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

[mickdundee63]

Hahaha I can appreciate your incredulity, it doesn't look great, but it may be the lighting. I have built u67, u47, u87, c12, 251, la2a, 1176, Fairchild 670, a pair of Neve 1073s and the ssl style SB4000. I have had a few errors with some of these builds but they are all working and I have never had a cold solder throughout my 7 odd years of DIY.

I have also checked continuity of every component, from the pre solder leads to the post solder leads at the next component, to confirm a cold solder is not the issue.

The reason the soldering looks so bad is because I have pulled apart and rebuilt different elements of the thing looking for an error and solution.

But I appreciate any feedback and assistance, I will try and tidy up soldering again and triple check continuity of components.

Any other advice also appreciated.

 

[mickdundee63]

And to add, in terms of "social distancing" (enjoyed the pun lol) I have been looked at any joints that look a bit close for comfort and confirmed there is, or isn't continuity as should be the case according to the schematic and in comparison with my working mic.

I know the first thing to do is to double check soldering and any silly wiring errors - I've had errors in previous builds and these are always the first things I do and have often fixed the issue this way - a couple of similar colored wires confused or a missed solder resulting in a floating lead.

I've been over this build many many times.

As I said, I appreciate the feedback, it does look a bit ugly in there. I will go over it again.

But in the meantime, if anyone has had issues with polar patterns would be very helpful to know how they manifested sonically and what the final solution was.

 

[Purplenoise]

And to add, in terms of "social distancing" (enjoyed the pun lol) I have been looked at any joints that look a bit close for comfort and confirmed there is, or isn't continuity as should be the case according to the schematic and in comparison with my working mic.

I know the first thing to do is to double check soldering and any silly wiring errors - I've had errors in previous builds and these are always the first things I do and have often fixed the issue this way - a couple of similar colored wires confused or a missed solder resulting in a floating lead.

I've been over this build many many times.

As I said, I appreciate the feedback, it does look a bit ugly in there. I will go over it again.

But in the meantime, if anyone has had issues with polar patterns would be very helpful to know how they manifested sonically and what the final solution was.

Haha...hey I am just teasing you, it comes from a good place. On one of my 67’s I had a little noise and I tried a couple of things. I rearranged and shortened the cables in the high impedance sections and added some tape between the body rail and pcb where I thought a couple of solder points touched the rail. The noise was gone completely but I can’t be sure which one it was. The other thing to check is some of the switches are sensitive to overheating so if you applied heat for too long they might have been damaged...maaaaybe

 

[FarisElek]

I can confirm those switches can be jerks about heat. I did the same thing purple noise mentioned with the tape and rearranging the wires. I still have an ever so slightly warmer figure 8 and an ever so slightly brighter Omni. I still don’t know if it’s normal because my u87 doesn’t do that at all in the other polar positions. But I’ve read that u67’s kind of do this...so idk.

Your solder joints arent just bad-looking, they may not be properly passing signal. I recommend trying your best to clean them up. Also try to prevent bare leads from touching wires.

I had a similar thing as you but it was that I installed a resistor into a wrong hole on the tube pcb and I didn’t realize because it’s kind of confusing at first.

Double check your capsule wiring and compare it to the working one.
Also have you tried the power supply for your other one on the new mic? Is there potentially a bad connection in your power supply or it’s not properly biased?

 

[mickdundee63]

Thanks for the input guys - I've solved my grounding issue so it's just the pattern that's the problem.

Interesting to hear about overheating of the switches - they check out continuity wise but might be worth replacing them if I don't find any other solution.

I understand poor soldering can prevent signal passing but I've tested continuity on literally every solder point on the board and an adjoining joint - or wherever possible, between the leads of the actual components, to ensure that signal is being passed. Is it possible they could be showing continuity but the signal could still be compromised? My meter generally shows zero resistance, maybe 1 or 1.5 ohms in some areas.

I confirm I've checked capsule wiring and all component orientations against the schematic and my working mic. I will check again, wouldn't be the first time I've double checked and still made a dumb mistake.

And yep I've tried swapping PSUs, swapping cables and swapping tubes - no change and all work with the other mic.

I haven't changed the capsule recently but originally I had a neumann k67 in there with the same issue (weird patterns) and swapped a cheap chinese one in there to avoid damage while testing. That was a while ago, but I'm pretty confident pattern problems transferred from one capsule to the other.

I have gotten a bit lazy with the soldering - basically I'm pretty sure I'll be pulling it apart again so there's little incentive for me to be meticulous. But the consensus seems to be its a poor job so I may as well reflow the dodgy looking joints, clean up with some isopropyl and triple check for shorts, cold solders and component/wiring placement error.

I considered junking the board and starting again (I've spent THAT long staring and probing at it) but my theoretical understanding of these circuits is pretty poor and troubleshooting is an excuse to understand things just that little bit better.

 

[Purplenoise]

Thanks for the input guys - I've solved my grounding issue so it's just the pattern that's the problem.

Interesting to hear about overheating of the switches - they check out continuity wise but might be worth replacing them if I don't find any other solution.

I understand poor soldering can prevent signal passing but I've tested continuity on literally every solder point on the board and an adjoining joint - or wherever possible, between the leads of the actual components, to ensure that signal is being passed. Is it possible they could be showing continuity but the signal could still be compromised? My meter generally shows zero resistance, maybe 1 or 1.5 ohms in some areas.

I confirm I've checked capsule wiring and all component orientations against the schematic and my working mic. I will check again, wouldn't be the first time I've double checked and still made a dumb mistake.

And yep I've tried swapping PSUs, swapping cables and swapping tubes - no change and all work with the other mic.

I haven't changed the capsule recently but originally I had a neumann k67 in there with the same issue (weird patterns) and swapped a cheap chinese one in there to avoid damage while testing. That was a while ago, but I'm pretty confident pattern problems transferred from one capsule to the other.

I have gotten a bit lazy with the soldering - basically I'm pretty sure I'll be pulling it apart again so there's little incentive for me to be meticulous. But the consensus seems to be its a poor job so I may as well reflow the dodgy looking joints, clean up with some isopropyl and triple check for shorts, cold solders and component/wiring placement error.

I considered junking the board and starting again (I've spent THAT long staring and probing at it) but my theoretical understanding of these circuits is pretty poor and troubleshooting is an excuse to understand things just that little bit better.

Maybe it would be a good idea to start fresh. You have the expensive parts...why risk damaging them on a compromised pcb. I know it’s a lot of work but at least it doesn’t cost much and you end up with a mic that kicks ass. No mic under $4k can touch it if you make it with good parts and you fine tune it. We have 2 original reissue u67s here and my d67 pair with k870s and moby/haufe trafos sound just as good if not better

 

[Reallyjake]

My vote is to start fresh too. My mic sounds phenomenal. It is now my favorite. Worth the effort for sure. I’m building another next week. Thank you very much Dan. 

 

[mickdundee63]

Yeah I hear you. My working version is with my friend in a pretty successful commercial studio and it's his star mic. I think the quality of these DIY mics is absolutely stunning and for the price it almost feels like cheating. I actually prefer my D-87 for my own voice which is why this non-working 67 sat idle for a long time.

I find the troubleshooting process frustrating but it also forces you to learn a lot which is helpful for future builds and troubleshooting. I learned a lot about reading schematics, how polarisation works, how the switches integrate into the circuit, how tube mics are powered and not least to keep a clean build from the start!! Particularly around those floating areas.

But its true I've got the body, tube, transformer and a working PSU. In fact I've got a Neumann k67 sitting idle as well. A new mic PCB and components will not break the bank.

Very much appreciate all the help, I might try briefly hard wiring figure 8 and omni to rule out the switch and if that fails redo the mic PCB a bit more carefully from scratch.

Thanks Dan for making these projects available, really an incredible resource.  In fact I recently ordered the D-251. It's an addiction!

 

[Purplenoise]

Yeah I hear you. My working version is with my friend in a pretty successful commercial studio and it's his star mic. I think the quality of these DIY mics is absolutely stunning and for the price it almost feels like cheating. I actually prefer my D-87 for my own voice which is why this non-working 67 sat idle for a long time.

I find the troubleshooting process frustrating but it also forces you to learn a lot which is helpful for future builds and troubleshooting. I learned a lot about reading schematics, how polarisation works, how the switches integrate into the circuit, how tube mics are powered and not least to keep a clean build from the start!! Particularly around those floating areas.

But its true I've got the body, tube, transformer and a working PSU. In fact I've got a Neumann k67 sitting idle as well. A new mic PCB and components will not break the bank.

Very much appreciate all the help, I might try briefly hard wiring figure 8 and omni to rule out the switch and if that fails redo the mic PCB a bit more carefully from scratch.

Thanks Dan for making these projects available, really an incredible resource.  In fact I recently ordered the D-251. It's an addiction!

Yeah, Dan and the community are doing some tremendous work. I’ve build successfully 4 of his mics ( d87, 2xd67s and just recently a 251) and are by far the best mics I have ever owned...surpassing sometimes in sound the aged legends that they recreate. It’s the real deal.

 

[Purplenoise]

I have a question guys. In my room I have pretty high voltage 124v.. Now that the mic/psu have settled I can get the B+ up to 209v but the pot is all the way up. Since it’s unregulated if I take it to another place with, let’s say 110v the voltage in the mic will drop significantly but there is no way to calibrate higher. Does that mean there is something wrong with the psu? Should I just change the 56k resistor at the pot? If yes what value should I install? Thanks.

 

[Phrazemaster]

I have a question guys. In my room I have pretty high voltage 124v.. Now that the mic/psu have settled I can get the B+ up to 209v but the pot is all the way up. Since it’s unregulated if I take it to another place with, let’s say 110v the voltage in the mic will drop significantly but there is no way to calibrate higher. Does that mean there is something wrong with the psu? Should I just change the 56k resistor at the pot? If yes what value should I install? Thanks.

I had to do exactly what you're talking about, but it was a few years ago so I don't remember the value I ended up using. I think I just did a bit of trial and error.

Good luck!

 

[Purplenoise]

I had to do exactly what you're talking about, but it was a few years ago so I don't remember the value I ended up using. I think I just did a bit of trial and error.

Thanks, as long as there isn’t an “underlying condition” it shouldn’t be hard to find out. Only asking because I don’t have that issue with my other d67 psu

 

[TLRT]

I have a question guys. In my room I have pretty high voltage 124v.. Now that the mic/psu have settled I can get the B+ up to 209v but the pot is all the way up. Since it’s unregulated if I take it to another place with, let’s say 110v the voltage in the mic will drop significantly but there is no way to calibrate higher. Does that mean there is something wrong with the psu? Should I just change the 56k resistor at the pot? If yes what value should I install? Thanks.

Yes,you can go downfrom 56k  to 43k or even 33k /2W.

 

[Purplenoise]

Yes,you can go downfrom 56k  to 43k or even 33k /2W.

Great, thank you so much.

 

[Phrazemaster]

Thanks, as long as there isn’t an “underlying condition” it shouldn’t be hard to find out. Only asking because I don’t have that issue with my other d67 psu

If you test that other psu on your current household voltage, does it go high enough? I’d be surprised if it did, If it’s the same DIY design...

If it’s a new Neumann supply I think it’s regulated.

 

[Purplenoise]

If you test that other psu on your current household voltage, does it go high enough? I’d be surprised if it did, If it’s the same DIY design...

If it’s a new Neumann supply I think it’s regulated.

I am not sure to be honest since I reached desirable voltage before I run out haha...I calibrate at around 208v. I believe though that my first psu has more room. My two d67s though have different caps and transformers so I don’t know if that plays into it.
The psus are the diy ones not original.
Thanks for chiming in

 

[Phrazemaster]

I am not sure to be honest since I reached desirable voltage before I run out haha...I calibrate at around 208v. I believe though that my first psu has more room. My two d67s though have different caps and transformers so I don’t know if that plays into it.
The psus are the diy ones not original.
Thanks for chiming in

Interesting. Thx for clarifying.

If the two PSU’s both had same value components then I can’t explain the difference other than a fault somewhere.

 

[Purplenoise]

Interesting. Thx for clarifying.

If the two PSU’s both had same value components then I can’t explain the difference other than a fault somewhere.

Yeah that’s my thought too but so far they work great...no noise, drop outs...fire haha. I will check the first again to see how much room I have on the pot and maybe switch mics and recalibrate to have a better idea.  I just remember reading on this thread that someone had a similar issue and solved it by changing the 56k resistor.

 

[FarisElek]

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

 

[FarisElek]

Now I'm positive it's wired wrong. I changed some things on it trying my best to see what primary, secondary, and tertiary the T67 uses and I ended up swapping two wires. Now the Cardioid sounds even better, the the figure 8 sounds the same as cardioid but with a figure 8 pattern, and omni sounds flat and bad but louder than before. Also, I'm getting an electrical buzz lightly in the back that I can only hear if I crank it.

Please. Still need wiring help.