Topic: Overwhelming bass or mic overloaded? UPDATE: PROBLEM SOLVED!

[greppson]

updated the first post with some waveforms and audio samples.

[George]

show starts out fine, sounds fine, but then the left channel just goes nuts as the shoe goes on and basically drops out as the show goes on.

doesn't make any sense cause i just had the mics fixed by audix about 2 months ago and i just used them 2 weekends ago to tape the same band with no problems.

and it's the advanced concert mod 671 done by oade.

I had the same thing happen to me back in June at a Nelly Furtado concert.  The right channel had the same exact symptoms.  Ran hot, then dropped out, I clicked up the volume on the mma6000 and I eventually brickwalled the right channel about half way into the show. 

Afterwards, I tried the same 9V with the mma6000 at a friends house (I was taping him playing guitar and piano for a school project) and the same symptoms popped up.  I switched to a new 9V and all was well.  Maybe a battery (or more) were just "bad" for you?

[greppson]

I have a hard time thinking it is the batteries though as they were brand new...

[greppson]

couldn't have been too long on the shelf as they had 3 or 4 pegs and these were the some of the last few packs.

did some testing the other night and found that one channel appeared to increase in gain throughout the recording until it was very noticeable. that was on batt power, i'm going to try it again but this time plugged into the wall and see if i get the same result. lastly, i'll probably give a 9v batt a try to see if that does the same thing.

from there, it will be trying the RCA ins.

[SmokinJoe]

What does Doug have to say about all this?  If it's new, then that means there are a bunch of new components in there.  Who knows if a resister that cost pennies is changing with it gets hot....

Here are some suggested "living room tests"?
- run your stereo line out > 671 line in, and see how that sounds over time.  Put the same song on "repeat" for 2 hours.
   When you pull that waveform up on the computer it should be even and cyclical, not creeping up.
- I have some attenuator cables I could loan you... designed for running line levels into the XLRs on an AD-20...
  Then you could run line out of your stereo > attenuators > mic XLRs.  Repeat above test.  This is using 671 XLRs components, but not phantom power yet.
- Set your rig up, mics and all.  Blast stereo speakers > mics > rig, again, same boring song and see how the waveform looks.
- Let it all cool off.  Find a voltmeter, and run the rig (sound isn't important).  Check over time to if the 48VDC phantom power drops off when it warms up.
  If the voltage drops off, that would affect your mic's headroom.  You can probably test this with a particular resistor instead of real mics... not sure what value.

I suspect at that point you will have narrowed it down a bit.  Good luck.

[greppson]

Update.

I FINALLY had a night where I could set it up and let it run for a couple hours. This time, I tried it with plugged in power, phantom on, and the thing ran fine.

So, even though they are new batts (I've now got 16 batts that should be working no problem), it has to be something related to that. Was going to try the RCAs, but all I'm getting with those is a buzz, probably cause I've got different adapters and cords between the mics and the box.

In any event, Doug said he thought it MIGHT be a record level control. He said they can sometimes lose their ground. So, I've sent another email off to him and hopefully we can figure something out from there.

I just want to get the darn thing working so I can sell my 2 JB3s and w+ mod UA5. :lol

[greppson]

UPDATE 10/17/2007

So, I got a new battery holder from marantz and it seemed to solve the problem. The only real problem I am having now is with it shutting down. I think some of the contacts are not working all the way.

Any 671 users have this problem before?