Topic: more wacky wav forms -- updated 1/23 with test results

[jeromejello]

i hate abnormal wav forms!

usually it is just some wierd undulation that i can live with because it seems to be only an appearance thing, and not a detectable sonic thing...

this time, not so lucky...

i have about 4 seconds on one channel that is fubar... that same channel has some additional abnormalities later on, with some audible click.  the big one - the stand may have been kicked... but that wouldnt explain away the other smaller occurrances.

any idea what could cause this? (see attached pictures)

i think i will leave the tiny warts alone, but the 4 sec chunk i will probably just swap the other channel in there.

/this is why i should listen to recordings within 48 hours AND mark those mics ever so gently... (all i know its on the one channel, but i have no idea which mic it was...)
//should be some fun trouble shooting...    its like flying blind in the dark

[jhirte]

bad mic cable maybe?

[darktrain]

what was the rig, had this happen with a bad 1/8 jack from  a battery box

[jeromejello]

what was the rig, had this happen with a bad 1/8 jack from  a battery box

bad mic cable maybe?

the rig was 461 > darktrain's cables > 722

i still need some time to play with it to find out where and what is the problem... fwiw, i dont think its the cables, unless it was a shielding issue, which i dont think it was.... i had that already on my black crowes recording.

[rsimms3]

I had the same sort of thing happen to me a while back.  I finally decided I didn't have the cable plugged in all the way into my UA5.  They are shorties so there is no lock on them and I had just pulled them out to make an adjustment.  It was very random seeming where it showed up.  My other thought was the battery was wonky, it was a RC battery from Radioshack.  I know make sure my cables are plugged all the way into my UA5 when I am starting my recordings. 

[jeromejello]

damnit... had a huge ugly gremlin tonight... pretty much fucked the whole thing up today.... way to start off 2009.

same channel (left) is showing issues.  the bodies are different, i do not know if the cap is the same from the other incident, and the cable is still the same (that is to say it was still the same 'left' cable plugged in.  obviously i will have to set up in house tomorrow and do some cable/cap/channel swapping, but take a look at these beauties.  i tried to give a zoomed out as well as a zoomed in set of shots.

the consistent thing is that it is intermittent and the wav form is totally fucked... i knew when i first started recording that it wasn't right because the meter was all solid and not showing any dynamic.

just by looking... anyone got any ideas what makes this happen?  if i had to guess, i am leaning to either a bad connection in the cable (hopefully, since it wont cost as much to fix or replace) or a blown input on the 722 

any help would be appreciated.

[jeromejello]

anyone seen these new wav forms before?  it sounds like a grounding issue, but i dont know anything...

[rsimms3]

Well, if the right channel has been working I would say start testing and eliminating things, see if you can reproduce it.  First thing I would do is use the cable you have good results with on the right channel on the left channel to check for cable issue and connection issue in the 702.  It is a consistent modulation in that one picture, not so much a bad connection like when the cable is moved and you hear a pop.

[SmokinJoe]

I had some vaguely similar problems with my LSD2, and they ended up replacing the caps.  I'm not saying for sure that is your problem, but I had similar unpredictable waveforms.  A capsule is a diaphragm and backing plate with 48V charge across them, and the sound pressure effects this capacitance (bad explanation, but bear with me).  If there is a tiny piece of dust or some moisture in between those plates things like this will happen... at least that is the explanation I got from the Studio Projects repair folks.

In your case, it's going to be trial and error, and swapping.
a) Setup in living room and reproduce problem.
b) Swap mics where they plug into cables (swap Left and Right), wait for it to happen again. 
c) If it moved from L > R then it must be in mic body or capsule.  In that case swap capsules (Left and Right) and see if it moves with the cap, or stays with the body.
d) If it didn't move after swapping the mics at (b), then it must be cable/preamp.  Swap cables and see if it moves. If it does, it's cables, if it doesn't it's preamp...

Hopefully the problem isn't horribly intermittent and you don't have to wait for days for it to happen again.

[Swampy]

Ya, when I had a cap go bad in one of my ADK TLs, my waveforms looked very similar. Have the problems always been with one pair of mics? See if you can't reproduce it with other mics...

[barren4]

Hate to say it but when I had waveforms that looked like om glitch 1, it was a(can't remember right now) ck61 or ck63 capsule.  According to Richard Land who fixed it, the diaphram had lost it's seal allowing moisture/humidity to get between it and the backplate.   The moisture allowed the diaphram to intermittently short to the back plate.

[jeromejello]

well, i have finally had a free moment to fuck around with the mics and unfortunately, i think i found the problem... a bad cap 

the common element was one of the caps in all the tests that had fucked up shit... (granted i havent looked at the wav's yet, but i was seeing the crazy intermittent peaking on the meters).

i even swapped out to the 63's and had no issues replicating the same tests.

so... where do i send the cap off to?  how much would i possibly be looking at for repairs?  is it best to send both caps so whomever can get them both up to spec?

thanks in advance kind folks of ts.com

[barren4]

Did some searching and copied this from a post:

contact Richard Land at Land Audio
he is AKG's only out of warranty service tech
I had him refurbish my 451EBs last year
he has very fast turn around, but he isn't cheap
so you may want to keep looking for another one

Richard Land
Land Audio Services
615-338-4443

http://taperssection.com/index.php/topic,102750.msg1369634.html#msg1369634

[TNJazz]

http://www.akgmicrepair.com/
Email:  landaudio@comcast.net

[jeromejello]

http://www.akgmicrepair.com/
Email:  landaudio@comcast.net

thanks to dirk (and everyone else), i just sent and email to Richard at Land Audio.