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

[JerryPbury]

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

It’s all good. Can’t do anything about it but make her feel comfortable. It’s just life.

 

[dmp]

I had some time this morning to try measuring the transformer coils again and got the problems figured out out - I had a bad cable / connection.

Moby's BV12 specs out perfectly - really close to Neumann ratios of P:S 8, P:T 22. I measured the rms voltage across the P:S and P:T injecting a signal of 1Vrms at 1kHz and 15kHz
For Moby's, The P:S n=6.86 and the P:T n=21.02. I checked that the two coils were balanced as well and they were very close.

For the Ioaudio however, I found the problem. The P:S was correct n=6.86 but the P:T n=1.53. This means the tertiary voltage was almost 14 times higher than it should be. One interesting thing is I tested the two coils separately as well and one of the coils was correct, having a P:T n=22 but the other coil was way high and out of spec, so perhaps the winding plan was OK but there were shorts in some of the T coils. This would explain why some people were able to build correct mics with them. The ioaudio tested the same at 1kHz and 15 kHz

I have a second ioaudio in a m269 that I will pull out and test.

 

[Purplenoise]

I had some time this morning to try measuring the transformer coils again and got the problems figured out out - I had a bad cable / connection.

Moby's BV12 specs out perfectly - really close to Neumann ratios of P:S 8, P:T 22. I measured the rms voltage across the P:S and P:T injecting a signal of 1Vrms at 1kHz and 15kHz
For Moby's, The P:S n=6.86 and the P:T n=21.02. I checked that the two coils were balanced as well and they were very close.

For the Ioaudio however, I found the problem. The P:S was correct n=6.86 but the P:T n=1.53. This means the tertiary voltage was almost 14 times higher than it should be. One interesting thing is I tested the two coils separately as well and one of the coils was correct, having a P:T n=22 but the other coil was way high and out of spec, so perhaps the winding plan was OK but there were shorts in some of the T coils. This would explain why some people were able to build correct mics with them. The ioaudio tested the same at 1kHz and 15 kHz

I have a second ioaudio in a m269 that I will pull out and test.

Very useful info, cheers

 

[Delta Sigma]

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

My sig gen died when I was calibrating mine, haven't gotten around to replacing it. It certainly wasn't easy or quick, but I got mine to where it's versatile. Is it a U67? I don't really care. It's a great mic. Most versatile mic that I've ever used.

 

[Purplenoise]

My sig gen died when I was calibrating mine, haven't gotten around to replacing it. It certainly wasn't easy or quick, but I got mine to where it's versatile. Is it a U67? I don't really care. It's a great mic. Most versatile mic that I've ever used.

And it takes eq like a champ…boost high end 10db and it is still smooth. Not that it needs it but just saying

 

[Moby]

I had some time this morning to try measuring the transformer coils again and got the problems figured out out - I had a bad cable / connection.

Moby's BV12 specs out perfectly - really close to Neumann ratios of P:S 8, P:T 22. I measured the rms voltage across the P:S and P:T injecting a signal of 1Vrms at 1kHz and 15kHz
For Moby's, The P:S n=6.86 and the P:T n=21.02. I checked that the two coils were balanced as well and they were very close.

For the Ioaudio however, I found the problem. The P:S was correct n=6.86 but the P:T n=1.53. This means the tertiary voltage was almost 14 times higher than it should be. One interesting thing is I tested the two coils separately as well and one of the coils was correct, having a P:T n=22 but the other coil was way high and out of spec, so perhaps the winding plan was OK but there were shorts in some of the T coils. This would explain why some people were able to build correct mics with them. The ioaudio tested the same at 1kHz and 15 kHz

I have a second ioaudio in a m269 that I will pull out and test.

Thanks for measuring it. Actually ratio should be P/S 6,92:1, P/T 21,6:1. Of course, some magnetics loss is always present and of course small measuring errors.

 

[dmp]

Thanks for measuring it. Actually ratio should be P/S 6,92:1, P/T 21,6:1. Of course, some magnetics loss is always present and of course small measuring errors.

Thanks for that info. My scope may not be perfectly accurate also - it actually gives me a calibration error on boot up.

The Ioaudio doesn't measure any ohms on the tertiary winding, so it seems it is actually open. On the second Ioaudio BV12 I also found an open winding (primary). I removed the lams, which seemed to have some kind of glue between them. No holes in the lams. I would like to repair/rewind the bobbins by hand to make these usable.

From the winding spec, they should be 'mantel' wound with the layers first to last as:
S: 0.14 mm (35awg) by 390 turns
isolation: 2 layers (tape?)
copper shield -> black (ends insulated to not form a magnetic loop)
isolation: 2 layers
T: 0.06 mm (42.5awg) by 125 turns
isolation: 2 layers
P: 0.06mm (42.5 awg) by 2700 turns

 

[Janalex]

Hey everyone. Just starting on a build of a stereo pair of these. I have all the parts except the psu switch and lamp. Could someone please post which of these they ordered from mouser for the collective cases enclosure? These are not in the BOM and I’ve already ordered the wrong ones once

 

[Janalex]

Anybody?

 

[dmp]

Easier to order these from elsewhere.

Carling toggle switch
Fender type lamp holder
Either a 6.3v lamp (on heater circuit) or a 120v lamp
I usually use a 120v lamp as it doesn't add current to the heater circuit

 

[Janalex]

Thank you

 

[Studio Mollan]

Easier to order these from elsewhere.

Carling toggle switch
Fender type lamp holder
Either a 6.3v lamp (on heater circuit) or a 120v lamp
I usually use a 120v lamp as it doesn't add current to the heater circuit

+1. Much easier to source and also won't draw any current from the heater circuit. (But I'm using 220V lights as I'm in Europe)

 

[dmp]

So I have moby's transformer and c17=250pf and the mic sounds very good. Not too bright, not too dark
Does not measure as -10db @15khz however.
More to figure out.

 

[Janalex]

I just received the above recommended switch and lamp holder. The lamp holder is way too big again for the hole! I presumed the Poster didn’t modify the enclosure but he must have and didn’t understand the question. I don’t have a drill that can accommodate a bit that size. Do they make lamp holder that are smaller specifically the size of the hole in the enclosure?

 

[Studio Mollan]

I just received the above recommended switch and lamp holder. The lamp holder is way too big again for the hole! I presumed the Poster didn’t modify the enclosure but he must have and didn’t understand the question. I don’t have a drill that can accommodate a bit that size. Do they make lamp holder that are smaller specifically the size of the hole in the

That’s DIY. I you have limited tools it’s important to check specs on all parts.

 

[dmp]

I just received the above recommended switch and lamp holder. The lamp holder is way too big again for the hole!

What is the diameter of the hole? I have several collective cases psu enclosures and they have a ~17mm hole for that type of lamp, above the power switch.
I didn't modify them

 

[Janalex]

 

[dmp]

what's the diameter - 1/4" ?

 

[Janalex]

About 5/16”

 

[Moby]

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