Dr. Richard Edward Horner ([info]mechanyx) wrote,
@ 2008-10-19 21:00:00
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If at first you don't succeed, get a drill
A couple weeks ago, I went up to Boston to record the wonderful Julia Torgovitskaya aka [info]juliatorgo at Tufts' exceptional new Distler Performance Hall in the Granoff Music Center. I use an incredibly simple, cheap and effective rig to record live to two which consists of 2 AKG C 414 B-XLS microphones, 1 Aphex 207D and an M Audio Microtrack. This allows for pretty transparent and noiseless stereo 24/96 recording for around $2000 which is ideally suited to classical or anything else where you want to capture the true sound that needs no tonal manipulation.

Well, after more than an hour of recording, we were onto Monica's Waltz from Menotti's The Medium (which I must confess I am not fond of) and I started getting intermittent pops on the left channel. I had no idea why as I had never had any problems with this rig and there didn't seem to be any pattern to the pops or correlation with anything we were doing. My only guesses were that the tube in the Aphex was going or the power in the room was problematic as the readout on my power conditioner was up around 122 volts. Thankfully, we managed to get the takes we needed.

A few days later at home I plugged my 207D in and just watched it for a few hours. Sure enough, it eventually started popping randomly on channel 1 despite the fact that nothing was connected to it. I think the problem was that this unit has no cooling and being over volt and racked next to other gear was a recipe for disaster. I opened the unit up to make sure though.

What a mistake that was.

As much as I love this unit, they definitely skimped on the chassis. I have no idea how two of the top plate screws were held in place previously as they do not fit the threads. I can only assume that the less than precisely placed holes on the plate clamped the screws into place by not lining up with the threaded sockets. Well, I think I am correct as one of the screw heads got separated from its body when I forced it in with my Dewalt. This caused the face of the unit to bow rendering the spring on the digital rate selector inoperable.

So now I have to get this screw body out that is not extending beyond the chassis. After about 30 seconds of attempting to rotate it with a false head made out of putty, I opted to instead destroy the plate around the threaded socket with my drill.



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[info]captain_bland
2008-10-20 02:25 am UTC (link)
I'm going to assume that the screw was a pretty small one. Are you familiar with screw extractors (ez-outs)? Probably better for bigger screws, but very useful for just such an occasion.

Another option is to use Krazy Glue. Put a tiny dab on the sheared-off screw and tack on a similarly sized piece of metal. Wait for it to dry and just unscrew!

That's strange about the popping. I'd be interested to know what the root cause is once you've finished your detective work.

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[info]mechanyx
2008-10-20 02:30 am UTC (link)
Yeah, it was a 2.5mm shaft and probably too small for an ez-out.

Glue wasn't really an option here because the cross section was so small that I would have been just as likely to glue the head onto the surface as I would've been to the screw shaft.

I'm almost positive the over voltage caused either a heat or plate voltage problem with the 12AT7/ECC81 in this thing.

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[info]freekofnature
2008-10-20 03:25 pm UTC (link)
This is far from a "simple" setup!
Where did you get those condenser mics!!! They must make Yuliya sound awesome (and warm!)


My guess is either:
1) Vacuum tube going, replace in matched pairs (both stereo sides of the amp)
2) Static buildup in the chassis. Check the grounding circuits of the cables with an Ohm meter.

Btw, check the "fire-bottles" in the mic pre-amps too!! And make sure those are properly grounded as well!

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[info]mechanyx
2008-10-20 03:35 pm UTC (link)
It's EXTREMELY simple considering that my studio setup was based around a Yamaha 02R96 and my old live rig used a Yamaha 01X.

As for your guesses, there is no amp here. There is only a single tube in the Aphex which is the mic pre. The static buildup theory is good thought though. I had swapped cables though.

The AKG C 414 B-XLSes are widely available. Most engineers dislike transparent gear because they primarily capture sound sources that sound like shit and therefore need a lot of help - i.e. Marshall stacks or singers who can't sing very well.

That hall was really out of control though as it was super wet (most halls are wetter when they are new). We need to record again so I can do it right now that I know the problems that are gonna come up in post.

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[info]freekofnature
2008-10-20 06:31 pm UTC (link)
It may not be your equipment.
Take a VTVM or similar and check the neutral-to-ground of the power receptacles your stuff is plugged into. If there is ANY resistance, then that is most likely the source of phantom static and/or electric charge of one type or another build-up in your equipment.

(as well as being incredibly unsafe for the performers, as well as tech staff)

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[info]mechanyx
2008-10-20 06:52 pm UTC (link)
Well, I can't do that because I'm 200 miles away but I know for a fact the problem is not localized to the venue because I was able to reproduce it in my living room.

"A few days later at home I plugged my 207D in and just watched it for a few hours. Sure enough, it eventually started popping..."

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[info]freekofnature
2008-10-21 09:49 pm UTC (link)
Check the power cable's ground in the 207D for continuity.

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[info]freekofnature
2008-10-21 09:51 pm UTC (link)
You know what, you may have a burned out capacitor and/or a shorted out resistor in the mic's circuitry. Check the resistors and capacitors with a test meter.

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[info]mechanyx
2008-10-21 09:53 pm UTC (link)
I was able to reproduce the error with a different power cable with NOTHING hooked upto the 207D so it's not the power cable and it's not the mics.

I'm telling you, over volt caused excessive heat and a lack of ventilation exacerbated the problem.

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[info]freekofnature
2008-10-21 10:10 pm UTC (link)
Ummm, actually, if that's the case, it's a send-back-to-AKG type of repair...

Those FET's are really really sensitive and fragile electronically

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[info]mechanyx
2008-10-21 10:13 pm UTC (link)
This has nothing to do with the AKGs. The AKGs are fine. The problem was with the Aphex 207D.

I don't have a warranty as I got the unit second hand for a great price. Furthermore, they would probably be hesitant to service my now modded one :)

Have you not been sleeping or is something wrong? I don't mean that as an insult or to be rude or anything. You're just usually very on the ball and you seem to be very not on the ball in this thread and it has me somewhat concerned.

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[info]freekofnature
2008-10-22 05:42 pm UTC (link)
Damn, you are prescient!
Yeah, I am back in smoky So. Cal and a bit disoriented after all the tumult of back home and working non-stop on the LHC and Europe and everything...
The Santa Ana's are shriveling up my brain and my LJ skills have gone to pot...

I need a vacation! (What is this "vacation" thingy of which you speak???) aanndd there is a mob of students here that want to get into my getting into leading a precept, It's the middle of the semester and they want me to just jump right into it on a moments notice!!!
And the fiancé wants his Fiancé BACK too, has a whole round of social events with his peers all scheduled for the Halloween season that we are expected to attend and HOST too!!! My poor car needs a brake job (funny sounds when I hit the pedal!) and new tyres (Back to Costco for a Quad of Michelin's and I don't have the time to drop the car off at the mechanics for a brake job & then a day at Costco (and there is no realistic public transportation around here anyway)
--I may be able to borrow a friends spare Viper for a couple days however, she's working the runway in Milano... (that thing doesn't get Miles per Gallon, it gets Gallons per Mile!)
The apartment has been turned into a mass disaster scene of a bachelor pad, with more empty soda and beer cans around than I have ever seen before, and a totally empty 'fridg and pantry... *sigh* I have a lot of work to do...
AND I have another Journal article due! The editor is screaming like a hungry two month old, AND my dissertation needs a significant input of research work and redaction time!!! My advisor is e-mailing me weekly, and sounds concerned! I need to steal a few dozen hours from the future sometime-where!!

yeah, bitch, bitch, bitch, thanx for putting up with my angst! I'll compartmentalize and figure it all out somehow...

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[info]mechanyx
2008-10-22 05:53 pm UTC (link)
I ask you to recall our talk about me remembering the future :) lol

My philosophy is that we should do the things that only we can do. Anything else you should just pay someone to do. If I were in your situation, I would pay someone to clean the apartment, go grocery shopping and take care of the car. You don't need to borrow a car. You can just rent one. You need to write your article, work on your dissertation and tend to your fiancé.

Here's something to look forward to. When I move to Southern California, we'll hang out. OK? :)

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[info]freekofnature
2008-10-22 10:46 pm UTC (link)
Sounds great,
But I may wind up in Camarillo (Mental "Health" Institution) by that time, if I don't deal successfully with this...

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[info]freekofnature
2008-10-23 10:03 pm UTC (link)
OMG!!!

I finally got a lot of sleep last night - 10+ hours and am in much much better shape!

It was jet-lag, an awful awful brain wasting case of accumulated jet-lag!
I will be spending as much time outdoors as physically possible the next few days to reset the internal biorhythm clock...

I gotta figure out how to use the D-alpha-tocopherols to avoid this from happening the next time I travel across timezones. I've done it a million times before but it's never been this bad before!! I must be getting old(er).

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[info]mechanyx
2008-10-23 10:07 pm UTC (link)
I'm glad you're feeling better.

For the longest time, I thought jet lag was a made up excuse for like being hung over until recently I learned that there is actually a purported cause for it.

I've never experienced any sort of jet lag. Then again, I used to not sleep so...

I am getting old though.

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