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

[jpertusi]

Sounds like the different  capsule  output, polarisation voltage or possible high Z components parasite capacitance. Moving hi Z leads also can help because small amount of parasite c can make few db difference in signal.

Thanks! A few followup questions:

- If it's the capsules, I guess there is nothing I can do.
- How would I test for Polarization Voltage / Parasitic Capacitance?
- You'll need to school me a bit on the HiZ leads issue if you don't mind.

For reference, you're talking to an electronic idiot who is good with a soldering iron and can follow directions well... that's it.  ;-)

-JP

 

[Moby]

Thanks! A few followup questions:

- If it's the capsules, I guess there is nothing I can do.
- How would I test for Polarization Voltage / Parasitic Capacitance?
- You'll need to school me a bit on the HiZ leads issue if you don't mind.

For reference, you're talking to an electronic idiot who is good with a soldering iron and can follow directions well... that's it.  ;-)

-JP

Unfortunatelly you can't measure the polarisation voltage directlly on capsule because it's also Hi Z (too much for DMM's) but you can measure it before the resistor. Parasite capacitacne can be ommited if your leads and hi Z components are not too close. Especially to the GND. Sorry, it's hard to explain this in short sentence but you can search around and read about other DIY experiences.
At the end, if the diference is in the capsules, you can try to swap them and figure out the problem.

 

[TLRT]

Thanks! A few followup questions:

- If it's the capsules, I guess there is nothing I can do.
- How would I test for Polarization Voltage / Parasitic Capacitance?
- You'll need to school me a bit on the HiZ leads issue if you don't mind.

For reference, you're talking to an electronic idiot who is good with a soldering iron and can follow directions well... that's it.  ;-)

-JP

You can measure the correct polarization voltage with an electrometer only. old Keithley's are great.

 

[jpertusi]

Unfortunatelly you can't measure the polarisation voltage directlly on capsule because it's also Hi Z (too much for DMM's) but you can measure it before the resistor. Parasite capacitacne can be ommited if your leads and hi Z components are not too close. Especially to the GND. Sorry, it's hard to explain this in short sentence but you can search around and read about other DIY experiences.
At the end, if the diference is in the capsules, you can try to swap them and figure out the problem.

I MAY have it.  But I wanted to check with the forum first...

I opened up both mics again just to visually inspect.

There is a jumper on the main PCB labeled 'IS' or '1S' (just below the low cut jumper).

In one mic it's jumpered and on one it's open.

I can't seem to find info on the function of this jumper (although I vaguely remember reading about it when I built them).

What does that jumper do?  Could it cause the 3db difference?

Thanks everyrone for your help! Stay Safe.


MODIFYING POST...

I found the info. I assume this could certainly cause one mic to be hotter, especially when close up on the mic. I'm going to open them both and test again.

"IS is jumpered for default configuration , you will get more bass response and proximity with the jumper off..."

 

[jpertusi]

I MAY have it.  But I wanted to check with the forum first...

I opened up both mics again just to visually inspect.

There is a jumper on the main PCB labeled 'IS' or '1S' (just below the low cut jumper).

In one mic it's jumpered and on one it's open.

I can't seem to find info on the function of this jumper (although I vaguely remember reading about it when I built them).

What does that jumper do?  Could it cause the 3db difference?

Thanks everyrone for your help! Stay Safe.


MODIFYING POST...

I found the info. I assume this could certainly cause one mic to be hotter, especially when close up on the mic. I'm going to open them both and test again.

"IS is jumpered for default configuration , you will get more bass response and proximity with the jumper off..."

OK, that was not it.  With the jumpers in either position, mics are still 3db apart.  :-(

 

[aharmonson]

My mic was working great after testing it, but R8 on the PSU burned out when using a different 7 pin cable (not sure if that had anything to do with it). What would cause that 5.1 ohm resistor to fail? I was getting -16.6 v on one side of the resistor, -3v on the other. All the caps checked out with an ESR and the B+ side is doing fine.

 

[FarisElek]

My mic was working great after testing it, but R8 on the PSU burned out when using a different 7 pin cable (not sure if that had anything to do with it). What would cause that 5.1 ohm resistor to fail? I was getting -16.6 v on one side of the resistor, -3v on the other. All the caps checked out with an ESR and the B+ side is doing fine.

 

Maybe too obvious but are you sure the resistor was the right wattage?

 

[aharmonson]

 

Maybe too obvious but are you sure the resistor was the right wattage?

It seemed to be about the right size for a 1/3 watter. A connection of the red wire (heater) seemed to look pretty sketch on the cable. I'm guessing that is the likely culprit being that R8 is a dropping resistor for the H- voltage.

 

[TLRT]

My mic was working great after testing it, but R8 on the PSU burned out when using a different 7 pin cable (not sure if that had anything to do with it). What would cause that 5.1 ohm resistor to fail? I was getting -16.6 v on one side of the resistor, -3v on the other. All the caps checked out with an ESR and the B+ side is doing fine.

If you do the math, the resistor is dissipating 36watts? Are you sure the PSU assembled well? - You cannot have 16V on the R8 leg as there are 2 other resistors before R4 and R6,something is wrong with your PSU or the measurement is incorrect.

 

[TLRT]

If you do the math, the resistor is dissipating 36watts? Are you sure the PSU assembled well?

Use a 32ohm load resistor on the output(between XLR pin3-4 or 4-7), On R8 you should have max 1V normally loaded,but even without load you cannot have more than 1V drop on R8.

 

[Delta Sigma]

My mic was working great after testing it, but R8 on the PSU burned out when using a different 7 pin cable (not sure if that had anything to do with it). What would cause that 5.1 ohm resistor to fail? I was getting -16.6 v on one side of the resistor, -3v on the other. All the caps checked out with an ESR and the B+ side is doing fine.

Do you mean a 7 pin cable from a different mic? Don't use a cable that doesn't have the same pinout and doesn't have the larger wires for H- and 0V. You may have shorted your H- to ground.

When did you measure the large drop across R8 (5.1ohm)? It may be that you measure the large drop as the resistor was dying (failing to open).

 

[aharmonson]

If you do the math, the resistor is dissipating 36watts? Are you sure the PSU assembled well? - You cannot have 16V on the R8 leg as there are 2 other resistors before R4 and R6,something is wrong with your PSU or the measurement is incorrect.

I took the resistor out of circuit and it measured 13k, so I would think that it is dissipating something like 1/4 watt. The tutorial mentioned that -16v unloaded was normal for the h- point which is after R8, right? When I connected the mic with tube (before R8's demise), the voltage drops to about -6v and can be adjusted with the pot.

 

[aharmonson]

Do you mean a 7 pin cable from a different mic? Don't use a cable that doesn't have the same pinout and doesn't have the larger wires for H- and 0V. You may have shorted your H- to ground.

When did you measure the large drop across R8 (5.1ohm)? It may be that you measure the large drop as the resistor was dying (failing to open).

The cable I was using had thick wire for the heater and b+. I thought the thick red (h-, pin 4) wire was sketch because it was frayed and might have been shorting to one of the ground pins.

 

[TLRT]

I took the resistor out of circuit and it measured 13k, so I would think that it is dissipating something like 1/4 watt. The tutorial mentioned that -16v unloaded was normal for the h- point which is after R8, right? When I connected the mic with tube (before R8's demise), the voltage drops to about -6v and can be adjusted with the pot.

-16V is the zener regulation voltage, but tt makes no sense to run the psu without load, you can add resistors to check if the psu is working correctly, 230kohm for B+ and 32ohm for the heaters to simulate EF86 load.(you can connect the resistors to XLR or the terminals between B+ to GND and H+ to GND)

 

[Naterbater]

I just ordered my D67 kit today. I am excited to get working on it. After reading through a lot of the conversation, I have a few questions. Are the assembly instructions on theVintageMicrophonePCBKit a good guide? I noticed that there are a lot of mods and changes throughout this thread and just want to make sure that I follow the path of most success.

My next question is about the power supply. Someone may have asked this already, but will any of the off the shelf PSU's work? While looking at the mic bodies on studio 939 I noticed that they sell a tube mic PSU.

https://store.studio939.com/product/tps100-tube-microphone-power-supply

Let me know if anyone has tried it. Thanks-Nate

 

[Purplenoise]

I just ordered my D67 kit today. I am excited to get working on it. After reading through a lot of the conversation, I have a few questions. Are the assembly instructions on theVintageMicrophonePCBKit a good guide? I noticed that there are a lot of mods and changes throughout this thread and just want to make sure that I follow the path of most success.

My next question is about the power supply. Someone may have asked this already, but will any of the off the shelf PSU's work? While looking at the mic bodies on studio 939 I noticed that they sell a tube mic PSU.

https://store.studio939.com/product/tps100-tube-microphone-power-supply

Let me know if anyone has tried it. Thanks-Nate

Yes instructions are very accurate for the mic itself. For the psu there is a difference in the 20V transformer wiring but it is explained in the thread...if I remember well it is the wiring of the primary. If you want to use a different transformer the usual ones are covered in the thread ( Ami bv12, Moby bv12, haufe bv12).
The psu you have on your link is mostly for mics requiring B+ 120v max I believe and different topology like c12 or 251 and even then you can build it much better. The u67 needs 210v. If you don’t feel confident or comfortable with high voltages you could have someone more experienced build one for you. If you need a suggestion on someone to build you one feel free to PM me.
It is a good idea to go through the thread first and take notes on posts the you find interesting.

 

[Naterbater]

Not worried about the high voltages, just trying to save some time and money. I will build up the PSU that comes with the kit. Thanks- Nate

 

[doqmemory]

I started building my D67 last night, and here are a couple of points on the P/S:

• There are two alternatives for R2, 22 Ohms (5W) or 25 Ohms (5W).  I could not find a clear final decision on that, so I put in the 25 Ohms option.
• R9 is 560 Ohms in the BOM, but still listed as 536 Ohms in the schematic.
• The power switch is not included in the BOM.  I got one from Amazon, but you can get an illuminated one, if you like.
• The indicator light is not included in the BOM. I chose a neon 120v one, so it could be inline with the power switch.

Also, I am using the excellent case from Collective Cases.  It is much nicer than the stock Hammond case in the BOM.  I think it was about $40 more, but was worth it for me.

Happy building!

 

[Naterbater]

Great info! I will make sure to research those items on the psu. One question I have is what I should order for the 7 pin connector on the microphone. My donor mic has a 3 pin xlr. Is there a drop in solution? Thanks - Nate

 

[Delta Sigma]

Great info! I will make sure to research those items on the psu. One question I have is what I should order for the 7 pin connector on the microphone. My donor mic has a 3 pin xlr. Is there a drop in solution? Thanks - Nate

I think Chunger has a link to a 7 pin part under one of his donor bodies on his site.