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MKH 8060 + Lectrosonics plug-on failure


axel

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I have experienced a sudden failure of a new MKH 8060 with 3 different Lectrosonics Plug-on Tx. The Combo has been working flawlessly with this particular Mic for 2 weeks and with 2 older MKH 8060 for the last 4 years. Out of the sudden on an indoor shoot the new 8060 started to create high noise as if related to a malfunctioning P48 supply. It shows this behaviour with both UH400a and a HMa Plug-on Tx. Any other mics, including the 2 older MKH 8060 units work as ever with all Tx, and the faulty unit is behaving totally OK when on a cabled connection to a symmetrical Mic input providing +48V.

Any other parts, like cables or Rx issues can be ruled out as culprits, system has been A/B tested, including the XLR Adapters of the 8060

I will send the Mic back to Sennheiser as a warranty issue, but I don't know how to adress the malfunction. They Sennys will probably not have  Lectrosonics transmitters at hand at their service departement ;-)

Any clues what might be going on inside the faulty mike that makes it fail?

Thanks for any input

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Did you measure the power output of both the plug-on and your cabled connection? Maybe, because of some fault, the mic needs the exact voltage of your cabled connection and doesn't like that of your HMa. This is just a guess, of course, I only have an older 8060 which I rarely use. Is the 8060 still modular? If so, did you also swap preamps?

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yes, I swapped XLR modules. And yes, Lectrosonics Plugon Tx only deliver 42,5 V, versus 48V at the cabled connection. But why did the 8060 work before and the other ones still do? And other P48 mics also do, all but the Neumann KM100 series, which have to be phase reversed, which - Lectro says- has to do with the internal unbalanced signal flow of the Lectro Tx.  I am not good enough techie wise, to have a detailled image what really happens inside that Lectrosonics Tx and what makes it different to real balanced P48 inputs...

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24 minutes ago, axel said:

yes, I swapped XLR modules. And yes, Lectrosonics Plugon Tx only deliver 42,5 V, versus 48V at the cabled connection. But why did the 8060 work before and the other ones still do? And other P48 mics also do, all but the Neumann KM100 series, which have to be phase reversed, which - Lectro says- has to do with the internal unbalanced signal flow of the Lectro Tx.  I am not good enough techie wise, to have a detailled image what really happens inside that Lectrosonics Tx and what makes it different to real balanced P48 inputs...

Hi Axel,

Hma design can provide higher currents than conventional 48 Volt Phantom power setups with less voltage drop. It starts out at 42 Volts since the voltage drops less under load. As you sumised, voltage isn't the problem.

The Hma is not a balanced input though it presents a balanced resistive load to the mic. As I  remember, pin 2 is audio in and pin 3 is a resistor to a big capacitor to ground. My guess as to what is going on, is that the mic is putting out audio on one pin only (pin3) and that pin is not the hot pin on the Hma. Into a conventional input, audio on either 2 or 3 produces a good signal.

You can test this with a phase reverser at the mic to see if it now works with the Hma. The mic is still not right.

Best Regards, Larry F.

p.s. "Guess" is the most important word in my post above.

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hi Larry,

thanks you for your comrehensive answer (like always). I connected the faulty mic with a phase reverse cable to the Tx. I could see modulation on the HMa, but a minute later when I had finished booting the Recoder/Rx combo to listen to the signal, the 8060 had gone completely dead. No signal even on regular balanced P48 inputs. In any case, Sennheiser cannot argue anymore that the mic is working within specs ... 

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yes, I swapped XLR modules. And yes, Lectrosonics Plugon Tx only deliver 42,5 V, versus 48V at the cabled connection. But why did the 8060 work before and the other ones still do?

Well, that's where I thought a faulty component in the mic would come in.

Anyway, Sennheiser's always been pretty good with repairs for me. They always could repair everything and they never shied away from picking up the fee if the fault was due to a faulty part, even if it was out of warranty
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I just had an 8050 fail on me. Something came loose inside the mic and make a clunk sound when moved quickly or inverted. They warrantied it and the customer service was excellent from Sennheiser Canada however the interesting part for me was hearing from the Sennheiser tech that the 8050 was 'not a serviceable microphone' and that that generation (2 years old) gets replaced rather than being fixed. I think he said it was because the internals were glued into the mic body? Makes me a bit nervous for a few years down the line after my other 8050 is out of warranty to have a high end mic that cant be fixed or taken apart.

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