home build U47 trouble

I built a U47 a few years ago using an ef14 a cinemag TX and a peluso capsule and it's been great but recently it's developed noise which builds up to a pop crack and squeal that starts at a high pitch and drops to a low pitch.before I rip into it I was hoping someone might have some clues to what it could be....I don't want to be changing every cap etc
Thanks in advance for any help
Lance :thumb:

rodabod has a point there. I have experienced the sqeeky noisy wave hiss sounds from problematic capsules as well.

still check your voltages, you may have done this already.

I've had mics that do this when the capsule has been dirty and they got moist - sometimes just a thump, but also an oscillation like effect.

Can you get the same effect to occur by breathing deeply onto the capsule?

[quote author="rodabod"]Can you get the same effect to occur by breathing deeply onto the capsule?[/quote]
+1

Keith

Hi Lance,
yep, does sound like the capsule's a little dirty :wink:
Any pics of the U47 , you'd like to share ?

Regards,
Steve :thumb:

Thanks guys
I think you're all are spot on there
I was thinking it was just damp/moist but after a while of warming up it can still be doing it....so does this mean the capsule is dirty and I need to clean it?.....and is it possible I can clean it myself without damaging it?
when you say check the voltages..do you mean fluctuations in the voltage or different voltages than they should be?
As for pictures...I think I'd scare you :shock: it's a bit of a frankenstein....built into a B&Q square alloy chair leg..

thanks
Lance

B&Q... "Bodge-it & Quit"

A freshly oven-dried silica gel pouch inside a plastic bag with the mic. -Then leave it in a warm place sealed up for a day or three, then see if it's stopped.

Otherwise make sure that there's NO finger grease on ANY of the wires, components, etc between the capsule and the grid.

Keith

Bring on the pics , Lance-san :thumb:

There's some good posts , if you do a search on capsule cleaning,
Keith (SSLTech), and myself, are amongst a few, who have previously been through it :wink:

Just take your time, and be as feather light as you can be !
Very, Very fragile.......
I'm sure you can pull it off tho :thumb:

Steve

B&Q Chair leg - now thats inspiration !, I bet you were off in a dream world, as the missus dragged you around looking at kitchens n stuff. :roll:

AS I recall , without special ultra sonic cleaning equipment and moisture evaporation and contaminates (dust)is the issue.

I cleaned a couple of my M7/KK47 capsules and they did sound much nicer afterwards. Although ,on one there was a 1/4" of m7 diapham on one side that came unglued due to age so that side needless to say needs service. other side sounded great. I used distilled water and a plastic lab style water squirter. Let the capsule air dry for a few hours near sunlight, not direct sunlight, and works fine.

If your capsule is older , take a magnifiying glass and inspect the surface of the diaphram for any irregularity before applying distilled water wash.
One of my KK87 capsules had two weird pin holes in it, very small, they looked like black specs of dirt. Distilled water bath would not help anything in this case eventhough the caspule was slightly dirty.

[quote author="Kid Squid"]

B&Q Chair leg - now thats inspiration!, I bet you were off in a dream world, as the missus dragged you around looking at kitchens n stuff. :roll:[/quote]

Funnily enough, my first G7 was built into a round desk/bench leg, also from B&Q. It was steel, a bugger to cut and now I'm embarrassed to luck at it. I also tried one in a cocktail shaker. And I got two copper candlesticks from habitat recently...

May be it's a bit late, but I just finished building a similar mic this afternoon, and I experienced the same kind of problem: random noises
The question was: is it the capsule or the tube?
What I did was disconnecting the capsule and replace it by a 47pF cap...
Quick and easy and it tells you where to search...
In my case the noises were still there, so I changed the tube.
The best thing is that you can still test the tube amplification by gently tap on the cap...

axel

Yes, +1 to humidity.

Put the mic in silica gel.

Dan.-

And if you can put a original neumann capsule or a good clone capsule on it and tell me what you and your customers think about this!.

[quote author="mad.ax"]May be it's a bit late, but I just finished building a similar mic this afternoon, and I experienced the same kind of problem: random noises
The question was: is it the capsule or the tube?
What I did was disconnecting the capsule and replace it by a 47pF cap...
Quick and easy and it tells you where to search...
In my case the noises were still there, so I changed the tube.
The best thing is that you can still test the tube amplification by gently tap on the cap...

axel[/quote]

You have constructed completely the microphone, including a capsule? For the big membrane at you the capacitance of a capsule is small. Probably, too big backlash between a membrane and a motionless electrode of a capsule, and from it there can be also noise. What diameter of your membrane?

He did say that he was using a Peluso capsule, so no.. he didn't build the capsule himself.

Keith

i saw a lot of dirty capsules in DIY mics over the time.
one reason for that lies in using very wide meshes for the grille, or/and taking out the inner mesh layer.

cleaning a not-so-old mylar membraned capsule should not be very difficult. the gold adheres much better than on the old m7 pvc diaphragms.

but your oscillation might originate from something else, i remember i heard the sound you described in a diy microphone - i just cannot remember what it was...