Ribbon mic basics: galvanic reaction on ribbon contacts?

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geedy

Member
Joined
Dec 28, 2021
Messages
6
Location
British Columbia
Hey everyone,

I, like many before me, am embarking on the adventure of building my own ribbon microphones, because I am going crazy during this pandemic.

I have a super basic question I can't seem to find the answer to anywhere on the internet. A lot of the videos/threads I've seen on YouTube and other places suggest using copper tape for where one attaches the ribbon to the motor body.

I am aware that aluminum and copper don't mix well (galvanic reaction) and I really don't want to end up loving the sound of something I need to fix. I've also seen people mill aluminum blocks, but if they use copper wire...

What are better solutions? Aluminum contacts with aluminum wire? As an easy solution, would aluminum tape work? What do you all think?

Thank you for your time.

P.S. Any idea where one can buy XLR connectors for the microphones themselves? I live in Canada, but so long as they ship anywhere...
 
Geedy
Hey everyone,

I, like many before me, am embarking on the adventure of building my own ribbon microphones, because I am going crazy during this pandemic.

I have a super basic question I can't seem to find the answer to anywhere on the internet. A lot of the videos/threads I've seen on YouTube and other places suggest using copper tape for where one attaches the ribbon to the motor body.

I am aware that aluminum and copper don't mix well (galvanic reaction) and I really don't want to end up loving the sound of something I need to fix. I've also seen people mill aluminum blocks, but if they use copper wire...

What are better solutions? Aluminum contacts with aluminum wire? As an easy solution, would aluminum tape work? What do you all think?

Thank you for your time.

P.S. Any idea where one can buy XLR connectors for the microphones themselves? I live in Canada, but so long as they ship anywhere...

Geedy,

indeed, it is something to be aware of… that’s the reason I was surprised when AT issued a patent with Al Gold plated ribbon ends. The Gold and Al are on the opposite ends of the chart.
Not sure who suggested Copper, but it is also pretty far away, with only Silver and Gold being worse.
The closest is Zinc, followed by Iron. Nickel and Tin.
It is also important to remember the metal dissimilarity starts to be a problem in certain conditions—dump environment, etc. In our mics we use Ni and Tin plated contacts and in many years did not have one single problem.

For XLR’s search for Switchcraft QG3M insert.

Best, M
 
A similar question I have pondered is how does the aluminum ribbon stay in contact with any terminal? I have measured aluminum chassis before, and as expected they are very high impedance if you use a flat contact, you have to scratch with a pointed test lead to break through the aluminum oxide before you get a low resistance reading. Why does an aluminum ribbon not get an aluminum oxide layer growing between the metal of the ribbon and the contact pad in the motor assembly?
 
A few microphone companies including Coles (and the earlier STC 4038 mics) use aluminium blocks, (albeit with silver below). That always made a lot of sense to me. You still need to connect to a different metal somewhere but let's move it away from the thin ribbon.

Most of the old British ribbons use silver plate or bare brass.

The B&Os used some weird plating that turns to water soluble white powder with age. I wash it off my hands very quickly!

Keep in mind that these were never supposed to last for four or five decades without service.

>how does the aluminum ribbon stay in contact with any terminal?

Roughen the clamps before use and bite down hard. It sounds primitive but it does work.

Some of the Japanese ribbons use glue and then solder the ends of the ribbon. No ribbon clamps needed.
 
solder the ends of the ribbon

What kind of solder will wet aluminum? I have never had any luck soldering to aluminum with standard tin/lead. Maybe I was just trying to solder to metal which was too thick and the heat was being carried away to quickly to raise the temperature enough.
 
What kind of solder will wet aluminum? I have never had any luck soldering to aluminum with standard tin/lead. Maybe I was just trying to solder to metal which was too thick and the heat was being carried away to quickly to raise the temperature enough.
Aluminum oxide isn't terribly reactive; even then the things that do react with it (and would then allow wetting) can't do it quickly.

There are also surface treatments, such as chromate conversion coating, and there are newer/safer versions than the older hexavalent chromium versions (which are banned in the EU, heavily regulated in the US, and just a bad idea to use everywhere). Pricey, though.

Getting good connections with aluminum wire generally happen due to pressure welding: pressure forces the (hard) nanometer sized aluminum oxide crystals deeper into the (soft, ductile) aluminum, and the much softer ductile aluminum metal is extruded to the surface. The unoxidized aluminum touch in the absence of oxygen, forming a good electrical circuit.

I'm pretty sure pressure welding (ie. clamping tightly) is more than enough for good conductivity with the aluminum ribbon, and is how they've always worked.

It's also important to consider the difference between natural oxide layers, and anodized layers. Anodizing is great because it's a cheap and nearly diamond-hard layer that resists scratching and wear.

Natural layers (especially after polishing a contact) of aluminum oxide are very thin, just 1-2 nm thick. Anodized Aluminum, however, has an oxide layer that's typically 5 µm thick.
 
surface treatments, such as chromate conversion coating,

I don't think that is something you want to do to a ribbon, though.

pressure forces the (hard) nanometer sized aluminum oxide crystals deeper into the (soft, ductile) aluminum,

Thank you, that is the most concise description I have seen of the mechanism explaining how you can still make electrical contact to aluminum materials even though they oxidize so quickly.
 
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