Oh I see. Thanks for the quick reply! Should I contact the merchant or RME itself in this case?

Got it, thanks!

Hey,

Curious to find someone else in the exact same situation, but I'm happy to share my findings with you.

After making this thread and reading the replies, I sent my Adi in for repairs and got a new one. I've been using it for two months now, averaging about 6 hours of use every day on Hi-power mode with the HD800s connected. The unit has never once overheated, or short-circuted or anything. It works flawlessly and it gets way less hot than the previous unit did.
I can't say for sure that the problem won't occur again eventually, but the older device started exhibiting problems after using it for only one month so maybe it was just faulty.
But so far everything works just as it should.

Me too, only in summer in Rome. Probably the ADI is not climate change ready :-)

Mine is back from assistance.
The motherboard has been replaced and now it works well.
The heat is always high. (my room temperature is now 28 ° C = 82.4° F)
I use a very silent fan by Noctua to keep the temperature more acceptable.

Ah, I have the same problem now after a year, as the weather gets hotter. It’s now 28C here. I was using my 300ohm HD600 in low gain With volume at -30db. 2.5 hours later it displayed such message and the entire body is untouchable.

Is it because of a bad batch of components?

I will try 1/2 hp out tomorrow and see if problem presents there as well. As far as I remember it’s equally hot as 3/4.

I doubt if that is the case. Yesterday HP 3/4 shutdown after 2~3 hours running at 28C ambient temperature. Today I tried HP 1/2 and after less than an hour of using at 27C room temperature. the unit display the overcurrent message and runs extremely hot. I almost never used HP 1/2 before, and having issues with both HP outs should be extremely rare...

Running low gain at -30db for 300Ohm headphone shouldn't stress the HP out that much.

Thank you MC. Just shipped my unit back to the dealer. You'll receive it soon.
oh btw, don't forgot the price https://forum.rme-audio.de/viewtopic.ph … 86#p154486!

Just curious,  is it because those opamps fighting each other which leads to shorter lifespan? (based on online picture I assume the outs are directly summed together without a resistor. the 47.0s seems to be feedback resistor?) No intention to criticize the design. Just want to learn more electronics knowledge.

Thank you KaiS, I learned a lot!

Unfortunately you need to send your device to your dealer (if in warranty) or RME (if not).

It's a 10 layer pcb and the output buffer has thermal pad soldered on board so no way to fix it. Motherboard replacement is required.

it's just a normal opa1602.
it's a pity that it's not configured as the master op amp in the nested feedback configuration. otherwise the noise will be even lower.

the feedback path goes back to the first 1688 which is also driving the load (or put it in a fancy way, "feedforward").
Circuit is similar to the "Apheared 47 Headphone amplifier" (https://headwizememorial.wordpress.com/ … scrapbook/) in the DIY community long, long ago (2001).
RME didn't even change the resistor value (47ohm).
The master opa is also applied with a miller compensation to make the full circuit stable.

the above 1602 is just for gain adjust and lpf.

according to the datasheet, 1688 has higher noise than 1602, which makes the noise of the headphone amplifier higher.
Had the feedback path gone through the 1602, with no feedforward path, and the 6 1688s equally in parallel, RME could provide IEM out for Pro for free.

> More NFB loops - more stability problems.

HP Amp stability issues caused by capacitive load are easy to solve and various compensation solutions are available.
Miller compensation used by ADI-2 is a good example.
Recent trend is to also incorporate solutions usually found in speaker amps.
transitional miller compensation, for instance, is now used in many HP amps and achieved good results(such as JDS, Topping, etc).

> The 47 Ohm is suggested in the 1688’s datasheet.

1688 datasheet does not use that. the buffer itself when using alone can drive headphone load stably without compensation such as additional output resistor.

> Interestingly, the topology of my 1st version ADI-2 Pro seems different, the 3 OPA1688 are all wired as voltage follower, with the non-inverting inputs tied together.Or I haven’t recognized it, I wasn’t after that.

based on the images posted by RME and Synthax,

The HP amp circuit hasn't been changed across the versions.

The 5 channels close to the headphone jack are in parallel.
The one channel far away from the jack is the master
it's also driving the load, but accepting feedback from the final output.
You can even see the 1K feedback resistor and compensation capacitor behind the first 1688 channel.
(on the picture, the feedback resistor is below the 6 pairs 47ohm resistors. the capacitor is located on left/right of the feedback resistor)

On the clearer image (https://i.postimg.cc/08P9Kk1j/V3.jpg) you can see pcb traces on the left hand side that the 1K feedback resistor connects the output of 6 paris of 47ohm resistors to the first 1688 channel.

> How old are you? I read about this configuration in 1993, in Burr-Browns App note AB-051.

The AB-051 paper is linked in the "47 Headphone Amplifier" webpage discussed above as reference.
So I didn't think it would be necessary to link it here again.

> I remember headphone amp circuits that had 10 x 5532 parallel in that configuration.

douglas self published a power amp circuit using 37 x 5532 in parallel each channel.

> Holy moses - you accuse me of having known and copied that circuit? Seriously?

Calm down... Certainly not!

It's public domain knowledge that has existed for a long time.
perhaps 51ohm resistors are hard to find so people just grab whatever easily available, for instance, 47ohm....
the 47 HP Amp is listed above simply because it's widely known in the DIY community.
No offense at all.
As long as RME delivers good performance, using public knowledge should be encouraged.

All I wanna say in the initial post was, using the 1602 for error correction should in theory improve the noise performance.
KaiS deviated the topic to something different and I end up showing him the DIY 47 HP Amp to help him understand the topology in ADI-2.
I should have draw a ADI-2 HP Amp circuit diagram to avoid such confusion.

Spec is +5 - +50 C. 75% humidity. Maybe you shouldnt operate in a sauna, but a hot summerday without direct sunlight should be well whitin range.

I have spent many hours to find the ideal resisiors for this circuit and the reasons they are in there. I could write an app note about it but won't. Whoever wants to know the background has to find it out himself.

Point is those resistors were neither copied nor just 'grabbed and put in there'. This kind of devaluating speculation is not helping.

I don’t wanted to devaluate your efforts building a great high-power headphone amp that exceeds the quality of the DAC-chip in every regard, being overload protected by a unique circuit etc.

In contrary, I just wanted to point out that it’s not easy to do so, making an amp work stable on widely varying loads.

Yours are probably fine.  An easy way to check is measure the wattage consumption. If it is over 12W when idle something must be fried. If it’s below 12W then it is normal.

I did some checking around and Im not worried.

That said its no secret that the ADI-2 PRO is a hot, small and crowded box. So its prob OK to be mindfull of ambient temps and air circulation. Not to put it on top of other hot equipment. No direct sunlight etc.

Generally this goes for all electronics

I still don’t clearly see the traces and part’s prints.
A single 1 kOhm resistor with a cap like described would serve as compensation to increase the load’s phase margin.

The 6 47 Ohm resistors for each side serve for current summing of the 6 OPA1688 channels.

Dear RME team,
I really appreciate what you've done in terms of technology and performance of the Adi-2 Pro Be , and I have several questions about it.

Today, I’ve tried to use Audeze LCD-X’s with Adi-2 Pro FS using balanced cable, and after pushing the gain to around -14db in low power mode, one of the channels had stopped playing and I’ve received the error message (Overload/Short Detected).

Fist of all, I thought that I was pushing the gain too hard, but after this situation I’ve tried my headphones with their basic cable and switched RME to the High Power mode. Everything was fine, phones even played louder than it was in balanced mode. So, what could probably lead to this issue? I’ve tested many times, R channel is always goes off by this error. Here the link to the video, where you can see all the volume values and the error itself.

https://drive.google.com/file/d/1CDU81e … sp=sharing

All the best,

Evgeny

Tnanks KaiS.

I've tried reversing cables, so the R goes to the PH 3/4 and L goes to 1/2. Problem appears again, I saw the same error and my left channel goes off.(in case of reversed connection) Also, I've tried to use single ended, standard cable connecting to the PH 1/2 and everything worked fine, no issues even with higher levels.

After a while I've tested balanced connection again (in reversed connection as I wrote before) and saw exact same error in PH 1/2, and after few seconds with P/H 3/4.

Link to the video here:
https://drive.google.com/file/d/12oviyr … sp=sharing

All the best,

Evgeny

Hello KaiS,

I apologize for such a long reply. The cable was the issue in my case. I’ve contacted cable manufacturer, and  he made a new one for me. The issue was in the ground, which was connected to one of the pins. Still testing this setup at the moment, have no problems experienced yet.  Simple conclusion of this situation - always double-check the manuals and schemes inside them. I’m really happy that we found the solution, It won’t be possible without your comprehensive recommendations. I sincerely thank you, KaiS and wonderful RME community.

What do you think, is high-power mode really matters in balanced connection? It seems to be that low-power mode is loud enough for my phones.

All the best,

Evgeny