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Objective Desktop Amp.....A Version from AGDR - Page 2

post #16 of 40
Thread Starter 

Hello!

 

I have not listened to the wire, so I cant personally speak to a comparison.

 

AGDR and Owen are over at DIY, you could ask them etc, I will ask AGDR if he has ever listened to them both.

 

I am usually am skeptical when people tell be they can tell the differences in amps etc, at "high" levels etc... most of us don't listen at real high levels.

 

I respect Owen and the "wire" very much and am not saying that there are not differences.

 

In my blind testing I could not tell any difference in the o2 and this ODA V2 amp.

 

I was really hoping to hear a difference but to me its just not reality.

 

I have cranked up the ODA all the way at the highest gain and its dead silent with no inputs attached.

 

As far as an assembled board etc you should PM Agdr directly over at DIY or his site agdraudio.com.

 

I think getting a board is a good possibility.

 

All the best!

Alex


Edited by adydula - 5/23/14 at 9:22am
post #17 of 40
Thread Starter 

Well I finally got the front panel almost completed, still needs some minor work, labeling etc..

 

But it looks pretty good so far...

 

I have my AKG Q701's plugged into the 1/4 jack and the Beyer T90's in the 3.5 mm jack.

 

Both playing just fine.:)

 

 

 

 

Alex

post #18 of 40

Nice amp, it's cool to see an ODA come out, I look forward to seeing the Objective side of it when someone gets it into some scopes.

post #19 of 40
Thread Starter 

Thanks...the measurements should be in the near future....

 

Alex

post #20 of 40
Thread Starter 

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

post #21 of 40
Thread Starter 

Agdr just completed the following testing on the version 2 , 12.5 volt rail ODA and I just completed this upgrade:

 

what might be good enough is not good enough for this engineer.....:)

 

Old 27th May 2014, 12:32 AM   #441
agdr is offlineagdr  United States
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DefaultTuning the ODA's snubber

I've had a chance this weekend to make a test I've been wanting to for awhile. Tuning the ODA's snubber for the specific transformer being used, now that the WAU16-2400 is the pick for the standard +/-12.5Vdc power rails. Turns out changing the 110R resistor to 52R will result in being closer to critical damping with this specific transformer.


Details:

The snubber in the ODA comes right out of Hagerman's famous paper:

http://www.hagtech.com/pdf/snubber.pdf

0.01uF (C5) to lower the ringing frequency, then the series 0.068uF + 110R pair (C8, R13) to damp what is left.

The rest comes out of Mark Johnson's excellent Quasimodo thread:

Simple, no-math transformer snubber using Quasimodo test-jig

As mark points out, a person could go to a lot of effort and math measuring the leakage inductance of the specific transformer winding and plugging it in the equations. Or...simply replace the 110R with a pot, as Mark did, and adjust for critical damping. Then read the value off the pot. Simple and easy! In my case I used a 500R linear 25 turn taper. I think Mark used a 1K in his writeup.

My appologies upfront for the fuzzy photos below. I should have had the room lights on instead of just relying on the scope screen's brightness.

The scope is across one of the ODA's power rectifier diodes, D1.

* The first photo shows the transformer's secondary leakage inductance ringing in the lower right corner of each half-cycle, that small part that fades out at this level of resolution. This is with the orignal 110R resistor.

* The next photo is a closeup of the ringing with the scope's timebase stretched out. This is still the original 110R resistor. I can see the ringing dying out after one cycle. Not bad, but we can probably do better.

* The next photo shows the test setup, with the 500R linear trimpot soldered onto the SMD pads where the 110R R13 used to go. The blue wire is going to the end-munted end of D1 for the scope probe. I pre-set the trimpot to 110R on that side so it would start out the same as the original resistor. I've soldered the pot directly on the board like this to keep from introducing any additional inductance or capacitance from using wire leads.

* The next waveform shows pretty close to critical damping at 52R. For each of these I unsoldered the pot, measured it, then soldered it back in. Note I've increased the vertical scale on the scope from the first two pictures to show the ringing more clearly.

* The next waveform is with the pot in the other direction at 190R. Clearly we have ringing! I count three cycles before it damps out.

* Next I just turned the pot until the waveform was damped inone cycle and measured the pot: 102R. Nearly the same as the 110R.

* The final waveform is back to the original 110R resistor.

If you use a different transformer than the 16Vac 2.4A in the BOM and have access to a scope, just use this procedure to tune the snubber. I would suspect though that most transformers in this general voltage and amperage range will be snubbed adequately by something in the 52R range. 51R or 49.9R would be standard values
 

 

 

 

 

 

 

 


Edited by adydula - 6/1/14 at 8:37am
post #22 of 40
Thread Starter 

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

post #23 of 40
That is excellent news
post #24 of 40
Thread Starter 

Yup its really good that this will be done.

 

My ODA is absolutely superb to me..

 

Alex

post #25 of 40
Quote:
Originally Posted by adydula View Post
 

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

wow... I read this entire thread

 

I wonder too if we will see a JDS labs ODA amp for sale soon? Heck I migth be intersted in giving one a listen! 

post #26 of 40

Assuming these can drive HE6 well.. these surely can feed the power hungry LCD2/3s? (Optimal 1-4W input)

 

Looks amazing!! Subbed!

post #27 of 40
Thread Starter 

I had a set of LCD2 R2's for awhile and I never used them with the ODA I now have.

 

They are 91 dB/1mW efficiency rating..

 

From what I know and experienced with other amps I used to have the ODA would drive them very well.....

 

I don't know if JDS will or would put together and ODA for sale etc..
 

I do know that you can build one or have one built.

 

Just go to DIYAUDIO.COM or AGDRAUDIO.COM and you can get a pc board or have one built for you by AGDR from my understanding.

 

A.


Edited by adydula - 6/6/14 at 5:42pm
post #28 of 40
Quote:
Originally Posted by adydula View Post
 

I had a set of LCD2 R2's for awhile and I never used them with the ODA I now have.

 

They are 91 dB/1mW efficiency rating..

 

From what I know and experienced with other amps I used to have the ODA would drive them very well.....

 

I don't know if JDS will or would put together and ODA for sale etc..
 

I do know that you can build one or have one built.

 

Just go to DIYAUDIO.COM or AGDRAUDIO.COM and you can get a pc board or have one built for you by AGDR from my understanding.

 

A.

hmm that's not bad, still John is a pretty smart fellah I'd be willing to bet after he measures this he'd be willing to start sale of it within his company. Their O2 was great and I'd love to see them put out a more powerful amp

post #29 of 40
Thread Starter 

Time will tell....

 

John has taken some measurements of AGDR's O2 Booster Board and has some concerns that with the licensing etc its still a DIY product.

 

The ODA I think could become a product, again time will tell.

 

I do know that you can contact AGDR and have one built etc....

 

Alex

post #30 of 40

adydula, is there a source for the PCB boards?

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