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

[poctop]

Hey guys, wanted to give an update on my capsule. I had it sent out to Ben, it was repaired and shipped back within a week! Sounds great now and performing like the other mic.

I'm still trying to lower some of the noise in my mics. I have that sorta wind/bubbling sound down there. I thought it may be the tubes at first but I replaced them with some low noise tele silver shield hilumins from the nos store, and the noise is still down there. I've been cleaning the circuit with alcohol which seems to be helping. Maybe it's just a matter of getting the circuit really clean? Has anyone else had any successful tricks to lowering noise? Thanks!

Make sure the tube Grid node does not touch anything and it is floating , Check the turrent point also , cleanliness is very important in this build, make sure all the floating connection do not touch anything as well , if also can make sure the component on the tube socket board do not touch each other , look for cold solder and flux , are both mics equally noisy  , is it a systematic building error ?  can ou measure the anode point  (a)  on the mic pcb and check it does not vary
Hope this helps,  check your pol voltage , B+ , check the lead from the capsule also ,
Can you post a clip of the noise .

 

[Tedrummerx]

thanks for the reply dan.

Here's mic 1(the noisier of the two): https://soundcloud.com/tedfreeman/u67-1
And mic 2, which i'm pretty happy with as far as the noise: https://soundcloud.com/tedfreeman/u67-2

Through vp26s with maybe 45-50ish db of gain

 

[poctop]

disconnect the capsule ( is the noise still there ) ?  and then start measuring reference voltage such has B+ , H-, and bias voltage, with the tube in , at the mic PCB and then remove the tube and take the same reading at the tube socket  . double check you wiring and the HZ bridge for short , sounds like a snow storm to me.  if you turn the light off can you actually see the tube glowing in the dark ?  take your time and be carefull  the sound i hear is not like an typical HZ contamination tough,  seems like somthing is not wired correctly or cold soldered,
Best,
Dan,

 

[Dylan W]

Heads up for anyone who's ordering:

Mouser is out of the 0.01uf polyester film caps, Vishay part number MKT1813310404. I emailed Dany about several alternatives, and he was kind enough to respond with 5 minutes and point out that Newark carries them.

http://www.newark.com/jsp/search/productdetail.jsp?sku=18M2494

Mouser is also out of the 2 watt 18 ohm resistors and 22uf/350V electrolytics, both of which Newark also carries, and the CTS 25K pot, which Digikey carries.

Dylan

 

[poctop]

you can always check for similar components with mouser ,  the 18 ohm resistor is 5% they might have stock for 1% also ,
the compare tool from mouser is very effective ,
Best,
DAn,

 

[nolivdacom]

same problem for me...
Here are the parts numbers from digikey:
pot 25k 5W: CT2160-ND
resistor 18ohms 2W: 18ZCT-ND
Capacitor 22uF 350V: P5932-ND

I found 0.01uf polyester film caps at mouser's so I don't have any part number from digikey.
Hope it will help.

You also have to know that you have to pay about 18€ for shipping. It was more expensive for me then parts...

best,
Olivier

 

[Jim50hertz]

Banzai in the EU stock those 0.01 poly caps.

Conrad stock a 4W 25k pot.  I used this one with no issues.

 

[nolivdacom]

Just a silly question for European people about the PSU:
Do we need to use a transformer to convert 230V to 230V? 
Am I wrong if I think that we can go without this tranformer?
Is there any voltage regulation here?
Thanks for any explanation!

:-\

best,
Olivier

 

[poctop]

Just a silly question for European people about the PSU:
Do we need to use a transformer to convert 230V to 230V? 
Am I wrong if I think that we can go without this tranformer?
Is there any voltage regulation here?
Thanks for any explanation!

:-\

best,
Olivier

you need it to isolate yourself from everything that happens in the wall-wart, specially Hum
Best,
Dan,

 

[nolivdacom]

you need it to isolate yourself from everything that happens in the wall-wart, specially Hum

Ok thanks!

Another question about fuse for psu:
I read that (for europe) we have to use 0,1A fuse. I tried but it doesn't work. I tried with 0,3A from mouser bom. My psu works well. So, my question is, what is the good value for europe?

best,
Olivier

 

[poctop]

you need it to isolate yourself from everything that happens in the wall-wart, specially Hum

Ok thanks!

Another question about fuse for psu:
I read that (for europe) we have to use 0,1A fuse. I tried but it doesn't work. I tried with 0,3A from mouser bom. My psu works well. So, my question is, what is the good value for europe?

best,
Olivier

in therory you should be fine with a 0.1A  but it needs to be a slow-blow type but here i have used 0.3A instead of point 0.2A America and it works fine ,
somtime it is just not enough slow blow type to work if everything reads proper and you have a 0.3A you'll be fine the worst thing that could happen is that you cook the toroid that is why you need a slow blow type fuse,

Best,
Dan,

 

[Winetree]

Received a P.M.

I saw you had a magic donut on your 67 tube , what is it  and where did you get this ?
Let me know if you have a chance , this is very nice , i'd like to test with a smaller one for th 5840w also ,
intersting material,
Best
Dan,

 

[Tedrummerx]

So I've been playing around with the noisy mic. I've disconnected the capsule, noise is still there. Checked voltages, all seem good. Then I tried swapping the tube from the noisy mic with the quiet mic and sure enough the noise switched to the other mic too. So, maybe my issue is I need to continue my search for low noise tubes?

Also, does it make any sense trying to come up with a test to see if the noise is within the specs of a u67? I'm really just comparing the noise to that of my other mics, like my mk47. Maybe the noise is close to normal for a u67.

With all said, I've been using my 67s and they sound amazing. On sources like drums, the noise isn't even close to an issue, they sound great!

Thanks for your input guys, really appreciate it!

 

[bkbirge]

So I've been playing around with the noisy mic. I've disconnected the capsule, noise is still there. Checked voltages, all seem good. Then I tried swapping the tube from the noisy mic with the quiet mic and sure enough the noise switched to the other mic too. So, maybe my issue is I need to continue my search for low noise tubes?

Also, does it make any sense trying to come up with a test to see if the noise is within the specs of a u67? I'm really just comparing the noise to that of my other mics, like my mk47. Maybe the noise is close to normal for a u67.

With all said, I've been using my 67s and they sound amazing. On sources like drums, the noise isn't even close to an issue, they sound great!

Thanks for your input guys, really appreciate it!

My vintage U67 was quiet as a church mouse. It has probably already been mentioned but the wiring on this build is of utmost importance for noise, take your time and be very meticulous with keeping it clean and short.

 

[dmp]

Then I tried swapping the tube from the noisy mic with the quiet mic and sure enough the noise switched to the other mic too.

Seems pretty conclusive that the noise is following the tube. Get some more tubes?
My build was quiet. Never occurred to me to measure the noise floor - it was just not apparent doing room recordings of acoustic music. Using a telefunken tube.
So if you notice the noise, I would say it is too much.

 

[micaddict]

Telefunken is the quietest (and most expensive) on average, but even those vary.
Cheapest are the Russian EF86s (OK, not counting the Chinese). That means you can buy more and there will be quiet ones among them.
I'm not talking about tone here, mind.

 

[poctop]

just added this for reference,

http://www.levytubes.com/servlet/the-Vacuum-Tube-Dampers-fdsh-Dampeners/Categories

(thanks Winetree)

Dan,

 

[Volume11]

Are those things really necessary?

 

[Tedrummerx]

Thanks for the replies guys.
So far in my search for tubes I purchased two telefunken silver shields off ebay which were not advertised for microphone use, and were a bit noisy, one more than the other. So I then decided to purchase a matched pair of tele silver shield (simens branded), tested for low noise from the nos store. Again lower in noise but one nosier than the other. NOS is actually shipping me a replacement for free which is great. So my search will continue. Anyone having good luck with the 806s?

My build was quiet. Never occurred to me to measure the noise floor - it was just not apparent doing room recordings of acoustic music. Using a telefunken tube.
So if you notice the noise, I would say it is too much.

And this is the bottom line, is the noise really so apparent that it affects the sound I'm trying to capture. I think maybe i'm being too picky. When really will I be using 50-60+ db of gain with this mic? I feel not often. If i can get my noisy mic around the level of the other quieter mic, I'll be a happy camper.

 

[poctop]

Received my capsules friday and finished my first of two 67's yesterday. After initial testing and a really long burn in period, I'm really happy with this mic! I expected an extended debugging period, but it worked first time I plugged it all in, thanks to Dany's great documentation. I'm building a stereo set with Beesneez capsules (matched!) and ioaudio transformers. I'll get started on the next one after some more testing this week. Mine is going up against two original u67's later this week

Thanks Ken,  Any updates this great idea of comparaison with the real thing ,
best,
Dan,