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

[Barton]

Still seems that the overall volume is pretty low.  I'm running the mic through an EZ1073, which I have to set the input gain to about 60.  I have an AKG 414 EB that I've never cranked higher than about 40.  Is this usual for the U67?  The tone of the mic is good, no popping, etc., it's just that with the volume so low, you begin to pickup some of the noise from the preamp when raised to usable volumes for the mic.  I checked the capsule connections to make sure they weren't going to ground in any way.  Here's a couple of pics of the mic and psu.

 

[Barton]

Another pic.  Also not sure that it matters, but I'm using a JJ EF 806s tube.

 

[Barton]

And the PSU.

 

[poctop]

I just finished my D-U67 and have a few questions.  The volume on the mic is extremely low.  To the point where I have to turn the gain on my  my mixer almost all the way up.  Below are the voltages I'm getting.  i removed the 56k resistor on the psu trim because I couldn't get any higher than about 194v  at B+ on the mic pcb.  The below measurements were measured after I removed the 56 k.

PSU Not loaded

B+ = 284v
H = -6.3v

PSU Loaded

B+ = 245v
H = -6.3v
a = 78.5V

Pin 1 = 330mV
Pin 2= 330mV
Pin 3= 1.7mV
Pin 4= -6.4 V
Pin 5 =  246V
Pin 6 =  -10.4mV
Pin 7 = -0.1 mV

FD = 0.933V
BD = 0.933V (Cardiod), 3.5V (Omni), 3.5V Fig. 8)
BCK = 7.9 V

XLR 1 = -0.2mV
XLR 2 = 347 mV
XLR 3 = 345 mV

Please heeellp.  This is driving me crazy.

First I would consider adding a resistor back on the B+ line to get the corret voltage on B+ if 56K is too much then go for 27K you should then be able to get the proper 210B+ with the mic connected ,

start by checking all the important voltage on the mic as well not just on psu,
measure backplate voltage before the High Meg resistor because it will fool your meter , should be arround 58V
double check the connection and check bias on tube should be somthing like 1.6V at the cathode,
double check your wiring , the D-67 is a high gain mic so there is no way you need that much of gain so somthing is defo wrong with your build ,  Make sure nothing is touching somthing it is not suppose to touch in the HZ bridge between the socket board and the main board this is a critical area and since everything is floating ......  check for cold solder at the grid point (isolation teflon pin on both side and also to the floating tube grid point.

if you can hear something , that mean you are not that far off but only a small details is preventing the output to go Glory,
verify capsule connection and make sure it is correct , you can also replace the capsule with a 50pf and inject a 1K sine tone from there and check the output to transformer then work you way down from there ,  I already had a similar problem where the tube was bad also. replace to make sure , and also use any stock capsule also to confirm that it is not a problem. Like said you are very close.....

it feels like a little something is missing or the grid connection might be touching something ,
hope this helps,
Best,
Dan,

 

[Barton]

Thanks for the help.  I ordered some different resistors for the trim which should be here in a day or so, as well as another tube.  We'll see what happens.

 

[friesdan]

Hi guys, quick question here.. I don't see  a PSU lamp in the BOM or mouser cart - does anyone have a part number or recommendation? I'm getting Dan's case (realized I'm not too good a cutting square holes in metal) so hopefully it will be one which fits in the pre-cut holes, or is bigger.

Thanks so much for the project - It's the first non-chunger-tutorialized mic build I've tried, and it has been more challenging and different. I'm hoping it'll fire up once it's turned on!

Thanks!

 

[wave]

Hi guys, quick question here.. I don't see  a PSU lamp in the BOM or mouser cart - does anyone have a part number or recommendation? I'm getting Dan's case (realized I'm not too good a cutting square holes in metal) so hopefully it will be one which fits in the pre-cut holes, or is bigger.

Thanks so much for the project - It's the first non-chunger-tutorialized mic build I've tried, and it has been more challenging and different. I'm hoping it'll fire up once it's turned on!

Thanks!

What kind of lamp do you want? A jewel lamp?
Also, Where are you located?

In mine I used a jewel and lamp holder from antique electronic supply and got a lamp that runs off of 120-130V AC and tied it into the power switch

Dave

 

[dmp]

In mine I used a jewel and lamp holder from antique electronic supply and got a lamp that runs off of 120-130V AC and tied it into the power switch

Do you know the bulb number? I know #47 is the 6.3v variety, but I'm not sure where to get a 120v version. This is a good idea.

 

[stitch-o]

I am in need of a third screw to hold the pattern, pad, shelf switch PCB to the underside of the headbasket
of my DU-67. I have the ShuaiYin SYT-5 donor.
Could anyone tell me the size and length of screw I need to buy?

Cheers!

 

[wave]

In mine I used a jewel and lamp holder from antique electronic supply and got a lamp that runs off of 120-130V AC and tied it into the power switch

Do you know the bulb number? I know #47 is the 6.3v variety, but I'm not sure where to get a 120v version. This is a good idea.

This is what I got,

http://www.mouser.com/Search/ProductDetail.aspx?R=8-3995virtualkey60600000virtualkey606-CM8-3995

Dave

 

[Mahasandi]

I bought a great DU67 build from a member here - He wanted to find the right fuse on the power supply (iyt has a wrong value one in there)
we could never find a time to meet - (busy lives)
he also wanted to re-wire the x former.
It sounds great- but would a x former rewire change the sound much? does any one no where I can get the correct fuse value for the power supply?

Any and all help appreciated!

 

[poctop]

I bought a great DU67 build from a member here - He wanted to find the right fuse on the power supply (iyt has a wrong value one in there)
we could never find a time to meet - (busy lives)
he also wanted to re-wire the x former.
It sounds great- but would a x former rewire change the sound much?

See here for complete relationship between pad number and transfomer on the AMI and various transformer mic pcb version
http://groupdiy.com/index.php?topic=50021.msg720336#msg720336

if you Have the T67 AMI transformer (Rewire is only valid for the AMI T67 of D-67 or D-269c any other transformer can be wired correctly from the wiring guide of the pcb ) yes it will make the sounds better the top end will be much sweeter with the corrected feedback wiring as seen in this thread,

does any one no where I can get the correct fuse value for the power supply?
i usually stick a 0.3A if you are in north america,

Hope this helps,
Dany,

with wiring error
https://dl.dropboxusercontent.com/u/43869772/U67/Feedback%20winding%20Correction/Orginal.wav

With wiring correction  WoW
https://cdn.groupbuilder.com/groupdiy/u/39511/58d028199444d.wav


Any and all help appreciated!

 

[micaddict]

Hope this helps,
Dany

I would think so. 

 

[Mahasandi]

Thanks Dany! Yes it was the T67 AMI - and I'm in North America!

 

[Mahasandi]

So i'm not gifted with this stuff I looked at the diagram and wasn't positive what i would be soldering?
can anyone identify from my pictures what needs changing - this would make the diagram more useful to me...

 

[Mahasandi]

and the back side

 

[Mahasandi]

see I'm only good at making the outside look good ....
(thanks to my wife for hand modeling)

 

[micaddict]

Hey Mahasandi, good to "see" you.
So, you got the bug so bad you are now rolling your own. 
Brave guy.

Do be careful with them high voltages, will you?
They can be lethal, you know.

Oh wait!
You're modding the one you bought.
My bad; I should have scrolled back.

Time for coffee.



Henk

 

[poctop]

see I'm only good at making the outside look good ....
(thanks to my wife for hand modeling)

Just Make sure of this connection Scheme,

AMI T67 Corrected Wiring to main microphone pcb

From transformer board to mic PCB

Pad 5 ----->  mic pcb pad T1212
Pad 12 -------> mic pcb pad T55
Pad 1 --------> mic pcb pad T44
Pad 4 --------> mic pcb pad T11
Pad 7 --------> mic pcb pad T1010
Pad 10 ------> mic pcb Pad T77

Thanks For the Pictures,
Best,
Dan,

 

[Spencerleehorton]

HI Guys,

just thought id post a little mess around groove with my newly tweaked U67.
U67 as room mic put it through my LA2A and through SSL 9k pre amp. Mic about 6-8 foot away at chest hight.
not great upload quality unfortunatly

https://soundcloud.com/spencer-lee-horton/sleepy-groove

regards

Spence.