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

[mrerdat]

@ mrerdat
Regarding the slight tone difference between  DU67 1 and 2. You automacilly (?) asssume the difference is in the capsule. But the tranny plays a big part in the sound, too, perhaps even more so in a U67 circuit. So by te same token, we could ask ourselves if the (affordable) AMI T67 trannies are consistent one from the other. The way to (maybe) find out would be switching capsules or trannies.
Oh, and and then there's the tube. From my experience, tubes, especially the EF86, vary a lot, even within the same brand. But they're easily swappable and you may have tried that already. Still, to be at their best, they all need a slightly different touch so to speak. They're almost human that way. 
Finally, there are other parts still that might not behave identically. But I'd say the ones mentioned above would be the usual suspects.

Good point regarding swapping out the transformer/tube to check for (in)consistencies.  When I built DU67 #1 in the summer I swapped out different Telefunken EF86s to see what my best tubes were.  I had one noisy tube in the lot and the two that I'm using in my mics right now were both really quiet.  I didn't notice a tone change between the good tubes, but admittedly I wasn't really looking for one.  Curious to hear what the effects of swapping T67s would be. 

But I suspect the capsule to have more of an influence on the sound than the tubes or transformer.  I could be wrong, but the only way to find out is to break out the good old soldering iron.  In mic #1, there's more of a difference between the front and rear diaphragms than in mic #2.  So I'll see what I gain (or lose) first by swapping the sides of the capsule in mic #1 before I do any transformer swapping.

 

[micaddict]

Good point regarding swapping out the transformer/tube to check for (in)consistencies.  When I built DU67 #1 in the summer I swapped out different Telefunken EF86s to see what my best tubes were.  I had one noisy tube in the lot and the two that I'm using in my mics right now were both really quiet.  I didn't notice a tone change between the good tubes, but admittedly I wasn't really looking for one.  Curious to hear what the effects of swapping T67s would be. 

But I suspect the capsule to have more of an influence on the sound than the tubes or transformer.  I could be wrong, but the only way to find out is to break out the good old soldering iron.  In mic #1, there's more of a difference between the front and rear diaphragms than in mic #2.  So I'll see what I gain (or lose) first by swapping the sides of the capsule in mic #1 before I do any transformer swapping.

Great! Do keep us posted.

Oh, and please don't damage anything or I'll feel guilty.

 

[micaddict]

This M269c was brighter in a pleasant yet somehow not sibilant way, but it lacked the midrange and low end definition/thickness that the DU67 had. Go figure.

This seems to be a pattern. Dany reported this when building his prototypes and a similar thing was found in the originals, as discussed on the REP forum.
Fixed bias versus self bias.
Or U67/M269b and M49b versus M269c and M49c.

Apart from that, an EF86 may typically sound a little thicker than an AC701k subminiature, too (although the Telefunken EF86 is likely the cleanest of the bunch).
The magic is in the mids.
Got to love the EF86.
And the (D)U67.

 

[Phrazemaster]

Hate to see you take the damn thing apart just to see why it's better, even though you did build it. This is DIY after all.

Still, it's like you're messing with its soul...

 

[jm.music]

I got my mic working!

The problem was I had swapped the wires 4 & 6 coming from the xlr pin out.  :-[ Not sure if I did this after I went through looking for my original problem, or if I had them swapped the whole time. Anway the mic is working now and sounds fantastic.

Thanks, Matt Nolan for your help.

 

[micaddict]

Hate to see you take the damn thing apart just to see why it's better, even though you did build it. This is DIY after all.

Still, it's like you're messing with its soul...

Hey, good to see some romanticism among all the technical stuff. 

I do hear you.
On the other hand, experimenting, testing, comparing, measuring; aren't those the roots of science?
Without them there wouldn't have been a U67 in the first place.

Also, building a very nice microphone period is one (great) thing, building a clone is another.

But like I said, I do hope he doesn't damage anything.
No operation is without risks.

 

[Phrazemaster]

Hate to see you take the damn thing apart just to see why it's better, even though you did build it. This is DIY after all.

Still, it's like you're messing with its soul...

Hey, good to see some romanticism among all the technical stuff. 

I do hear you.
On the other hand, experimenting, testing, comparing, measuring; aren't those the roots of science?
Without them there wouldn't have been a U67 in the first place.

Also, building a very nice microphone period is one (great) thing, building a clone is another.

But like I said, I do hope he doesn't damage anything.
No operation is without risks.

Heh heh Henke!

Funny.

 

[mrerdat]

Great! Do keep us posted.

Oh, and please don't damage anything or I'll feel guilty.

Hate to see you take the damn thing apart just to see why it's better, even though you did build it. This is DIY after all.

Still, it's like you're messing with its soul...

Noooooooooo I broke my capsule! Curse you all!



......... just kidding 

I put  DU67 #1 in figure 8 and listened to the rear capsule to hear the differences from the front.  When I initially built the mic, I remember seeing a tiny speck or blemish on one of the diaphragms which was why I put it in the rear position.  But listening to the mic in figure 8  tonight I discovered that this rear diaphragm sounded so much better, like a veil of mud was lifted with an extension in the top and bottom range.  So naturally I swapped the front with the rear capsule. What a world of a difference! I think it sounds better than mic #2 now actually.  

I rarely use fig-8 or omni with these mics and when I do it is usually quite far from the source, so the difference between the front and rear is perhaps more tolerable for me than it would be for some others on here.  If it bothers me down the road, I'll splurge and stick a Neumann cap in there.

Lesson learned after using my eyes instead of my ears.

Listening to mic #2, I found a slight difference between the front and rear diaphragms, but they are a lot closer to each other than in mic #1.

It's amusing to me that the HK67 diaphragm quality was (relatively speaking):

mic #1
front  (old rear) - the best!
rear - the worst!
mic #2
front - pretty good
rear - pretty good

@ mrerdat
From my experience, tubes, especially the EF86, vary a lot, even within the same brand. But they're easily swappable and you may have tried that already. Still, to be at their best, they all need a slightly different touch so to speak. They're almost human that way. 

I feel that way with entire mics.  A different personality and soul in each one.  It's crazy what building a pair of anything can teach you about component tolerances.

 

[micaddict]

Thanks for the update!

And yes, if one can afford it, do build in pairs.
There's more than one advantage.

 

[sargethebard]

Hey! Hoping someone can help me out. A few days ago my mic was working fine and sounding great! But I moved it to set up a recording space elsewhere and now it doesn't work properly :-\  At first when I plugged my power supply in it blew a fuse so I checked it and sure enough an earth point was loose, easy fixed. Now i'm testing for faults and i've noticed my H- sits at -16v unloaded but when I have the mic attached it reads 0v on the PSU and mic. I'm guessing this isn't supposed to happen...is it possible I have blown something? Thanks

EDIT:  Ok, so maybe it's not the mic. I seem to lose all H- as soon as I plug the lead in with the other end not even attached to the mic. Not sure what to think. All the wires seem clear of each other at each connector I thought maybe a stray wire from the shield might have been touching the H- red wire but it doesn't seem to be...??

 

[ln76d]

Hey! Hoping someone can help me out. A few days ago my mic was working fine and sounding great! But I moved it to set up a recording space elsewhere and now it doesn't work properly :-\  At first when I plugged my power supply in it blew a fuse so I checked it and sure enough an earth point was loose, easy fixed. Now i'm testing for faults and i've noticed my H- sits at -16v unloaded but when I have the mic attached it reads 0v on the PSU and mic. I'm guessing this isn't supposed to happen...is it possible I have blown something? Thanks

EDIT:  Ok, so maybe it's not the mic. I seem to lose all H- as soon as I plug the lead in with the other end not even attached to the mic. Not sure what to think. All the wires seem clear of each other at each connector I thought maybe a stray wire from the shield might have been touching the H- red wire but it doesn't seem to be...??

Another similar advice, to another guy with faulty gear
At least put some good quality picture of your PSU guts.
Probably more people will help you

 

[Khron]

Continuity tester (ie. 'beeper') on the multimeter, perhaps?

 

[mrerdat]

EDIT:  Ok, so maybe it's not the mic. I seem to lose all H- as soon as I plug the lead in with the other end not even attached to the mic. Not sure what to think.

Continuity tester (ie. 'beeper') on the multimeter, perhaps?

Bingo. Definitely sounds like a short at the mic cable.

 

[sargethebard]

Continuity tester (ie. 'beeper') on the multimeter, perhaps?

Re-soldered the entire cable and checked continuity, seems fine to me. Also checked to see B+ and H- voltages were reaching the end of the cable, and again, seems fine. So now i'm baffled. Inside the mic there is continuity from the mic input to the B+ and H- yet when I load the mic to the power supply I read nothing for either...what is happening?! It was working fine a few days ago.

EDIT:  So i'm an idiot...re-soldered all the cable points backwards    but good news is when I plug the cable in I don't lose my heater voltage in the PSU anymore so chances are it was shorting beforehand soooo now back to doing it correctly and I feel like everything should work fine. Thanks for the help guys

 

[Khron]

Good thing the B+ didn't end up on the heater pin or across the transformer, at least

 

[TLRT]

Finally I finished my 67 also(I have to prepare a  new PSU house also, as it has no pattern switch) everything sounds great even with a cheap Alctron capsule. (I have the HK67 of course I tested some tubes, and I found those old Tungsrams are pretty great with low noise floor, I have many TFK EF86/EF806S also,maybe with the HK67 I will hear more difference.

 

[micaddict]

Congrats!

Arguably the best mic design ever.

Sound samples?

 

[Christopher L]

What amperage switch should I use with the power suppy for this mic?

 

[ln76d]

What amperage switch should I use with the power suppy for this mic?

Low, nothing exciting
DC current is ca. 1mA and 200mA

 

[Christopher L]

Thanks for your help.