Neumann U67 Clone : D-U67 Tube Microphone Build Thread.

[egroys]

I am getting what appears to be very normal switch behavior when I check continuity.

Curious if there is something else I am missing...

 

[Khron]

I swapped them and now in the fig8 (right) switch position, Cardioid works beautifully.
In the center Cardioid and left Omni positions, the signal is extremely low as exhibited before.

Does that confirm that I have a bad switch?

Ok, your description of switch positions / settings is really confusing.

So you now have the "red wire" coming from the REAR diaphragm, connected to the tube grid, and the "orange wire" coming from the front diaphragm, connected to the pattern switch, right?

So both before AND after the diaphragm connection swap, fig-8 works fine, but cardioid and omni are not? In both situations?

 

[egroys]

Ok, your description of switch positions / settings is really confusing.

So you now have the "red wire" coming from the REAR diaphragm, connected to the tube grid, and the "orange wire" coming from the front diaphragm, connected to the pattern switch, right?

So both before AND after the diaphragm connection swap, fig-8 works fine, but cardioid and omni are not? In both situations?

Apologies. Yes I swapped the rear and front connections as you suggested.

Before only fig8 worked.
After, only cardioid worked.
I then returned the connections to normal and once again only fig8 works.

What I am now noticing is it’s more accurately ‘reverse’ cardioid while in fig8…meaning the rear diaphragm sounds clear but the front is not.

 

[Khron]

So the issue is following the (originally front) diaphragm?

You could measure the resistance between the front diaphragm and backplate - anything less than "out of range" is a problem. Could also check capacitance between the front diaphragm & backplate.

Are you using a capsule with factory-joined backplates, or isolated ones?

 

[egroys]

So the issue is following the (originally front) diaphragm?

You could measure the resistance between the front diaphragm and backplate - anything less than "out of range" is a problem. Could also check capacitance between the front diaphragm & backplate.

Are you using a capsule with factory-joined backplates, or isolated ones?

My understanding is that the front diaphragm isn’t working w the correct wiring, and the rear isn’t working with inverted wiring. It’s a BeesNeez K67 so I believe joined.

What’s the best way to measure? At the capsule or the same way you suggested I measure voltages?

 

[Khron]

You could measure the resistance between the front diaphragm and backplate - anything less than "out of range" is a problem. Could also check capacitance between the front diaphragm & backplate.

What’s the best way to measure? At the capsule or the same way you suggested I measure voltages?

Well, since the measurements concern the capsule's own resistance & capacitance, you'll want to measure the capsule itself, right?

My understanding is that the front diaphragm isn’t working w the correct wiring, and the rear isn’t working with inverted wiring.

As i said, your description was a bit confusing, but I'll have to re-read things. So after all then, the issue does NOT follow the diaphragm connections, but stays with the circuit?

 

[Khron]

So my 67s have been workin wonderfully for a few years but recently I lost almost all signal in one.

Then I noticed is fig8 works fine but cardioid and omni have extremely low signal levels.

Apologies. Yes I swapped the rear and front connections as you suggested.

Before only fig8 worked.
After, only cardioid worked.
I then returned the connections to normal and once again only fig8 works.

So after all then, the issue does NOT follow the diaphragm connections, but stays with the circuit?

Ok, upon re-re-re-reading, the issue, AFTER ALL, does indeed follow the diaphragm, does it not???

In which case...

You could measure the resistance between the front diaphragm and backplate - anything less than "out of range" is a problem. Could also check capacitance between the front diaphragm & backplate.

Photos of both sides of the capsule may or may not help...

 

[egroys]

Here is a summary of my findings:
-Cardioid and Omni have extremely low signal.
-Fig8 produce’s normal signal levels but only from the rear diaphragm.

After reversing the connection of the front and rear diaphragm:
- Omni and Fig8 have extremely low signal
- Cardioid works as expected on the front diaphragm

Hopefully that’s more clear!

Just read your last post. I will measure and post photos shortly

 

[Khron]

Yeah, really starting to sound (no pun intended) like something's very off between the backplate and front diaphragm then.

 

[egroys]

I can't seem to get a reading measuring resistance between the diaphragms and backplate?
I'm assuming the mic should be powered on. My Klein Tools MM400 just keeps jumping around when I touch the probes to the backplate and the capsule leads. Again, forgive me for any major noob mistakes!

Here are capsule photos:
Front:



Rear:

 

[soliloqueen]

what are the voltages going to each capsule lead for each pattern

 

[egroys]

Measured at the capsule

Card:
- Front: -0.710V
- Rear: 0.4mv
- BCK: 150mv

Omni:
- Front: -0.710V
- Rear: -0.7V
- BCK:150mv

Fig8:
- Front: -0.7V
- Rear: 3.0V
- BCK: 150mv

 

[Khron]

Measured at the capsule

As mentioned (and also demonstrated) previously, measuring at the capsule is MEANINGLESS.

I'm assuming the mic should be powered on.

No, it should not.

 

[egroys]

My bad, I took 'capsule lead' literally

Card:
- Front (R9): -204mv
- Rear (R16): 108V
- BCK (R2): 49V

Omni:
- Front: -204mv
- Rear: 108V
- BCK: 49V

Fig8:
- Front: -204mv
- Rear: 108V
- BCK: 49V

 

[egroys]

Resistance between either side diaphragm and backplate does NOT give me a reading at all now with the mic powered off.
I do get a reading of 0.2ohm between backplate screw and top of the backpate but I imagine that means nothing

Capacitance between backplate and:
Front = 0.07n
Rear = 0.07n

 

[Khron]

To clarify, where the front and rear diaphragms connect at the pattern switch, yes?View attachment 122619

Starting to sound like there might be an issue with the grey orange connection in this wiring diagram then, possibly..?

 

[egroys]

Starting to sound like there might be an issue with the grey orange connection in this wiring diagram then, possibly..?

What's interesting is that I get solid continuity beeps on each of those ends on both orange and grey.

 

[Khron]

Then you explain how, in fig-8, you ARE getting signal (but only from the rear diaphragm, via the "grey" connection), but not in cardioid or omni.

Although that does still throw some suspicion over the switch, but as you've tested, the fault stays on the circuit side (doesn't move with the capsule connections).

Can you snap a photo or two of where the capsule wires connect to the circuitry?

 

[egroys]

I get continuity beeps at every step of these junctions as well
Meant to write: Front Diaphragm

 

[Khron]

I get continuity beeps at every step of these junctions as well

Continuity beeps, between what and what?

That "orange"-"grey" connection on that isolation pin looks a bit so-and-so, though...

Side-note: apart from the heater connection, nothing else should be conducting any meaningful amount of current, so particularly thick wiring doesn't really help anything (imho).