Destroyed front diaphragm on a brand new K67

[ZHOUJUN]

This capsule actually has two tiny plastic rods that sit in holes to line them up.

Some early Neumann capsule copper plates had some plastic rods inside to block the holes to adjust the sound cavity. Other manufacturers that imitated Neumann capsules did not follow this completely, so the sound was somewhat different.

 

[soliloqueen]

Some early Neumann capsule copper plates had some plastic rods inside to block the holes to adjust the sound cavity. Other manufacturers that imitated Neumann capsules did not follow this completely, so the sound was somewhat different.

i never did figure out what these are for. they're dots of epoxy

 

[cyrano]

i use the type of brush they use to clean antique gold leaf for this. usually white goat hair. you can find them from museum equipment suppliers

My better half restores antiques. She uses a brush made of marten hair.

I can imagine these being no longer available, as that's a protected species. Perhaps it's only a name?

 

[soliloqueen]

My better half restores antiques. She uses a brush made of marten hair.

I can imagine these being no longer available, as that's a protected species. Perhaps it's only a name?

they were only banned in 2013 in the US, so her brush is likely real? if you're in europe (i see you are) i think they can be bought with paperwork.

 

[cyrano]

Once upon a time, I was going to purchase a Studer mixer from a guy so I went to see it at his house. He had smoked so much weed that not only were the outer mixing surfaces coated in resin, but the inner circuit boards too. I didn't think I could ever clean it well enough, and so passed on it. His weed smoking was a terrible thing to do to such a fine piece of gear.

That's easy enough to remove. I used to service audio gear from pubs, way back when most pubs were filled with smoke. Just set in a bath of hot water with some dish washer soap. Very few failures after the bath. The bath usually looked like coffee after. Not that anyone would drink that 'coffee'. Of course, you don't do that with speakers, but these never were cleaned.

 

[soliloqueen]

That's easy enough to remove. I used to service audio gear from pubs, way back when most pubs were filled with smoke. Just set in a bath of hot water with some dish washer soap. Very few failures after the bath. The bath usually looked like coffee after. Not that anyone would drink that 'coffee'. Of course, you don't do that with speakers, but these never were cleaned.

people are unnecessarily afraid of getting electronics wet when they aren't running, IMO. soap and water solves many issues.

 

[TLRT]

I have some unopened Neumann k67 if somebody needs them. Did the poster realized what caused the issue? Usually those capsules are very reliable.

 

[Khron]

I have some unopened Neumann k67 if somebody needs them. Did the poster realized what caused the issue? Usually those capsules are very reliable.

"Unopened"..?

 

[TLRT]

"Unopened"..?

Yes brand new.

 

[granger.frederic]

Some early Neumann capsule copper plates had some plastic rods inside to block the holes to adjust the sound cavity. Other manufacturers that imitated Neumann capsules did not follow this completely, so the sound was somewhat different.

I noticed those dots long time ago. Each time the holes were fully filled.
I don't think that changes a lot the the sound , it reduces a bit the capacitance , maybe 2/3%...
Maybe Neumann use that for the manufacturing process...i don't know...

 

[soliloqueen]

They're not filled holes, it's just a circle of epoxy dots. I think they were just using it to keep the membrane from hitting the back plate at max travel or when over polarized? There was a period there near the beginning where they didn't really know what would be a problem and what wouldn't be a problem with the design so they were kind of worrywarting about everything. They still put the plastic pegs in there even though they aren't strictly necessary and use backplate linking screws that close fit into the holes just to be double triple quadruple quintuple sure the capsule can't twist. In my opinion it's overkill but I understand the concern.

 

[soliloqueen]

There was a period there where they didn't really know about their own design yet and its long-term stability. They probably wanted to make absolutely positively sure that it wouldn't be another complete fiasco like the M7. I think the mythologization of this stuff kind of does a disservice to the very human people behind these products and their motivations, hopes and fears. There are so many little touches in the k67 and K87 design that I would describe variably as both "inspired attention to detail" and "abject terror at putting out a fragile product again" which I really relate to recently. Makes me wonder if in a couple years people are going to be trying to recreate my first generation of finicky capsules and insisting they're the best.

 

[granger.frederic]

They're not filled holes, it's just a circle of epoxy dots. I think they were just using it to keep the membrane from hitting the back plate at max travel or when over polarized? There was a period there near the beginning where they didn't really know what would be a problem and what wouldn't be a problem with the design so they were kind of worrywarting about everything. They still put the plastic pegs in there even though they aren't strictly necessary and use backplate linking screws that close fit into the holes just to be double triple quadruple quintuple sure the capsule can't twist. In my opinion it's overkill but I understand the concern.

OK but my capsules were in the 70/80 era , not really the fist batch...
As far as i remember the epoxy (if it's epoxy) was even with the surface, thus near zero impact on diaphragms collapsing...
Strange...
I'm curious, other theories ?

 

[soliloqueen]

OK but my capsules were in the 70/80 era , not really the fist batch...
As far as i remember the epoxy (if it's epoxy) was even with the surface, thus near zero impact on diaphragms collapsing...
Strange...
I'm curious, other theories ?

Not super early, no, but only 10 or so years after the debut of the capsule compared to now (60). They were finnicking like crazy with the M7 too. Changing the diaphragm thickness, moving where the vent is, changing the glue troughs and the gap that goes around the electrode surface. they were always worrying about one thing or another it seems. It is epoxy. Dots of epoxy. It's an enduring mystery honestly. They appeared for a short period on some capsules and then disappeared, never to return. Even among the few all original ivory ring K87s I've got currently, none of them have the dots. None of the capsules I've got from before or after have them either. I've only seen them in capsules I've been lent.

There is no purpose to them that I can think of. Modulating the flow of the air over the surface? Probably not. Providing some kind of buffer for the diaphragm as I suggested? Possible but probably not. Though, remember how relative "flush" is when you have such a flat surface. Arcing protection? It could be the by-product of a proposed alternate tensioning or other industrial process that was abandoned or even some strange ritual adopted by the assembly team.

 

[soliloqueen]

@Tim Campbell What do you know about these

 

[granger.frederic]

Another thing that always amazed me was the quality of surface finish...
Very nice lapping, very thin, no scratches, with a typical color ...
Maybe a very thin micro-sandblasting or vibrations inside thin sand...???
Perhaps those epoxy dots were artefacts of the lapping process ???

 

[Delta Sigma]

I have some unopened Neumann k67 if somebody needs them. Did the poster realized what caused the issue? Usually those capsules are very reliable.

It was the signal I was injecting for calibration. I had measured 1kHz and 15kHz and left my cheap sig gen hooked up. It's a cheap eBay sig gen. I must've bumped it, because when I came back, the level was cranked. Putting such a big swing on a capsule polarized at 60V must've caused it to contact the backplate.

 

[TLRT]

It was the signal I was injecting for calibration. I had measured 1kHz and 15kHz and left my cheap sig gen hooked up. It's a cheap eBay sig gen. I must've bumped it, because when I came back, the level was cranked. Putting such a big swing on a capsule polarized at 60V must've caused it to contact the backplate.

Where did you injected the AC signal? I dont know u67 circuit by heart but for example M49 has an extra RC circuit for calibration.

 

[Delta Sigma]

Where did you injected the AC signal? I dont know u67 circuit by heart but for example M49 has an extra RC circuit for calibration.

Same for U67. I injected via the power supply. There's a 600ohm cal input.

The stupid thing is that I'm a Telecom tech who works on old obsolete tone equipment. I have the exact test set that would make this simpler, at my workplace, but I was off work recovering from knee surgery.

 

[Tim Campbell]

@Tim Campbell What do you know about these

Yes. I posted about them here more than 20 years ago. They are exactly as you said, there to help prevent the membrane from being too attracted to the perfectly flat backplate.

My photo that I posted on the original forum.