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

[poctop]

Im gonna remove the transformer and test the ratio's to figure out where primary secondary and feedbacks are on mine. but isn't it symmetrical and wouldn't the transformer be the same regardless of which side gets bridged?

i beleive the symmetry is actually the key here as well if it would not have any effect but the polarity if we assume the windings are correct on Oliver drawing and his webiste info ,
the good thing if if this is the case it could be corrected just correcting to the proper wiring to the main mic pcb , so there would be no change to the PCB adaptor itself.

If I compare what Olivers sent me as a hand drawing and the info on the website they 100% match togheter.

Looking forward to have a confirmation on this as well, 

Best,
Dan,

 

[Studio Mollan]

I have checked consitency again and again and again...... and again during the developpment of the mic wich was the hardest challenge for me till the mic pcb project ,
but I have done it again with the board file and the schematic and i have compared the hand drawn drawing from Oliver today just for the cause  ,
audio output is set for 200 ohm impedance (output coil in series) , checked the adaptor pcb again and the main board again and everything is as expected still,
feedback winding output winding primary winding connection to pcb and hopefully i cannot find deadly squat of an error. 

here is the documentation i refered to and compared it to original drwaing from oliver and everything is inline ,
I am really curious if this could not be a systematic miswiring issues or the adaptor pcb or transfomer is installed the wrong way ,
well keep up the good work, i too want to see the end of this , Let me know if you find anything

Hope this helps,
Best,
Dan,

I actually thought about this the very minute you posted. Maybe the transformer is mounted backwards? Would that explain the feedback not working?

This would make a lot of sense, my u67 sounds like it has no de emphasis at all, the top end sounds wide open like c12 and mids sound scooped. also could have something to do with my 5db down.

Im gonna remove the transformer and test the ratio's to figure out where primary secondary and feedbacks are on mine. but isn't it symmetrical and wouldn't the transformer be the same regardless of which side gets bridged?

It sure looks symmetrical. I also thought about that. I can't see how reversing it on the pcb would change anything. I still haven't had the time to follow up on it but will try to work with them next week.

 

[JessJackson]

we really need to contact oliver and get the wiring diagram of whats going on inside this transformer because on the original you have 6 connections on one side and 8 on the other,

and by the looks of things 1 of which goes to chassis and one is left undetermined. leaving the 12 colored on the schematic.

 

[Studio Mollan]

we really need to contact oliver and get the wiring diagram of whats going on inside this transformer because on the original you have 6 connections on one side and 8 on the other,

and by the looks of things 1 of which goes to chassis and one is left undetermined. leaving the 12 colored on the schematic.

hmm.. thats interesting. Can you try to contact him? I've been trying to get a hold of him for months about servicing a V78 and i get dead silence back.
/
Emil

 

[poctop]

we really need to contact oliver and get the wiring diagram of whats going on inside this transformer because on the original you have 6 connections on one side and 8 on the other,

and by the looks of things 1 of which goes to chassis and one is left undetermined. leaving the 12 colored on the schematic.

There should be 6 point of connection to the  mic schematics, 2 Feedback , 2 for audio and 2 for primary ,
the internal link ( series primary and series audio output and series feedback are actually on the adaptor board)
there is no core ground on oliver Traffo but max has them, )
Let me know,
Best,
Dan,

 

[JessJackson]

we really need to contact oliver and get the wiring diagram of whats going on inside this transformer because on the original you have 6 connections on one side and 8 on the other,

and by the looks of things 1 of which goes to chassis and one is left undetermined. leaving the 12 colored on the schematic.

There should be 6 point of connection to the  mic schematics, 2 Feedback , 2 for audio and 2 for primary ,
the internal link ( series primary and series audio output and series feedback are actually on the adaptor board)
there is no core ground on oliver Traffo but max has them, )
Let me know,
Best,
Dan,

yeah I'm with you, all the additional wiring is internal or unnecessary due to single impedance.

1 pair to primary (c9 +ground)
1 pair to feedback (r18)
1 pair secondary (xlr 1-2 / c13 c12)

 

[Studio Mollan]

we really need to contact oliver and get the wiring diagram of whats going on inside this transformer because on the original you have 6 connections on one side and 8 on the other,

and by the looks of things 1 of which goes to chassis and one is left undetermined. leaving the 12 colored on the schematic.

There should be 6 point of connection to the  mic schematics, 2 Feedback , 2 for audio and 2 for primary ,
the internal link ( series primary and series audio output and series feedback are actually on the adaptor board)
there is no core ground on oliver Traffo but max has them, )
Let me know,
Best,
Dan,

yeah I'm with you, all the additional wiring is internal or unnecessary due to single impedance.

1 pair to primary (c9 +ground)
1 pair to feedback (r18)
1 pair secondary (xlr 1-2 / c13 c12)

So do you think it's necessary trying to reverse the transformer then? I would do it in a snap but i'd rather not desolder a PCB transformer if its not necessary. Really easy to break a wire even with a desoldering station.
/
Emil

 

[dmp]

Flipping the transformer around won't make any difference, based on the wiring diagram.
Someone with a scope should test the windings. Since everyone is getting sound out  of there mics, the primary and secondary seem correct. But the feedback seems to be whacked. It could be that one of the feedback windings is connected backwards or not at all.
If you feed a 1v signal into the primary, the signal on the feedback should be 1/22.
If I had a t67 I could test it on my scope, but I don't have a transformer.

 

[Studio Mollan]

Flipping the transformer around won't make any difference, based on the wiring diagram.
Someone with a scope should test the windings. Since everyone is getting sound out  of there mics, the primary and secondary seem correct. But the feedback seems to be whacked. It could be that one of the feedback windings is connected backwards or not at all.
If you feed a 1v signal into the primary, the signal on the feedback should be 1/22.
If I had a t67 I could test it on my scope, but I don't have a transformer.

Thanks for confirming that!
Well iäve meassured the fedback windings for DCR and they show upp identical. ca32r both and they make connection to the R18.
/
Emil

 

[dmp]

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

 

[Studio Mollan]

Flipping the transformer around won't make any difference, based on the wiring diagram.
Someone with a scope should test the windings. Since everyone is getting sound out  of there mics, the primary and secondary seem correct. But the feedback seems to be whacked. It could be that one of the feedback windings is connected backwards or not at all.
If you feed a 1v signal into the primary, the signal on the feedback should be 1/22.
If I had a t67 I could test it on my scope, but I don't have a transformer.

Can i do that with a wavegenerator? Just send 1kHz 1v to the input and then meassure the Feedback? You need an AC generator right? not sure if mine is that.

 

[dmp]

Yeah, send a 1kHz 1V sine wave to the input and monitor the feedback. If you pull C17 and R18 and monitor the voltage at the 'ws' points on the image I just posted, you should see a step down of 1:22. 
1 kHz implies it is a AC generator. DC doesn't have a freq.

 

[Melodeath00]

This would make a lot of sense, my u67 sounds like it has no de emphasis at all, the top end sounds wide open like c12 and mids sound scooped. also could have something to do with my 5db down.

Wait, I thought you said it was "right there" with a real U67, just 5dB down.

 

[poctop]

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.

Best,
Dan,

 

[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.

Best,
Dan,

Thanks for checking!
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.

It's a hard thing to miss since the microphone actually sounds really good this way. Nothing like the original i assume but none the less a very good sounding microphone.

/
Emil

 

[0dbfs]

Presumably if the feedback audio is reversed polarity it would "Add" instead of "Subtract".... Making the de-emphasis inverse...

Glad someone caught this! You guys rock!

Cheers,
jb

 

[dmp]

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

 

[JessJackson]

This would make a lot of sense, my u67 sounds like it has no de emphasis at all, the top end sounds wide open like c12 and mids sound scooped. also could have something to do with my 5db down.

Wait, I thought you said it was "right there" with a real U67, just 5dB down.

So did I, until i got it home and cut some unusable female vocals with it yesterday. on my voice just talking and using ns-10s i couldn't tell the difference much but after cutting a female driven song at home studio i realized the vocals weren't in keeping with the other u67 vocals on the rest of the album.

could also be that the head grill is more open, capacitor is not electrolytic, 0.01s are not wimp tfm's. could be so many factors

but I'm about to build another custom u67 inside u87ai so i really want to get to the bottom of this.

J

 

[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

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

 

[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?