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

[micaddict]

Audio transformer question I read thru this thread reading most folks love the sound of their builds thats great & how close they sound to original 67s but it reads like there is quite a difference between the AMI transformers & IOaudio.... is there a definative answer to which is closest ........I have always noticed in my mic DIY that capsule make way the most impact on the sound followed by transformer followed by circuit ..... I would guess that in this circuit the transformer is more important that usual have the feedback to deal with as well.

Thanks Gary O.

I'm wondering that myself, as well. I'm interested in building a pair of those mics, and after reading the whole thread, still not sure which are the most true transfomers to the original U67?
Thanks

There's only one way to find out.
A proper shootout. 

Candidates would be the AMI T67 and BV12, IOaudio BV12, the new Cinemag, the Samar.
And ?

We need a pristine, original, unmodded U67 for comparison plus at least one original K67 capsule.

Anything else?

 

[jm.music]

Hi everyone,

I was hoping someone here could help me pinpoint my problem. I was working on the build and had the B+ at 210v and H- at -6.3v, but my Plate voltage (a) kept fluctuating rapidly between a range of 40v-80v or staying steady at 0v. I couldn't find the problem so I went back through, looked for cold joints and redid all the wiring in the HI-z area. Now the B+ is higher, (lowest I can adjust to is 230v, and the H- is around -1v. The plate voltage (a) is now exactly what the B+ readout says. 230v and changes as I adjust. Before I tear it down again, I was wondering if anyone had an idea of what the problem may be or any suggestions.

Thanks

(these readings are with tube inserted and psu readings check out okay) 

 

[Matt Nolan]

Hi everyone,

I was hoping someone here could help me pinpoint my problem. I was working on the build and had the B+ at 210v and H- at -6.3v, but my Plate voltage (a) kept fluctuating rapidly between a range of 40v-80v or staying steady at 0v. I couldn't find the problem so I went back through, looked for cold joints and redid all the wiring in the HI-z area. Now the B+ is higher, (lowest I can adjust to is 230v, and the H- is around -1v. The plate voltage (a) is now exactly what the B+ readout says. 230v and changes as I adjust. Before I tear it down again, I was wondering if anyone had an idea of what the problem may be or any suggestions.

Thanks

(these readings are with tube inserted and psu readings check out okay) 

Have a look at the voltages around the divider resistors that generate the grid bias from the negative heater voltage.

 

[jpertusi]

Hey folks, just an update on my issue with the -10db pads not working.

Switch itself is working as expected.  Continuity back to the PCB is good.

Since it's on / off it's simply connecting 2 points on the PCB or not connecting them.  It seems to be doing that according to my Multimeter.

Those points being the turret labeled Z1 and the point on the opposite side just above the word "Pad"

See attached image.

So... if the switch is indeed making (or breaking) that connection as expected, but the switch has no effect on the signal...

What's next?

As always any help is appreciated.

-JP

 

[dmp]

The pad puts a capacitor in parallel with the capsule. Trace the wiring - you should have a styrene cap switched in with the pad on.

 

[jpertusi]

Yep.  C10,  from the pad to the pin of the tube socket that passes through the PCB.

Does C10 have a polarity?  I remember it was difficult to tell.  Perhaps they are in the wrong way round?

Also, forgive my ignorance but what's the procedure to test if C10 is in with the pad engaged?

Thanks for your help!!!

 

[dmp]

Styrene caps do not have a polarity, but they can be ruined from too much heat.
If you have a Farad measurement on your DMM, you could check the cap.

 

[jpertusi]

OK, well at least I did not put them in backwards.  ;-)

Reads 0.322nf

 

[dmp]

Measure the capacitance of the capsule with the pad switch on and off. You should see a jump when you flip the switch, otherwise check the wiring again.

 

[jpertusi]

Measuring across the 2 turrets (which I think is front diaphragm / backplate) there is no change with the position of the pad switch.  Reads +/- 0.0856nf.

 

[jm.music]

Hi everyone,

I was hoping someone here could help me pinpoint my problem. I was working on the build and had the B+ at 210v and H- at -6.3v, but my Plate voltage (a) kept fluctuating rapidly between a range of 40v-80v or staying steady at 0v. I couldn't find the problem so I went back through, looked for cold joints and redid all the wiring in the HI-z area. Now the B+ is higher, (lowest I can adjust to is 230v, and the H- is around -1v. The plate voltage (a) is now exactly what the B+ readout says. 230v and changes as I adjust. Before I tear it down again, I was wondering if anyone had an idea of what the problem may be or any suggestions.

Thanks

(these readings are with tube inserted and psu readings check out okay) 

Have a look at the voltages around the divider resistors that generate the grid bias from the negative heater voltage.

Thanks for the response. Which resistors would those be?

I went ahead and took voltage readings for some of the junctions.

R12 and R13: 56.7v
R13-R16: 110v
R9-R12 143mv (should be -1.6v?)
C9 and R14 230v (should be 75v?)

Thanks for any advice.

 

[Matt Nolan]

Hi everyone,

I was hoping someone here could help me pinpoint my problem. I was working on the build and had the B+ at 210v and H- at -6.3v, but my Plate voltage (a) kept fluctuating rapidly between a range of 40v-80v or staying steady at 0v. I couldn't find the problem so I went back through, looked for cold joints and redid all the wiring in the HI-z area. Now the B+ is higher, (lowest I can adjust to is 230v, and the H- is around -1v. The plate voltage (a) is now exactly what the B+ readout says. 230v and changes as I adjust. Before I tear it down again, I was wondering if anyone had an idea of what the problem may be or any suggestions.

Thanks

(these readings are with tube inserted and psu readings check out okay) 

Have a look at the voltages around the divider resistors that generate the grid bias from the negative heater voltage.

Thanks for the response. Which resistors would those be?

I went ahead and took voltage readings for some of the junctions.

R12 and R13: 56.7v
R13-R16: 110v
R9-R12 143mv (should be -1.6v?)
C9 and R14 230v (should be 75v?)

Thanks for any advice.

If you could point me to where the schematic for this mic is in this thread, I'd be able to tell you.

 

[jm.music]

Hi everyone,

I was hoping someone here could help me pinpoint my problem. I was working on the build and had the B+ at 210v and H- at -6.3v, but my Plate voltage (a) kept fluctuating rapidly between a range of 40v-80v or staying steady at 0v. I couldn't find the problem so I went back through, looked for cold joints and redid all the wiring in the HI-z area. Now the B+ is higher, (lowest I can adjust to is 230v, and the H- is around -1v. The plate voltage (a) is now exactly what the B+ readout says. 230v and changes as I adjust. Before I tear it down again, I was wondering if anyone had an idea of what the problem may be or any suggestions.

Thanks

(these readings are with tube inserted and psu readings check out okay) 

Have a look at the voltages around the divider resistors that generate the grid bias from the negative heater voltage.

Thanks for the response. Which resistors would those be?

I went ahead and took voltage readings for some of the junctions.

R12 and R13: 56.7v
R13-R16: 110v
R9-R12 143mv (should be -1.6v?)
C9 and R14 230v (should be 75v?)

Thanks for any advice.

If you could point me to where the schematic for this mic is in this thread, I'd be able to tell you.

Thanks Matt,

The schematic is in the build folder. https://dl.dropboxusercontent.com/u/43869772/U67/Safety%20Manual%20and%20Considerations.pdf

If you don't want to download that, here's an online link
http://www.gyraf.dk/gy_pd/g7/u67.gif

 

[Matt Nolan]

Hi everyone,

I was hoping someone here could help me pinpoint my problem. I was working on the build and had the B+ at 210v and H- at -6.3v, but my Plate voltage (a) kept fluctuating rapidly between a range of 40v-80v or staying steady at 0v. I couldn't find the problem so I went back through, looked for cold joints and redid all the wiring in the HI-z area. Now the B+ is higher, (lowest I can adjust to is 230v, and the H- is around -1v. The plate voltage (a) is now exactly what the B+ readout says. 230v and changes as I adjust. Before I tear it down again, I was wondering if anyone had an idea of what the problem may be or any suggestions.

Thanks

(these readings are with tube inserted and psu readings check out okay) 

Have a look at the voltages around the divider resistors that generate the grid bias from the negative heater voltage.

Thanks for the response. Which resistors would those be?

I went ahead and took voltage readings for some of the junctions.

R12 and R13: 56.7v
R13-R16: 110v
R9-R12 143mv (should be -1.6v?)
C9 and R14 230v (should be 75v?)

Thanks for any advice.

If you could point me to where the schematic for this mic is in this thread, I'd be able to tell you.

Thanks Matt,

The schematic is in the build folder. https://dl.dropboxusercontent.com/u/43869772/U67/Safety%20Manual%20and%20Considerations.pdf

If you don't want to download that, here's an online link
http://www.gyraf.dk/gy_pd/g7/u67.gif

Ah, OK. I didn't realise that this clone used the same schematic and component numbers as the original. Well, that makes it easy. Its all the stuff around R9, R10, R11, R12. The reference voltages are right there on the schematic for you.

 

[gary o]

Audio transformer question I read thru this thread reading most folks love the sound of their builds thats great & how close they sound to original 67s but it reads like there is quite a difference between the AMI transformers & IOaudio.... is there a definative answer to which is closest ........I have always noticed in my mic DIY that capsule make way the most impact on the sound followed by transformer followed by circuit ..... I would guess that in this circuit the transformer is more important that usual have the feedback to deal with as well.

Thanks Gary O.

I'm wondering that myself, as well. I'm interested in building a pair of those mics, and after reading the whole thread, still not sure which are the most true transfomers to the original U67?
Thanks

There's only one way to find out.
A proper shootout. 

Candidates would be the AMI T67 and BV12, IOaudio BV12, the new Cinemag, the Samar.
And ?

We need a pristine, original, unmodded U67 for comparison plus at least one original K67 capsule.

Anything else?

Wow this would be great !

I think a U67 U87 head basket would be essential

Im in the process of making a U67 circuit in a large body & Im going to be able to plug in my U87ai head basket n capsule will look strange I know but sound & usability is king for me ...... so other thans looks the main thing I having missing is a known accurate sounding transformer...... Im sure they would all sound great but would like to get close as I can.

 

[micaddict]

Gary, where about in the UK are you?

You van PM me, too.



Henk

 

[gary o]

Hi Henk not sure if my PMs are working Im in Essex in basildon

 

[micaddict]

Thanks, Gary. I received it and I replied.
We might be able to work something out.
With a little help from our friends.

 

[mrerdat]

I brought one of my DU67s and Bock 251 to a test session where we compared them to 5 other tube mics in different applications - vocals, electric guitar, acoustic guitar, mono drum overhead, and cello.  The studio owner had two Brauner VM1s (both Klaus Heyne Edition, not matched pair, about 40 serial numbers apart),a KM56, M269c, and a M49b (which sadly only got to be used in the last few tests bc the B room was using it for most of our session). 

The DU67 I used for this shootout is the 2nd one I built which is using the Heiserman H67 capsule, AMI T67, and silver shield Telefunken EF86.  It sounds better to me than the first one I built because of the capsule most likely.  There's a little bit more low and top in mic #2.  I ordered the HK67 that's in my latest 67 2 years after I ordered the first one, so it could be that the capsule construction is a bit more refined, the tensioning was different, or Eric just got better at building them.  He claimed in a PM from a while ago that the construction is the same, so it could just be different tolerances between capsules.  Despite what I just wrote though  I still use DU67 #1 all the time.

Of course with these threads YMMV, this is not a scientific test, yada yada. I don't have the audio from this session at the moment.

So here are my comments/first hand opinions:

We put up one mic at a time, taking care to place mics in the same location every time they were swapped. 

The VM1s sounded quite different from each other - one was brighter than the other, but the other had more of a defined low end.  They fared well on everything and had modern clarity to them, but everyone in the room liked the DU67 better on the male vocalist (upper tenor-alto range) we were recording. The bright VM1 was particularly great on drums but the darker one felt more balanced, especially for guitars and cello where it felt like the focus was on the whole instrument instead on a specific higher frequency range.

The KM56 was incredible on drum overhead and was also really nice on guitars, but it didn't impress us too much on vocals and have the low end presence we would have liked on the cello.  There's something old timey sounding about the mic with the way it saturates the upper mids that is really cool for certain applications.

The Bock didn't match well with the singer we were recording and left something to be desired when recording guitars (the studio owner said it sounded a bit "generic"), but sounded great on the cello and perfectly useable as a mono overhead.  The low end on that mic is beautiful.

We only got to try out the M49b on cello and acoustic guitar but didn't really like it too much for close miking applications.  The mic was backed off a feet from the source after that and we liked how wonderfully mellow the tone was.  TBH, I think I have to spend more time to get to know that mic better before drawing any conclusions.  It does seem to do this thing though where it takes a lot of the harshness out of whatever you're trying to record without sacrificing any high end clarity.

Going into the session I was almost certain that studio's M269c was going to straight up destroy the DU67, but the results were surprising to us because the DU67 did better in every application.  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.  I don't know if this M269c has the original capsule, AC701k, or whether if it had been reskinned or modded.  It was using a Korby PSU.  I'll definitely want to look for other M269c mics at other studios in the area and compare my DU67 to those. 

The only test that the 67 didn't do that great on was the mono drum overhead, which while sounding nice on the cymbals the overall sound was not as detailed on the toms and kick drum as they would need to stand on their own without any close mics for my tastes.  It sounded a bit too 1960's to me in this application (which some people might actually prefer).  The KM56 was the clear winner in this situation, though the VM1 and Bock 251 were quite usable too. On cello and guitars, the DU67 sounded especially great and balanced throughout with the low end that we wanted from the proximity effect (I have the 40hz filter removed on mine).

The studio owner was so impressed with my DU67 that he decided to rent it from me(!) to record cello and violin at his studio the next day.  I wasn't expecting that.  ;D

I was so surprised with the results of this session to the point where I am questioning my future plan to upgrade my HK67 cap to a Neumann cap and swap out the T67 for the AMI BV12.  To me it's uncertain if paying $1300 for these parts would result in a mic that's better or just different.  And at that price I can build myself another DU67 (lol).  Maybe I should just leave well enough alone, we'll see.  Like the VM1s used in this session, the vintage 67s I've used before sound different enough from each other tonewise that I know I am definitely in the ballpark with mine.

 

[micaddict]

Mrerdat wrote:

I brought one of my DU67s and Bock 251 to a test session where we compared them to 5 other tube mics in different applications - vocals, electric guitar, acoustic guitar, mono drum overhead, and cello.  The studio owner had two Brauner VM1s (both Klaus Heyne Edition, not matched pair, about 40 serial numbers apart),a KM56, M269c, and a M49b (which sadly only got to be used in the last few tests bc the B room was using it for most of our session). 

The DU67 I used for this shootout is the 2nd one I built which is using the Heiserman H67 capsule, AMI T67, and silver shield Telefunken EF86.  It sounds better to me than the first one I built because of the capsule most likely.  There's a little bit more low and top in mic #2.  I ordered the HK67 that's in my latest 67 2 years after I ordered the first one, so it could be that the capsule construction is a bit more refined, the tensioning was different, or Eric just got better at building them.  He claimed in a PM from a while ago that the construction is the same, so it could just be different tolerances between capsules.  Despite what I just wrote though  I still use DU67 #1 all the time.

Of course with these threads YMMV, this is not a scientific test, yada yada. I don't have the audio from this session at the moment.

So here are my comments/first hand opinions:

We put up one mic at a time, taking care to place mics in the same location every time they were swapped. 

The VM1s sounded quite different from each other - one was brighter than the other, but the other had more of a defined low end.  They fared well on everything and had modern clarity to them, but everyone in the room liked the DU67 better on the male vocalist (upper tenor-alto range) we were recording. The bright VM1 was particularly great on drums but the darker one felt more balanced, especially for guitars and cello where it felt like the focus was on the whole instrument instead on a specific higher frequency range.

The KM56 was incredible on drum overhead and was also really nice on guitars, but it didn't impress us too much on vocals and have the low end presence we would have liked on the cello.  There's something old timey sounding about the mic with the way it saturates the upper mids that is really cool for certain applications.

The Bock didn't match well with the singer we were recording and left something to be desired when recording guitars (the studio owner said it sounded a bit "generic"), but sounded great on the cello and perfectly useable as a mono overhead.  The low end on that mic is beautiful.

We only got to try out the M49b on cello and acoustic guitar but didn't really like it too much for close miking applications.  The mic was backed off a feet from the source after that and we liked how wonderfully mellow the tone was.  TBH, I think I have to spend more time to get to know that mic better before drawing any conclusions.  It does seem to do this thing though where it takes a lot of the harshness out of whatever you're trying to record without sacrificing any high end clarity.

Going into the session I was almost certain that studio's M269c was going to straight up destroy the DU67, but the results were surprising to us because the DU67 did better in every application.  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.  I don't know if this M269c has the original capsule, AC701k, or whether if it had been reskinned or modded.  It was using a Korby PSU.  I'll definitely want to look for other M269c mics at other studios in the area and compare my DU67 to those. 

The only test that the 67 didn't do that great on was the mono drum overhead, which while sounding nice on the cymbals the overall sound was not as detailed on the toms and kick drum as they would need to stand on their own without any close mics for my tastes.  It sounded a bit too 1960's to me in this application (which some people might actually prefer).  The KM56 was the clear winner in this situation, though the VM1 and Bock 251 were quite usable too. On cello and guitars, the DU67 sounded especially great and balanced throughout with the low end that we wanted from the proximity effect (I have the 40hz filter removed on mine).

The studio owner was so impressed with my DU67 that he decided to rent it from me(!) to record cello and violin at his studio the next day.  I wasn't expecting that.  ;D

I was so surprised with the results of this session to the point where I am questioning my future plan to upgrade my HK67 cap to a Neumann cap and swap out the T67 for the AMI BV12.  To me it's uncertain if paying $1300 for these parts would result in a mic that's better or just different.  And at that price I can build myself another DU67 (lol).  Maybe I should just leave well enough alone, we'll see.  Like the VM1s used in this session, the vintage 67s I've used before sound different enough from each other tonewise that I know I am definitely in the ballpark with mine.

What a great review! Thanks, man.

As I've suggested before, we need more of this sort of thing. OK, it's a build thread we're in, so you could debate about that. But AFAIC it fits right in and actually shows what people are bulding them for. (!)

And it was among some serious mics there.  The best of the best I would say. Still the DIY mic wasn't a boy among grown men, but held its own, to say the least.
This may sound funny to some, but it doesn't really surprise me.

@ mrerdat
Regarding the slight tone difference between  DU67 1 and 2. You 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.  (Tricky things to make, windings and all.) 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.