarity," "transients ... became sharper," and now things "are more thumpier?"

 

Just curious, but was that a subjective or objective conclusion?

 

 

P.S. I am certain that agdr has come up with something worthwhile.  In no way am I attempting to state that it's not an improvement.  If I had an O2, I'd build his booster board, too. ;)

 

We can quite comfortably say that it's subjective. I sadly do not have any measuring equipment, and do not have another O2 to do any A/B testing with. Only my very likely biased memory of how it used to sound, and my ears. I may have been subjected to some mental voodoo magic in this case. I now have 2 additional green LED's I can oogle at though....

 

I'm not going to defend the O2, or the booster board though it did "feel" like it has some sort of improvement on my HD650s after the mod, and by no means (from what I've read so far) that the O2 can get any close to a BH Crack in terms of pairing with the HD650. Which of course will be my next acquisition to save up for.

 

I'm quite midway in this sort of topic: I find the subjective viewpoint as important as the objective. I could use analogies, but we are all of different backgrounds, perspectives, ear sizes, and appetite. 


Sorry, I couldn't resist.  Thank you for your thoughtful and considerate reply, despite my smart-alecky irony. ;) 

post #2147 of 5287
Quote:
Originally Posted by JacobLee89 View Post

 

However I am now curious as to how an amplifier's output impedance would affect headphones. Currently reading up on Benchmark Media's article on it, which is convincing me to try it out.

 

 

You might want to try actually going in the other direction and *adding* some series resistance and then see how that sounds.  I'm not entirely convinced that near-zero ohms output impedance yeilds the best results for some heapdhones, even though I know the O2's designer cited this paper from Benchmark showing that was the case:

 

http://test.benchmarkmedia.com/discuss/sites/default/files/Headphone-Amplifier-Performance-Part-2.pdf  (opens PDF)

 

I asked that question too about headphone amp output impedance to the Harmon/AKG tech support foks about the AKG-K550s.  The surprising answer that came back was an amp output impedance within +/-20 ohms of the headphone impedance (which is 32 ohms) is what they recommend.  That equates to an amp output imipedance of 12 ohms - 52 ohms.  Adding series resistance effectly changes a headamp's damping factor.  

 

An easy way to try that out with the O2 is get a "bare" 3.5mm plug and 3.5mm jack.  Then just solder resistors between the L and R channels on the plug and jack, but run the ground straight across of course.  Then plug that into the amp output and your headphones into that adaptor.  That way you don't have to mess with anything inside the O2 to try it out.

 

On my O2 Desktop Amp board (also DIY, not commercial) I've left a provision for adding a series resistor on the output of each channel. Those holes can also be wired to an external 5 position front panel switch with resistors set for something like 1R, 10R, 20R, 80R, and the ubiquitous 120R to give 5 different damping factors.  I see this HA-501 headamp by Teac has that fetaure:

 

http://www.teac.com/product/ha-501/


Edited by agdr - 3/10/14 at 8:59pm
post #2148 of 5287
Quote:
Originally Posted by agdr View Post

Quote:
Originally Posted by adydula View Post

 
The booster  board has a long and well worth reading thread on the diyaudio site.
I have heard no real world audio improvements that my ears can detect.
Booster Board Details (Click to show)
Hi Alex!  This is good news, since you know what they say about medical doctors - "first do no harm". regular_smile%20.gif   Alex and the other builders know I've stayed away from making any comments on how I think the booster board sounds or making any sound claims.  That is all your guy's jobs! biggrin.gif    There are a lot of folks here on the foum with critical listening ears much better than mine.  I'm just the engineer. 

If the booster does make any headphones or IEMs sound better it is probably due to some combination of the stuff that is objective (measureable) with the booster board:

* Like Alex says that 93% or so reduction in output DC offset from 3mV for the standard O2 to 30uV or so with the booster means that the transducers in headphones or IEMs stay much closer to their natural mechanical "zero" resting point.  If this makes a difference at all in the sound it is more likely to be with sensitive IEMs than headphone.  In fact, for my fairly sensitive AKG-K550s, I wrote their tech support once about the issue.  The answer that came back was 3mV being no problem at all since the standard volume level is around 40mV and maximum around 130mV.  3mV just put the transducer diaphram slightly to one side.  But I've read posts where people with some IEMs swear it makes a huge difference to have the transducer resting in the middle.  So... you tell me from the listening! regular_smile%20.gif

* The latest version 3.0 with the relay completely eliminates all O2 turn-on and turn-off thumps with the one wire addition going from the booster to the O2 board.  This won't change listening sound any, but at least the thumps are gone.  One anoyance nailed.

* Double the slew rate as mentioned in posts above from the O2 amp's 3V/uS to the 6V/uS limit of the O2's input NJM2068 gain chip.  As per the discussions above the digital 16/44 signal processing chain limits slew such that the O2's 3V/uS *should* be adequate, but there are certainly many other opinions here.  Again, you guys tell me from the listening if there is a difference.

* +/-15Vdc upgrade capability for folks with high impedance and low sensitivity phones that can't get enough volume from the O2.  This would be a fairly small subset of users.

* Those mezmerizing green LEDs! biggrin.gif    They perform a couple of useful diagnositic functions.  The LEDs are hooked in after the O2's power management mosfets vs. the O2's red which is before the mosfets.  So when the green LEDs come on you know your mosfets have turned on and the O2 amp circutis are getting juice.  And since one LED is on each power rail, if only one LED ever comes on you know you have lost on power rail, and even know which one based on which LED went dark.  When the O2's batteries run down and the O2's power management circuit shuts it down, you finally have a way to know what has happened.  The O2 red LED will still be on but both green LEDs will go off.

* Should be slightly lower noise and distortion from the datasheet numbers, but this is yet to be fully measured.  I've recently bought one of the QA400 analyzers (essentially a USB soundcard in a box set up for distortion measurements) and ran some initial tests on both the standard O2 and one with the booster.  To the limit of the QA400, which is 10 or 20dB  noiser than a dScope or AP analyzer, the two looked essentially identical within the margin of error.  The booster was just a tad better in THD+N, but again figuring in the margin of error it is a wash.  But most likely both units are bumping up again that higher noise floor in the QA400.  I'm in the process right now of stuffing a notch filter PCB I built to try to take those noise THD+N numbers down further.  But again, the good news here is that the booster board did not appear to make the O2's THD+N any worse.  Even if the THD+N numbers eventually do measure better than the stock O2 there is a good argument to be made as to whether that would even be audible or not.  You tell me with the listening!

* Higher current drive capability for folks with low impedance low sensitivity headphones.  Again this is likely to be a small subset of headphones or IEMS out there.

* Zero output impedance capability.  The folks who have built booster boards should keep in mind they can short the four O2 1-ohm resistors straight across, as shown in the diagrams here, to get true zero ohms out.  The stock O2 needs those resistors to balance up the two paralleled sections of the NJM4556A output chips.  To make the booster board plug and play I designed it to use those 4 resistors as they sit when you plug in the board, so you still wind up with the O2's 0.5 ohm output resistance.  But the booster chips don't need any resistor.  You can just short those right across underneath the O2.  Whether having zero ohms out vs. 0.5 ohms makes any difference in the sound, well... you tell me with your listening! regular_smile%20.gif





Hm, this sounds very interesting. Maybe you can work with JDS Labs to get some things measured. After all, they do have the same PrismSound dScope Series III analyser that NwAvGuy used for his measurements. It would be interesting to see if a group could do blind tests too in lieu of what NwAvGuy did with the O2 vs DAC1PRE (I believe it was).

I would be interested in one of these.


Also, the higher current could be beneficial for planar magnetic headphones, which are current-dependent from what I understand.
Edited by miceblue - 3/10/14 at 9:16pm
post #2149 of 5287

I wanted to follow-up on what I posted earlier in the slew rate discussion about possibly being able to fit a LME49990 dual-SMD to DIP adaptor in place of the O2's NJM2068 gain chip to raise the end-to-end slew rate all the way up to 20V/uS.  Well turns out the adaptor does fit and work just fine, photos below.  I'm listening to an O2 + booster board with the dual LME49990 chips in place of the O2's NJM2068 chip as I write this.

 

That dual LME49990 op amp "roll" beats the NJM2068 in datasheet parameters in all areas, unlike the LME49720 which is more of a straight across wash.  The O2 designer noted in his blog that the LME49720 was similar to the NJM2068, with the major downside just being it was more expensive.  He never did evaluate the LME49990, probably beause it only comes in surface mount and at the time was quite a bit more expensive.  Back then one cost around $8 as I recall, but now they are down to $2.50 or so.  The LME49990 is also the chip that opc uses in his "Wire" DIY headphone amp, wrapped around the LME49600.  I used the OPA140 instead in the booster board since it is a DC precision chip, along with having good AC parameteres, and getting the O2's output DC offset down was a big design goal.

 

I see that folks on eBay are selling these dual LME49990 adaptors with the two chips already soldred on for around $15.  Not bad, assuming the chips are real which is always a concern on eBay.  If you buy one make sure you get the adaptor for DUAL chips to DIP.  Folks are also selling just a single LME49990 to DIP adaptor.

 

Using a LME49990 dual SMD adaptor in a standard O2 that has the original NJM4556A output chips probably won't buy much in terms of either slew rate or THD+N improvement.  Even though the LME49990 slews at 20V/uS the overall slew rate would still be limited by those output chips which are just 3V/uS.  Same with the THD+N, even the O2's designer noted in his blog the THD+N of the output chips are the O2's limiting factor, being higher than the THD+N of the NJM2068 gain chip.  But the O2 booster board also slews at 20V/uS.  With the booster the whole thing is 20V/uS slew rate end to end.

 

The first two photos show both sides of the adaptor (both LME49990 chips) vs. the size of the O2's original NJM2068 chip.  The next photo shows good clearance around the adaptor in the O2.  The final shows plenty of clearance to the top of the booster board.

 

 

 

 


Edited by agdr - 3/10/14 at 9:36pm
post #2150 of 5287
Quote:
Originally Posted by miceblue View Post


Hm, this sounds very interesting. Maybe you can work with JDS Labs to get some things measured. After all, they do have the same PrismSound dScope Series III analyser that NwAvGuy used for his measurements.

 

Good thoughts!  I've actually already had that discussion with John (JDS) in another forum regarding my version of an O2 Desktop Amplifier DIY project.  His position at that time was that he feels blocked in performing a test by the O2 designer's license terms of "no derivitives", which is certainly a valid point   A bunch of PM correspondence proceeded to head my way from various folks about the issue. The net result I've run with is the belief that the ODA is different enough not to be considered a derivitive.  Then there is that nagging problem of the O2 designer having dissapeared and being out of contact for a license release.

 

As for the booster board, by making it a separate board I'm trying to do an end-run around the O2 designer's terms.  But viewed a certain way - probably John's - it would still be considered a modification of the O2 since it plugs in and replaces the O2's output chips.

 

So that is why I'm messing around with using a QA400 + notch filter for THD+N measurements.  Eventually I may just rent an Audio Precision system 2 and make some measurements.


Edited by agdr - 3/10/14 at 9:56pm
post #2151 of 5287

Some very talented EEs here! I wonder how much the booster board with components would cost me? Also, how difficult would it be to install the booster board? Would any O2 board traces have to be cut? I know some holes would have to be drilled and some soldering would be involved. Now that there is a way to increase slew rate, besides having better output chips, all of you now have my interest in this project.

 

BG

post #2152 of 5287
Quote:
Originally Posted by agdr View Post

 

That dual LME49990 op amp "roll" beats the NJM2068 in datasheet parameters in all areas, unlike the LME49720 which is more of a straight across wash.  The O2 designer noted in his blog that the LME49720 was similar to the NJM2068, with the major downside just being it was more expensive.  He never did evaluate the LME49990, probably beause it only comes in surface mount and at the time was quite a bit more expensive.  Back then one cost around $8 as I recall, but now they are down to $2.50 or so.  The LME49990 is also the chip that opc uses in his "Wire" DIY headphone amp, wrapped around the LME49600.  I used the OPA140 instead in the booster board since it is a DC precision chip, along with having good AC parameteres, and getting the O2's output DC offset down was a big design goal.

 

 

For the UK guys, there's an ebay seller that does these in the UK. The problem is that the width of the adapter seems to too wide to fit in the space the O2 board has:

 

 

I would probably sand it down, but since I am in no rush and the price including postage varies little, I shall play the safe game and buy one from the US seller.

Quote:
Originally Posted by agdr View Post
 

 

I asked that question too about headphone amp output impedance to the Harmon/AKG tech support foks about the AKG-K550s.  The surprising answer that came back was an amp output impedance within +/-20 ohms of the headphone impedance (which is 32 ohms) is what they recommend.  That equates to an amp output imipedance of 12 ohms - 52 ohms.  Adding series resistance effectly changes a headamp's damping factor.  

 

http://www.teac.com/product/ha-501/

 

It seems like playing about with the output impedance is more of an experimental procedure, than of one that yields much rewards in terms of audio improvement. Since I've already done the mod I guess I can play about with the resisters, without the need to calculate that 0.5 ohms.

post #2153 of 5287
Quote:
Originally Posted by adydula View Post
 

locksbury...

 

post some pix of your project and let us see how you fitted the ODAC in the O2 assembly...

 

Alex


Finally got it complete today! Sounds good on the Mac! Will try running it under Windows 7 later and I suspect I'll have to a little digging to get it to work in Linux.

 

Otherwise, I couldn't be happier! :L3000: Pics attach as promised! To fix the ODAC in, I had to resort to bolting it to the bottom of the case (taped over the connections that went to the wires) and no I'm not taking it apart again. :tongue_smile:

 

 

 


Edited by locksbury - 3/12/14 at 11:27am
post #2154 of 5287

Just received my O2+ODAC from JDS Labs. Unfortunately, the wall wart I ordered didn't work. I use a wall wart from a previous order and it worked fine. Contacted JDS Labs and they responded immediately. They had a solution already in place within 30 minute of my contacting them. I can't recommend them enough. Great customer service. Great products also. Currently listening to music through the O2 and HD650s. Sounding great.

post #2155 of 5287

Has anyone directly compared the O2 made by JDS Labs to the Epiphany Acoustics version. Any difference in sound? 

post #2156 of 5287
Quote:
Originally Posted by PTom View Post

Has anyone directly compared the O2 made by JDS Labs to the Epiphany Acoustics version. Any difference in sound? 
I own both, they sound identical .
post #2157 of 5287
Quote:
Originally Posted by JacobLee89 View Post

 

I would probably sand it down, but since I am in no rush and the price including postage varies little, I shall play the safe game and buy one from the US seller.

 

.....

 

Thanks for pointing this out!  For whatever reason, when I searched yesterday, the US seller didn't even come up.  Just ordered 1 to go along with my agdr board.  

 

My alpha dogs and ML Mikros 90's both sound great with the stock O2.  Can't wait to give them a listen with the booster and 49990's in place :) 

post #2158 of 5287
Quote:
Originally Posted by r010159 View Post
 

Some very talented EEs here! I wonder how much the booster board with components would cost me? Also, how difficult would it be to install the booster board? Would any O2 board traces have to be cut? I know some holes would have to be drilled and some soldering would be involved. Now that there is a way to increase slew rate, besides having better output chips, all of you now have my interest in this project.

 

BG

 

The bill of materials for the O2 booster boards adds up to around $56 at Mouser, including the LEDs, but minus shipping costs.  The at-cost price on the PCB was $8 on this last run ( I had 10 made and was charged $80 at Seeed Studio, including shipping).  I will probably do another board run in the next month or so.  I'll post in the board's thread in the DIY forum here when those are back.

 

The booster board just plugs right into the O2 amp  in place of the two NJM4556A chips (the ones next to the battery in the middle).  You unplug those two chips then plug in the booster board.  It slides into the top slot in the standard O2 B2-080 case.  There are 3 wires that go from the booster board to the O2 PCB that have to be soldered on.  Two are grounds, one going to either middle battery terminal and the other in front going to a resistor.  The 3rd one is for the no-thump relay circuit and goes from the booster board to another resistor in the power management section of the O2.   Pictures of exactly where those 3 wires attach are posted at the google drive link.  After all the surface mount soldering one does in soldering up the booster board those 3 wires will be a piece of cake! :regular_smile :

 

No holes have to be drilled anywhere except for two small ones in the front panel if you want to be able to see the LEDs on the booster board. I have the measurements of where those holes need to be posted in the build instructions.

 

Good questions!

post #2159 of 5287
Quote:
Originally Posted by agdr View Post

 

 

No holes have to be drilled anywhere except for two small ones in the front panel if you want to be able to see the LEDs on the booster board. I have the measurements of where those holes need to be posted in the build instructions.

 

Or you can waste even more time and manually shape out a panel out of clear plastic. Just to avoid drilling two extra holes (which makes no sense because I had to drill and expand 11 holes regardless)

 

I also realised that we of the O2 Output Booster board thread, have began hijacking this thread. Unsure whether I should feel sorry or not.

post #2160 of 5287
How does it compare to Meridian Explorer, and in general is there any other dac+amp for 300$ that is better than this? thanks.
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