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

[gary o]

Hi Mike could be many things maybe dry solder joint dodgy capacitor dirt on high impedance parts I guess first thing give it a good clean are tube pins clean.....

 

[0dbfs]

Yeah. I had all those Gary mentions cause that sound. Bad cap was specifically a back-to-front styro which was probably heat stressed but also on different mic's. Cleaning the hi-z connections on others, and "even a tube" on another. Once had a cathode bypass cap cause that sound or similar and the heater dropping resistor on a 47 style on another. Same sound though (or very similar) in all of those cases but probably "louder" from a snr standpoint.

Cheers,
Jonathan

 

[DUDE GUY]

...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...

OK, here are my results:

(B+): 210V

(H-): -6.4V (as low as I can get it)

Junction R12 and R13 (Polarization): 50V

Junction R13 and R15: Starts at around 110V and slowly drops down to 98.6V

Junction of C9 and R14 (Plate): 80V

Junction of R9 - R12 (Bias): -1.8V

So it looks like my polarization voltage is low and my plate is too high. Any ideas?

Thanks,

-Kevin

 

[gary o]

Hi Kevin Im not enough of an expert but I would say your plate is ok as schematic says about 75V yours not much higher less than 10% & your cathode bias is about right at 1,8V..... if you have another tube you could pop that in and measure voltages again it prob would be different but hopefully there abouts too but this tube seems ok to me.

Regarding the capsule polar voltages Im not convinced your meter is telling the truth..... I dont totally understand this myself something like connecting our not really expensive super meter to that part of the circuit adds load & buggers up the readings ( please help me out clever chaps to explain this & learn myself)...... I usually check all resistor values and B+ voltage as you have and trust that capsule voltage should be correct & as long as mic works correct I leave it..... when I made my version of this circuit  I didnt add the omni & fig 8 patterns by the way...my R12 R13 junction measured 50V too, I did experiment & swapped the 3.3M R15 for a 2.2M & in brought voltage up to 60V on my meter mic sounded the same so I swapped resistor back incase voltage was really higher trying to measure capsule voltage with my cheap meter in other mics I have made also was strange in most cases.

 

[gyraf]

Regarding the capsule polar voltages Im not convinced your meter is telling the truth..... I dont totally understand this myself something like connecting our not really expensive super meter to that part of the circuit adds load & buggers up the readings ( please help me out clever chaps to explain this & learn myself)...... I usually check all resistor values and B+ voltage as you have and trust that capsule voltage should be correct & as long as mic works correct I leave it.....

Remember that your voltmeter has a finite input resistance - most often 1M Ohm or 10M Ohm - specified in it's manual.

Then recalculate expected voltages at the point in question by adding in this value across the measuring point.

If you have e.g. a 10M input voltmeter, and measure a point with a 10M source resistance, you'll get a readout of half the actual voltage

Jakob E.

 

[gary o]

Thankyou Jakob that make sense the way you put that..... so its like adding 10M resistor between ground & test point .....so in our U67 circuit here how do we work out our source resistance as we are in a chain of resistors do we add up some resistor values ?

thanks

 

[MikeFFG]

Alright thanks Gary and Jonathan! That was my fear...

Was hoping it was like "hey that's TOTALLY a bad tube" lol.

Will have to really get in there and check it out.

Thanks guys.

 

[Barton]

I haven't been able to find a clear wiring diagram for the D-U67 PSU, and just wanted to make sure that I have it correct.  If someone could take a look at the attached diagram and provide feedback I'd appreciate it.  I plan on using 2 lamps, as the collective cases PSU case already has holes pre-drilled for both.

 

[Winetree]

The extra hole is for the fuse holder. Where's the fuse in your diagram?

 

[poctop]

I haven't been able to find a clear wiring diagram for the D-U67 PSU, and just wanted to make sure that I have it correct.  If someone could take a look at the attached diagram and provide feedback I'd appreciate it.  I plan on using 2 lamps, as the collective cases PSU case already has holes pre-drilled for both.

if you are based on 120V this is correct,  the thing is to understand why we wire in parralle and in series but clearly you understand that as per your diagram
there is also one posted in the thread the TSKGUy have done for it 120V and also another one for 230V europe ,

Best,
dAN,

 

[poctop]

...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...

OK, here are my results:

(B+): 210V

(H-): -6.4V (as low as I can get it)

Junction R12 and R13 (Polarization): 50V

Junction R13 and R15: Starts at around 110V and slowly drops down to 98.6V

Junction of C9 and R14 (Plate): 80V

Junction of R9 - R12 (Bias): -1.8V

So it looks like my polarization voltage is low and my plate is too high. Any ideas?

Thanks,

-Kevin

this looks in the range  to drop your heater voltage even more increase the value of the series resistor attached to the Heater trimmer pot it will increase your dropping range ,
BEst.,
dan,

 

[kpearsall]

If anyone is still looking for cases, I recently got a Pelican 1550 which fits everything nicely, you just need to sit the microphone in it's bag on top of the cables.

 

[JessJackson]

I was about to shootout the u67 against an all original vintage u67 yesterday but mine needed 1 click on the neve 1081 and a little trim resulting in +6db of extra gain to match the vintage u67

This contradicts the last time i tested the mic, http://groupdiy.com/index.php?topic=50021.msg689359#msg689359

All my voltages are good (210+, 6.3v H, 84v plate)

I'm running an eric capsule with the two backplates tied together ami t67 trans.

what could be causing this much lower output level?

J

 

[ben_studio]

I've recently done some tests with original U67.
If you want to have a listen to them, here is the link :

http://benoitlaur.com/a-b-original-neumann-u67-vs-clone-u67/

Hope this will encourage people to go into the project,

Ben

 

[micaddict]

Great samples, Ben. Thanks.

They both sound like 67s to me, but I actually like the D67 better. Wow, what a sound! Big, lush and hifi at the same time.
To my ears the U67 is a little more middy (mid-mid, hi-mid) or the D67 a bit more extended on both ends.
Because of stronger high mids and less bass (and low mids even), the U67 may seem brighter, but I hear more true air in the D67.
This is noticeable in the sound of the fast moving slide bar (vibrato) on the wound strings, for instance. And in the breathing sounds.
The U67 has a little more "cut", though.

The U67 will probably be about half a century old. Makes you wonder if aging caps and all would cause some loss of bass and such. In other words, could it be the D67 sounds like the U67 did when it was brandnew?

But other factors could play a part. E.g. the tubes. What exactly is in the U67 and what in the D67?
And did you jumper S2 (40 Hz high pass) in the new build?
Oh, and what about the capsule and tranny?


Henk

 

[poctop]

I've recently done some tests with original U67.
If you want to have a listen to them, here is the link :

http://benoitlaur.com/a-b-original-neumann-u67-vs-clone-u67/

Hope this will encourage people to go into the project,

Ben

Thanks For Taking The time for doing this , in the End i wish you are happy with your new toy
Best,
Dany,

 

[jpertusi]

I hope this is the correct method of posting questions...

This is a USA 115v build.

I have 3 quick ones, please see attached image.


1. - Is the 56k resister in the upper left labeled "RTRIMPLATE" the same one some folks are hanging off one leg of the trim pot?  Are they just doing that because its easier to swap out?

2. - R9 (upper right) was 560r and not 536r as the PCB is labeled.  Is this intentional?

3. - The location labeled "lin 50R-2W" had nothing to populate it with in my kit, is this OK?



Thanks everyone,

-JP

 

[poctop]

I hope this is the correct method of posting questions...

This is a USA 115v build.

I have 3 quick ones, please see attached image.


1. - Is the 56k resister in the upper left labeled "RTRIMPLATE" the same one some folks are hanging off one leg of the trim pot?  Are they just doing that because its easier to swap out?

No this is not the same resistor the 56K is a custom trimming resistor that is not on the pcb this location mentioned on your picture is the spot to install a Fixed resistor in case you dont install the Pot and need to have this replaced as a fixed resistance

2. - R9 (upper right) was 560r and not 536r as the PCB is labeled.  Is this intentional?
yes 560R is for this resistance as 536r is not available and not really important to have this one at that precision

3. - The location labeled "lin 50R-2W" had nothing to populate it with in my kit, is this OK?

this location on your picture is the spot to install a Fixed resistor in case you dont install the Pot and need to have this replaced as a fixed resistance for the Heater

Thanks everyone,

-JP

Hope this helps,
Best,
DAn,

 

[jpertusi]

Thanks for your quick reply Dan, perfectly clear.

So... is the 56k resistor on the leg of the trim pot always necessary?  Or only if you can't get the voltage right with the pot alone?

-JP

 

[poctop]

Thanks for your quick reply Dan, perfectly clear.

So... is the 56k resistor on the leg of the trim pot always necessary?  Or only if you can't get the voltage right with the pot alone?

-JP

Yes you need it to adjust your range , from 33K -56K ?  To have the Sweet-Zone on the Pot as you wish.

Best,
DAN