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

[JerryPbury]

I used a lamp for a Marshall guitar amp. Works perfect! 120v

 

[Janalex]

Turns out my neighbor has a drill press and I’ll buy an 11/16 bit. We will get it done but yeah had I known a Marshall light would perfectly fit I would have went with that

 

[dmp]

I guess maybe I drilled out the holes to 11/16" and don't remember?
Clearly your product support here has been terrible. I'll certainly try to do better in the future.
Anyway, good luck with your build.

 

[Janalex]

It’s all good. Got it done. Looks nice with the bigger lamp

 

[Janalex]

I found an alternate capsule mount on eBay like the one Danny uses in the build guide

 

[Janalex]

Can someone please share pics of their d67 with moby transformer? I’m interested how it’s mounted for reference.

 

[JerryPbury]

 

[Janalex]

Thanks

 

[klem]

"Tube mic cable length" for future searching... Is 30' a bit too long for the cable between mic and PSU? If working a hostile RF/EMI environment, would it be better to have the cable 10' or so? Don't know how I could go shorter than that for things like OHs.

 

[dmp]

Is 30' a bit too long for the cable between mic and PSU?

I usually go at least 20'
I think you will be fine at 30'
The audio is twisted pair and should reject common noise in a hostile environment.
The heater and power will have some voltage drop due to length (which you could calculate based on the AWG) but it shouldn't be signficant until you are >>30'

 

[klem]

yeah, i need to gather up the relevant specs for this to do the VD calculation. or just go 20' and call it a day. seems simpler than the potential need to recalibrate based on different cable run lengths of 10 vs 30!

 

[dmp]

So I was curious...
Tube: EF86 H+ I=200mA

Cable:
https://www.redco.com/Mogami-W3172.htmlHeater 22AWG, 0.015 ohms/ft

For the heater, with ohm's law, Vd = 0.2*0.015*feet
For 30 ft, you expect 0.09 V drop (keep in mind the ground return carries the same current).
For 20 ft, you expect 0.06 V drop

 

[klem]

Thanks - didn't have the mA values handy, am just in verrrry initial stages. Which should be noted when taking into account the following:
I had assumed 7 conductor though, so Mogami W2642, no? For that all lines are 26AWG, and it looks like 20AWG for GAC7. Still negligible Vd.

 

[dmp]

There's been previous discussion on 6 vs 7 conductors. 7 is needed to have a pattern, power ground, and shield ground (plus B+, H+, balanced signal)
Unfortunately, the Mogami 3172 tube mic cable has 6 with thicker AWG for H+ and ground and I don't like the Gotham 7c as much (stiffer). Unfortunately, Redco doesn't make their brand tube mic cable with 7 any longer (it was really nice)
The Mogami 3172 does have a wire wrapped shield which could connect to the mic body and serve as the shield ground, I think, but I would rather have the 7th conductor serving as a shield ground.

The W2642 has thinner wires but would work. You will expect more voltage drop and dissipation in the cable with the thinner AWG.

 

[JW]

Might be a Belden version?

 

[NiColAs]

Hi guys!

Maybe there is something I don't understand but it seems nothing matches between T67 specifications, the T67 PCB and the U67 schematic.

Is there anyone the AMI T67 and T67 transformer board PCB works for ?

If someone has an answer...

EDIT July 2022 : all instructions are correct, I follow the errata feedback winding polarity and the mic works fine. Thanks to Dan!

 

[doqmemory]

Is there anyone the AMI T67 and T67 transformer board PCB works for ?

Yes, I followed the instructions on page 1 of this thread labeled "Errata Feedback winding polarity... AMI T67 Corrected Wiring to main microphone pcb" and it worked the first time. It is the same wiring for Dan's D-M269b/c. Did you match the "Black Mark" on the transformer (it was silver on mine) to the PCB? I wish that AMI would not have made them symmetric, since that allows you to put them in backwards.

 

[NiColAs]

Yes, I followed the instructions on page 1 of this thread labeled "Errata Feedback winding polarity... AMI T67 Corrected Wiring to main microphone pcb" and it worked the first time. It is the same wiring for Dan's D-M269b/c. Did you match the "Black Mark" on the transformer (it was silver on mine) to the PCB? I wish that AMI would not have made them symmetric, since that allows you to put them in backwards.

Thanks for your answer @doqmemory, the mic works great now and sounds fantastic!

 

[doqmemory]

Thanks for your answer @doqmemory, the mic works great now and sounds fantastic!

Congratulations! When you build your next one (you know you will), try Moby's Bv12. It sounds "right ", in my opinion. I have a T67 in my D67 and Moby's Bv12 in my D269. While the T67 has a good sound, his Bv12 has something special.

 

[Whoops]

Anyone has any source for the 400M (1/2W) resistors?

Mouser and Farnell don't seem to stock any

Thanks