BV12-style Transformers

[Studio Mollan]

I don't blame you for tweaking the thing to your liking. More power to those who brew their own. 

I will add, though, that a healthy (stock) U67 should not sound dark. The Neumann plots don't suggest this, either. (And I have an original, so I know.) Old ones that need service might be dark, but it can go the other way with old ones, too (when certain caps start to fail). A U67 does "behave" in a relatively dark way. That's the magic of the U67. The clever circuit (with all the feedback in place) sort of dynamically tames spikes/nasty transients. This may be responsible for the "darker" feel some experience.
It would seem to me that lifting a feedback cap (at least partly) kills that magic treat. It will then "just" be another tube microphone.

Also, I've asked Ben about the K6 and he said it specs identical to the Neumann. Now Max claims the same about his tranny, so that doesn't take us much further. However, people who use other brand capsules (including original Neumann) have reported the same darkness as you have.

I can wouch for he Beesneez k6 being EXTREMELY close to the original. Ive listened to comparisons of the same spec Du67 one with k6 and one with a brand new neumann k67. the closest word i can find is identical. An ever so slightly difference in the very low end if i remember correctly.

Did anyone have the data on the BV12? If so i can ask my tech to compare the Ioaudio transformer to the factory spec. I don't have tools for that but my tech, hes got it all.

 

[Delta Sigma]

Based on the samples I've heard privately, all with Neumann capsules, and the TLM67 I own with Max's mod, I agree completely with TLRT's assessment.  In my own, I've removed C17 entirely, and it changes almost nothing. .....

I'm home sick this afternoon so I had another listen to my three C17 values. I listened to all three and heard no difference. Thought I must be crazy. Finally dawned on me to shut off the little heater I had blowing at me (I am sick afterall). I can distinctly hear the difference between the three. Trouble is, I can still hear a dark or dull sounding in the upper mid. Changes in C17, with its small value, seems to add a part of what was missing but not all.

My DU67 with K6 wouldn't be classified as bright, but knocking down that feedback cap certainly keeps it from sounding dark.

I think I jumped the gun on that comment. 10pF allowed a little more high end through but there's still something a little dark. I still like 10pF C17 over both 100pF and open but there is something missing.I recorded two songs with the three values and the DIY U67 with 10pF C17 sounded good on one but not so much the other. I also listened back to a recording I hated of a female friend singing into it (C17=100pF). What I hated about it doesn't seem to have changed with differing C17 values.

Looks like I'm up for a trying out your transformer Spencer!



-Neil

 

[Delta Sigma]

Also, I wonder about the manufacturing variance of the originals. I'm guessing the feedback circuit was designed with a theoretical transformer then possibly tweaked when prototyping. Who knows, maybe C17 wasn't added until they prototyped with a BV.12.

The schematic shows C17 is selected from 80-160pF. Is that  for the BV.12 manufacturing variance? Doesn't seem like a huge swing.

 

[emrr]

The schematic shows C17 is selected from 80-160pF. Is that  for the BV.12 manufacturing variance?

Yes

 

[micaddict]

I can wouch for he Beesneez k6 being EXTREMELY close to the original. Ive listened to comparisons of the same spec Du67 one with k6 and one with a brand new neumann k67. the closest word i can find is identical. An ever so slightly difference in the very low end if i remember correctly.

Plus the BeesNeez has the "brass" (bronze actually) ring of the early K67. 

 

[Spencerleehorton]

Could someone make a list of various good capsules which are available in this thread by any chance please?
I'm wondering whether with one of my capsules, the one from Eric whether it's my problem.
I've got both my U67s sounding close ish, but the one with Eric's capsule and the sowter in it just doesn't have the transients or clarity in the mid range, I'm going to first change the valve then change the capsule and see what gives.
With my other U67 it sounds great on everything, very open, lovely clarity, reacts to EQ very well, can't get a bad sound out of it.
Interesting what your saying about C17, I've got 100pf in both of mine.
I have changed the 400meg resistors to 1gig, would be interested in anyone's thoughts of what impact this would have?

 

[emrr]

I hear from a lot of people with significant Neumann collections that not many of the other capsule options cut it, in any type Neumann clone they've built.  Not at least if you really want the last possible shred of 'the' sound.  I can't speak from experience. 

 

[micaddict]

I hear from a lot of people with significant Neumann collections that not many of the other capsule options cut it, in any type Neumann clone they've built.  Not at least if you really want the last possible shred of 'the' sound.  I can't speak from experience.

I hear the same thing about the transformers ...

 

 

[Delta Sigma]

I hear from a lot of people with significant Neumann collections that not many of the other capsule options cut it, in any type Neumann clone they've built.  Not at least if you really want the last possible shred of 'the' sound.  I can't speak from experience.

Though I've only built clones, I'm not one to care if my mic sounds like the classic it's cloning. With my U67, I'm just trying to get as versatile as possible. I hope my Beesneez K6 can get me there; whether it sounds like the original or not.

As much as I think it's easy to get hung up on sounding like the original, I also worry that I can convince myself that something sounds great when it doesn't - because of the investment of time, money & labour... I'd like to think I'm smarter than that but the truth is I'm not even close!

 

[Spencerleehorton]

I thought I'd do a test and I mic' d up a mackie 450 speaker with my cheap capsule U67 clone with my txf in it and A/B'd it against the computer out, use and aux out to feed the mackie, surprising results. Very close tonally, needed a little EQ. I know this doesn't mean a great deal but to me at least I know it picking up all the frequencies I want and I know it's fairly true and flat response wise.
With the sowter and the other capsule it was less inspiring, think I'm going to rest this capsule by Eric and put something else in there.

 

[Khron]

... Although the thing about (comparing with) vintage mics is, you have no idea, and can't know, what shape the old mics are in ;D
In some cases, even comparing two of the same model, side by side, can yield very different results, so... How can you (really) know what the average, in this case, U67 truly sounds?

Just a little "demonic advocacy"...  :

Though I've only built clones, I'm not one to care if my mic sounds like the classic it's cloning. With my U67, I'm just trying to get as versatile as possible. I hope my Beesneez K6 can get me there; whether it sounds like the original or not.

As much as I think it's easy to get hung up on sounding like the original, I also worry that I can convince myself that something sounds great when it doesn't - because of the investment of time, money & labour... I'd like to think I'm smarter than that but the truth is I'm not even close!

 

[TLRT]

... Although the thing about (comparing with) vintage mics is, you have no idea, and can't know, what shape the old mics are in ;D
In some cases, even comparing two of the same model, side by side, can yield very different results, so... How can you (really) know what the average, in this case, U67 truly sounds?

Just a little "demonic advocacy"...  :

Best if you have multiple U67's That is working for me

 

[Spencerleehorton]

Ive got a confession to make!!!

I revisited the wiring on this problematic U67 as it was one of the first builds i did, it has been checked by another person for whether it was wired correctly as well!!
And yes, it wasn't wired correctly, needless to say ive wired it correctly now and put a cheap capsule in and its sounding much better!!!
at least i can truly test the Sowter against my one now, and i suspect its gonna sound great now!! sorry Brian for doubting you!!!

at lest i've gotten to the bottom of it!

regards

Spence.

 

[Delta Sigma]

Doug, where are you tweaking the feedback circuit?

It's a bit over my head to figure out. Gotham has nice document describing the 40Hz internal high pass - feedback network from anode to backplate. What I don't see is how exactly the capsule high frequesncy de-emphasis works. C3 (and C2) have a reactance of 1k at 15kHz but only 3k at 5kHz. This doesn't imply a very steep or targeted filter.

1) Is the frequency response dependant on the response of the winding?
2) Does the 40Hz high pass alter the tertiary feedback network (820k, etc it seems unlikely)?
3) Am I way out to lunch on analyzing the circuit?

-Neil

 

[micaddict]

Ive got a confession to make!!!

I revisited the wiring on this problematic U67 as it was one of the first builds i did, it has been checked by another person for whether it was wired correctly as well!!
And yes, it wasn't wired correctly, needless to say ive wired it correctly now and put a cheap capsule in and its sounding much better!!!
at least i can truly test the Sowter against my one now, and i suspect its gonna sound great now!! sorry Brian for doubting you!!!

at lest i've gotten to the bottom of it!

regards

Spence.

Does this mean that the Sowter tranny and perhaps Eric's capsule may have been misjudged?
Or am I misunderstanding this?

 

[Spencerleehorton]

Exactly, the capsule has now come to life along with the transformer. To early to make any real observations as I was rushed in finding the problem and monopoly with the kids was more important!!!

 

[Spencerleehorton]

interestingly enough, both the £150 capsule and the £40 capsule now sound very close!!! little bit more top end on the cheaper one but only a fraction, both U67 sounding very nice now!!
If i'm honest the bottom end sounds just slightly nicer on my TXF, along with the mid range a little less undefined but really pleased with the results now as compared to the playback from itunes the mic'd up sound, sounds so much better!!
apologies to both Eric for the capsule and Brian Sowter for not having faith!!,both do great stuff, well worth checking out.


regards

Spence.

 

[micaddict]

Interestingly, Stam Audio has a U87 clone out that has Dany's PCB, Eric's capsule and Brian (Sowter)'s tranny (as an uprade over the less expensive Cinemag). There was a shootout with an original Neumann U87 and the clone actually sounded nicer to most (assuming the shootout was done properly).

 

[TLRT]

Interestingly, Stam Audio has a U87 clone out that has Dany's PCB, Eric's capsule and Brian (Sowter)'s tranny (as an uprade over the less expensive Cinemag). There was a shootout with an original Neumann U87 and the clone actually sounded nicer to most (assuming the shootout was done properly).

Those comparisons can mislead you easily, Neumann doesn't sound "nice",sometimes the raw tracks sounds even strange,but it fits to the music very well. I tried Eric's HK67, and although it is a bit different than the original I think it is good capsule for the price. I wanted to try the BeesNeez K6,but their K7 was such a disappointment that I just give it up and bought some NOS Neumann K87's I think in the U67 the tranny/tube combination is very important, I just repaired a groupdiy member's failed D67 clone and with the proper tube /tranny selection you can easily balance out the mic, that's why I recommended here to use "bright" tubes for IOaudo trannies,and "dark" tubes for the cheap K67 capsules and AMI T67 trannies.

 

[micaddict]

Those comparisons can mislead you easily, Neumann doesn't sound "nice",sometimes the raw tracks sounds even strange,but it fits to the music very well.

I hear you. And I'm not going to sell my Neumann U67. 
That said, I'm a singer who accompanies himself on guitar (mostly fingerstyle). So there's not much competition with other instruments there. Also, I have a bit of a problem with the modern way of mixing, that is the squeezing in of a vocal track, by means of EQ and such (or mic selection). I prefer old recordings where the vocalist (or other soloist/frontpart) was allowed to be a little louder than the rest.