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

[Khron]

So I  have finished my D-U67 and its quite the microphone!
something that is bothering me is that it is out of phase with my other mics
i've built it with the AMI T67 trafo and i have checked the wiring from the transformers to make sure that it was all correct by checking continuity between points 1 and 2 from the mic pcb and pins 2 and 3 on the xlr and it seemed fine. (1->3 2->2) also checked pin 3 xlr out to 7 from xformer pcb and pin 2 xlr out to pin 10 from the xformer pcb (3->7, 2->10)
all seems well or am i missing something? is the trafo backwards? or is this just how it is?

sorry if its hard to interpret , it is quite early for me 

It won't change the sound if you only swap the wires going to pins 2 and 3 on the XLR

 

[Zjcc56]

So I  have finished my D-U67 and its quite the microphone!
something that is bothering me is that it is out of phase with my other mics
i've built it with the AMI T67 trafo and i have checked the wiring from the transformers to make sure that it was all correct by checking continuity between points 1 and 2 from the mic pcb and pins 2 and 3 on the xlr and it seemed fine. (1->3 2->2) also checked pin 3 xlr out to 7 from xformer pcb and pin 2 xlr out to pin 10 from the xformer pcb (3->7, 2->10)
all seems well or am i missing something? is the trafo backwards? or is this just how it is?

sorry if its hard to interpret , it is quite early for me 

It won't change the sound if you only swap the wires going to pins 2 and 3 on the XLR

Yes that would fix it but I want to make sure that it is not a sign of a larger problem or bad wiring or something

Edit:
Let me clarify, I'm worried that the transformer is backwards because when I got it it had dark markings on both ends (on both I ordered) so I went with the darker marking as the one to match up with the pcb. Ive seen that having the transformer wired wrong will have a polarity problem and the feedback section won't work correctly I don't have a real u67 or similar to compare. So what I'm really asking is IF everything else is wired correctly according to the build pdf and the transformer is wired according to the corrected transformer wiring at the beginning of this forum and the polarity is still inverted is that just how this build is or is the transformer backwards or is it some inconsequential wiring error that I can just switch pins 2@3 and call it a day

 

[Matt Nolan]

AMI transformers seem to be somewhat notorious for having wire colours swapped and mixed up on a regular basis. I have seen it myself and have heard it reported elsewhere. Swap the polarity by swapping the wires to the XLR. If you have a scope, check that the polarity is the same on the primary, secondary and feedback windings and that the amplitudes also check out.

 

[zandru]

You See!, The problem Is most assuredly “Faux AMi Foreign Bootleggers……..

Cheers……A Merry New Year…….

 

[Zjcc56]

AMI transformers seem to be somewhat notorious for having wire colours swapped and mixed up on a regular basis. I have seen it myself and have heard it reported elsewhere. Swap the polarity by swapping the wires to the XLR. If you have a scope, check that the polarity is the same on the primary, secondary and feedback windings and that the amplitudes also check out.

so i used an o-scope and a polarity checker (popper) to check the polarity of the transformer and all is well.  I put the scope on pin 2 of the output  xlr 3 and inject the phase popper in to what i assumed is the positive of the primary wiring  pin 4 on the t67 transformer pcb and it was in phase so with that section troubleshooted to the best of my ability, i moved on. i powered on the mic and injected the phase popper in to the cal input with the scope still on pin 2 and it was out of phase soo this is where i got confused.... it seems like this is just how it is? but I'd like to know why

 

[Matt Nolan]

AMI transformers seem to be somewhat notorious for having wire colours swapped and mixed up on a regular basis. I have seen it myself and have heard it reported elsewhere. Swap the polarity by swapping the wires to the XLR. If you have a scope, check that the polarity is the same on the primary, secondary and feedback windings and that the amplitudes also check out.

so i used an o-scope and a polarity checker (popper) to check the polarity of the transformer and all is well.  I put the scope on pin 2 of the output  xlr 3 and inject the phase popper in to what i assumed is the positive of the primary wiring  pin 4 on the t67 transformer pcb and it was in phase so with that section troubleshooted to the best of my ability, i moved on. i powered on the mic and injected the phase popper in to the cal input with the scope still on pin 2 and it was out of phase soo this is where i got confused.... it seems like this is just how it is? but I'd like to know why

The tube stage is inverting, so anything injected ahead of there will be in opposite polarity to anything injected after there.

 

[Zjcc56]

Regarding the out of phase thingy ,  must be a simple thing ,
the only confusing part but you probably check that already is that the german pin 2 is our pin 2 and the german pin 1 is our pin 3 and the german pin 3 is our pin 1 ,
check the Schemo of the power supply it actually show the inversion already made and mic togheter and trace those to the Transfo to make sure it is in the right order, the tuchel and cannon are not the same and depending on number and times also the hot and cold differs also,
Keep us posted,

thanks Again Guys,
Dan., 

i think this was confusing me ,  2 from the 7 conductor and 2 from the xlr are connected on the pcb and would explain why its out of phase

The attachment i clipped out of the u67 manual makes it look like that the german pin one is actually positive.....

 

[sargethebard]

Regarding the PSU, is there different wiring for the transformer to make it suitable for 240v in aus? Found a 230v transfo diagram in the build folder that just made me wonder whether I need to do something different...THANKS

 

[poctop]

Regarding the PSU, is there different wiring for the transformer to make it suitable for 240v in aus? Found a 230v transfo diagram in the build folder that just made me wonder whether I need to do something different...THANKS

Important Note
The only 2 parts that is not (Europe 230V) compatible is the hammond 20VAC and the PSU pilot Lamp wich is 120V everything else is fine except the fuse will need to be 0.1A instead of a 0.2A for north America, you will need a minimun 6VA traffo for the filament side,
alternative part number are discussed in this thread here :
http://www.groupdiy.com/index.php?topic=49675.20
http://www.groupdiy.com/index.php?topic=49675.40

if you have 240V to your coutry you need to have either a 240V version of the transformer or a dual winding 120V-240V
then you need to woire the primary in parallele for 120V operation and series for 240V ,
in any case please follow the datasheet of the selecvted transformer you cant go wrong with the datasheet ,
hope this helps,
Dan,

 

[sargethebard]

Thanks for the help!

I've hit another little snag on the PSU. Trying to measure AC voltage out of the toroidal transformer which has been configured in series for 240v (grey + violet and red + orange connected). Not receiving any voltage out of the yellow or black wires when measured between the pcb connectors and earth point.
Side note: hammond traffo has also been configured in series and working fine. Rtrim H is reading -16v unloaded.

 

[poctop]

Thanks for the help!

I've hit another little snag on the PSU. Trying to measure AC voltage out of the toroidal transformer which has been configured in series for 240v (grey + violet and red + orange connected). Not receiving any voltage out of the yellow or black wires when measured between the pcb connectors and earth point.
Side note: hammond traffo has also been configured in series and working fine. Rtrim H is reading -16v unloaded.

UnLoaded -16V is what it should be ,
for the other reading , mmmmmmmmmm.. should not ,
what about you red between yellow and black,
pretty sure you are not referenced properly or the neutral connection is doubfull or eacth,
reading between black an yellow should Determnie that
D.

 

[sargethebard]

Thankyou again. The neutral connection was indeed doubtful and has been fixed. Now getting 271v between black and earth and between black and yellow. Also same between B+ and black....and then nothing between the B+ and earth?

 

[jpertusi]

Hi folks,

Just finished my pair of D67's!  Voltages look good and the mics power up and pass audio, all switches seem to function as expected.

However... lots of hum (regardless of any switch position).

Both mics exhibit this issue.

I'm assuming its a grounding problem (perhaps with the 7pin cable?). I used mogami cable specifically for tube mics.

6 conductor plus braided shield which I used for ground.  No pins jumped.

I'm good with a soldering iron and following directions but trying to diagnose is not my strong point.

Any recommendations?

Thanks in advance,

-JP

 

[poctop]

Hi folks,

Just finished my pair of D67's!  Voltages look good and the mics power up and pass audio, all switches seem to function as expected.

However... lots of hum (regardless of any switch position).

Both mics exhibit this issue.

I'm assuming its a grounding problem (perhaps with the 7pin cable?). I used mogami cable specifically for tube mics.

6 conductor plus braided shield which I used for ground.  No pins jumped.

I'm good with a soldering iron and following directions but trying to diagnose is not my strong point.

Any recommendations?

Thanks in advance,

-JP

Did you install the Jumper in the PSU where it says SHLF,
this Jumper needs to be installed for the cable shield to ground ,
Veriffy your Grounding Scheme ,

D.
Hope this helps,
Dan,

 

[jpertusi]

Thanks Dan,

Jumper on or off seems to make no difference as I recall.  I will double check of course.

I should have continuous ground from the mic body (or any ground point) to the ground pin of the power inlet, is that correct?

I read earlier on the thread that I could try lifting the shield inside the PS. Is this the shield on the 3 pin XLR out or the shield coming from the mic?

Thanks for your help all,

-JP

 

[gary o]

Audio transformer question I read thru this thread reading most folks love the sound of their builds thats great & how close they sound to original 67s but it reads like there is quite a difference between the AMI transformers & IOaudio.... is there a definative answer to which is closest ........I have always noticed in my mic DIY that capsule make way the most impact on the sound followed by transformer followed by circuit ..... I would guess that in this circuit the transformer is more important that usual have the feedback to deal with as well.

Thanks Gary O.

 

[jpertusi]

Sorted!!!

I had pins 1 and 3 swapped on the XLR out section of the PS.  Mics are dead quite now!!!

-10bd pad does not seem to work so... on to that.

Also not sure what the jumper in the mic is for.

 

[jpertusi]

OK,

On to the next issue (grounding issue sorted).  ;D

-10db pad does not work on either mic.  Seems to be wired properly.

Could it have anything to do with the jumper in the mic labeled "1S".  What does this jumper do?

Thanks folks!

-JP

 

[gbruler]

Audio transformer question I read thru this thread reading most folks love the sound of their builds thats great & how close they sound to original 67s but it reads like there is quite a difference between the AMI transformers & IOaudio.... is there a definative answer to which is closest ........I have always noticed in my mic DIY that capsule make way the most impact on the sound followed by transformer followed by circuit ..... I would guess that in this circuit the transformer is more important that usual have the feedback to deal with as well.

Thanks Gary O.

I'm wondering that myself, as well. I'm interested in building a pair of those mics, and after reading the whole thread, still not sure which are the most true transfomers to the original U67?
Thanks

 

[jpertusi]

Right, so the "1S" jumper inside the mic is (I assume) the 40hz High Pass filter.  Good.

Only issue left is why the -10db pad switches do not work.


--Switches are good. (tested with multimeter)
--Wiring back to the PCB is good. (tested with multimeter)
--Stumped.

I though maybe I was not letting the mics warm up enough before testing - maybe the tubes have no headroom when cold so the switch seemed to do nothing because all the signals were to hot for the cold circuit / tube.

This does not seem to be the case.

Thoughts anyone?