[dB Cooper]

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.

Wow... how much is enough? My O2 will drive my 300 ohm HD650's to ear splitting levels. Can't comment on the 600 ohm Beyers (haven't tried them).

[adydula]

Well I am happy to say the ODA is up and functional!!!

The designer of this ODA had some last minute concerns with the AC supply voltages and heat dissipation etc as well as a few minor "make it even better" items.

The voltage has ben reduced from 24VAC to 16 VAC. This means that no additional heat sinking will be needed and the unit will not get overly warm, unlike some other headphone amps I have had the you could fry and egg on!

This version of the ODA has a 1/4 jack and a 3.5mm input jack for headphones. It has RCA inputs and outputs. It has a 4 position gain selection switch, a clipping LED indicator, and two power rail LEDS.

The DC offset voltages are down to 2 micro volts on one side and 4 micro volts on the other side or channel.
This is 21 times lower than the original O2 amp.

So I hope to find some time in the next few days to do some serious listening and report on how it sounds compared to the original O2 with several headphones.

I still have to drill out the front panel and get it mounted in its nice shiney RED case!!! LOL.








In the last picture you can see the back panel which is being used as a heat sink for the voltage regulators etc.

Alex

[adydula]

I will have the ODA and new AC xfmr this Saturday and can do some listening finally!!!

Alex

[adydula]

its here! It works.....

One word: Superb!!

I will take pix and do a review soon....

Alex

[adydula]

I have the new "AGDR" ODA Version 2.0 up and running, playing wonderfully here.....I am waiting on a tool to complete the front panel alignment for the holes drilled for all the jacks, switches etc...

Here are some pix:




Fig 1: The venerable O2 on the left the new ODA in the middle and one of my external ODACS on the right.
The rear RCA jacks allow for a second DAC if you want via RCA jacks and you can easily compare dacs with the press
of the input selection switch second from the right.



Fig 2: Lots of room inside for mounting an internal ODAC if you want as well as other
options that you can include in your ODA.



Fig3: Size Differences.



Fig 4. Simplicity



Fig 5: Will put feet on the ODA in the near future.



Fig 6. Preliminary Pilot holes



Fig 7. Back Panel, RCA inputs, On/Off Switch and the AC Power input.



Fig 8. Ready for Case.



Fig 9.Playing music!!

 

More to come...

Alex

[adydula]

Ok,

I have been able to listen to the new ODA Version 2.0 for a few days and it is as good as the O2 sonically IMO.

It hasn't been measured "yet" but that will happen in the near future and I will report on the results.

We did a double blind test with carefully set levels and I was not able to reliably pick out either amp and three runs of ten switches. It was a pretty even split between the two.

As much as my bias wanted the new ODA to sound better than the O2 this is not the reality to me.

That said the ODA has many things going for it that the O2 just did not have the room or desire to include due to the design criteria of nwavguy.

The ODA with 3x the current available should be able to even drive those hard to handle or drive headphones like the HE series...to earsplitting levels....

It has a rear mounted on/off switch, rear AC power jack, and rear RCA inputs which are switch selectable.
The Switches in this ODA are made by Switchcraft and are a higher quality switch...remember nwavguy was designing on a budger. The ODA was not.

On the front panel are two parallel heaphone outputs....one 1/4" and the other 3.5mm, RCA pre-amp outputs that can be wired in several ways depending on your requirements, volume control, two green power rail leds, a clipping led indicator, a 4 position switch, and finally a 3.5 mm input for your dac etc..

If you want an ODAC can easily be integrated inside the B3-080 case if desired.

There are several other customizable options that can be had with the ODA, all these are in the build and consideration section on AGDR's google drive

I will post final pix when I get the front panel done.

Alex

[adydula]

I just discovered another really neat thing that the ODA provides:

Two headphone outputs, one 1/4" and one 3.5mm jacks.

This means you can have two headphones connected at the same time and easily compare one to another in just a few seconds.

I queried AGDR on this and he indicates this is absolutely OK to do.

In fact he indicates is a great use of the current capability of the ODA!

Just figure out what your parallel impedance out first. For a total of 32 ohms or above any volume setting works.

For 16 ohms voltage swings up to at least 4 Vac are just fine. It all depends on the sensitivity of the headphones being driven at 16 ohms say.....ther are spreadsheets that AGDR has provided that may be helpful here etc.

I am using Beyer T90's, Beyer DT 1350's and AKG Q701's at present and have no issues driving both sets at the same time with the ODA.

Plugging in and out of one set while listening to the other seems to make no audible difference at all.

The cans I have are fairly sensitive.

The ODA output impedance is .083 ohms...so from a voltage divider standpoint  neither headphone knows the other is hooked up as well!

Resistance in parallel = R1*R2 / R1 + R2.

My T90's are 250 Ohms, and my DT 1350's  are 80 ohms.

So the combined parallel resistance is = 60.6 Ohms...so the ODA has no issue driving them at any volume setting.

What a really convenient way to quickly compare headphones.....

All the best

Alex

[adydula]

Here's the amp with the front panel finally on...still needs labeling.

I have two headphones plugged in and playing.

On the left a set of Q701's in the 1/4 jack and a set of Beyer T90's in the 3.5mm on the right of it.

ODAC on the right.

The amp handles both cans with aplumb!

Diana Krall never sounded so good!! LOL!

[adydula]

Well I have over 10 hours of listening to the ODA and it is indeed a superb amp that can handle most headphones out there.
The original O2 had some issues with HE6 and HE500 headphones. These will work perfectly on an ODA built with the +/-12.5Vdc option.

These types of headphones are very high levels simply overtax the O2's current capacity.

With these not so efficient headphones the O2’s output chips would go into current-limiting mode, which would
drop the output voltage swing.

The ODA with 3x times the current capacity simply eats these cans for lunch...

This is not meant to cast a shadow on the O2, which still is simply a stellar design and performer..it wasn't meant to handle these cans. For the size of the pc board and case there is no room for the stuff needed to make this happen etc...

The ODA is a desktop unit in a larger box and not portable and the O2 is "portable", runs on batteries and is in a small enclosure.

I have found myself getting lost in the music the last couple of nights and really am appreciating how well this amp plays...totally transparent as well as the O2.

Alex

[terry parr]

very good, alex.  your desktop version of the O2 looks very professionally done, so hats off to you for that.  i knew you would take just as much care with how it looks from the outside, judging by the way you took pains with how everything looked inside the unit. excellent job. you've got to be proud of this.  i would be.

well, the fact that the desktop version's sonics don't put the original O2's sound in the shade is a testament to NWAVguy's original design.  even with the additional current that the destop version is putting out, the sonics of the humble, original O2 still compares favorably, huh?

very insightful of you, too to remain objective (ha. ha) in comparing the one you built with the sound of the original.  i've bought pieces of audio gear in the past where you want so bad for it to sound "better", that it actually does.  until some time goes by and you realize it just sounds "different." although, nothing wrong with owning multiple pieces of the same type that sound different.  (as long as we're not fooling ourselves that a new piece of gear sounds "better" when it's still new to our ears, during the initial, audition stage).  so, way to go for recognizing that potential trap. (one that i've fell into before!) 

i wish you still had your audeze phones to plug into the new desktop version.  i would've appreciated your thoughts on how your new O2 pairs with those phones.  (as you know, i've had a love/hate relationship with these h/p's, ever since i got them. my most recent change was deciding on a pair of JPS UltraConductor 2 interconnects, out of the four pair that i had on hand at the same time, on loan from  the cable company  in the last couple of weeks).  yes, these interconnects did make a noticeable difference with these audeze headphones). in my opinion, these h/p's are a bit finicky and fussy about source, cabling, ...everything. but, they definitely have their strengths, as you know.  but, they also have their drawbacks.

anyway, great job with the fit and finish of your desktop O2.  (if you've been "losing yourself in the music" with it lately, then hey, man that's what it's all about).

sounds like it was a successful project to me! your new desktop O2 is an attractive-looking piece.  you did an excellent job with it.

enjoy!             

[adydula]

Hi Terry!

Thanks for the nice comments.

Yes there is a part of me that wanted this amp to sound better than the O2. I did the same blind testing with a Schitt ASgard, Schiit Lyr (many tubes) and several other DIY projects, AVR's etc...sold them all and kept the O2's.

I had the LCD2's for about a year or so...and at first they were like no other to me, but after the newness wears off you start wondering and looking...I bought a few pairs of Beyers and compared them etc and really liked these T90's a  lot and sold the LCD2's to finance them and the 1350's.

I believe the sensitivity of the LCD2's are 91 dB/1mW. So the ODA will handle these with aplumb for sure...if your ever in Raleigh, NC let me know and bring your LCD2's!! LOL. Whether they would sound better or different would remain to be seen, my gut tells me probably not.

When I was comparing the two amps I found the level had to be set really very carefully your ears seem to pick the loudest one as the better ones every time. I tried that with a 5 db difference and you always pick out the loudest of the two as the better sounding...

The designer of this ODA amp is going to send his build to John Seaber at JDSLabs soon for measurements of his DScope to see where it is in comparison to the O2 and other amps.

We are looking forward to that. 

Thanks again and have a nice Memorial Day weekend!

All the best
Alex

[adydula]

More refinements....

 

I noticed that IC11 was a little warm to the touch and measured it with a thermocouple and it was 140 degree's F. Well within its spec but hotter that we would like it to be.

AGDR did some engineering and two small resistor changes now allows this to run cooler at 125 deg F and we also will heatsink it as well.

A great example of how the DIY community works to make things better...

Also the final xfmr for the standard 12.5VAC rail version is a 16 VAC 2.0 amp xfmr. This change lead to AGDR looking at the snubber circuit which he tuned to reduce ringing to close to none.

 The ODA is working its way close to perfection!

Alex

[jtwrace]

When do the dScope measurements get published?

[adydula]

dScope measurements will be done by John Seaber at JDSLabs as soon as AGDR sends him his unit. I know there were very minor changes that he wanted to do before sending the unit out.

As soon as I see the results I will post that link and results here etc..

Alex

[terry parr]

alex, thanks for the invite!  you'd always be wecome here, too.  i'm in clayton (probably less than an hour from you.  can't remember if i have that in my profile or not, or whether or not you knew.  i think you did). 

i think i remember talking about where i got my carver amp serviced (in new bern), and i also posted about it over on head-fi.  can't remember if we exchanged any messages about that, or not.  (so, you might not have had any idea where i was.  i could check my previous posts, but it's getting late on sun. night, and i just decided to pop on here for a few minutes).   

anyway, if you have a couple of hours to spend doing some comparative listening, on a sat. or sun. afternoon, i think that would be great.  i'd especially like to hear how your new desktop 02 compares with the spl phonitor that i still have.  (and i think a question about the phonitor was the reason for my very first post here on audio circle).

i have all the amps and headphones here at home that i've discussed here on a.c. 

and i have the lcd-3.  not the lcd-2.  (the 3's being less "dark", and with a bit more low-end "detail", but with a bit less low-end "impact" [but not by much], than the lcd-2's).  also, with the new JDS Labs interconnects that i just got,  i would say the 3's definitely out-do the 2's as far as mids and highs. 

who knows?  demo-ing the 3's might turn you back into an audeze fan, again.  doubt it.  but, hey.  you never know.  still might be worth a listen, though. 

i can't do very much during the week because of the hours that i work (have to stay gainfully-employed in order to finance this crazy, and sometimes too-expensive hobby).  sometimes it seems like we're dogs chasing our tails, but when you do hit on an equipment piece that does make a difference, and improves the sound you're getting, then it seems to make all the frustrations and "mistakes" worth it.

anyway, alex,  most weekend afternoons are open for me.

terry.     

[adydula]

Hey Terry...

Thanks for the reply, its good that your nearby!

I will PM you and hope I can come by and listen, I would bring my new DIY ODA for sure!!

I would hate to listen to LCD'3's....LOL Gosh that could wind up costing me an arm and a leg!!

Alex
 

[adydula]

Ok folks AGDR just posted this at DIYAUDIO.COM

"I'm also going to let the cat out of the bag about something. John at JDS labs has agreed to dScope test the O2 booster board too, along with the ODA, and is in-process with that right now as time permits on his end. We will finally have some dScope measurements for the O2 booster board! A huge thanks goes out to John for the testing."

I knew this was in progress and had to wait until AGDR made this public....so hopefully we will have some discrete data soon!

Alex

[adydula]

Well I have about 30 hours on the ODA and it has been working flawlessly and is a really good headphone amp.
The addition of a 1/4 jack and a 3.5mm jack and the ability to attach 2 headphones at the same time for auditioning is a really neat option.

I am going to open it up next week and wire up the front panel RCA preamp outputs with a unity gain buffer. This will allow me to attach it to my Onkyo receiver to use to send the sound from my master listening pc to a set of external speakers I use for gaming and flight sims!! LOL.

All the while I can easily listen to music via JRiver etc without moving an external dac around.

The clipping indicator has been very useful to let you actually know when it is occurring....I never use much gain because the odac and HRT MSii+ have a full 2.0 and 2.25 volt output.

This indicator has led me down a path to better understanding gain, volume control, volume leveling and replay gain.

Many interactions here...that a lot us really do not understand.

All the best
Alex

[jtwrace]

When will John have the measurements done?

[adydula]

Good Morning!!

From what I know they were sent the O2 Booster board first to measure. This I believe has happened but that testing that was done was not conclusive according to the designer.....something like it was tested at levels and loads it isn't designed for.

My guess was after this the desktop ODA would have been sent for testing now from what I see at DIYAUDIO, Agdr is looking for another entity with a dScope or AP to do the analysis.

I hope he finds someone that is not in the industry as a retailer that is totally neutral etc to test and measure.

Here is the post from DIY:

Fsatsil - good thoughts! The booster board does provide for more dynamic headroom in terms of peak current avalability. The maximum current of the NJM4556A output chips in the O2 is around 70mA, for 140mA for the pair. The LME49600 are good for 250mA each, and although you can't run them continuously with anywhere near that much current, you can have musical peak currents much higher than the stock O2.

Pretty much from day one in the build instructions I've said that if 140mA (70mA per chip) is the maximum continuous for the stock O2, as NwAvGuy posted in his blog, then with the booster board you should be able to continuously do around 180mA, or 90mA per chip. But... for short musical peaks it can go all the way to 200mA and for very short peaks up to the 250mA. I posted a set of photos in the thread here a few months ago, using an external power supply and desktop speakers, that verified there is no problem with peaks at 250mA with the booster board.

It sounds like John at JDS Labs and I have had a miscommunication somewhere on along the way on what it is that the booster board is intended to do. It is NOT intended to run the LME49600 chips at anywhere near their full output power capability. The top goals for the booster board have been:

1. Lower distortion and noise based on the datasheet numbers for the OPA140 + LME4600 combo and, better, the OPA827 + LME4600 combo, and then both of those with the NJM2068 replaced with the LME49990 adapter board. And with those numbers at the same Vrms output levels that NwAvGuy used in his tests for the O2, which at 32 ohms is about 4.25Vrms with sine wave testing. The one dScope test John sent me was with the OPA140 + LME49600 into 150 ohms and it showed the THD+N just slightly better than the O2 amp. So the good news is I didn't make the THD+N any worse. But the bad news is that I was hoping is would be significantly better than the O2 based on the datasheets and NwAvGuy's comments in his blog that the O2's THD+N was limited by the NJM4556A chips. I was quite surprised to learn that the OPA140+LME49600 combination (with the 150R load) didn't signifantly beat the stock O2's NJM4556A chips, even with the NJM2068 left in for the gain chip!

So the big discoveries from John's testing are that the NJM4556A is apparently even better than NwAvGuy thought, which is probably good news for the ODA since that is the same chip in a different package, and that the THD+N may actually be limited by the O2's NJM2068 gain chip instead of theNJM4556A chips. So hence the importance of trying the test with the LME49990 adaptor in place of the NJM2068, in all the cases: NJM4556A chips (original O2 output), OPA140+LME49600, and OPA827 + LME49600. I'm still quite eager to see dScope or AP THD + N tests results here at normal listening levels, such at 1Vrms into 32R or 150R, to see if the THD+N really is reduced over the stock O2, and would be happy to send boards out to anyone with a recent model dScope or AP to test. Again, that test should be up to 4.25Vrms maximum into a 32 ohm load if using sine waves, and even then testing with sine waves may need to be limited to 10 minutes at a whack, as NwAvGuy wrote for the stock O2. But I'm less concerned abouut the numbers at maximum output than at normal listening levels.

I'm still hoping that the OPA827 + LME49600 combo and an LME49990 adaptor in the for the NJM2068 will come up with significantly reduced THD+N over the stock O2.  If it doesn't then my hat is definitely off to NwAvGuy and the stock O2! At that point the usefullness of the booster board would no just be the following points below.

2. No-thump relay. No turn-on or turn-off thumps. Improved THD+N completely aside, this function alone is usefull if the booster board is proven not to degrade the basic O2 THD+N, which apparently is the case at 150R.

3. Vastly lower DC output offset which may make a difference for some sensitive IEMs. Again, as long as the booster board doesn't make the stock O2's THD+N any worse, another useful function.

4. Slighly more continuous output current with a great deal more peak (burst) current for musical peaks. At 180ma total that would be 90mA per chip continuous vs. 70mA per chip half with the stock O2.

5. LEDs after the mosfets to show when the O2 mosfets are on or off and that both power rails are up

6. In the latest V3.1 schottky power rail clamp diodes, something that really should have been on the O2 given that one O2 mosfet is coming on before the other.

7. Higher slew rate. The stock O2 should be around 3V/uS. With the NJM2068 gain chip as the limiting factor, the booster board should give around 6V/uS. With the NJM2068 replaced by the LME49990 adaptor the full 20V/uS of that chip and the booster board chips should result. As NwAvGuy pointed out in his blog, 3V/uS should already be in excess of what the digital audio recording chain limits the slew rate to. But regardless I know that some folks would prefer a higher slew rate.

What the booster board is definitely not designed to do, and has never been a goal, is to run higher than the 4.25Vrms in 32 ohm with sine wave testing that NwAvGuuy shows in his blog graph as the maximum output for the O2. I haven't tried it yet, but I suspect the booster board could indeed be cranked higher to 6 or the full 7Vrms output swing into 32R with sine waves since it has larger output transistors than the NJM4556A, and does not internally current limit at around 90mA like the NJM4556A half-sections. And that would definitely cause it to overheat. But again, not a problem, since the actual usage of the booster board is music and not sine waves. As my previous posts shows music can peak up to 7Vrms with no resulting heating problems. It just means that that sine wave testing at the maximum 4.25Vrms into 32R will probably have to be limited to 5 or 10 minutes then allowing the chips to cool.

So the one thing the booster board is not intended to be is a solution for low impedance & low sensitivity headphones for the O2 headamp. I doubt there would be any way to fit a solution for those into the tiny B2-080 case for that matter. For that it would take the ODA, AMB's b22, or any other headamp designed for that much voltage swing and current.

So you can get some snippets about the new ODA, but the full range of measurements still haven't been done yet.

From what I have done as far as listening and comparing to the O2 I am totally satisfied at the results and would think the measurements would be as good as if not better in some regards, whether these translate into audible differences to the human ear / brain will always be up for the classic debates that we all partake in!! LOL.

If I had to choose the original O2 vs this ODA I would choose the ODA with out a hesitation. Its sonically the same in m blind AB tests, if it wasn't it I would sell it in a heartbeat like I have done with other amps I have built etc.....but the things I have mentioned in this thread that make this a wonderful headphone amp are the 1/4" jack AND 3.5mm jack that can be used at the same time, the clipping LED indicator to show you when clipping is occurring, selectable gains (4), actual power rail LEDS (+/-), adjustable attenuation resistors to allow for volume position adjustments if needed, Rear RCA inputs that are switch selectable with the front 3.5mm input, Front panel RCA preamp outs that can be wired to several configurations, rear panel AC power jack, rear panel on off switch, more durable switches, room in the enclosure to integrate an internal ODAC if desired and lastly the ability to attach (2) dacs, one via RCA and one via 3.5mm to make for easy DAC test comparison.

All in all this ODA design does all I want and more. I has about the same voltage swing of the O2 but 3 times the current capacity. The one caveat that the designer has stated here is his post:

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.

Ok if I hear of any definitive measurements that are done on the ODA I will let you know!!

All the best
Alex