Need help diagnosing DIY Vintagemicpcb U67 Mic problems

[youngshu]

Wanted to build the Vintagepcbkit u67. It is my first Mic build and i have no idea how to trouble shoot and have no mentor to ask. Hoping you guys could take a listen and give me ideas on where to go from here.

All psu B+ H- measurments are correct. They are also correct with the mic connected.
I have swapped tubes that i know are working because i tested them in my Lauten Eden.
I swapped a styroflex that i thought might have been the issue because i slightly burned the edge that had no effect.

I would not have picked such a difficult mic for my first build but i had no idea about Hi Z or plate voltages. All things considered i have learned alot with my failure so far. Any recommendations would be helpful.

Below is a recording so you can listen and theory craft.

Thank you

 

[Khron]

Photos of the build..?

 

[youngshu]

I didnt take photos while building unfortunately. Any ideas based on the audio clip? Thanks for taking a look!

 

[ElSmurf]

The audio clip doesn't open for me. I do see a lot of solder holes that aren't properly filled on the component side of the board.

 

[youngshu]

The audio clip doesn't open for me. I do see a lot of solder holes that aren't properly filled on the component side of the board.

I went through and reflowed everything. There are a few empty holes but those are by design of the pcb if that's what you are referring too.

 

[Accelerator]

@youngshu​

I attached for you the Vintage Microphone PCB Kit D-67 Build Guide (PDF) to re-check step by step the whole soldering process and also the Neumann U-67 Pre Schematic & Neumann U-67 PSU Schematic so you can follow it for checking the placing & the values of the components…

I hope this will helps you a little bit more to your task…

 

[ElSmurf]

There are a few empty holes but those are by design of the pcb if that's what you are referring too.

In the first picture I see quite a few holes that aren't flowed all the way through where the film caps are, that's what I was referring to. Any changes after the reflow?

Still can't open the audio file btw.

 

[youngshu]

In the first picture I see quite a few holes that aren't flowed all the way through where the film caps are, that's what I was referring to. Any changes after the reflow?

Still can't open the audio file btw.

ok so new developments.

I Reflowed and cleaned everything joint and got a good improvement on output volume.

Still the same amount of noise.

So i plugged the power supply into me interface turned it on with no mic connected and cranked preamp to listen to noise.
there is very little noise from the power supply at very high preamp levels.
As soon as i bring the 7pin close to the mic the noise iv been fighting appears.
any ideas?

i tried to make the sound clip a google drive link im not sure why thats not working ill try something else.

 

[pasarski]

It would be really helpful to hear what kind of noise it is (the audio link doesn't work). Or maybe you could describe it? Is it hum or some other kind of noise? If it's hum, what frequency?

 

[youngshu]

It would be really helpful to hear what kind of noise it is (the audio link doesn't work). Or maybe you could describe it? Is it hum or some other kind of noise? If it's hum, what frequency?

 

[youngshu]

In the first picture I see quite a few holes that aren't flowed all the way through where the film caps are, that's what I was referring to. Any changes after the reflow?

Still can't open the audio file btw.

 

[pasarski]

Ok, it's buzz. Is the microphone body and head grille properly grounded?

 

[youngshu]

I thought it was but how would I know for sure?

Ok, it's buzz. Is the microphone body and head grille properly grounded?

 

[pasarski]

I thought it was but how would I know for sure?

Check the continuity from the mic ground pin to the body and the head grille with DMM.

 

[Vetsen]

Can you tell us more about your setup? What audio interface are you using? Is the mic fully assembled when making this recording (Capsule grill and body installed)? Sent you a PM.

 

[youngshu]

That recording was into a neve 511 preamp into Apollo 6x into pro tools. I’ve been recording mixing and mastering for about 5 years.

Yes the test are with the grill and body installed.

My 251 and Lauten Eden have no noise in the same chain.

I believe I have grounded the psu correctly. The voltages are all correct. I don’t really know how to tell if I didn’t ground it right. When I plug the mic into the preamp with no gain there is no noise it only comes up with preamp gain. (I don’t know if that is helpful)

Ill check the 400 meg resistors tonight but I was very careful when putting the mic together to not mix anything up.

I have tried the mic on multiple preamps and the signal to noise is still unusable.

Yes my gain staging is correct.

No offense takin I can’t tell you how much I appreciate the help.

 

[Vetsen]

I can't see any errors in your build. Double check the Hi-impedance wires and make sure there aren't any cold solder joints, shorts or other errors. Did you clean all the solder flux of the switch PCB and the high-Z connections. The flux can act as a resistor to adjacent nodes if it isn't cleaned off.