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Author Topic: Right channel slowly losing volume  (Read 1044 times)

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Offline dunebug81

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Right channel slowly losing volume
« on: September 10, 2021, 11:51:50 AM »
I went to a show this weekend and taped 3 bands (see attached picture of wav form).  You can see that around the half hour mark of the 2nd recording the bottom channel starts to gradually get much lower and in the 3rd recording its like i turned down the gain in the right channel by 10db.

I use a set of DPA4061s with an MMA6000 into a Sony PCM-M10 recorder.  The MMA had a brand new Duracell 9V put in just before the show and PCM-M10 had some new Duracells that only had about an hour or so on them.  No settings were changed between sets and I only slightly adjusted the input down from 6 to 5 on the recorder when the 3rd band came on as they were a bit louder since they were the headliner.  I run a +7.5db on both channels on the MMA with the bass filter off.

Any idea why my right channel is slowly turning down?  I've had this MMA since 2006 and the mics were replaced / repaired about 6 years ago after my dog chewed up the cords.

**edit**. I’m using a Sony PCM M10 solid state recorder, not the M1 DAT recorder.
« Last Edit: September 10, 2021, 01:13:50 PM by dunebug81 »
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Offline seethreepo

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Re: Right channel slowly losing volume
« Reply #1 on: September 10, 2021, 11:58:15 AM »
pretty sure this is a known issue with the dpa 40XX series.  Especially if this was originally a used set from Broadway or similar.  IF they were factory  new DPA sourced  then disregard and maybe try cleaning your connections and of course try and replicate the results.
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Offline dunebug81

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Re: Right channel slowly losing volume
« Reply #2 on: September 10, 2021, 12:35:58 PM »
pretty sure this is a known issue with the dpa 40XX series.  Especially if this was originally a used set from Broadway or similar.  IF they were factory  new DPA sourced  then disregard and maybe try cleaning your connections and of course try and replicate the results.

Both were new from DPA and one has since been replaced after the dog got a hold of one a few years ago.

I think it has something to do with the MMA. No reason for that one channel to drop over the course of 30 min. A mic wouldn’t just lose sensitivity after working fine for an hour.
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Offline vanark

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Re: Right channel slowly losing volume
« Reply #3 on: September 10, 2021, 12:42:58 PM »
Perhaps low voltage in the battery, even if new. Sometimes that happens.
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Offline dunebug81

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Re: Right channel slowly losing volume
« Reply #4 on: September 10, 2021, 12:54:29 PM »
Perhaps low voltage in the battery, even if new. Sometimes that happens.

That’s a thought. I usually use Duracell Procell 9v but I forgot to replace it before I left the house and stopped by the CVS to pick up some new ones. I guess I can put in the usual Procell and see how it goes.
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Offline nulldogmas

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Re: Right channel slowly losing volume
« Reply #5 on: September 11, 2021, 01:06:25 AM »
This exact thing happened to me tonight, with an M10 and a Church Ugly battery box, and new batteries. Weirdly, if I unplugged the cable from the M10 mic in and replugged it, it seemed to fix itself, but then would fade again.

(That's all from monitoring it live; I haven't checked the waveform yet, as it's 1 am and I just got home.)

This has happened to me a couple of times before, and I blamed a dying battery at the time. But this one is just weird.

Offline nulldogmas

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Re: Right channel slowly losing volume
« Reply #6 on: September 11, 2021, 11:10:32 AM »
This exact thing happened to me tonight, with an M10 and a Church Ugly battery box, and new batteries. Weirdly, if I unplugged the cable from the M10 mic in and replugged it, it seemed to fix itself, but then would fade again.

Here's the waveform from last night (zoomed in at 2x to make the loss of volume in the R channel easier to see; the L channel isn't actually clipping). You can spot the momentary jumps in volume when I unplugged and replugged the cable, and how the R channel volume was (mostly) restored to full volume after that, then abruptly faded again 30-60 minutes later.

« Last Edit: September 11, 2021, 11:12:47 AM by nulldogmas »

Offline dunebug81

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Re: Right channel slowly losing volume
« Reply #7 on: September 11, 2021, 11:15:42 AM »
This exact thing happened to me tonight, with an M10 and a Church Ugly battery box, and new batteries. Weirdly, if I unplugged the cable from the M10 mic in and replugged it, it seemed to fix itself, but then would fade again.

Here's the waveform from last night (zoomed in at 2x to make the loss of volume in the R channel easier to see; the L channel isn't actually clipping). You can spot the momentary jumps in volume when I unplugged and replugged the cable, and how the R channel volume was (mostly) restored to full volume after that, then abruptly faded again 30-60 minutes later.

So do you think it’s the recorder or the battery box?
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Offline nulldogmas

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Re: Right channel slowly losing volume
« Reply #8 on: September 11, 2021, 11:54:41 AM »

So do you think it’s the recorder or the battery box?

I would guess it's the recorder, and something is up with the preamp fading out on one channel. But that's solely a guess — I'll need to do more tests swapping out different recorders and battery boxes to say more.

Offline admkrk

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Re: Right channel slowly losing volume
« Reply #9 on: September 11, 2021, 03:03:11 PM »
Just swap channels. If it stays on the right - deck, if it moves to the left - mics.
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Offline nulldogmas

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Re: Right channel slowly losing volume
« Reply #10 on: September 11, 2021, 05:45:00 PM »
Just swap channels. If it stays on the right - deck, if it moves to the left - mics.

Single 1/8" stereo plug, so that's not happening.

Offline jefflester

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Re: Right channel slowly losing volume
« Reply #11 on: September 11, 2021, 06:22:09 PM »
Just swap channels. If it stays on the right - deck, if it moves to the left - mics.

Single 1/8" stereo plug, so that's not happening.
You could use a pair of 1/8" to RCA adapters back-to-back to facilitate the troubleshooting.
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Offline nulldogmas

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Re: Right channel slowly losing volume
« Reply #12 on: September 11, 2021, 08:48:44 PM »
Just swap channels. If it stays on the right - deck, if it moves to the left - mics.

Single 1/8" stereo plug, so that's not happening.
You could use a pair of 1/8" to RCA adapters back-to-back to facilitate the troubleshooting.

Hmm, that's an idea.

Or I can just swap out different mics, battery boxes, and recorders and see where the problem recurs.

Offline Gutbucket

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Re: Right channel slowly losing volume
« Reply #13 on: September 13, 2021, 10:28:15 AM »
I think it has something to do with the MMA. No reason for that one channel to drop over the course of 30 min. A mic wouldn’t just lose sensitivity after working fine for an hour.

This exact thing happened to me tonight, with an M10 and a Church Ugly battery box, and new batteries. Weirdly, if I unplugged the cable from the M10 mic in and replugged it, it seemed to fix itself, but then would fade again.

(That's all from monitoring it live; I haven't checked the waveform yet, as it's 1 am and I just got home.)

This has happened to me a couple of times before, and I blamed a dying battery at the time. But this one is just weird.

A sensitivity drop like this IS a somewhat common problem phenomena with these mics after many years of use, but when that happens the change in sensitivity does not continue to vary up and down over time.  I think that failure mode is related to the loss of the quasi-permanent charge of the dielectric material that provides polarisation in these back electret type microphones.  In this case the sensitivity drop is permanent and will not vary.  The mic should perform the same when swapped from one side to the other, if batteries are changed or if used in another rig.

My first suspicion in these cases is the state of charge of the 9V battery in the preamps.  Easiest way to check this with certainty is to measure voltage across the battery before and after the recording session with the battery remaining in circuit and powering the preamp.  The thin test leads of a voltmeter will reach the battery terminals without first disconnecting the battery from the battery clip of the MMA6000 or CA preamp.  With the load removed, a spent battery will tend to quickly return to a higher nominal static voltage, yet cannot and will not continue to hold that voltage if placed under load again.  However, the initial recovery may be sufficient to temporarily bring the sensitivity back up for a brief time.

I've experienced both these things over the years.  Check batteries first.
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Offline Cedric

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Re: Right channel slowly losing volume
« Reply #14 on: September 13, 2021, 12:57:25 PM »
Hi,

I had the same problem this year with my Sony M10 on long run sessions (typically 24 hours unattended nature recordings), can't remember if it was the left or the right side.
The sound would vanish completely, and then come back again
The problem is internal as I don't use external mics with my M10:
- Fisrt because the internal mics are good enough (read: excellent!) for my needs.
- Second because the mic jack input is dead on this unit.
I turned the limiter off, the problem didn't happen again since then.
In my case, the issue might have been excess of humidity as well...

Cedric

 

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