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

[FarisElek]

I'm moving on to a new transformer because it seems the turns ratio is completely off. Maybe it's just wired wrong, but I haven't been able to figure out a configuration that works.

So anyway, I've got a t67 in the mail and I know they're brighter so I'd like to go through with the calibration procedure and I have a question.

Calibration appears to be:
- Inject a 1khz at -18dbm which is about -6.15VAC
- Alter c17 until 1.5khz is -10db in relation to 1khz

So here are my questions:

1) How do I inject the tone? Can I send it through the mic output? That sounds sketchy.
2) How would a 1khz tell me what's going on in 1.5hz?

Thanks y'all. Hopefully this is the last question i'll ever have on this board.

Ryan

 

[Delta Sigma]

Thanks y'all. Hopefully this is the last question i'll ever have on this board.

Ryan

Don't worry about posting too many questions. Gotta learn bit by bit! Remember sometimes people are too busy to answer. I read your post on my lunch break, typed a reply but somehow didn't hit post!

Keep your mind open in troubleshooting. It's still very likely that your problem is in your Hi-Z section. It's suprising how hard it can be to trace your own wiring mistake. Sometimes, you make the same mistake when tracing as when wiring.

Listen to your mic after you put in your T67 and see if you need to chnge your C17. C17 is a minor change. Also, -18dBm would be in the millivolt range.

 

[FarisElek]

Thank you for your reply. I’ve checked my hi-z section so many times. I did a pretty clean job and have spent a large amount of time carefully cleaning it and comparing it to photos and schematics. I found a problem early on but fixed it a long  time ago. There is still always a chance it’s the hi-z section, but the odd thing is that different transformer configurations led to different problems on different polar patterns. Also, the secondary and tertiary windings weren’t getting the voltage ratio they’re supposed to get. Not even close.

Sending in 19v into primaries got me around .03 secondary and .01 out of tertiary.

 

[Purplenoise]

I'm moving on to a new transformer because it seems the turns ratio is completely off. Maybe it's just wired wrong, but I haven't been able to figure out a configuration that works.

So anyway, I've got a t67 in the mail and I know they're brighter so I'd like to go through with the calibration procedure and I have a question.

Calibration appears to be:
- Inject a 1khz at -18dbm which is about -6.15VAC
- Alter c17 until 1.5khz is -10db in relation to 1khz

So here are my questions:

1) How do I inject the tone? Can I send it through the mic output? That sounds sketchy.
2) How would a 1khz tell me what's going on in 1.5hz?

Thanks y'all. Hopefully this is the last question i'll ever have on this board.

Ryan

I believe you mean 15khz? The issue here is that I don’t think anyone has used the BeesNeez bv12. Plenty of info though on t67. As far as the c17 depending on capsule get a few caps ranging from 100 to 300pf ( JustRadios has all the values). I would solder sockets so that you could swap caps without disoldering all the time...you could get a dip8 opamp socket and cut two sockets off. For the t67 my guess would be around 250pf but it could be more. Since the change is not really that drastic you could get the following values: 100,150,200,250,300,350pf. Those are for taming the big 10k bump of the k67 capsule with a gentle roll off so the higher the value the earlier the roll off starts...if you go too high you will loose too much “air”. Remember that the original 67 is not the smoothest mic ever ( soloed) when you use it up close...give it a foot of distance and the track will sit perfectly in the mix

 

[FarisElek]

That's a great idea. Thanks for the advice. I have a 150pf and a 270pf on hand. Would be nice if one of those did the trick.

I've reheated the solder in some hard to reach areas on the Hi-Z area while also double-checking placement. I'm hoping that installing the T67 fixes all problems and that I can be done with it. Maybe then while viewing how the T67 works and the ratios, I can troubleshoot the Beesneez BV12 and make another 67 in the future. At first I thought the Beesneez was faulty, but I actually think it's not after looking up for tests for the transformer. It could still be that the transformer wasn't wired right, the Hi-Z section needed some attention, or that the Capsule is faulty. Really hoping for a happy ending soon.

Ryan

 

[Purplenoise]

That's a great idea. Thanks for the advice. I have a 150pf and a 270pf on hand. Would be nice if one of those did the trick.

I've reheated the solder in some hard to reach areas on the Hi-Z area while also double-checking placement. I'm hoping that installing the T67 fixes all problems and that I can be done with it. Maybe then while viewing how the T67 works and the ratios, I can troubleshoot the Beesneez BV12 and make another 67 in the future. At first I thought the Beesneez was faulty, but I actually think it's not after looking up for tests for the transformer. It could still be that the transformer wasn't wired right, the Hi-Z section needed some attention, or that the Capsule is faulty. Really hoping for a happy ending soon.

Ryan

That’s the nature of the beast called DIY. A lot of second guessing, trial and error, and learning. Don’t get disappointed, I think you are almost there. The t67 is very well documented so with the transformer out of the equation if there are other issues it will be easier to isolate. Keep up the good work

 

[FarisElek]

Also, does anyone know how to use the Calibration input?

It says “sig” and “signalnd”

Does that mean signal and signal ground?

So I send 1khz at -18dbm into sig/signalnd and monitor it through the regular output to calibrate?

 

[FarisElek]

On this picture of Dan's "overall connection" PDF, it shows that the pcb hole for Z1, located behind c2, connects to the hole beside one of the turrets (the one on the left if you're look at it from tube side.

What the HECK is that? I can't find any pictures of anything connected there on anyone's build, or maybe it's just hard for me to see. Am I supposed to connect those by wire?

Ryan

 

[mickdundee63]

Used this mic a lot today and I'm finally annoyed with it.

Polar paterns aren't right. Figure 8 lacks high end  air on front diaphragm, but not bad on back, almost normal. Cardioid most likely perfect.  Omni just quiet, but just noticeable enough to feel off. I have to move 2-3 inches closer to get the volume the same as cardioid.

I could tell I singed C10 so I changed it today. Nothing. I had a bad resistor in there that didn't match the others, so I changed it. No change. I checked tons of solder joints I could reach. No change. Part of me thinks that the transformer isn't wired quite right. Like, almost right, but not quite.


Any ideas?

I've attached a picture of the Beeznees BV-12. Can anyone that is more knowledgeable than myself show me how you'd wire it to make sure I did it right?


Ryan

I had very similar issues to this. cardiod fine, figure 8 off  (one side full but dull, one side thin), omni thin and low output and some minor grounding noise overall. I pulled the whole thing apart twice and checked everything a million times. Eventually I gave up. It sounds great in cardiod and that's mainly what I use so just sticking with that. I have an AMI t67 in it. Grounding one of the pins cleared up the grounding issue so I was thinking transformer issue as well but I checked the wiring many times. I guess its possible its the capsule but I also swapped front for back and the issues followed the electronics, not the diaphragm so I don't think that's the issue.

 

[FarisElek]

I wonder if like the d-u87 this has to do with some resistors in the hi-z section...

 

[FarisElek]

Ok, some things I’ve noticed about my build while waiting for the transformer to arrive. One side of C9 touched the mic frame, so I put electric tape against the frame there. They didn’t have continuity, but honestly they were clearly touching, so maybe it wasn’t a lot but enough? I found several point in which resistors were touching leads. I don’t know if that’s a problem, but I fixed it anyway. Found several points on the PCB in which the outside layer had flaked off and copper was touching the mic frame, potentially grounding a point where signal goes to figure 8 (I followed the schematic, it literally did), I noticed a lead sticking out pretty far under the tube socket because I had to move something after the fact due to a misread of the socket silk. I was able to get tweezers in there and just move the lead so it wasn’t touching the tube socket from behind.
I also retouched up almost every solder joint I could reach on the socket pcb and the main pcb.

I built this back when I was using this very thick solder and I’m ashamed at how bad some of the joints I hadn’t seen in awhile looked like. They’re all silver and smooth now.

If my new transformer workers perfectly, it may also be some of those changes. Wish me luck.

 

[Purplenoise]

Ok, some things I’ve noticed about my build while waiting for the transformer to arrive. One side of C9 touched the mic frame, so I put electric tape against the frame there. They didn’t have continuity, but honestly they were clearly touching, so maybe it wasn’t a lot but enough? I found several point in which resistors were touching leads. I don’t know if that’s a problem, but I fixed it anyway. Found several points on the PCB in which the outside layer had flaked off and copper was touching the mic frame, potentially grounding a point where signal goes to figure 8 (I followed the schematic, it literally did), I noticed a lead sticking out pretty far under the tube socket because I had to move something after the fact due to a misread of the socket silk. I was able to get tweezers in there and just move the lead so it wasn’t touching the tube socket from behind.
I also retouched up almost every solder joint I could reach on the socket pcb and the main pcb.

I built this back when I was using this very thick solder and I’m ashamed at how bad some of the joints I hadn’t seen in awhile looked like. They’re all silver and smooth now.

If my new transformer workers perfectly, it may also be some of those changes. Wish me luck.

Good luck haha...sometimes it’s the simplest thing ( like a small piece of stray resistor lead logged in a bad place). Since it’s very time consuming and hard sometimes to trace back a problem I really take my time and double check every step of the build from the get go. So far knock on wood I’ve built 5 mics that worked from first power up ( and a lot of valuable help from this community)....maybe the occasional noise issue but after some more cleaning and moving some stuff around it was all good.

 

[FarisElek]

Didn't solve my problems! haha
although, I think some of the "dull" sounds are simply because figure 8 is getting less volume but the same amount of proximity effect. I tested with high pitches out of a speaker. So it's a volume loss thing and not a "dullness" thing. Which is good. It just means I need to turn up a couple 5db when in the other patterns besides cardioid.  Obviously this is not ideal...but whatever. As for the transformer, it's a tad bit brighter than the beesneez, but I'll leave it in because I like it. I switched the c17 to 150pf, it's fine there.

I want to be done with this because I like cardioid on this mic more than any of my other mics. If anyone is pretty certain what causes this problem, I'd love to to know I'm just done spending time on it shooting in the dark.

Thank you,
Ryan

 

[FarisElek]

My partner and I are recording a cover of Laura Nyro's the wind. We tracked some vocals with her today. I don't have access to a vocal booth right now so we did in an only mildly treated room that has a terrible 250-ish hz thing going on that I can't stand because it makes things muddy and unclear. Despite that...we tracked it in there because we didn't want to bother our roommates today.

Let me know what you think of the mic. It's a little bright because of the T67 but I honestly like it. It places itself in the mix really well.

It was tracked with:

D-U67 (LC on because of room) < EZ1073 < Hairball FET/500 rev a < Lucid ADA8824

https://soundcloud.com/ryan-virgilius-daniel/the-wind-67

Just realized it's mixed really low because of the mix it's sitting in is quiet right now.

Thanks,
Ryan

 

[Purplenoise]

Awesome...it sounds pretty good man. I don’t think it’s overly bright, the es’s sound natural and it sounds balanced. What tube are you using?

 

[FarisElek]

Awesome...it sounds pretty good man. I don’t think it’s overly bright, the es’s sound natural and it sounds balanced. What tube are you using?

Thank you! I think it sounds good too but it’s reassuring to know others do too.

The tube is an NOS Telefunken

 

[Purplenoise]

Thank you! I think it sounds good too but it’s reassuring to know others do too.

The tube is an NOS Telefunken

Ef86 or ef806? If you like the sound of your mic now you can play around with different tubes to “mellow” it out if you want. A Mullard will tame the highs just a touch.  A NEC ef86 ( very affordable) will tame it even more with a little more mids

 

[FarisElek]

It's a EF86. I'm pretty happy with it. Depending on the mix my D-U87's can be a touch on the dark side, so I'd prefer the U67 to be a touch brighter anyway. I'd like to end the microphone building days....at least until I decide to build a U47.

Ryan

 

[FarisElek]

A question for any vets of the U67 build:

Plugged this mic in for the first time in about a month. Maybe longer. It made popping bubble sounds for about 45 seconds until I switched it off. What tends to cause this? I imagine it's just dusty somewhere inside it due to not having a case and living in Texas. I blew lightly on the capsule and turned it back on after a minute and only did it for about 10 seconds and then acted normal. Do you think my capsule is dirty? is it safe to clean? Also,  does anyone recommend a case for the cheap Chunger bodies? Chunger's site says that the cases are only for the nicer bodies.


Ryan

 

[Delta Sigma]

A question for any vets of the U67 build:

Plugged this mic in for the first time in about a month. Maybe longer. It made popping bubble sounds for about 45 seconds until I switched it off. What tends to cause this? I imagine it's just dusty somewhere inside it due to not having a case and living in Texas. I blew lightly on the capsule and turned it back on after a minute and only did it for about 10 seconds and then acted normal. Do you think my capsule is dirty? is it safe to clean? Also,  does anyone recommend a case for the cheap Chunger bodies? Chunger's site says that the cases are only for the nicer bodies.


Ryan

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.