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

Zjcc56 said:

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 

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Khron said:

Zjcc56 said:

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 

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

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Matt Nolan said:

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.

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Zjcc56 said:

Matt Nolan said:

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.

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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

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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., 

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sargethebard said:

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

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sargethebard said:

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.

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jpertusi said:

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

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gary o said:

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.

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