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Objective Desktop Amp.....A Version from AGDR - Page 3

post #31 of 48
Thread Starter 

Yes absolutely....contact AGDR at diyaudio.com under the headphones section, here is the link:

 

http://www.diyaudio.com/forums/headphone-systems/229934-version-o2-desktop-amp-oda.html

 

OR

 

contact him directly on his site at www.agdraudio.com

 

Alex

post #32 of 48
Thread Starter 
Hey,

After being on now for a few days here are the temps I have measured with a thermocouple:

Front Panel 3.5mm jack: 88 degrees F. Inside about 1/2 inch its 90 deg F

Front Panel RCA Jack: 86 deg F

Front Panel Screw Upper Right Corner: 85 deg F

Top middle case: 87 deg F

Side center/middle case: 85 deg F

Rear Panel Middle Regualtor screw : 89-90 deg F

Front panel 1/4" jack internal about 1" insertion to back of jack : 93 deg F

The entire rear panel is relatively uniform in temp distribution.

Then entire case is relatively uniform in temp distribution as well.

I have no ventilation holes in my build.

I think I will add the holes / slots in the back panel to see how well that goes.

My gut thinks not that much.

I also had a 1/4 headphone plugged into the 1/4 jack all the time except when I measured the internal temp there. So this precluded any air entering that opening.

All in all the case is slightly warm at a 88-89 temp etc.

All the best
Alex
post #33 of 48
Thread Starter 

Check this out the little ODA driving a set of full range speakers to 90+ db!!

 

https://www.youtube.com/watch?v=VTbWVEKzVpY

 

Quite amazing!!

 

Alex

post #34 of 48
Quote:
Originally Posted by adydula View Post
 

Check this out the little ODA driving a set of full range speakers to 90+ db!!

 

https://www.youtube.com/watch?v=VTbWVEKzVpY

 

Quite amazing!!

 

Alex

Looks very interesting, but I still don't understand what are the benefits of using ODA over lets say O2. Would be there any sound quality advantage, if I listen from my O2 on fairly low volume (9-10 o'clock)?


Edited by ieee754 - 8/3/14 at 12:59pm
post #35 of 48
Thread Starter 

Hello,

 

Honestly from a pure sound quality perspective there is no real sonic difference that I can detect.

 

I have done a/b testing against the O2 and could not detect which one was playing.

 

There are many benefits to the ODA which I have mentioned several times in this thread and in the other ODA thread due to its more connections, more current capacity, a pre-amp and bass option. Two dac inputs, clipping led, power led and other stuff that just make it a nicer all around amp.

 

If you ever got a set of hard to drive cans like the HE6's the ODA would drive them better than the O2.

That said I have 2 O2's that sound as good.

 

Alex

post #36 of 48
Thread Starter 

Several updates on the ODA amp from AGDR at DIYAUDIO.COM....

He has sent the ODA  to Mike G and Mike has done measurements that are posted here and at DIY Audio. Mike also hooked up the ODA and played his 15" Alec's with the ODA....amazing etc.

AGDR is working on some THD measurements and has received the ODA back from Mike G and has modified it and will be sending it back for round two... of testing.

Mike has possibly discovered a THD issue with the original O2 with the volume pot being at mid way etc..AGDR has been analyzing this and thinks he knows what the issue might be. Its still below audible hearing etch.

You can read the techie stuff again over at DIY Audio.

That said none of this affects the sonic equality at all but AGDR being a perfectionist has continued to make improvements to the ODA. None of them really would be audible but makes the ODA better, safer from line input transients and more easy to build. So the latest V2.1 boards are going to be sent out shortly after he gets parts from Mouser. The 2.1 can be seen in this thread above and photos.

Details on the 2.1 revisions are listed in great detail on agar's Google drive under the 2.1 area.

I will be updating my 2.0 ODA with a few of the component updates, one being a transorb across the AC power inputs to help with any surges, two regulator capacitors from 10uf to 22uf..based on data sheet errata, no sonic issue here, just one of a corner case oscillation possibility.... and a Pico amp fuse in series with one of the ac line inputs.

Also the big news is that agar asked me to share he will be offering ODA BOARDS with the small hard to solder SMD parts' Here is his post:

"In other news I have decided to sell ODA boards with just the SMD stuff soldered on for an additional $39 labor fee plus the $32 or so worth of SMD parts. All as time permits, lol, which will probably mean weekends, just doing them as ordered. If you run into anyone in your travels wanting a through-hole only ODA, feel free to point them to the posting:"

You can send AGDR a pm directly and/or read the post at diyaudio in the vendor area.

Alex


Edited by adydula - 8/11/14 at 8:27am
post #37 of 48
Thread Starter 
post #38 of 48

Hmm... Somebody is considering making these for sale soon. :) 

post #39 of 48

Would be nice to get a pre-built unit.

post #40 of 48

Agdr is offering to sell one at a premium of $530. He is hoping that Mayflower will soon buy items in bulk and sell them for a cheaper price (not like Agdr asked to be a businessman). Mayflower told me that they are looking into it and they have a prototype in their shop.

post #41 of 48
Thread Starter 

ODA Power Specs:

ODA maximum output power into various loads with +/-12.5Vdc power supply rails

 

Can you tell us the real wattage at 16, 32, 64, 120, 300 and 600 ohms please?

 


Good question!  :)   A lot of folks looking at the ODA would want to know.

The ODA will output a maximum swing of 7.25 volts rms without the attenuation resistors (or with them jumper-shorted), or half that at 3.75Vrms with the attenuation resistors, unless the output current exceeds about 60mA per output chip.  There are 6 chips in parallel, so that would be 60ma * 6 = 360mA maximum per channel. I often write 300mA for the ODA just to be conservative.  Sort of my reaction to the commercial stuff where everything is over-rated, I prefer to under-rate a little bit. :)  The output chips can actually do 70mA too, according to xxxxx, but i knock that down to 60mA to be conservative.

For output current it is necessary to switch back from rms (for power) to peak to make sure the peak currents don't exceed what the output chips can do.  So at 300R, the maximum current with a 7.25V swing would be (7.25Vrms * 1.414)/300R = 34.2 mA(peak) vs. the 360mA, well within bounds.  With the atten resistors gives even less current draw, (3.75Vrms * 1.414)/ 300 = 17.7mA.   In fact the biggest problem you may run into with some 300R  (and 600R) headphones, if they have lower sensitivity, is that even 7.25Vrms isn't enough voltage swing.  That is why the +/-15Vdc option is available, to give about 2.5Vrms more swing for 300R and up phones that need it.

The maximum power output into 300R is then (7.25Vrms)^2 / 300R = 175mW.   With the atten resistors it is (3.75Vrms)^2 / 300R = 47mW.

Using the same math on the rest:

Max current with 120R load = 85.4mA(peak), and with the atten resistors = 44.2mA(peak).  Both OK vs. the 360mA available.
The maximum power into 120R is 438mW, or 117mW with the atten resistors.

Max current with 64R load = 160.2mA(peak), and with the atten resistors = 82.9mA(peak). Both OK vs. the 360mA available.
The maximum power into 64R is 821mW, or 220mW with the atten resistors.

Max current with 32R load = 320mA(peak), and with the atten resistors = 166mA(peak). Both OK vs. the 360mA available.
The maximum power into 32R is 1.64W, or 439mW with the atten resistors.

Note that things are starting to get interesting with the current at 32R.  The maximum current with the 7.25Vrms output at 320 is getting close to that 360mA maximum.  We can expect that with a 16R load the ODA won't be able to go all the way up to 7.25Vrms without distorting.  Sure enough, that is what mgalusha's dScope tests showed.  The ODA went up to round 4.4Vrms at 16R load with THD+N levels 36% less than the O2, but then the distortion rose going up to around 6Vrms, which was the maximum before the distortion rose exponentially.

This set of numbers is for the 4.4V4ms output level, and 2.2Vrms with the atten resistors:
Max current with 16R load = 388mA(peak), and with the atten resistors = 194mA(peak).
The maximum power into 16R is 1.21W, or 302mW with the atten resistors (again, this is with 4.4Vrms and 2.2Vrms levels).

Notice the 388mA peak vs. the 360mA "max".  Remember above that I said I was being slightly conservative and using 60mA max for each output op-am vs. the 70mA that xxxxxxxx used.  Looks like xxxxxx is right once again, and Mike's dScope measurement prove it.  Using the full 70mA number the maximum output rating of the ODA goes up to 6 * 70mA = 420mA instead of 360mA.  So 388mA actually is within the OK range.

And finally, at the 6.0Vrms level (or 3.0Vrms with atten resistors) where Mike measured the maximum output before distortion zooms up, we get:
Max current with 16R load = 530mA(peak), and with the atten resistors = 265mA(peak).
The maximum power into 16R is 2.25W, or 562mW with the atten resistors (again, this is with 6Vrms and 3Vrms levels).

 

Updated for +/1 15 Vdc:

 

Here is a continuation on my post above about maximum wattage of the ODA into various loads.   The post above was all done for the "standard" +/-12.5Vdc power rail option.  Here I'm going to work the same numbers with the higher voltage +/-15Vdc power rail option that is only to be used with 300R and higher headphones.  The limitation of "only 300R and up" phones is to keep the output chips from overheating while running on the +/-15Vdc power rails.  With that limitation any volume control position is OK to use.

The +/-15Vdc power rails increase the maximum voltage swing to around 9.75Vrms, 2.5V higher than the 7.25Vrms you get with the +/-12.5V rails.  The extra voltage swing is useful for some 300R and higher headphones that are lower sensitivity and need the extra voltage. 

Max current with 600R load =23mA(peak), and with the atten resistors = 11.5mA(peak).  Both OK vs. the 360mA available.
The maximum power into 600R is 158mW, or =39.6mW with the atten resistors.

Max current with 300R load = 46mA(peak), and with the atten resistors = 23mA(peak).  Both OK vs. the 360mA available.
The maximum power into 300R is 317mW, or =79mW with the atten resistors.

 

FYI

Alex

post #42 of 48
Quote:
Originally Posted by adydula View Post



The maximum power output into 300R is then (7.25Vrms)^2 / 300R = 175mW.   With the atten resistors it is (3.75Vrms)^2 / 300R = 47mW.

Using the same math on the rest:

Max current with 120R load = 85.4mA(peak), and with the atten resistors = 44.2mA(peak).  Both OK vs. the 360mA available.
The maximum power into 120R is 438mW, or 117mW with the atten resistors.

Max current with 64R load = 160.2mA(peak), and with the atten resistors = 82.9mA(peak). Both OK vs. the 360mA available.
The maximum power into 64R is 821mW, or 220mW with the atten resistors.

Max current with 32R load = 320mA(peak), and with the atten resistors = 166mA(peak). Both OK vs. the 360mA available.
The maximum power into 32R is 1.64W, or 439mW with the atten resistors.

 

 

Looking forward to listening to this! If this really is as clean as the O2 with almost 3x the power...

 

What are the AC power options? I'm hoping it could be usable between 110v, 220v, and 100v AC. 

post #43 of 48
Thread Starter 

Hey I have used my DIY ODA for almost a year now and its as good and better than the O2, which I have 2 and have AB tested them.

 

The ODA is hands down more versatile and more powerful than the O2.

 

We are waiting on a second round of objective measurements and some re-check measurements on the O2 itself.

 

You can build one or there may be a site that might in the near future be selling them

 

Alex

post #44 of 48
What are some approximated prices for DIY and commercial versions?
post #45 of 48
Thread Starter 

Hello,

 

About $180 +/- for parts or so and another $60 for pc board, case, misc.

 

Here is a link to the BOM on AGDR's Google link for a list of parts and prices then:

 

https://drive.google.com/folderview?id=0B67cJELZW-i8N0dMYUlyTmVIczg&usp=sharing&tid=0B67cJELZW-i8VmhVNk5PODNtZnc

 

You can PM AGDR directly at Diyaudio.com and ask him about a finished or already built and tested one.

 

Alex


Edited by adydula - 1/12/15 at 9:03am
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