U67 Build

[Moby]

I was wondering about this. I know that the faraday shield can affect interwinding capacitance, but what point would grounding the actual core have? It looks to be grounded in the original 67 because the screws meet a plate which is screwed to the main rails, which are of course grounded.

Right. It's grounded trough the screws/plate/side rails/body. Core is grounded to reduce hum/noise. TBH, I'm not sure if it really helps but it does not hurt.

 

[egroys]

I would absolutely be in for a pair!

 

[mesajoe]

Here's one I made...
[snip]

@wave - is that a Neumann mic body or sourced elsewhere - if so, where?

 

[Murdock]

The plastic parts from the head assembly look like the ones from the infamous chinese U87Ai copy.

 

[dmp]

Tube socket installed and boards connected together. The high impedance board is connected and it fits in the SYT-3 body. Isolation with Keystone PTFE isolated terminals. I wanted to make a board set that would work without the custom head assembly.
Next: attach the switch board that came with the mic body and final assembly.

 

[doqmemory]

I would absolutely be in for a pair!

I would like a pair, too! Your build looks sweet. By my count, that makes at least 24 sets of boards so far requested in this thread. I don't imagine they will perform any differently from Dan's boards (which were fun to build, but look less like the original than these do).

By the way if anyone building an U67 needs 2,2nf Feed-Through caps for it, I have a lot of spare from a build, just pm me

Where did you find them?

 

[dmp]

By my count, that makes at least 24 sets of boards so far requested in this thread. I don't imagine they will perform any differently from Dan's boards

These boards will fit moby's transformer. That was the main goal - I found the Ioaudio BV12 had an open winding but could not fit in moby's transformer very well. Of course following the original layout was cool too.
Once I have this tested and working I'll get a count on people who want boards and place an order. It's cool that so many people are interested in this DIY build!

 

[doqmemory]

I found the Ioaudio BV12 had an open winding but could not fit in moby's transformer very well

I used Dan's BV12 adapter board to fit Moby's transformer into a D-269c, but it was a tight fit and would likely not work for EF86 in a D-67.

It would be great to have an M 269b or c version of these boards, if this takes off.

 

[dmp]

It would be great to have an M 269b or c version of these boards, if this takes off.

Very similar. In originals, the tube is inverted because of the top grid lead of the AC701. But using a 5840, 5703, etc... you would not need the tube inverted.
Other differences are minor. I could easily make a m269b. But let's get this one working first

A few build notes before I forget them:
- The holes for the teflon pins are a little too tight (I spec'd them at 0.07" which should have been perfect?). I used a wire size drill bit to widen them slightly just by hand and then the pins fit snugly. I didn't use glue.
- The syt-3 body was also a little tight for the round boards to pass through, so I filed them a bit.
- Getting Moby's transformer through the rectangular hole was a little tricky because of the wire leads. I pushed one side in and then worked each wire though. The wires were close to too short and I had to extend one. If the wire leads were slightly longer it would fit better. I think a 'real' u67 has the connections lower, but I didn't want them under the metal core so I put them up higher.

 

[Drosselmeier]

Wow! I want to do the same, can you share Gerber or something?

 

[dmp]

Update: summer arrived and I have a ton going on but I almost have the prototype built. The top is tight for space connecting the switch board. I am doing it with teflon iso pins which makes it much more difficult.

Wow! I want to do the same, can you share Gerber or something?

If it works I can sell some boards.

 

[Buttercup1]

Yay! I'm up for a set of boards.

 

[GREAT TIME]

I would also be down for a pair of boards, great build!!

 

[dmp]

Summer slowed down progress but I finished wiring up the head last night. The switch board was a tight fit (I put in teflon pins for isolation), but I was able to get it assembled. If not for isolating the high impedance connections from the PCB, it could have been simpler.
Plugged it in and got some initial sounds that exceeded my expectations. Will do some testing of the patterns and frequency response.

 

[dmp]

Top switch board that came with the mic body. Drilled out the switch pads and added teflon pins. Made this quite a bit more complicated and may not have been necessary

 

[bremusound]

Are there any U67 or M269 pcb kits for genuine Neumann bodies available?

 

[Whoops]

Are there any U67 or M269 pcb kits for genuine Neumann bodies available?

No U67 PCB kits for original Neumann bodies are available for sale as far as I know.
The reason is that original Neumann bodies are not available for sale, so people use mostly Chinese bodies options

 

[jeremynothman]

^huh? Isn’t that exactly the idea of the Max Köcher (ioAudio) mod? It is to convert a TLM67 or U87Ai to a U67 circuit. I’ve heard them, they sound good!

 

[dmp]

Tested the mic last night and everything works correctly. Pad, low cut, omni / fig8 / cardiod. I swept the frequency response using the calibration input and it looks good (using 100pF for C17). Down about 9-10dB at 15kHz.
But the mic sounds incredibly good (comparing to M49 & U47 builds, I don't have access to a vintage U67). The 'off' behavior that I battled for years in the U67 build with the BV12 is gone. No 'dark' character. Balanced and rich. Moby's transformer is excellent.
I will start a list for people who want a set of boards then do a order. Probably around $50 per set of boards. Send me a PM including the number of boards you want, shipping country, and your email. Also if you have interest in a PSU pcb. I have a prototype.
It will be straightforward to build as all the component designations are the same as the original schematic. The head connections are labelled the same too, with kk1 - kk6. I have a couple other 'tie points' that are connected at the upper boards.

 

[RuudNL]

Isn't 9-10 dB @ 15 KHz a bit too much?
The original Neumann documents specify:
-5 dB @ 40 Hz.
-7 dB @ 16 Khz.
(Everything referred to 1 KHz.)