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

[TLRT]

Measure the total consumption with a multimeter, probably your trafo is overloaded.(tube consumption+bleeder resistors needs more than 300mA)

Hmm, will try the 40 Ohm resistor and a new diode.

Another question: When I ordered the parts for my U67 build, Mouser only had 68M resistors instead of the 60M ones.
I saw in one schematic that Neumann once also used this value...
How critical is it? 

EDIT: The 25 Ohm resistor definately wasn't the right one. It constantly tried to draw 320mA of current although my transformer is only rated for 300mA.
I've put in the 40 Ohm resistor of my second PSU and a new diode while I wait for the new resistors. Now the diode doesn't get that hot anymore but the hum is not really better. Maybe a little bit but it's still there...

Could the power transformer be damaged after being driven into saturation for some time?

I'll also try  to increase the filter capacitors to 47uF and 1000uF.

I'm puzzled why the hum doesn't decrease when I switch in the -10dB pad....

 

[Murdock]

Measure the total consumption with a multimeter, probably your trafo is overloaded.(tube consumption+bleeder resistors needs more than 300mA)

How can I measure total consumption?
And which bleeder resistor do you mean? I think there is only one, in the B+ line. And that's only drawing something like 2mA.
I calculated a heater current of around 200ma.

 

[TLRT]

How can I measure total consumption?
And which bleeder resistor do you mean? I think there is only one, in the B+ line. And that's only drawing something like 2mA.
I calculated a heater current of around 200ma.

You need to put your multimeter in Amper measurement position between pin 3-4(GND+heater) in series. For EF86 with usual 200mA consumption you need a dummy 32ohms/2w resistor,. Still I think you need a higher rating mains trafo, when I tried with 16V secondary winding I had hum also even when I raised the filter caps value.

 

[Murdock]

You need to put your multimeter in Amper measurement position between pin 3-4(GND+heater) in series. For EF86 with usual 200mA consumption you need a dummy 32ohms/2w resistor,. Still I think you need a higher rating mains trafo, when I tried with 16V secondary winding I had hum also even when I raised the filter caps value.

Thanks!
I measured around 250mA.
The hum is not present when I have the dummy loads in place. This is an indicator for a grounding problem with the mic, right?
If it would be ripple or an overloading transformer then I would also hear the hum with the dummy loads?

EDIT: It seems to be my mic cable... If I put the dummy load resistors directly into the Tuchel at the power supply, without the mic cable attached, I get no hum.
But If I put the resistors into the Tuchel at mic cable I get the hum...

 

[Murdock]

Yep, cable was the problem.
I now have shield, 0V and chassis (pin 3) all connected to the connector shell on both ends. This made the hum almost completly dissapear.

Thanks alot TLRT for your time and help!

Still wondering about the HT shunt resistor... As I have a 10mA secondary I would have to decrease it to 27k to shunt about 8mA to ground which would leave max 2mA to the Anode. But then I had to decrease the RC resistors which in turn would decrease their effectiveness...
How important and safe do you think this "regulator" is?

 

[TLRT]

Yep, cable was the problem.
I now have shield, 0V and chassis (pin 3) all connected to the connector shell on both ends. This made the hum almost completly dissapear.

Thanks alot TLRT for your time and help!

Still wondering about the HT shunt resistor... As I have a 10mA secondary I would have to decrease it to 27k to shunt about 8mA to ground which would leave max 2mA to the Anode. But then I had to decrease the RC resistors which in turn would decrease their effectiveness...
How important and safe do you think this "regulator" is?

You're welcome! I have 0.1A trafo, but it depends on your wall voltage and your tube's consumption. For EU with 235V avarage mains voltage I use 30-33k 2w resistors for Telefunken tubes.

 

[deeptubez]

I've been trying to download the PSU build pdf, but I only have through page 12, then the rest are blank....anybody have the full file?  Thanks

 

[Murdock]

Got another question about the PSU. When I switch on the power supply the B+ jumps to around 240V until the tube starts to conduct about 10 seconds later. Then it falls to 210V.
Is there an easy way to slowly ramp up the B+ because I would like to use a 160V cap for C9...

 

[Phrazemaster]

Got another question about the PSU. When I switch on the power supply the B+ jumps to around 240V until the tube starts to conduct about 10 seconds later. Then it falls to 210V.
Is there an easy way to slowly ramp up the B+ because I would like to use a 160V cap for C9...

I added a special module to my power supply for soft start. Ended up getting rid of it because it needlessly complicated things.

K & K audio has (or had) the board I used; might want to ping them.

 

[Joekkel]

hi there

i think i want to try a moby-transformer in my d-u67 build. it's the mkbv12-pcb. does anyone happen to know how to wire the moby-trafo to the max kircher-pcb? 

many regards
joachim

 

[Delta Sigma]

I'm not sure about the BV.12 but my two Moby transformers use the same colour codes as Neumann. Try the Neumann schematic.

 

[Joekkel]

Thanks fou your reply. Thats good to know, that the colors are the same.

If someone who replaced the transformer on a max kircher/poctop-pcb is reading this: how did you fix the new transformer, did you have to modify the pcb to make place for the trafo?

 

[AEarth]

Hi All. It seems that the usual places are out of 400M Ohm resistors at the moment (mouser has 1/4W only). Does anybody have any suggestions so I can get my second D-U67 up and running? I only need the small parts and can't wait much longer knowing how good they sound!

 

[Banzai]

Hi All. It seems that the usual places are out of 400M Ohm resistors at the moment (mouser has 1/4W only). Does anybody have any suggestions so I can get my second D-U67 up and running? I only need the small parts and can't wait much longer knowing how good they sound!

1/4W is more than enough for high-ohm in tube mics.

Can even use these, much cheaper:
https://eu.mouser.com/ProductDetail/TE-Connectivity-Neohm/RGP0207CHJ470M?qs=ip69W3eHERXPnniX7vee4A%3D%3D

 

[AEarth]

Thanks for the info.

 

[Joekkel]

hi there,

i just replaced my max kircher transformer in my beloved d-u67 after the impression that it was unexpectedly dark. when i discovered (in this thread i think) that there might be a problem with the feedback-winding in at least some transformers from max kircher, i decided to give moby's transformer a chance.

as i had the max-kircher pcb installed, i literally had to butcher the microphone to fit moby's transformer in the syt-5 body including lowering the pcb by several mm (i had to put it inside the long u-bracket-thingies, ouch...).  so i wouldn't recommend this trafo-swap from an mechanical pov.

but to me, this "upgrade" was really worth it! please listen to the soundcloud-link for yourself. and  know that i was really happy with the mic with max's transformer installed for more than three years ! i just used it for sounds like electric guitar and mono drumoverheads etc. where i wanted that darker, beefy tone. but i was always wondering, what this mic could do, if it had more high end...

https://soundcloud.com/jbudweiser/du67-maxkirchermoby/s-tMVoT

 

[Delta Sigma]

hi there,

i just replaced my max kircher transformer....

What capsule do you have in your D-U67?

 

[Delta Sigma]

I also installed a Moby BV.12 in my D-U67; SYT-5 body.

I'll second that the  replacement isn't fun, but wow; what a difference.

I have yet to get it into a good room to find out what it really can do but the Moby BV.12 is a significant upgrade. I previously converted the high pass switch into a feedback kill to flatten(ish) out the amp. I had done a recording with the feedback kill engaged (won't post clip, it's me and I'm not a singer). After changing transformers, I re-recorded the same song with feedback engaged, then killed.

I compared all three to find: Moby BV.12 with feedback had a beautiful and practical high end glimmer and Moby BV.12 without feedback had more high end content than the MK BV.12 without feedback.

Speculation time: I'm thinking that Max's BV.12 probably has the correct feedback windings as Max has claimed. I think that the difference is in the core. Moby's lams look thinner though more layers to make up a larger core.

Either way, I liked my D-U67 before but I like it much more now. I really don't recommend the change unless you're willing to put in some good elbow grease to change the transformers. It was not easy.

If you're building a DIY U67 from scratch, buy Moby's BV.12. I should add that I had a similar experience changing the AMI BV11r in my M49 (6S6B) to a Moby BV.11.

 

[dmp]

hi there,

i just replaced my max kircher transformer in my beloved d-u67 after the impression that it was unexpectedly dark. when i discovered (in this thread i think) that there might be a problem with the feedback-winding in at least some transformers from max kircher, i decided to give moby's transformer a chance.

Thanks for posting the info and the samples.

I measured the frequency response of the mic amplifier with Max's transformer and it was correct. If the feedback winding were wrong, the mic would have a ton of high end.  (the feedback from the transformer is negative feedback to reduce the high end of the amplifier)

Here is the measurement I made:
https://groupdiy.com/index.php?topic=50021.msg646101#msg646101

The mic amp should be -10 dB at 15kHz to compensate for the high end boost of the U67 capsule.

Can you measure the frequency response of the mic with Moby's transformer? To me, it sounds like it has MUCH more high end. I know you "want" more high end, but the question is if it's an apple-to-apples test between the transformers.  If they have the same windings and are correctly hooked up, they should have the exact same frequency response.  I'm not saying they will be perceived to have the same amount of high end, but they will both measure that way.

I compared all three to find: Moby BV.12 with feedback had a beautiful and practical high end glimmer and Moby BV.12 without feedback had more high end content than the MK BV.12 without feedback.

Speculation time: I'm thinking that Max's BV.12 probably has the correct feedback windings as Max has claimed. I think that the difference is in the core. Moby's lams look thinner though more layers to make up a larger core.

Interesting, thanks for your observations too.  Any chance you could do frequency sweeps?

I built this mic years ago and it's never really shined for me so I'd love to figure this out. I used a beezneez capsule.

 

[Delta Sigma]

...Any chance you could do frequency sweeps?

Unfortunately, I don't have any way to so sweeps.

... I used a beezneez capsule.

I also used a Beesneez K6. As far as I can tell, it sound great! It sounded good with Max's transformer and the feedback killed. It sounds better with Moby's transformer and the feedback active. The only time I wasn't happy with the sound was with Max's transformer and the feedback active. Still had its uses but it was my least favourite mic.