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

[0dbfs]

I used the pads on the pcb mentioned for the "fixed-resistor" and cut some traces/made some jumper connections so I could have the trimmer resistor mounted directly on the PCB instead of flying. I thought it a little more robust that way as the B+ is going through there and it makes me feel a little more comfortable if other people are going to ever be "trimming".

Same with H-. I used the fixed resistor pcb position (cut traces and routed jumpers) for a series-resistor to get more "Useful Play" out of the trimmer with the desired H- value ending up near "the middle".

Cheers!
-jb

 

[jpertusi]

Next question...

Anyone know if ioaudio's bv12 transformers are still available?  I sent an email but have not heard back.

Thanks,

JP

 

[JessJackson]

Next question...

Anyone know if ioaudio's bv12 transformers are still available?  I sent an email but have not heard back.

Thanks,

JP

Yeah i never heard back from him either.

 

[ioaudio]

I have been in contact with JP.

Jess, not sure if i missed your emeil, pls try again at [email protected].

 

[JessJackson]

Cheers I'll shoot one over max.

I'm still 5db down from original u67. Ive replaced Capsule, Coupling Cap and Tube with no difference in level.

My voltages are as follows:

B+ (+210v)
H (-6.3v)
Plate (+84v)
R12 - R13 (+49.7v)
R10 - R11 (-1.83v)

It seems capsule voltage is 10v low and bias is off slightly?... Any suggestions?

I haven't checked transformer for ratio's but that would be my last resort.

J

 

[poctop]

is your R12-R13 Polarisation Divider well matched ,
you should be getting 55V at least for the backplate , it has to be measured before the capsule Charging resistor tough,
but this would not explain a 4db difference
keep us posted,

Best,
Dan,

 

[jpertusi]

OK so, I've got the power supplies built.

No funny blue smoke on power up (good sign)!!!

I'm wondering if anyone has testing/calibration instructions.  I don't have the mics built yet so I know the voltages will be off but I want to make sure I'm in the ballpark.

The trouble is, I'm a good follower of instructions, built a fair number of kits, but I'm not SUPER experienced with this kind of thing and I don't want to electrocute myself or worse yet, fry my multimeter ;-)

I'd like to know what kind of voltages to expect expect with the PS unloaded, and I quite literally where to place my multimeter probes...

Any help is appreciated.

Also, thanks to Max at audio for getting back to me quickly and shipping out the bv12's.  Can't wait to get going o the mics!!!

 

[poctop]

OK so, I've got the power supplies built.

No funny blue smoke on power up (good sign)!!!

I'm wondering if anyone has testing/calibration instructions.  I don't have the mics built yet so I know the voltages will be off but I want to make sure I'm in the ballpark.

The trouble is, I'm a good follower of instructions, built a fair number of kits, but I'm not SUPER experienced with this kind of thing and I don't want to electrocute myself or worse yet, fry my multimeter ;-)

I'd like to know what kind of voltages to expect expect with the PS unloaded, and I quite literally where to place my multimeter probes...

Any help is appreciated.

Also, thanks to Max at audio for getting back to me quickly and shipping out the bv12's.  Can't wait to get going o the mics!!!

There is Test point on the PSU PCB and also on the Mic PCB take some time to locate them ,
basically reading of the psu with no mic connected will look like this , if you dont feel comfortable doing the reading ask someone who has experience to show you and help you with this. Safety is everything , one thing to always remember is that when you switch off the PSU there will still be Voltage for a little while slowly dischragin from the caps ,  it is always recommended to monitor those voltage B+ and H- before sticking your in hand in there , and the good thing is that this is valid with any working electronics you will work on.

Heater = -16VDC
B+ 275VDC

with mic connected,
Heater H- = -6.3VDC when adjusted
B+ 210 VDC when adjusted.

There is also a little test point on the mic pcb label a wich you should be able to read the Plate voltage 75-85VDC

hope this helps,
Dan,

 

[jpertusi]

Thanks Dan,

I see the B+ and H- test points on the PCB.  I assume the hot lead of my multimeter goes to one of them and the ground lead goes to one of the points labeled CAL (either"siggnd" or "sig"?)

Thanks as always for your help.

-JP

 

[poctop]

Thanks Dan,

I see the B+ and H- test points on the PCB.  I assume the hot lead of my multimeter goes to one of them
yes

and the ground lead goes to one of the points labeled CAL (either"siggnd" or "sig"?)
No, the ground Lead will go to 0V near the Ac supply you will have a label call 0V

CAL is for audio measurement

Thanks as always for your help.

-JP

 

[jpertusi]

Got it.  I suspected as much but when I saw the CAL points I wanted to be extra sure.

I'm going in... one hand behind my back ;-)

 

[jpertusi]

OK, so here are the results:

H- is at -16.7vdc (the trim pot seems to have no effect on this... maybe that is normal with no load?)

B+ varies from 236vdc to 260vdc (at the extremes of the B+ trim pot settings)

It could be I need to let it warm up a little longer? I took those readings right away.

My multimeter is fine and I am still very much alive.

-JP

 

[poctop]

OK, so here are the results:

H- is at -16.7vdtc (the trim pot seems to have no effect on this... maybe that is normal with no load?)
yes no effect normal
B+ varies from 236vdc to 260vdc (at the extremes of the B+ trim pot settings)
yes this is correct with no mic,
It could be I need to let it warm up a little longer? I took those readings right away.
yes it will take a little moment until the capacitor Charges
My multimeter is fine and I am still very much alive.
-JP

Then The story is that you are doing Great ,
keep on the good work,
D

 

[jpertusi]

Brilliant!!!  I thought I was looking for exactly 275vdc.

Thanks for all your help Dan (I'm sure I'll have more questions once I dive in to the mics).  Much appreciated!

 

[jpertusi]

OK, last PS question... 

Do the numbered locations on the PCB (1, 2, 3 on the XLR out and 1 thru 7 on the MIC out) correspond to the pin numbers I should be connecting them to?

Thanks as always,

-JP

 

[Studio Mollan]

Hi guys!
I built 4 u67's. 2 each of the AMI and IOaudio transformers. All have Beesneez K6 and vintage telefunken EF86.

The IOaudio transformers seem to be very dull sounding as compared to the AMI. To get close match of the two using ears and spectrogram the ones using IOaudio transformers need +6,5db shelving from ca 1,5kHz. Quite a difference... They work as amb for drums but that's about it unless your looking for a dull-/lofi-ish sound. Anybody else have the same experience? Could i have gotten transformers form a bad batch or is that just what they sound like?

Also when troubleshooting one of the AMI versions i noticed the output measures 50ohm. Shouldn't that read 200Ohm for modern use?
/
Emil

 

[Melodeath00]

Hi guys!
I built 4 u67's. 2 each of the AMI and IOaudio transformers. All have Beesneez K6 and vintage telefunken EF86.

The IOaudio transformers seem to be very dull sounding as compared to the AMI. To get close match of the two using ears and spectrogram the ones using IOaudio transformers need +6,5db shelving from ca 1,5kHz. Quite a difference... They work as amb for drums but that's about it unless your looking for a dull-/lofi-ish sound. Anybody else have the same experience? Could i have gotten transformers form a bad batch or is that just what they sound like?

Also when troubleshooting one of the AMI versions i noticed the output measures 50ohm. Shouldn't that read 200Ohm for modern use?
/
Emil

Unfortunately I can't answer you, but are we talking about the AMI T67 or the BV12?

 

[dmp]

Hi guys!
I built 4 u67's. 2 each of the AMI and IOaudio transformers. All have Beesneez K6 and vintage telefunken EF86.
The IOaudio transformers seem to be very dull sounding as compared to the AMI. To get close match of the two using ears and spectrogram the ones using IOaudio transformers need +6,5db shelving from ca 1,5kHz. Quite a difference... They work as amb for drums but that's about it unless your looking for a dull-/lofi-ish sound. Anybody else have the same experience? Could i have gotten transformers form a bad batch or is that just what they sound like?
Also when troubleshooting one of the AMI versions i noticed the output measures 50ohm. Shouldn't that read 200Ohm for modern use?
Emil

Interesting observation. I built one with ioaudios bv12 (with Beesneez K6 and vintage telefunken EF86) but don't have an AMI to compare.
Can you post sound clips showing the comparison?
Mine is a great mic, but it does not sound bright. It does work great as a front mic for a drum kit, or on a guitar amp. A lot of people I work with love it.

 

[Studio Mollan]

Hi guys!
I built 4 u67's. 2 each of the AMI and IOaudio transformers. All have Beesneez K6 and vintage telefunken EF86.
The IOaudio transformers seem to be very dull sounding as compared to the AMI. To get close match of the two using ears and spectrogram the ones using IOaudio transformers need +6,5db shelving from ca 1,5kHz. Quite a difference... They work as amb for drums but that's about it unless your looking for a dull-/lofi-ish sound. Anybody else have the same experience? Could i have gotten transformers form a bad batch or is that just what they sound like?
Also when troubleshooting one of the AMI versions i noticed the output measures 50ohm. Shouldn't that read 200Ohm for modern use?
Emil

Interesting observation. I built one with ioaudios bv12 (with Beesneez K6 and vintage telefunken EF86) but don't have an AMI to compare.
Can you post sound clips showing the comparison?
Mine is a great mic, but it does not sound bright. It does work great as a front mic for a drum kit, or on a guitar amp. A lot of people I work with love it.

Im using the T67 not the BV12. I'll try to get some clips
Here's files to compare.
https://dl.dropboxusercontent.com/u/42125780/AMI%20T67.wav
https://dl.dropboxusercontent.com/u/42125780/IOaudio.wav

 

[Studio Mollan]

Could it be a combination of two extremes? A bright AMI transformer and a duller IOaudio.
I would not call the AMI version bright as compared to other microphones even though it sounds veri bright in comparison here.
It might be an error in my stuffing the boards but i made all four in parallell. Both of my IOAduio ones sound identical. As do the AMI ones though i have a weaker output in one of them which im currently investigating.