Antelope Orion stereo output gain issue

[benqbasic]

Hi All,

I have an Antelope Audio Orion Studio rev 2017 that I've recently taken out of storage. I'm experiencing a gain balance issue with the main stereo output. The right output has 8dB less gain than the left. It doesn't seem to be a software or digital problem since the output discrepancy fluctuates with volume adjustments. As I increase the output, the imbalance grows. I can see the output voltage is lower on the faulty channel.

Unfortunately, this unit is out of warranty, and I'd like to attempt to fix it myself first. Although I'm not very experienced with SMD, I want to pinpoint the issue and only replace the faulty components if possible. The main output utilizes a BB PCM1792. Each channel has two OP1662 opamps. Based on the datasheet, I assume it is just the V/I to filter circuit, this is followed by some transistors (balanced output?) into a relay to select A/B output.



Any assistance would be greatly appreciated. What should I be looking for. Sending the unit back to Antelope would be a costly endeavor as I'm located in New Zealand.

Thanks in advance!

 

[Khron]

Got an oscilloscope? Or would you dare MacGyver a makeshift probe, and poke around on that board, using the unit itself to view / monitor said signals?

If it were my unit, i'd reverse-engineer that entire output stage and see what's what, in order to get an idea what to expect at the various circuit nodes. No idea how feasible something like that might be, in your case, though...

 

[benqbasic]

No scope anymore, but i probably have a probe that could use with an audio interface and a software scope.
There is a secondary board that sits above this and which feed the DAC. I would also need to MacGyver up some jumpers as well or inject a signal post DAC. Tomorrow i will start measuring all the voltages at least.

 

[evil grill]

Aren't those outputs impedance balanced?

 

[Ike Zimbel]

Do you have a means of testing capacitors? I would look at the 47/35 electrolytics first. You might also get an indication of it being a bad cap (or not) by doing a frequency sweep. If it's down at LF but closer to normal at HF, could be a bad cap. And, I do not like the look of the lower solder joint on the cap above the upper 1662 on the right. One more thing, might be a relay failure so check that relay. None of the other parts in the picture (besides e-caps and relays) should be prone to failure from prolonged storage.

 

[benqbasic]

Aren't those outputs impedance balanced?

Will test between cold and earth when I get home. It looks like it.

 

[benqbasic]

Do you have a means of testing capacitors? I would look at the 47/35 electrolytics first. You might also get an indication of it being a bad cap (or not) by doing a frequency sweep. If it's down at LF but closer to normal at HF, could be a bad cap. And, I do not like the look of the lower solder joint on the cap above the upper 1662 on the right. One more thing, might be a relay failure so check that relay. None of the other parts in the picture (besides e-caps and relays) should be prone to failure from prolonged storage.

I have replaced the 2 near the output as that was my first thought. I have some capacitors on the way so I'll change them when they arrive. Quick and easy to do. Will check the relay but both channels exhibit the same issue so it would only be on the common side.

 

[benqbasic]

Small update: The main outs are underneath the upper PCB (which contains the DSP/USB & thunderbolt controllers) and controls the power circuit. I will need an IEC extension cable to keep it connected (I will pick one up next week). In the mean time i have started tracing out the circuit and found out my eyes are not as good as they were 10 years ago so this has proven to be slower than i thought.
I much prefer working on Microphone...haha.

 

[benqbasic]

Update 2: I managed to make a 90 degree plug from an IDC connection extension, so was able to power up the unit and take some voltage measurements. From quick observation, the output voltage of the right side OPA1662 which is driven directly by the DAC is lower than the left side. So the problems seems to be in the first stage of the circuit.

In the mean time Antelope audio tech support has gotten back to me advising that the OPA1662 is the most likely candidate if I wanted to get it repaired locally. Or they are happy to repair if I can ship it back. Cost is around $400-500usd.

I had ordered some OPA1662s anyway, but will not get a chance to do any further investigation until the weekend.

 

[Khron]

I had ordered some OPA1662s anyway

Hopefully not from eBay or AliExpress though...

 

[benqbasic]

Hopefully not from eBay or AliExpress though...

Haha no no. Rs components. They have the most reasonably priced shipping to NZ and don't sell fakes.

 

[benqbasic]

Update: I replaced the OPA1662 opamps and everything's functioning perfectly now.
It turned out to be the 4th one I swapped out. There's still some cleaning up to do on the PCB, but it's working. This was my first time working with SMD, so it was a learning process. I removed the opamps by cutting the legs and cleaning the pads.
I also replaced the power rail capacitors with some Nichicon Fine Golds that fit the requirements. Not sure if it makes any audible difference, but it's worth a shot.

I'll post some photos of the full PCB if anyone is interest.

Thanks for the support, everyone!