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

[Purplenoise]

250pf seems about right from what I’m measuring so far, I don’t have an original or reissue to compare. I’ve a K67 and a K6, testing with the K67.

Reissue was a little brighter and upper mid forward than the vintage…cleaner too. Tubes play into it too…tfk 806 and 86 are less bright than mullards and amperexs that I tried. The reissue had an electro harmonix which I believe is a bright tube

 

[Jim50hertz]

Reissue was a little brighter and upper mid forward than the vintage…cleaner too. Tubes play into it too…tfk 806 and 86 are less bright than mullards and amperexs that I tried. The reissue had an electro harmonix which I believe is a bright tube

That’s good info thanks, I’ve noise tested TFK EF86s in mine, though I’ve some Mullard EF86s to hand, not noise tested though, bought more for guitar amps. Probably worth a taste test once I get the freq response right

 

[dmp]

I have not measured it. What was your test procedure?

I used the program RMAA and send a signal from the soundcard into the calibration input (shown on schematics). Mic output connected to preamp and into soundcard. You want to make sure the soundcard / preamp is flat freq response. You can just do this with the mic capsule as is in a quiet room or replace the capsule with a small (68pf) capacitor.
Adjust the levels appropriately and measure frequency response.

 

[Studio Mollan]

Those are the values I ended up with in both my 67s. One is with Moby but the other one is with haufe ( same as Neumann reissue) so I don’t think Mobys transformer is bright. Maybe something is different in the circuitry compared to Neumann?

I think we are all using film caps on the output. Original Neumann was an electrolytic. That could answer for a little of the very high end extension, but might not be enough to even measure. Just thinking out loud.

 

[Moby]

I think we are all using film caps on the output. Original Neumann was an electrolytic. That could answer for a little of the very high end extension, but might not be enough to even measure. Just thinking out loud.

Film capacitor can be subjective "brigter" charachter for sure. I avoid coupling film in my U67 builds. Also, my transformer measure exact the same response compared to the vintage Neumann Bv.12. i don't have those measurments with me but I have a photo of the build standing besides the vintage one If you need those graphs I can search for it or repeat the measurings.

 

[Purplenoise]

I think we are all using film caps on the output. Original Neumann was an electrolytic. That could answer for a little of the very high end extension, but might not be enough to even measure. Just thinking out loud.

I tried also an electrolytic…the high end was a touch different. A little metallic and spitty. I prefer the sound of a film cap…not my favorite but a touch smoother and less gritty than the electrolytics I have tried. I used clarity cap which is a bit darker than others I tried. Wish there was room for an mp or PIO there haha

 

[Moby]

I tried also an electrolytic…the high end was a touch different. A little metallic and spitty. I prefer the sound of a film cap…not my favorite but a touch smoother and less gritty.

It also depends from the manufacturer. I'm really happy with the Vishay 30D105M250BA2A

 

[dmp]

Moby, what C17 value did you use?
Those are beautiful mics!

 

[Moby]

Moby, what C17 value did you use?
Those are beautiful mics!

I think 120pf. Sorry, I'm not 100% sure

 

[Purplenoise]

It also depends from the manufacturer. I'm really happy with the Vishay 30D105M250BA2A

Thanks Moby, I’ll try those.

 

[Moby]

Thanks Moby, I’ll try those.

I don't say that those are the best possible but it served me well

 

[Purplenoise]

I don't say that those are the best possible but it served me well

If you like them that’s good enough for me haha

 

[JerryPbury]

I used the program RMAA and send a signal from the soundcard into the calibration input (shown on schematics). Mic output connected to preamp and into soundcard. You want to make sure the soundcard / preamp is flat freq response. You can just do this with the mic capsule as is in a quiet room or replace the capsule with a small (68pf) capacitor.
Adjust the levels appropriately and measure frequency response.

Thanks but I am pure analog. Gave up on Computers for music in the early 90’s. I’ll figure it out.

 

[Moby]

Thanks but I am pure analog. Gave up on Computers for music in the early 90’s. I’ll figure it out.

Total respect!

 

[Delta Sigma]

Thanks but I am pure analog. Gave up on Computers for music in the early 90’s. I’ll figure it out.

You can do it by ear. Start with 80 or 100pF and work your way up in size. You'll notice it has too much high end if the value is too small. I think if C17 is too small, it leaves a bump right where it gets that audible air. That bump can sound pleasant on some sources but with a good capsule, tube and one of Moby's transformers, you should be aiming for the world's most versatile mic with a 67.

It also depends from the manufacturer. I'm really happy with the Vishay 30D105M250BA2A

Did you try 0.47uF and then settle on 1uF? I tried other cap types in my U67 but not values; I always tried 0.47uF.

 

[dmp]

You can do it by ear. Start with 80 or 100pF and work your way up in size. You'll notice it has too much high end if the value is too small. I think if C17 is too small, it leaves a bump right where it gets that audible air. That bump can sound pleasant on some sources but with a good capsule, tube and one of Moby's transformers, you should be aiming for the world's most versatile mic with a 67.

You absolutely cannot determine if the amplifier frequency response is correct by ear. It not only depends on a capsule response but it depends on what experience an individual has and wants out of a mic. Someone could dial in a mic to be something they like but it may be brighter or darker than how someone else would do it, and it may or may not resemble a real u67. It would say nothing about the amplifier being -10dB at 15kHz.
To do it without a computer, use a signal generator to inject a signal at the calibration input at a range of frequencies (40 Hz, 1kHz, 15 kHz) and measure Vrms of the output with a scope. The signal should be -10 dB with 15kHz WRT to 1 kHz. The Neumann manual describes how to do it before there were computers

 

[Purplenoise]

You absolutely cannot determine if the amplifier frequency response is correct by ear. It not only depends on a capsule response but it depends on what experience an individual has and wants out of a mic. Someone could dial in a mic to be something they like but it may be brighter or darker than how someone else would do it, and it may or may not resemble a real u67. It would say nothing about the amplifier being -10dB at 15kHz.
To do it without a computer, use a signal generator to inject a signal at the calibration input at a range of frequencies (40 Hz, 1kHz, 15 kHz) and measure Vrms of the output with a scope. The signal should be -10 dB with 15kHz WRT to 1 kHz. The Neumann manual describes how to do it before there were computers

Yes of course but do not underestimate the power of a trained ear. It’s a far more complex device than anything we have today. Depending on capsule and the synergy of components in general you might achieve more pleasing results than measurements. The best of both worlds of course is to follow proper tuning procedures and then fine tune by ear…Between 10 properly tuned vintage mics of the same model there are always one or two that stand out. You might argue of course that it’s not the same one or two for everyone haha

 

[Moby]

Did you try 0.47uF and then settle on 1uF? I tried other cap types in my U67 but not values; I always tried 0.47uF.

Hey, I used only 1uf, never tried or measure it with 0.47uf

 

[JerryPbury]

You absolutely cannot determine if the amplifier frequency response is correct by ear. It not only depends on a capsule response but it depends on what experience an individual has and wants out of a mic. Someone could dial in a mic to be something they like but it may be brighter or darker than how someone else would do it, and it may or may not resemble a real u67. It would say nothing about the amplifier being -10dB at 15kHz.
To do it without a computer, use a signal generator to inject a signal at the calibration input at a range of frequencies (40 Hz, 1kHz, 15 kHz) and measure Vrms of the output with a scope. The signal should be -10 dB with 15kHz WRT to 1 kHz. The Neumann manual describes how to do it before there were computers

I have a signal Generator and Scope. They’re buried under my workbench. In my spare time I am trying to put my home studio back in operation. Tons of soldering Patchbay connections. Its been in storage for the past 5 years. I retired due to age and cancer and moved to NC. Cancer is gone (so they tell me) but in the interim my wife came down with terminal Brain Cancer so my full time job is care giver. So it will be a while until I can test my U67 clone. Moby transformer, Eric’s Capsule and Valvo EF86. I have a pair and they sound great!

 

[Purplenoise]

I have a signal Generator and Scope. They’re buried under my workbench. In my spare time I am trying to put my home studio back in operation. Tons of soldering Patchbay connections. Its been in storage for the past 5 years. I retired due to age and cancer and moved to NC. Cancer is gone (so they tell me) but in the interim my wife came down with terminal Brain Cancer so my full time job is care giver. So it will be a while until I can test my U67 clone. Moby transformer, Eric’s Capsule and Valvo EF86. I have a pair and they sound great!

Oh man…that’s tough. I wish you the best possible outcome on everything.