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Author Topic: mystery volume fade (M10, UBB, CA-14 mics)  (Read 1751 times)

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Offline nulldogmas

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mystery volume fade (M10, UBB, CA-14 mics)
« on: December 17, 2017, 04:02:13 PM »
So this is a puzzler: Twice now I've had, during the course of a show, one channel slowly and inexorably decline in levels by about 20 dB as time passes. The second time, first one channel faded, then the other followed an hour or so later. Nothing changes about the sound quality otherwise — it's as if I were slowly turning down the gain on one channel, except the M10 doesn't have the ability to do that for only one channel.

Chain in question is CA-14 cardioid mics > UBB > M10 mic input. The same setup worked fine at other times before and after the problem nights. I checked the 9-volt battery and it seems fine.

Any guesses, anyone? Or anything I can do to help diagnose it?

Offline ilduclo

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #1 on: December 17, 2017, 04:05:11 PM »
if you have other gear, you can sub that in the chain and test for it, but since it's not consistent, it might be tough. The m10 can be tested alone using the onboard mics and if you have another bb or a preamp, you can check that. good luck!

Offline nulldogmas

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #2 on: December 17, 2017, 08:09:57 PM »
if you have other gear, you can sub that in the chain and test for it, but since it's not consistent, it might be tough. The m10 can be tested alone using the onboard mics and if you have another bb or a preamp, you can check that. good luck!

Yep, trying a different M10 tonight, in case it's something in the onboard preamp. If I keep testing iterations, I should have this figured out by the year 2030.

Offline nulldogmas

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #3 on: December 18, 2017, 12:36:52 PM »
No problems last night with a different recorder, but then, the last time this happened there were no problems the next night without changing recorders.

Anyone ever had something like this happen to them? Or know enough about electronics to theorize which link in the chain is most likely the culprit?

Offline bombdiggity

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #4 on: December 18, 2017, 12:47:07 PM »
I'd suspect the UBB in the chain.  That would be what is providing the levels.  With it being a rare occurrence seems hard to determine. 
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Offline rocksuitcase

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #5 on: December 18, 2017, 03:19:10 PM »
I'd suspect the UBB in the chain.  That would be what is providing the levels.  With it being a rare occurrence seems hard to determine.
I would suspect the UBB also. And/or the battery or battery type. Are you using rechargaeables etc. The symptom sounds like the old days when a cassette deck batteries would be dying which would do odd things later heard on the tape-fuzziness, level dropouts etc before the deck would stop turning the tape.
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Offline Gutbucket

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #6 on: December 18, 2017, 05:57:46 PM »
I checked the 9-volt battery and it seems fine.

Check its voltage afterwards but while still under load if possible.  Should be easily doable with multimeter leads and a UBB where you can get to the battery contacts while in use.  That's exposed failing NiMH 9Vs for me in the past several times, each of which showed still-good voltage when measured in an open circuit condition yet the voltage dropped precipitously once placed under load.

That behavior threw me for a while the first time around, checking voltage of the batteries afterwards outside of the circuit, getting nominally good readings, and scratching my head. 
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Offline nulldogmas

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #7 on: December 18, 2017, 06:06:08 PM »
I'd suspect the UBB in the chain.  That would be what is providing the levels.  With it being a rare occurrence seems hard to determine.
I would suspect the UBB also. And/or the battery or battery type. Are you using rechargaeables etc. The symptom sounds like the old days when a cassette deck batteries would be dying which would do odd things later heard on the tape-fuzziness, level dropouts etc before the deck would stop turning the tape.

Plain old Duracell 9-volt. And if it were a voltage drop, I'd think the recording quality would suffer then, since the mics would be underpowered, but the sound is identical, just lower volume. Also, why would it only happen to one channel at a time?

I checked the 9-volt battery and it seems fine.

Check its voltage afterwards but while still under load if possible.  Should be easily doable with multimeter leads and a UBB where you can get to the battery contacts while in use.  That's exposed failing NiMH 9Vs for me in the past several times, each of which showed still-good voltage when measured in an open circuit condition yet the voltage dropped precipitously once placed under load.

That behavior threw me for a while the first time around, checking voltage of the batteries afterwards outside of the circuit, getting nominally good readings, and scratching my head.

That would be easily doable with a voltage meter if I had one. Guess I know what my next purchase will be...

Offline Gutbucket

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #8 on: December 18, 2017, 06:52:08 PM »
A cheapo voltmeter will work for simple voltage measurement.  I've even seen super cheapos for a buck at the dollar store.  A real battery tester should be designed put the battery under load to provide proper reading, but maybe not if its a cheapo.

Can't help with the mystery questions.  Good luck..
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Offline rocksuitcase

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #9 on: December 18, 2017, 09:50:30 PM »
I'd suspect the UBB in the chain.  That would be what is providing the levels.  With it being a rare occurrence seems hard to determine.
I would suspect the UBB also. And/or the battery or battery type. Are you using rechargaeables etc. The symptom sounds like the old days when a cassette deck batteries would be dying which would do odd things later heard on the tape-fuzziness, level dropouts etc before the deck would stop turning the tape.

Plain old Duracell 9-volt. And if it were a voltage drop, I'd think the recording quality would suffer then, since the mics would be underpowered, but the sound is identical, just lower volume. Also, why would it only happen to one channel at a time?
Yes, you make good troubleshooting points. Underpowering would affect sound quality and probably on both channels. Sorry for lame suggestion -  :o 
Gutbucket's advice seems the way to go.
music IS love

When you get confused, listen to the music play!

Mics:         AKG460|CK61|CK1|CK3|CK8|Beyer M 201E
Recorders:Marantz PMD661 OADE Concert mod; Tascam DR680 MKI

Offline nulldogmas

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #10 on: December 19, 2017, 02:38:37 PM »
Two nights of recording with the backup M10 (and a fresh 9-volt) and all is fine so far. Which means either one of those two was the problem, or it's just going to recur two months from now when I least expect it.

Thanks, all, for the moral support, anyway, which is genuinely appreciated. This one is looking even more puzzling than the Crazy Inverted Cable of 2016.

Offline Fried Chicken Boy

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #11 on: December 24, 2017, 03:15:18 PM »
Late to this thread, but glad to hear that your issue seems resolved. 

FWIW, I was going to jump on the "it's the battery box" wagon as well.  A few years ago I ran into the same issue that you described and the BB turned out to be the culprit.  Corresponded with Jon at Naiant (many thanks to him and the generosity with his time) and his long-distance diagnosis was a "leaking" capacitor in the BB; not leaking physically, but leaking current or voltage which is what was causing the volume drops.  A new battery box cleared up the problem immediately. 

Offline nulldogmas

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #12 on: December 24, 2017, 03:40:53 PM »

FWIW, I was going to jump on the "it's the battery box" wagon as well.  A few years ago I ran into the same issue that you described and the BB turned out to be the culprit.  Corresponded with Jon at Naiant (many thanks to him and the generosity with his time) and his long-distance diagnosis was a "leaking" capacitor in the BB; not leaking physically, but leaking current or voltage which is what was causing the volume drops.  A new battery box cleared up the problem immediately.

Interesting, since I've used the same battery box three times since with no problems. (Though also with a fresh battery.) Will post here if I get any more data points.

Offline Charlie Miller

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #13 on: December 27, 2017, 08:43:40 AM »
Absolutely sounds like it’s losing power. I had that happen with an AKG recently. Does the quality change or is it just volume?
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Offline nulldogmas

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #14 on: December 27, 2017, 11:01:20 AM »
Absolutely sounds like it’s losing power. I had that happen with an AKG recently. Does the quality change or is it just volume?

Just volume. If I amplify it in post it sounds seamless, though the noise floor rises.

With your AKG, did it lose power in just one channel at a time? That's the behavior that's puzzling me.

Offline Charlie Miller

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #15 on: December 28, 2017, 06:23:01 AM »
Absolutely sounds like it’s losing power. I had that happen with an AKG recently. Does the quality change or is it just volume?

Just volume. If I amplify it in post it sounds seamless, though the noise floor rises.

With your AKG, did it lose power in just one channel at a time? That's the behavior that's puzzling me.

It was just one mic on my end. May be a bad capsule.
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Offline nulldogmas

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #16 on: December 28, 2017, 10:41:24 AM »
It was just one mic on my end. May be a bad capsule.

Except then for me the other channel faded to match a couple of recording hours later, so it's not just affecting one mic.

I kind of want this to happen again so I can get more data, but I also don't want it to mess up another recording...

Offline Charlie Miller

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #17 on: December 28, 2017, 11:08:28 AM »
It was just one mic on my end. May be a bad capsule.

Except then for me the other channel faded to match a couple of recording hours later, so it's not just affecting one mic.

I kind of want this to happen again so I can get more data, but I also don't want it to mess up another recording...

Both mics? Gotta be a power issue. Something is draining the power
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Offline nulldogmas

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #18 on: December 28, 2017, 02:29:13 PM »
Both mics? Gotta be a power issue. Something is draining the power

Both mics, but one then the other, not both at the same time.

Offline icebox

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Re: mystery volume fade (M10, UBB, CA-14 mics)
« Reply #19 on: December 29, 2017, 07:25:26 AM »
No problems last night with a different recorder, but then, the last time this happened there were no problems the next night without changing recorders.

Anyone ever had something like this happen to them? Or know enough about electronics to theorize which link in the chain is most likely the culprit?
I've had this happen to me, with a CA9200 feeding CA-14s to an M-10, but the cause was a dying battery in the CA9200.  replacing the battery fixed the problem.  The first time it happened, it recorded a 30 min opener, then 70 minute main set, then faded out gradually during the first song of a 3 song encore, and couldn't figure out why.  Testing the unit after the show it seemed to be working fine again, but next time out, 2 openers recorded fine, then main set the last three songs lost because of the same issue.  My notes from that day show that I deduced it was a preamp issue, and changing the preamp battery before the next show fixed the problem.  With me the problem was both mics at the same time. 

 

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