Can mic capsules be recoated

[spiders]

Hello again friends. I have been going down a rabbit hole on old Sony Mics, and today a reportedly broken C37Fet showed up at my door. It uses the same capsule as the c37a/C38b
The mic actually does work, but noisily with quite low output.It appears that nearly all the gold is missing from the capsule. What do I do about this?
I thank you all in advance for your sage wisdom

 

[bremusound]

Drefahlaudio seems to be able to do that

http://www.drefahlaudio.com/mic/1_gallery.html

 

[spiders]

Hi, thank you so much for your reply. I have come across them in my googling . I’m wondering if anyone if anyone in the USA does this. I’d imagine this is out of the realm of normal DIY stuff. Seeing the absence of the gold did get me wondering about how it gets on there in the first place, and the different schemes to accomplish this goal

 

[Tim Campbell]

Well Sony used to offer the membrane as a spare part for many years. The stretched membrane came glued to a brass or pcb ring. You put it in the capsule and tuned it in place. Most techs offering remembraning capsules could repair this.

A batch that I repaired not so long ago.

 

[kingkorg]

Hi, thank you so much for your reply. I have come across them in my googling . I’m wondering if anyone if anyone in the USA does this. I’d imagine this is out of the realm of normal DIY stuff. Seeing the absence of the gold did get me wondering about how it gets on there in the first place, and the different schemes to accomplish this goal

http://www.10000cows.com/deposition_system.htm

 

[Tim Campbell]

my setup

 

[Tim Campbell]

Here is one on my bench right this minute. A client sent it without a fault report. I am using a Rode NT2 as an amplifier. The capsule measures perfectly but has lost a bit of gold.

By the way these capsules have a lower output and might be considered noisy.

 

[Philbo King]

I've seen youtube videos of people doing it in home setups. You basically need a high vacuum chamber and a way to heat the gold inside it into vapor. Expensive (requires high purity gold and lots of energy) and time consuming (to do trial runs getting the process variables perfected).

 

[spiders]

This stuff is making my day! King korg that setup is super cool. Tim Campbell, thanks so much for replying. You are the ultimate wizard of mic capsules and your input is beyond appreciated. The link showing your setup is wonderful. I sort of expected to see a tiny Darth Vader in there when the lid lifted up.
I’m actually quite familiar with the behavior of this type of capsule: I had a pair of c37a’s on loan to me for several years used them extensively. They are certainly low output and perhaps noisy. The capsule I’m dealing with right now is far past acceptable noise/output levels. FWIW it still actually sounds pretty good. It’s certainly possible that there are problems in the circuit, but the complete lack of gold leads me to suspect the capsule.
To leave my capsule behind for a moment, in general is it possible to recoat a membrane or must they always be replaced? Also, I’m wondering how the gold leaves a capsule in the first place. I know it could be “cleaned” off, but I wonder what some of the other ways are. I don’t suspect foul play in my situation, I think the gold just came off somehow.
Once again a gigantic thank you to all for the replies.

 

[granger.frederic]

my setup

Hi Tim, Am i wrong, thermal evaporation coating ?
What's the difference vs magnetron sputtering for capsule's membranes ?
Thanks
Fred

 

[ZHOUJUN]

I repaired two gold-damaged C38Bs according to the help Tim gave me. I would like to thank Tim again for his help. He is a very enthusiastic person and a very technical person.

 

[Tim Campbell]

This is actually a sputtering process using a very large ingot and can coat a large area. Dales chamber which kingkorg showed is a thermal coater which uses a small ingot and evaporates most if not all of the gold used.

 

[granger.frederic]

This is actually a sputtering process using a very large ingot and can coat a large area. Dales chamber which kingkorg showed is a thermal coater which uses a small ingot and evaporates most if not all of the gold used.

Yes, Tim, your machine is very impressive...
And what is your opinion about thermal evaporation vs magnetron sputtering (assuming nobody use Ion Beam or Pulsed Laser for microphones...) ?
Best
Fred

 

[Tim Campbell]

To be 100% clear I don't own this machine. A danish lab that does coatings for work like the CERN supercollider, etc. let's me come to their lab and use this machine but it is what I use when I make membranes. Both processes work. This machine gives me a very robust deposit of pure gold without a substrate that is very consistent and controllable in the thickness of the deposit. I would assume that a thermal process is harder to precisely control.

 

[soliloqueen]

gorgeous machine! I've heard of people adding varying tiny amounts of nickel to the ingot, but I haven't really toyed around with custom alloys much.

 

[Tim Campbell]

gorgeous machine! I've heard of people adding varying tiny amounts of nickel to the ingot, but I haven't really toyed around with custom alloys much.

Usually the membrane is coated with nickel or another metal first to make the gold adhere better but I get a very strong adhesion even at the same thickness as AKG or Neumann.

When you see old M7 capsules from Gefell discolor and fail that is caused by the fact of in trying to save money they used a gold alloy instead of pure gold and eventually some of the metals in the alloy oxidize

 

[ricardo]

There's a very long thread in [email protected] | Topics
by Les Watts that explains how he does his gold sputtering. You have to join.
One of the most important aspects is that, unlike Aluminium, the Gold has to be deposited on the film while it is at the correct tension.

 

[JPO]

Hi, thank you so much for your reply. I have come across them in my googling . I’m wondering if anyone if anyone in the USA does this. I’d imagine this is out of the realm of normal DIY stuff. Seeing the absence of the gold did get me wondering about how it gets on there in the first place, and the different schemes to accomplish this goal

Peluso microphone lab does this! Pelusomicrophonelab.com

 

[Sidebstudio]

In my experience is not necessary to use nickel before gold sputtering.
Maybe depends on the sputtering process (I'm talking only about magnetron sputtering that's the one I use)
I found a combination of distance/time/current that works so good that you can really walk over the mylar and the gold stay there.
However about the topic I'm in Italy so maybe not the nearest place to have the Sony reskinned.

 

[soliloqueen]

There's a very long thread in [email protected] | Topics
by Les Watts that explains how he does his gold sputtering. You have to join.
One of the most important aspects is that, unlike Aluminium, the Gold has to be deposited on the film while it is at the correct tension.

There is some wiggle room. It's best if the diaphragm is sputtered while it's under tension, but the exact amount of tension It needs to be under is not very precise. A lot of larger factories will bring the film up to a base tension, sputter it, and then bring it up to a fine-tuned final tension. I think I saw Neumann doing this in the how it's made video. You can even sputter at the base tension, completely let the tension out, and then tension the diaphragm at a second location and it still won't break the gold or cause stress quite like sputtering completely loose will.