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

[Moby]

Another question on C9, i have a 250v cap in there just now, can I get away with a 200v cap?

Anode supply is +210v and at the cold state it's possible that full suppy voltage will be on the capacitor. So, 250v is the safety recomended value. Also, the low leakage capacitor should be used to protect the primary winding of the transformer.

 

[Jim50hertz]

Thanks Emil and Srdjan

 

[dmp]

Anybody replace Ioaudio BV12 with Moby's? I removed the Ioaudio, but Moby's is too large physically to put the shell back on.
Any pics of how you guys did it?

 

[Purplenoise]

Anybody replace Ioaudio BV12 with Moby's? I removed the Ioaudio, but Moby's is too large physically to put the shell back on.
Any pics of how you guys did it?

There is thin clear plastic on the side of windings-core. Just snip the corners off

 

[dmp]

Thanks!
Did you drill holes through the PCB to mount the transformer?
And your pcb is inside the rails it looks like?

 

[Purplenoise]

Thanks!
Did you drill holes through the PCB to mount the transformer?
And your pcb is inside the rails it looks like?

Oh yes sorry..forgot about that. Yes from the inside of the rails. I believe you have to trim the sides a little of the trafo base/ pcb

 

[dmp]

Are you using the two pcb version where there was the seperate PCB for the AMI transformer?
I have the single pcb version that Ioaudio's BV12 mounted on directly. Not sure if I can put the pcb inside the rails and have enough room for the tube

 

[Purplenoise]

Are you using the two pcb version where there was the seperate PCB for the AMI transformer?
I have the single pcb version that Ioaudio's BV12 mounted on directly. Not sure if I can put the pcb inside the rails and have enough room for the tube

Oh I see. Yes I am using Danys pcbs. See if it will fit though by sniping the clear plastic edges first. I have a feeling it will
On my second 67 I use a haufe transformer and I have the pcb on top. I still had to snip the corners of the plastic

 

[Studio Mollan]

Are you using the two pcb version where there was the seperate PCB for the AMI transformer?
I have the single pcb version that Ioaudio's BV12 mounted on directly. Not sure if I can put the pcb inside the rails and have enough room for the tube

Watching this thread. I’m about to upgrade my ioaudio u67 with proper transformers. Would be great to be able to use the original pcb!

 

[dmp]

Moving the PCB within the rails did the trick. I didn't trim the transformer at all (and didn't want to). I held the transformer with a rubber band and pinched the pcb between the rails with screws from both sides - making it secure enough for testing.

 

[Purplenoise]

Moving the PCB within the rails did the trick. I didn't trim the transformer at all (and didn't want to). I held the transformer with a rubber band and pinched the pcb between the rails with screws from both sides - making it secure enough for testing.

Awesome, I am glad it all worked out.

 

[dmp]

Moby transformer sound great but is much brighter. I swept the amplifier and it is much different than the Ioaudio. Not at the -10dB at 15kHz of the Neumann spec. Maybe I have it miswired or it needs a different C17

 

[Purplenoise]

Moby transformer sound great but is much brighter. I swept the amplifier and it is much different than the Ioaudio. Not at the -10dB at 15kHz of the Neumann spec. Maybe I have it miswired or it needs a different C17

That was the main concern of people using the ioaudio…too dark. Some omitted c17 to get closer to the u67 response. Moby has more or less the same brightness as the haufe…or should I say flatness. In both my builds with Moby and haufe I have used 250pf c17

 

[dmp]

I don't see why the measured frequency response should be different if both the transformers have a n=22 feedback winding. I think they could sound different, but I measured a big frequency difference.

For some reason I couldn't measure the ratios of the secondary or feedback windings on either bv12? I was getting strange phase shifted signals that were not the right Vrms for those ratios (at 1kHz, 2.3 Vrms input on primary).
I think the Primary/secondary should be 7 and primary/feedback should be 22. Not sure why I was getting just strange results when I tried to measure (with a function gen and scope).

 

[Purplenoise]

I don't see why the measured frequency response should be different if both the transformers have a n=22 feedback winding. I think they could sound different, but I measured a big frequency difference.

For some reason I couldn't measure the ratios of the secondary or feedback windings on either bv12? I was getting strange phase shifted signals that were not the right Vrms for those ratios (at 1kHz, 2.3 Vrms input on primary).
I think the Primary/secondary should be 7 and primary/feedback should be 22. Not sure why I was getting just strange results when I tried to measure (with a function gen and scope).

No idea but I have read a few times that the ioaudio is darker than the rest. Haven’t used one but the ones I have used/heard have similar freq responses ( Moby, Ami, haufe).

 

[Studio Mollan]

No idea but I have read a few times that the ioaudio is darker than the rest. Haven’t used one but the ones I have used/heard have similar freq responses ( Moby, Ami, haufe).

Correct. The IOaudio transformer is faulty in some way. The only way of getting a good calibration (@15kHz) was to remove c17 completely. No-one knows why, but it is clearly not comparable to the original Haufe. At some point I will get a pair of Mobys, or similar, and try to fit them.
/
E

 

[Moby]

Correct. The IOaudio transformer is faulty in some way. The only way of getting a good calibration (@15kHz) was to remove c17 completely. No-one knows why, but it is clearly not comparable to the original Haufe. At some point I will get a pair of Mobys, or similar, and try to fit them.
/
E

I don't know why above mentioned transformer sounds dark but original Bv.12 was made by Neumann (in house production), so all other alternatives are aftermarket parts including mine

 

[dmp]

There's a big difference between 'sounds dark' and statements about the amplifier frequency response being wrong with the ioaudio. I have a build with ioaudio transformer, c17=100pf, and the freq response measures correct (-10db @ 15khz). Without c17 installed the mic will be MUCH brighter. Not sure how the calibration could be right without c17 since that is the negative feedback path.
Be nice to figure out with some measurements what is going on. I've been curious about this for years.

 

[Moby]

There's a big difference between 'sounds dark' and statements about the amplifier frequency response being wrong with the ioaudio. I have a build with ioaudio transformer, c17=100pf, and the freq response measures correct (-10db @ 15khz). Without c17 installed the mic will be MUCH brighter. Not sure how the calibration could be right without c17 since that is the negative feedback path.
Be nice to figure out with some measurements what is going on. I've been curious about this for years.

The guy probably made some mistake with the winding arrangement. It can't be fixed with omitting the filter network. Replacing the transformer is the only way to make it OK.

 

[Purplenoise]

The guy probably made some mistake with the winding arrangement. It can't be fixed with omitting the filter network. Replacing the transformer is the only way to make it OK.

You seem to know a thing or two about transformers
Is it possible though that the slope in the low cut with ioaudio transformer is more broad? That would explain the dark character despite the seemingly correct calibration