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

[FarisElek]

See if you can find a recording of humidity damage to a capsule and see if it sounds similar. You should always store your mic in a case or zip loc bag with a moisture absorbing desiccant.

good to know. i opened it up and noticed the mics capsule was covered in dust. i wiped it extremely lightly (using only gravity to wipe surface with q-tip and alcohol) and it seemed to fix it. i don't experience too much humidity where i live but quite a bit of dust. going to store it somewhere better. does any know a good case for the cheap changer bodies?

 

[Delta Sigma]

Contact Banzai; see if he has any ideas. He was working on velvet storage bags and even covers for when the mic is on its stand. I was lucky enough to get one of each of his prototypes and they're great.

 

[FarisElek]

Contact Banzai; see if he has any ideas. He was working on velvet storage bags and even covers for when the mic is on its stand. I was lucky enough to get one of each of his prototypes and they're great.

That sounds fantastic! I'll definitely see what he's got going on.

Just wanted to bring this up as this problem never disappeared and I was wondering if anyone that may be watching has seen this and can pin point exactly what it might be. My build is pretty clean. It's gotten less clean looking while trying to fix this problem if anything. My mic sounds perfect in cardioid, in omni it appears to lose a little bit of volume and maybe girth, but if I just turn up my mic pre a little it sounds perfect, so I'm not exactly horrified by this.

The real problem is that figure 8 loses a touch of high end. It appears however that it's because the phase is flipped. The back of the capsule matches the front when in cardioid. Is there a possibility I have a single thing flipped?


Ryan


Edit: after much research and speaking with the experts. This is normal. Literally what it’s supposed to do.

 

[aharmonson]

Hi All,

I assembled one recently and the tube isn't lighting up. The H- pad and pin 5 of the tube socket are both getting -16.3v unloaded (and loaded), and the B+ pad and pins 1 and 6 are both getting 232v unloaded. (my wall voltage is about 125v). What is the next thing to troubleshoot?

 

[FarisElek]

Hi All,

I assembled one recently and the tube isn't lighting up. The H- pad and pin 5 of the tube socket are both getting -16.3v unloaded (and loaded), and the B+ pad and pins 1 and 6 are both getting 232v unloaded. (my wall voltage is about 125v). What is the next thing to troubleshoot?

Already forgot all the details of this build. Are these voltages coming to the mic test points as well? Do you have a back-up tube? Are you getting any output? I don’t think the tube lights up very bright to be honest.

 

[aharmonson]

Already forgot all the details of this build. Are these voltages coming to the mic test points as well? Do you have a back-up tube? Are you getting any output? I don’t think the tube lights up very bright to be honest.

Yea, those are roughly the right voltages (since my wall voltage is on the high side, I have the trim pots turned down). I'm pretty much not getting any output - something like 5db beyond the noise floor when yelling into it. There isn't any voltage drop with the tube plugged in as well. I ordered a backup tube today.

 

[Delta Sigma]

The real problem is that figure 8 loses a touch of high end. It appears however that it's because the phase is flipped. The back of the capsule matches the front when in cardioid. Is there a possibility I have a single thing flipped?


Ryan


Edit: after much research and speaking with the experts. This is normal. Literally what it’s supposed to do.

Missed this one. To be specific, there is no low end, high end, etc lost on the back capsule in fig-8. The rear diaphram is ou of phase wih your headphones so you get phasind at certain frequencies when monitoring. When recorded, it should sound no different than the front diaphragm.

 

[Delta Sigma]

Yea, those are roughly the right voltages (since my wall voltage is on the high side, I have the trim pots turned down). I'm pretty much not getting any output - something like 5db beyond the noise floor when yelling into it. There isn't any voltage drop with the tube plugged in as well. I ordered a backup tube today.

May not be your tube. It could be that your 0V is wired incorrectly. You're measuring 16V at the tube socket, referenced to where? If your negative lead is on the mic's power supply and your positive lead is on the tube socket, and your 0V isn't wired correctly, you would see your unloaded H-.

Try powering down your mic (and unplugging the mic from the PS), putting your DMM in ohms and see if you have continuity between your heater (marked h1 on the Neumann schematic) and 0V in your power supply. You could also measure across the pins on the actual tube (should be a few ohms, maybe in the 30ohm range), then plug in your tube and measure on the PCB pads for H1/H2, then work your way to H- and 0V on your mic connection to the cable, then plug in the cable to check it and the power supply. This sectionalizes your troubleshooting.

Still could be the tube but ohming out the heater should prove that.

 

[aharmonson]

May not be your tube. It could be that your 0V is wired incorrectly. You're measuring 16V at the tube socket, referenced to where? If your negative lead is on the mic's power supply and your positive lead is on the tube socket, and your 0V isn't wired correctly, you would see your unloaded H-.

Try powering down your mic (and unplugging the mic from the PS), putting your DMM in ohms and see if you have continuity between your heater (marked h1 on the Neumann schematic) and 0V in your power supply. You could also measure across the pins on the actual tube (should be a few ohms, maybe in the 30ohm range), then plug in your tube and measure on the PCB pads for H1/H2, then work your way to H- and 0V on your mic connection to the cable, then plug in the cable to check it and the power supply. This sectionalizes your troubleshooting.

Still could be the tube but ohming out the heater should prove that.

I didn't have continuity between the heater and 0v on the power supply. For ground reference, I was using screw holes/chassis mainly, but also used 0v from the psu and the heater voltage was still -16.6.

 

[Delta Sigma]

Did you ohm out your tube's heater? Then install the tube and ohm out? All with power off.

 

[jpertusi]

Hi, hop eI'm posting in the correct place.

I built a pair fo the D67's a few years ago - love them!!!

Recently I've noticed that one is a few db hotter that the other.  The Mics themselves are dead on, but if I swap the power supplies, the increase in output follows the power supply - so it's something in the power supplies.

Hoping for some advice on where to start looking. I'm going to start by running throught he calibration of the PS's again I guess.

Thanks in advance and stay safe please!!!

 

[FarisElek]

Hi, hop eI'm posting in the correct place.

I built a pair fo the D67's a few years ago - love them!!!

Recently I've noticed that one is a few db hotter that the other.  The Mics themselves are dead on, but if I swap the power supplies, the increase in output follows the power supply - so it's something in the power supplies.

Hoping for some advice on where to start looking. I'm going to start by running throught he calibration of the PS's again I guess.

Thanks in advance and stay safe please!!!

Weird. And you’re sure the heater and B+ are the same? Are you swapping cables too? Cables can do crazy things.

 

[mickdundee63]

Missed this one. To be specific, there is no low end, high end, etc lost on the back capsule in fig-8. The rear diaphram is ou of phase wih your headphones so you get phasind at certain frequencies when monitoring. When recorded, it should sound no different than the front diaphragm.

i think I have a similar issue: when in figure 8 the front capsule is a bit dull, losing high end, whereas the rear capsule sounds crisp, like the front capsule does in cardiod.

My problem is also deeper though - sometimes I lose all low end in cardiod, if I flick the pattern switch it normally comes good again. I suspected a bad switch but removing the entire switch assembly and hard-wiring in cardiod did not resolve the issue.

If you go a few pages back you can see I pretty much took apart the entire mic trying to identify the issue and ultimately failed. Going to re-build the board.

 

[Delta Sigma]

i think I have a similar issue: when in figure 8 the front capsule is a bit dull, losing high end, whereas the rear capsule sounds crisp, like the front capsule does in cardiod.

My problem is also deeper though - sometimes I lose all low end in cardiod, if I flick the pattern switch it normally comes good again. I suspected a bad switch but removing the entire switch assembly and hard-wiring in cardiod did not resolve the issue.

If you go a few pages back you can see I pretty much took apart the entire mic trying to identify the issue and ultimately failed. Going to re-build the board.

Is the lack of low end while monitoring or when recorded and listening back. If you put the mic in fig-8, record yourself speaking into the front then the rear diaphragms. If your front diaphragm sounds bad compared to the rear while monitoring but not when listening back, it's only the phasing that you're hearing and your audio pair is wired backward. This would cause the mic to sound poor while monitoring in all cases except the rear diaphragm in fig-8. It would sound fine recorded though.

 

[FarisElek]

What delta said and the Figure 8 has a creamier sound with less air. It's in the U67 frequency response chart. Took me awhile to understand why this was happening too. However, your cardioid problem does not sound good.

Ryan

 

[jpertusi]

Weird. And you’re sure the heater and B+ are the same? Are you swapping cables too? Cables can do crazy things.

Thanks FarisElek!

Just finished recalibrating.  They are spot on at B+ 210v/210v and H- -6.35v/-6.37v. (I can't get H- any lower, the pots in the PS are maxed out)

I'll swap cables next and report.

It does not appear to be the cables. Swapping them makes no difference...

FYI:

Cardioid - difference is +/- 3db
Omni - difference is negligible (+/- 1db)
Fig. Eight  - difference is +/- 4db

 

[aharmonson]

Did you ohm out your tube's heater? Then install the tube and ohm out? All with power off.

It turned out to be a bad tube. Wasn't getting any continuity between pins 4 and 5. The new tube came today and the mic sounds great and everything is functioning. Thanks for the help!

 

[jpertusi]

Thanks FarisElek!

Just finished recalibrating.  They are spot on at B+ 210v/210v and H- -6.35v/-6.37v. (I can't get H- any lower, the pots in the PS are maxed out)

I'll swap cables next and report.

It does not appear to be the cables. Swapping them makes no difference...

FYI:

Cardioid - difference is +/- 3db
Omni - difference is negligible (+/- 1db)
Fig. Eight  - difference is +/- 4db

I'm going to next check the signal path connections in both power supplies and maybe swap tubes in the mics just in case i'm missing something.

To reiterate, it does not seem like the cables and the voltages are spot on spec in both mics.

I'll report back.

 

[jpertusi]

I'm going to next check the signal path connections in both power supplies and maybe swap tubes in the mics just in case i'm missing something.

To reiterate, it does not seem like the cables and the voltages are spot on spec in both mics.

I'll report back.

OK started testing from scratch.  It's not the power supplies.  So...

-- B+ and H- are correct measured at both mics. (+210v and -6.35v)
-- Swapped power supplies - no change, mic 1 still 3db hot
-- Swapped tubes - no change, mic 1 still 3bd hot
-- Finally, swapped the 7pin cables - no change, mic 1 still 3db hot

I was hoping it was just a tube, but this still makes more sense to me than it being a power supply issue given that the voltages are correct.

Any recommendations on where to start looking?

Thanks in advance for everyone's help.

-JP

 

[Moby]

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.