Topic: A strange case of microphone drop-out.

[ianmacd]

I'm using a couple of Schoeps CCM 41V microphones in combination with a Marantz PMD661 deck that has the OAD concert mod.

Most of the time, this combination works flawlessly, but two of the three times I've been out in the field this week, I've run into a strange problem.

Basically, after I rig up, turn the unit on and start to record, the right channel appears to be registering nothing. In actual fact, it's recording a very slight signal, but not enough to make the LEDs flicker.

Removing the batteries and reinserting them didn't help. Nor did unplugging both microphones and plugging them in again.

Eventually, I ran out of time. The support band came on stage and I was forced to go with what I had. My intention was to copy the left channel to the right in post-processing and reluctantly release the recording in mono. Better that than nothing at all.

Now comes the strange part. After about six or seven minutes, I checked my recording levels, expecting to see the same single channel recording being made, but now the right channel was recording at about 50% of the signal that it should have been. Huh? The problem had half fixed itself.

A further seven or eight minutes go by. I look down again. The right channel is now recording at full signal. Huh? Now it's fully fixed itself.

I later record the headlining band with no issues at all.

Back home, I check out the WAV file of the support band and, sure enough, it shows the right channel starting out as almost non-existent and then steadily getting louder until about 16 minutes into the show, by which time the signal has reached full strength.

I'm baffled. What could cause this?

A similar thing happened last night. Upon rigging up, the right channel was registering almost no signal. In an attempt to localise the issue to either the microphones or the recording deck, I swapped the left and right inputs. Both now recorded at full strength, so I switched them back. Pfff. Both were still at full strength, so I was none the wiser.

The support band came on and were recorded without issue, as were the main band later in the evening.

Clearly something is wrong and it's only going to get worse, but what is it? The experience of the microphone starting out with almost no signal and then gradually working up to full strength is the biggest clue, but I have no idea how to interpret it. Once the problem has corrected itself, there are no further issues all evening. if it were a loose connection, I'd expect to see intermittent problems throughout the evening. It's almost as if something needs to warm up before it can properly function.

Have any of you ever seen anything like this before?

[hi and lo]

It's purely speculation, but my instinct would point to an issue in the phantom power supply of the recorder. Next step would be to try and reproduce the issue at home, making sure you test this after the recorder has been powered down for a significant amount of time. I'd probably pull the batteries and let it sit for a day or two, and again try to isoloate the issue, but this time start with the channels swapped rather than swapping them after the unit has had any chance to 'warm up.'

[ScoobieKW]

Clearly something is wrong and it's only going to get worse, but what is it? The experience of the microphone starting out with almost no signal and then gradually working up to full strength is the biggest clue, but I have no idea how to interpret it. Once the problem has corrected itself, there are no further issues all evening. if it were a loose connection, I'd expect to see intermittent problems throughout the evening. It's almost as if something needs to warm up before it can properly function.

Have any of you ever seen anything like this before?

Not that it applies in this case as the ramping is gradual, but a cracked solder joint can be intermittent then become more reliable as the unit heats up and the solder expands.

In your case, as the power to the microphone is changing smoothly, I'd suspect power supply / capacitor in the phantom power section. Have you spoken to Marantz support?

[Phil Zone]

Maybe the cable is bad and one wire is touching another. I've had that problem before.

[kubacheck]

loose connection either in cable or mics?..... I've had a couple of recordings with the mbho's where basically the level on one of the mic's just "dropped off a cliff" during a show and after a few songs immediately popped back up to full "strength"..... don't know if vibrations caused it or not, but I'm figuring that something is loose, or that there's a short, somewhere in the chain.....

[ScoobieKW]

Back home, I check out the WAV file of the support band and, sure enough, it shows the right channel starting out as almost non-existent and then steadily getting louder until about 16 minutes into the show, by which time the signal has reached full strength.

Folks, a shorted wire / bad cable won't give the smooth increase in levels reported. It's most likely a bad component in the unit. Normally I'd suggest the manufacturer's service department, but as it's been modded, I don't know. Have you spoken to Oade Brothers?

[Phil Zone]

Maybe aliens? I swear they are after me 

[Fried Chicken Boy]

In your case, as the power to the microphone is changing smoothly, I'd suspect power supply / capacitor in the phantom power section.

I'm no electronics wizard but your issues, ianmacd, have similar symptoms to a wonky battery box I've been dealing with.  Jon at Naiant's long-distance diagnosis was that it was likely an intermittent fault or a leaky capacitor (thread is HERE).  As Scoobie and hi and lo surmise, it seems like the PMD661's phantom/mic powering components may be at fault. 

[trustthex]

I'm not a sparky, but that sounds like a slowly charging capacitor to me.   

[ianmacd]

Thank you for all of the replies, chaps.

All things considering, I'd rather the recorder be giving up the ghost than one of the microphones, so I do hope you're right that it's that. I haven't contacted OAD yet, because I'm waiting until I've ruled out the microphones as the source of the problem.

I'll post an update when I know more.

Thanks again.

[bombdiggity]

My Roland R-05 recently decided to go one channel on my line in for no apparent reason.  Have not diagnosed why yet but got a new recorder and all is well.  I'd tend to think it is there.  Your Schoeps are pretty new so not likely any issues there.  There's an outside chance it might be cabling but I'd agree with others here that gradually going from nothing to full signal strongly implicates the preamp.