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RME User Forum → Miscellaneous → Octamic II, crackling noise when mic is connected
Hello,
The Octamic's faulty channel sounded like sitting next to a campfire as soon as a mic was connected.
Solution: one of the 2 SMD 4,7 Ohm resistors next to LX50 inductivity on the input stage was faulty - e.g. measured several kOhm's.
After replacing those resistors everything worked perfectly again.
I thought I would share that here, in case somebody has the same problem - we had it on two different octamic's II
Thanks. Strange that resistors have failed.... Have they been burnt by phantom? Or like.... 48 V on them would mean 10 A current. They would not survive that.
We also thought that this kind of failure ist very strange. They did not look burnt at all. I don't know how it happened. Those octamics are in our rental stock and on the road 200 days per year - you never know how users are handling it.
I posted here for the benefit of other users, not to blame RME. Great units.
Sure, I understand it. My guess is that very high current has damaged it. It is few ohm resistor, few volts create high currents...For sure one cannot blame RME, the rentees had to do, most probably, something malicious.
And appreciate that info. I hope, I will not need it. :-)
Is it possible a condenser mic with shortage inside can produce this damage ?
Costumer don't realize the mic is broken and insert it into several devices, damege those one after one...?
Maybe some kind of short circuit in a cable? One would have to see the schema of circuitry to guess with decent confidence. I just wildly guessed. The resistor is of very low resistance, so even not so high voltage causes excessive current. If it is SMD it will not be rated for several ampers, I guess.
i dont believe that anyone, including RME, would be naive enough to design an input stage that can be knocked out by a shorted mic cable. shorted mic cables are a more or less daily issue in live business.
Correct. These resistors form a simple HF filter directly at the input. There is no significant current flowing at all. Never heard about them breaking either.
Dear George,
Thank you so much for taking the time and writing this post. I had the same problem with my OctaMic II on channel 4 and 7 and it was as easy as swapping out the 4 resistors and everything works great. You have saved me a lot of time and headache. I am very grateful!
And do you know, how it has happened? What did you do before resistors were damaged?
I'm not entirely sure. Channel 7 had been troublesome for a long time – I just assumed it was my patchbay that was the trouble. When channel 4 started crackling it was right after I used it with a sketchy multicore-cable which I believed had a wonky channel 4. So it might be that. I also noticed when I opened up the unit that the 220v earth chassis lug on the top of the enclosure looked burnt, as if there had been sparks. I have no idea what might have caused this, because there has never been any faults otherwise.
And do you always power gear from single one power socket? I mean power everything from one common socket.
I have experienced that two sockets just close to each other had 100+ voltage difference between its "earths". Since that time I strictly feed the gear from single one power socket....
Maybe that different "earths" might do that damage...
RME User Forum → Miscellaneous → Octamic II, crackling noise when mic is connected
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