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

[dmp]

This confused me a little... can you draw that and post it quickly please

In the schematic pic I posted, the feedback winding actually has two windings connected in series (top and bottom on the right side of the transformer). Each winding has a dot indicating where the winding starts. If one of the windings was 'flipped' and they were connected out of phase, they would fight each other. Someone just needs to scope out this transformer and see if anything's funky.
There isn't going to be voodoo with this for cap types or whatnot --  a -10db rolloff filter at 15khz is a HUGE difference from no rolloff.

Does anyone with the AMI transformer have the right amplifier response?

 

[dmp]

I exhaled very softly on to the capsule and the following noise came up. It's only Omni and figure of 8.Tare in the rear membrane?

Humidity is a no-no. Use a pop filter.

 

[Studio Mollan]

I exhaled very softly on to the capsule and the following noise came up. It's only Omni and figure of 8.Tare in the rear membrane?

Humidity is a no-no. Use a pop filter.

But I actually read somewhere on this forum that breathing on it and listening for artifacts is a test for checking torn membranes. I'm very into fixing these microphones right now. Think I'm loosing my mind a bit... We'll I'll try to run actual studio tests in the following days.
/
E

 

[0dbfs]

I exhaled very softly on to the capsule and the following noise came up. It's only Omni and figure of 8.Tare in the rear membrane?

Humidity is a no-no. Use a pop filter.

But I actually read somewhere on this forum that breathing on it and listening for artifacts is a test for checking torn membranes. I'm very into fixing these microphones right now. Think I'm loosing my mind a bit... We'll I'll try to run actual studio tests in the following days.
/
E

I didn't listen to the sound but you are correct. Performing the "Breath Test" should not cause snats/pops/wind/frying-bacon sounds.... And if it happens only in bi/omni then it may well be the back capsule like you mentioned.

It could be dirty or otherwise "contaminated" too. For instance with a hair or other foreign material bridging between backplate and the sputtering that causes these sounds when "humid". It doesn't necessarily mean there is a hole. The hole can be pretty microscopic too and still cause issues.

Cheers,
jb

 

[JessJackson]

Ok i just meassured the turns ratio of the feedback. I sent in 1V (actually 0,096) to the primaries and got back 0,043V from the feedback. That translates to roughly 1:22 ratio. Transformer works just fine.
I'll try to reverse polarity of the feedback.

great - good test.  Both feedback windings look good on there own, from your test.  I was thinking one of the two feedback primaries might be reversed phase with respect to the other, which would cause the two to fight and cancel out.
Can you do the basically the same thing with the signal running through both primaries in series, and measuring both feedbacks in series? So you would jumper the pins on the opposite side as in the pic above

I reversed polarity and on the feedback and now I', pretty sure the hf attenuation is working correctly. I'm not 100% cos i was unable to test them properly. Just speech and singing through headphones.

I also noticed this while speaking in very close proximity to the capsule. Lips almost touching the head basket.
https://dl.dropboxusercontent.com/u/42125780/Exhale%20U67%203.wav
I exhaled very softly on to the capsule and the following noise came up. It's only Omni and figure of 8.Tare in the rear membrane?

This gives me a little hope... did you literally just swap pin 5 and 12 on the ami pcb? I might try this quickly

 

[JessJackson]

Very interesting. I don't have a scope here unfortunately.

I'm in LA if anyone wants to use my mic to test this.. i also have spare t67 sitting here.

 

[Studio Mollan]

Ok i just meassured the turns ratio of the feedback. I sent in 1V (actually 0,096) to the primaries and got back 0,043V from the feedback. That translates to roughly 1:22 ratio. Transformer works just fine.
I'll try to reverse polarity of the feedback.

great - good test.  Both feedback windings look good on there own, from your test.  I was thinking one of the two feedback primaries might be reversed phase with respect to the other, which would cause the two to fight and cancel out.
Can you do the basically the same thing with the signal running through both primaries in series, and measuring both feedbacks in series? So you would jumper the pins on the opposite side as in the pic above

I reversed polarity and on the feedback and now I', pretty sure the hf attenuation is working correctly. I'm not 100% cos i was unable to test them properly. Just speech and singing through headphones.

I also noticed this while speaking in very close proximity to the capsule. Lips almost touching the head basket.
https://dl.dropboxusercontent.com/u/42125780/Exhale%20U67%203.wav
I exhaled very softly on to the capsule and the following noise came up. It's only Omni and figure of 8.Tare in the rear membrane?

This gives me a little hope... did you literally just swap pin 5 and 12 on the ami pcb? I might try this quickly

Yes.

 

[JessJackson]

any further results?

 

[Studio Mollan]

any further results?

No sorry. Busy working. I'll try to check them tomorrow.
/
Emil

 

[Studio Mollan]

Confirmed. Reversing the wires out from the feedback winding on the T67 fixes the problem. Its now rolling off perfectly as stated in the manual.
/
Emil

 

[Studio Mollan]

I exhaled very softly on to the capsule and the following noise came up. It's only Omni and figure of 8.Tare in the rear membrane?

Humidity is a no-no. Use a pop filter.

But I actually read somewhere on this forum that breathing on it and listening for artifacts is a test for checking torn membranes. I'm very into fixing these microphones right now. Think I'm loosing my mind a bit... We'll I'll try to run actual studio tests in the following days.
/
E

I didn't listen to the sound but you are correct. Performing the "Breath Test" should not cause snats/pops/wind/frying-bacon sounds.... And if it happens only in bi/omni then it may well be the back capsule like you mentioned.

It could be dirty or otherwise "contaminated" too. For instance with a hair or other foreign material bridging between backplate and the sputtering that causes these sounds when "humid". It doesn't necessarily mean there is a hole. The hole can be pretty microscopic too and still cause issues.

Cheers,
jb

Hi and thansk for answering!
I actually get this on 3 out of 4 U67 builds... Im thinking that it might be a dirty soldering on the Switch PCB? Any idéas?
/
Emil

 

[0dbfs]

You could confirm that by replacing the capsule with a couple 60pf caps to keep it electrically the same but no acoustic/audio.... Then breath-test into that area....

Flux or material contamination in those hi-z areas can cause the sounds too.

Cheers,
jonathan

 

[Studio Mollan]

You could confirm that by replacing the capsule with a couple 60pf caps to keep it electrically the same but no acoustic/audio.... Then breath-test into that area....

Flux or material contamination in those hi-z areas can cause the sounds too.

Cheers,
jonathan

Thanks for the tip!
I went through all the connetcions, tightened all the screws, cleaned all the terminals and solder joints. Now totaly gone. Success!!

I'll try to do a comparative test with the U67:s some day next week.
/
Emil

 

[dmp]

Thanks for the tip!
I went through all the connetcions, tightened all the screws, cleaned all the terminals and solder joints. Now totaly gone. Success!!

Awesome - glad you didn't follow my advice to just use a pop filter 

 

[JessJackson]

Confirmed. Reversing the wires out from the feedback winding on the T67 fixes the problem. Its now rolling off perfectly as stated in the manual.
/
Emil

ok gonna try that now. lets see what happens!

 

[Studio Mollan]

Confirmed. Reversing the wires out from the feedback winding on the T67 fixes the problem. Its now rolling off perfectly as stated in the manual.
/
Emil

ok gonna try that now. lets see what happens!

To all you out there this is really easy. Just take tip and ring from a jack out of your interface. Load it with a sine wave generator. Use alligator clips from the connector and hold them against the test poles in the psu. Record the output from the microphone output. Compare the levels from 1k and 15k or just do a sweep. Everything you need is in your DAW. 

 

[sedit1]

If the two feedback windings were connected out of phase it wouldn't work right.

Just had a quick chat with Oliver ,  he confirmed that if the feedback winding is reversed it would affect the de-emphasis portion as well as dmp says (Thanks for the pointer dmp  )
so this might be the issue ,  Oliver suggested to reversed the wire from the feedback winding and test it again with the amplifier sweep
i will be rechecking that as well from the mic pcb to make ultra sure the polarity is right , and Oliver said he would check out the drawing he made for me a the time to make sure it has not been inverted as well, hope this well get resolved.

Is there any new news regarding this?  Just thinking was Emils xfmr somekind of exception.

In many samples the D-U67 mic have been sounding littlebit bright for what I have used to hear from U67, always tought that It was tube or capsule choise but this could explain it.
Cant wait to finish my own, just few finishing touches

Thanks!

 

[Studio Mollan]

If the two feedback windings were connected out of phase it wouldn't work right.

Just had a quick chat with Oliver ,  he confirmed that if the feedback winding is reversed it would affect the de-emphasis portion as well as dmp says (Thanks for the pointer dmp  )
so this might be the issue ,  Oliver suggested to reversed the wire from the feedback winding and test it again with the amplifier sweep
i will be rechecking that as well from the mic pcb to make ultra sure the polarity is right , and Oliver said he would check out the drawing he made for me a the time to make sure it has not been inverted as well, hope this well get resolved.

Is there any new news regarding this?  Just thinking was Emils xfmr somekind of exception.

In many samples the D-U67 mic have been sounding littlebit bright for what I have used to hear from U67, always tought that It was tube or capsule choise but this could explain it.
Cant wait to finish my own, just few finishing touches

Thanks!

I think Dan has contacted Oliver. From what I gather I guess either the AMI T67 transformers feedback winding is not inverted, the circuit board is wrong (probably not from my comparisons to the schematic) or I've done something wrong with my build. Already a few members seem to experience the same thing with the AMI builds so most likely it's in the transformer.
Having gotten the first batch of mislabeled t13:s I'm starting to question AMI to be honest. Never answers emails either.
/
Emil

 

[poctop]

Important Notice

Hi All, 

I just got of the phone with Oliver and after all analysis done with the hand drawing I received and the schematic , the conclusion is that nothing is wrong with the AMI T67.  The connection from the adaptor PCB to the main microphone pcb has been inadvertly mirrored as my brain was about to blow up ( this meant not to be an excuse) i tought at first that inverting the polarity everywhere was nulling it out for audio and feedback but as dmp pointed out ( Thanks dmp) the fact that the feedback winding was inverted would not activate the de-emphasis at all since the assymetry from C17,  I am glad this can be fixed easy as the transformer connection are actually wired in and not fixed on the pcb for the AMI T67,  from data reported by Studio Mollan ( Thanks Emil) the feedback winding fixes the issue and the de-emphasis is working correctly after the the inversion of wire 5 and 12 on the mic pcb and the amplifier sweep test is inline with the Original U67 documentation.
I am still trying to confirm that swaping both audio transfomer tap is necessary and it will probably be in the best interest to make sure everything is 100% polarity Correct,  ( Polarity Happens "Albert Einstein")

So the complete Fixe will probably be to swap the both audio taps and the feedback winding for the AMI T67 build. "so we will take no prisonners"

I have prepared a huge mailing list to warn about this errata on this particular transformer configuration for everyone to be reached

I would like to thank Studio Mollan and dmp and all other fellow member of this group for catching this wiring mistakes.

As far as Max BV12 mic pcb is concerned the great and clear documentation from Max resulted in all the correct connections from the very beginning , ( Thanks Max)

thanks For your understanding and patience on this matter to be finally resolved ,

this is the real power of this community as no one is exempt from doing a mistake.

Best regards,

Dany,

 

[0dbfs]

Maybe we just need a "Bright" switch?

Cheers,
jb