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

[poctop]

Any guesses why they changed C9 in terms of both value, and voltage rating? First one is 250V and the next is 450V. Also not seeing a date/year on those schematics

the first schematis shown dates from 1960  serial after 343 the second one serial after 10,000 ,  that gives you an idea ,
the bypass cap has been tweaked a bit probably to alter the overall sound might 1uf instead of 0.5 will give slighlty different low end behavior,
for the rating 250V is sufficient as the voltage seen there is about 75V, might 450V is what they had handy a this time ,
just some toughts,
Dan,

 

[gary o]

Wasnt 1uf earlier and the to keep bass down swapped to .5uf also swapped 500M down to 400M & 68M down to 60M

question does the 60/68M positioned resistors add bass the higher the value as would R8 ? Im assuming they would....

 

[gary o]

sorry cross posted....

My schematic with no C17 is also 1960

I have just kinda breadboarded the U67 circuit to learn Im interested in the reversed polarty of the heater..... can anyone explain ? my breadboard 67 is working but was a little white noisy & cant get my plate below 62V BUT if I swap polartity of my heater back to the more common way my plate is then 73V & white noise mush much lower ?

Thanks

 

[poctop]

sorry cross posted....

My schematic with no C17 is also 1960

I have just kinda breadboarded the U67 circuit to learn Im interested in the reversed polarty of the heater..... can anyone explain ? my breadboard 67 is working but was a little white noisy & cant get my plate below 62V BUT if I swap polartity of my heater back to the more common way my plate is then 73V & white noise mush much lower ?

Thanks

Like it was mentionned before in this thread,  the negative grid bias is derived from the heater negative supply , a unique way of doing it
this tough should not prevent you from having he the proper plate voltage at setup since it is self bias,  the feedback capactitor coupled with this even more special transformer is (very very) sensitive to RF and surrounding and even crap from space. so if your breadboarding is not shielded and enclosed this wil have the you know effect on it , if you swap the polarity you will be changing your overall bias and affect the gain structure of the mic hence the white mush .

Just my 2 cents,
D

 

[gary o]

sorry cross posted....

My schematic with no C17 is also 1960

I have just kinda breadboarded the U67 circuit to learn Im interested in the reversed polarty of the heater..... can anyone explain ? my breadboard 67 is working but was a little white noisy & cant get my plate below 62V BUT if I swap polartity of my heater back to the more common way my plate is then 73V & white noise mush much lower ?

Thanks

Like it was mentionned before in this thread,  the negative grid bias is derived from the heater negative supply , a unique way of doing it
this tough should not prevent you from having he the proper plate voltage at setup since it is self bias,  the feedback capactitor coupled with this even more special transformer is (very very) sensitive to RF and surrounding and even crap from space. so if your breadboarding is not shielded and enclosed this wil have the you know effect on it , if you swap the polarity you will be changing your overall bias and affect the gain structure of the mic hence the white mush .

Just my 2 cents,
D

Thanks Dany the odd thing Im finding is that when I wire the special heater bais scheme the correct way as per schematic I get wrong plate voltage of between 51V & 62V & 1.9 to 2V at r 9 10 11 12 depending of my EF86 AND as a crap bonus white mush.......But if I reverse heater polarity mush goes away  well nearly plate between 71v 78V & 1.65V R9 10 11 12..... when I say breadboard I just mean made for testing not proper build but mic is enclosed , I have no humm or other issues the mic sounds very good not using bv12 using BV08 for test with no feedback circuit tim cambel capsule for now

Thanks for info

 

[gary o]

Aha ! realize my mistake I had reversed the heater connections in the first place  :-[ silly me so now all voltages are spot on mush noise is quieter except when S2 open.....

I think the mush is just the tube dont think Ive ever come across a quiet EF86, I need to find some more EF86s

Something interesting in my 1960 U67 schematic the heater polarity IS indeed reversed, ie 6.3+ connected to R10...... R4 R7 also different values ..... having by accident been running my U67 this way as I reported could get the voltages right ( the voltages on my starnge 1960 schematic are same as other schematics ive seen so far)  so I wonder how the voltages could ever be right, I did lower the plate resistor value to get correct plate voltage, wondering if R4 R7 values have any affect on the voltages so I will try the different values, Im wondering if they just effect the low frequecies ...... either way will be fun to eexperiment.

 

[0dbfs]

If the heater was reversed so it gets +6V3 wouldn't the grid then get a positive bias?

That would certainly not sound "good" if so.

Cheers,
jb

EDIT:
Reversed as in the 0V line gets -6.3V and the -6.3V line gets 0V?

 

[poctop]

Aha ! realize my mistake I had reversed the heater connections in the first place  :-[ silly me so now all voltages are spot on mush noise is quieter except when S2 open.....

I think the mush is just the tube dont think Ive ever come across a quiet EF86, I need to find some more EF86s

Something interesting in my 1960 U67 schematic the heater polarity IS indeed reversed, ie 6.3+ connected to R10...... R4 R7 also different values ..... having by accident been running my U67 this way as I reported could get the voltages right ( the voltages on my starnge 1960 schematic are same as other schematics ive seen so far)  so I wonder how the voltages could ever be right, I did lower the plate resistor value to get correct plate voltage, wondering if R4 R7 values have any affect on the voltages so I will try the different values, Im wondering if they just effect the low frequecies ...... either way will be fun to eexperiment.

can you post this schematic where the heater is reversed ?  both the schematic i posted yesterday were -6.3V,
DAn,

 

[gary o]

http://repforums.prosoundweb.com/index.php?topic=36297.0

schematic is in this disscussion.

 

[poctop]

http://repforums.prosoundweb.com/index.php?topic=36297.0

schematic is in this disscussion.

I looked at it and if you look at the voltage shown on the schematic at R10 node the voltage reading is negative , so it must be a typo or just an omission,
Best,
DAN,

 

[DUDE GUY]

Kevin,
Do you have any sound samples you can share with us? I'm interested to hear what your mic sounds like. I had an RK-67 in my D-U67 initially and it was def not as good sounding as my HK-67 (Heiserman Audio).
I am def a proponent of 80% of the mic's sound is in the capsule

just my 2¢
Dave

Hey Dave,

Yes I definitely agree, the capsule is 80% of the sound, no question. In my case, I feel like something has to be off. It's awfully dull. That being said, it's still is a nice sound overall, if you're going for that. Anyway, I recorded some acoustic guitar (Seagull S6 Spruce), if you wouldn't mind giving it a listen here:

https://soundcloud.com/kevinwinrich/u67-acoustic-guitar

Signal Chain: U67 into Digi 003 preamp (no EQ, compression, or effects)

Mic placement: 5 inches from the 10th fret, slightly of axis towards the nut

Mic Info: RK67, BV12, JJ EF806-S

Picture of the guts attached..

Any help is greatly appreciated.

-Kevin

 

[gary o]

OK, got the new capsule installed! As usual, there was a lot more to it than "drag and drop"! I had to do a lot of drilling/prepping the new capsule holder arrangement since the K6 capsule has its own stand and I wanted to use it. Sigh. As expected, anything custom takes more time!

So I'm posting links to clips, one using a Chinese capsule I got from a Chunger build, and the second the BeesKneez K6 capsule. It's yours truly singing, so please don't kill the messenger!

I was holding the mic (iknow!) about 4-6" from my mouth. Different days - actually weeks apart. Some of the difference is simply my voice was different between the two takes! This is not scientific at all! Only processing whatsoever was to use the "normalize" effect on each to within 0.5db of 0.

Thoughts?

Wondering if anymore samples from these capsules, dont know if its my ears but I dont hear a lot of difference between the capsules was kinda expecting night & day difference .....my ears are not great due to many years as a singer...... what do other ears think....

Mike

Chinese Capsule: http://pctrainingexperts.com/portals/0/audio/chinese.mp3
Beeskneez K6: http://pctrainingexperts.com/portals/0/audio/k67-2.mp3

 

[poctop]

Kevin,
Do you have any sound samples you can share with us? I'm interested to hear what your mic sounds like. I had an RK-67 in my D-U67 initially and it was def not as good sounding as my HK-67 (Heiserman Audio).
I am def a proponent of 80% of the mic's sound is in the capsule

just my 2¢
Dave

Hey Dave,

Yes I definitely agree, the capsule is 80% of the sound, no question. In my case, I feel like something has to be off. It's awfully dull. That being said, it's still is a nice sound overall, if you're going for that. Anyway, I recorded some acoustic guitar (Seagull S6 Spruce), if you wouldn't mind giving it a listen here:

https://soundcloud.com/kevinwinrich/u67-acoustic-guitar

Signal Chain: U67 into Digi 003 preamp (no EQ, compression, or effects)

Mic placement: 5 inches from the 10th fret, slightly of axis towards the nut

Mic Info: RK67, BV12, JJ EF806-S

Picture of the guts attached..

Any help is greatly appreciated.

-Kevin

i would start  by looking at the basic voltage ( Bias ), (Plate) , (Polarisation Voltage),  (Heater), (B+) and specially the Hz bridge and capsule connection ,
the HZ bridge is definitely the first place to look after checking all of this,
Keep us posted,
D

 

[mistasanshou]

Did u get a chance to put the neumann capsule in yet?

so i finished my build, sounds great and just shot it out against vintage unmodified u67 here at paramount studios

Im using:

T67
Eric's 87 capsule with backplates tied together in cardioid
ero 1uf cap as seen above.
I'm at 208v b+ at full turn and 6.3 heater

Going back and forth on female singer my mic instantly is 5db hotter than the vintage u67
The top end is slightly more harsh/brittle and the bottom end is massive, too much lower mids in comparison to the u67 but was thinking it could be using the 1uf instead of a 0.5 over saturating the transformer possibly.

Other than that its very similar but I probably wouldn't use it until I can tune it to sound right without additional eq

I may throw a neumann k67 in there as i suspect thats the culprit for the slightly harsher tops.

cheers.

J

Did u get a chance to put that k67 in? If so how does it compsre to the vintage u67 now?  Im thinking of going all out with the neumann k67. 

Dan, thanks for this awesome project, ive wanted a u67 ever since the day I heard one and now its within reach.  How do the ami t67 and the ioaudio bv12 compare and which one do you recommend? Thanks again

Nah I haven't had the chance yet… been too busy in the studio.. i'll do it this week. I did powder coat one side of the basket black though, lol

I would rock the k67 if I was you, there doesn't seem to be anyone able to match it and according to the greats, neumann senheiser still manufacture them to the highest quality.

 

[DUDE GUY]

i would start  by looking at the basic voltage ( Bias ), (Plate) , (Polarisation Voltage),  (Heater), (B+) and specially the Hz bridge and capsule connection ,
the HZ bridge is definitely the first place to look after checking all of this,
Keep us posted,
D

Hey Dan, thanks for the help.

Heater: -6.50V
B+: +210V

Where are good test points for Bias, Plate, and Polarization Voltage? I've searched the forum and the build folder, but couldn't find anything. Also, what voltage should i see for each of these? Thanks again.

-Kevin

 

[DUDE GUY]

Sorry to bump, but does anyone know where to test Bias, Plate, and Polarization Voltages on the PSU and/or the main PCB? Any help is appreciated, thanks.

-Kevin

 

[DUDE GUY]

Ok now I'm being a little less stupid . I realized I could take one step further and post my measurements across each XLR pin and ground. I also measured voltages at the capsule connections.

Please let me know if these voltages look right:

PIN1: XLR OUT PIN 3 (8.7 mVAC, noise floor? I'm guessing this is negligible)
PIN2: XLR OUT PIN 2 (1.6 mVAC, noise floor? Again, negligible)
PIN3: -36 mV (marked "CGND" on schematic)
PIN4: -6.4 V (H-)
PIN5: 210.5 (B+)
PIN6: -36 mV (marked "CAL" on schematic, calibration input?)
PIN7: -36 mV (marked "0V" on schematic)


Capsule Voltages (tested at their connection points to the tube PCB (FD and BCK) and the switch PCB (BD):

FD: -.87 V
BD: Omni= -.87 V, Cardioid= -35 mV, Figure 8= Starts at 4V, then steadily drops
BCK: 8.5 V

I've identified the Heater and B+ voltages, but I'm unsure as to which are the Bias, Plate, and Polarization voltages. Also, where can I test the Hz bridge?

Please help, I'm pretty lost. Thanks.

-Kevin

 

[gary o]

Hi Kevin dont know if I can help you help yourself I dont have the boards so its hard for me to help but I have been experimenting with this circuit....firstly you prob wont be able to measure the capsule voltages from the high impedances capsule connections with a usual meter but should be able to from by looking at original schematics measure from junction of R12 R13 should be 59V also I think from R13 R15....  again looking at the original schematic ( not sure if Danys schematic using same number cant see it on this PC but prob is) juction of 9 10 11 & 12 should be 1.6 or 1.8V for the bias ......for the plate its pin 6 of the tube junction of C9 output cap & R14 should be about 75V ...... need to find these junctions on your PCB & tube to measure I hope Im not leading you astray if anyone else wants to jump in as I say dont have the boards to look at your B+ & low tension look good, good luck

 

[DUDE GUY]

Thanks so much, Gary!! I'll definitely test voltages at the points you suggested, hopefully I can find them.

I'll post my results.

-Kevin

 

[MikeFFG]

Hi -

So a couple months ago I posted with my U67 having some noise issues, and it resolved itself. But a new noise is kind of back. It's totally intermittent (ie not all the time or every 3 seconds...just sporadic...but happens quite regularly). I've recorded it and uploaded it. Can anyone tell if that's a problem they've heard like a bad tube or a bad cap or something obvious? The mic did seem to pass the breath test so I don't think it's the diaphragm. And the recordings still sound good, they just have this intermittent low level popping throughout them. It's fairly low level (I have cranked it in the example) but enough that it would ruin a good take.

You can listen here: http://prettyuglyproductions.net/wp-content/uploads/2014/01/Noise.wav

In the recording, there's obviously background noise and hum and stuff, that's obviously not the part I'm talking about though!

Thanks!

Mike