Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1580 on: September 25, 2020, 10:46:10 AM »
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

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1581 on: September 25, 2020, 12:17:56 PM »
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.
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com

TLRT

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1582 on: September 25, 2020, 01:51:06 PM »
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.

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1583 on: September 27, 2020, 03:54:44 PM »
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..."
« Last Edit: September 27, 2020, 03:58:01 PM by jpertusi »

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1584 on: September 28, 2020, 04:22:39 PM »
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.  :-(

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1585 on: October 09, 2020, 11:26:26 PM »
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.

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1586 on: October 10, 2020, 12:40:09 AM »
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?

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1587 on: October 10, 2020, 04:40:39 AM »
 

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

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1588 on: October 10, 2020, 03:58:35 PM »
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.
« Last Edit: October 10, 2020, 05:08:11 PM by TLRT »

TLRT

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1589 on: October 10, 2020, 04:04:56 PM »
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.
« Last Edit: October 10, 2020, 05:09:40 PM by TLRT »


Delta Sigma

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1590 on: October 10, 2020, 06:30:17 PM »
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).

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1591 on: October 10, 2020, 07:14:10 PM »
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.

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1592 on: October 10, 2020, 07:17:51 PM »
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

Re: Neumann U67 Clone : D-U67 Tube Microphone Build Thread.
« Reply #1593 on: October 11, 2020, 05:35:07 PM »
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)


 

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