BV12-style Transformers

micaddict · Jan 19, 2017

OK, so Bonnie1 motivated me to start a new thread about this topic. We were in the Ela M build thread and Bonnie said the AMI T14 is a little brighter than the original Haufe T14/1.
So I asked if the same holds for the T67 versus an orginal Neumann BV12.

Going by various earlier audio samples, the builds with the IOaudio BV12 seemed somewhat darker than my Neumann and the ones with the AMI T67 perhaps a little brighter. This can be apples to oranges to some extent, e.g. when a Telefunken tube is used versus a Mullard etc. etc. But going by feedback (excuse pun) from others, there did seem to be a pattern.
Of course, for a true comparison, I'd need both versions, identical in every other way (yeah, I know) here with my U67.

And then there's the AMI Classic BV12.
And now there's a Cinemag CM-5701, as well.

So, Bonnie1, what do you have? From what I understand AMI TAB is working on a new website, with more info about these matters. But can you give us a preview?

Others are very welcome to chime in too, of course.

dmp · Jan 19, 2017

Interested...
My D-U67 build is IOaudio BV12, Telefunken tube, Beezneez capsule.
Sorry to veer right away, but has anyone compared the D-U67 (poctop) to IOaudio MK67 with the same tx, tube, & capsule?

TLRT · Jan 19, 2017

I built both with original Neumann capsules, AMI BV12 Classic is the closest to our original U67's

micaddict · Jan 19, 2017

TLRT said:
I built both with original Neumann capsules, AMI BV12 is the closest to our original U67's

Thanks!

Was that the AMI T67 (PCB mounted BV12) or the AMI Classic BV12?

And was the other the IOaudio BV12?

TLRT · Jan 19, 2017

micaddict said:
Thanks!

Was that the AMI T67 (PCB mounted BV12) or the AMI Classic BV12?

And was the other the IOaudio BV12?

Yes I tried T67 also - not a correct model, mic has less middle/bass response(in which the U67 really excels),and it has more highs(which is really unnecessary) - I think Wunder used the T67 in their models also. AMI BV12 Classic is good,but very expensive, if you have access to original Neumann capsules then it worths the price.

TLRT · Jan 19, 2017

For the price Max's kit is also good, but leave Telefunken tubes and search and test some other models, I have very good results with selected Tungsram EF86's(Siemens,Philips can be good also). Military selected versions has the same noise level as the TFK EF806S.

dmp · Jan 19, 2017

BV12 is good,but very expensive

IOaudio or AMI version? Can you edit your post to make it clear?

TLRT · Jan 19, 2017

dmp said:
IOaudio or AMI version? Can you edit your post to make it clear?

Yes I spoke about AMI, I don't think you can buy Max's BV12 separately(he is not answering to the emails at all)

dmp · Jan 19, 2017

Yes I spoke about AMI, I don't think you can buy Max's BV12 separately(he is not answering to the emails at all)

He used to sell them separately - quite a few people bought them for DU67 builds before he did the mk67.
Hopefully max comes back. His WM thread is gone.

emrr · Jan 19, 2017

Max is selling U67 retrofit preamps and PSU's on GS as fast as he can make them. He has little reason to mess with selling parts.

Bonnie1 · Jan 19, 2017

Hello everyone,
First to clarify about AMI T14, It does not have high freq. boost, per se. (Like all quality transformers, freq. response changes depending on how it is driven)

In an original AKG C12 circuit, AMI T14 the freq. response is slightly extended on both ends of the spectrum. Haufe T14/1 is 1db down at 20k, AMI T14 is flat at 20k and .25db down at 30k. Oliver based the stock AMI T14 on the Hiller T14 transformer.
As Micaddict stated, there will be test results with the setup documentation on AMI's new site coming soon.

T67 has the same ratio and winding scheme as BV12, however it uses different size bobbin and laminations. (Yes T67 has a bit different freq. response than BV12) Oliver recognized for diy projects not everyone can afford a proper BV12. There are quite a few diy builds using T67's that sound excellent. AMI will provide T67, BV12 freq results and test setup as well.

micaddict · Jan 20, 2017

Sneak preview for your fellow members?

TLRT · Jan 20, 2017

Just thinking to organize a groupbuy for Haufe T14/1, I already have 3 members in

micaddict · Jan 20, 2017

You may want to start a feeler thread to see who's interested.

dmp · Jan 20, 2017

Just thinking to organize a groupbuy for Haufe T14/1, I already have 3 members in

I'd be in -

lyricalgeek · Feb 6, 2017

TLRT said:
Just thinking to organize a groupbuy for Haufe T14/1, I already have 3 members in

I'd be in also

Studio Mollan · Feb 6, 2017

Hi,
I built a pair of u67s with poctop pcbs, ioaudio transformers, and found them dull. extremely dull in comparison to the pair i built with the AMI t67 transformers. When Max released his pcb set i bought a pair and converted my ioaudio fitted u67s just to rule out any faults. Max pcb design looks way better and helps with using larger capacitors but sounds the same to me. I haven't done any measurements on the difference but in a stereo setup i could easily use one of each without it sounding unnatural in any way.
I later did some experimentation on C17, the negative feedback filter for HF roll of, and came to the following.
For a correct measurement according to the neumann u67 original setup, injecting sinewave and meassuring 40, 1000, and 15000hz i think, the ioaudio version came closest (spot on actually) with no capacitor (c17) fitted at all. (!) The T67 fitted versions needed a C17 way out of spec to roll of correctly.
All my U67 are built with beeznees K6 capsules and telefunken/valvo ef86.
/
Emil

dmp said:
Interested...
My D-U67 build is IOaudio BV12, Telefunken tube, Beezneez capsule.
Sorry to veer right away, but has anyone compared the D-U67 (poctop) to IOaudio MK67 with the same tx, tube, & capsule?

micaddict · Feb 6, 2017

Studio Mollan said:
Hi,
I built a pair of u67s with poctop pcbs, ioaudio transformers, and found them dull. extremely dull in comparison to the pair i built with the AMI t67 transformers. When Max released his pcb set i bought a pair and converted my ioaudio fitted u67s just to rule out any faults. Max pcb design looks way better and helps with using larger capacitors but sounds the same to me. I haven't done any measurements on the difference but in a stereo setup i could easily use one of each without it sounding unnatural in any way.
I later did some experimentation on C17, the negative feedback filter for HF roll of, and came to the following.
For a correct measurement according to the neumann u67 original setup, injecting sinewave and meassuring 40, 1000, and 15000hz i think, the ioaudio version came closest (spot on actually) with no capacitor (c17) fitted at all. (!) The T67 fitted versions needed a C17 way out of spec to roll of correctly.
All my U67 are built with beeznees K6 capsules and telefunken/valvo ef86.
/
Emil

Thanks for this contribution!

Who's next?

As for the Haufe T14/1; guys, please start a separate feeler thread.

micaddict · Feb 6, 2017

So Emil, can I summarize that according to your findings IOaudio's BV12 is too dark and AMI's T67 is too bright?

micaddict · Feb 6, 2017

Oh, and this may be important to mention. Dany's D67 build thread was started September 2012. Then in April 2014 he posted the following:

Important AMI T67 Errata

applies to D-M269c and D-U67 with AMI T67 transformer only

Hi All, with the help of fellow member I have been able to have some testing done about the proper correction for the de-emphasis to work correctly,

it has been found that swapping only 5-12 from the mic pcb make a very sublte difference hence to permits the de-emphasis to work 100% correct,

it is imperative that you swap pad 5-12, pad 7-10 and pad 1-4 from the mic pcb as the connection have been mistakenly mirrrored.

so the complete 100% fix is
swap 5-12 , 7-10 1-4 pad on the mic PcB, this will correct for all winding polarity including feedback winding error and correct for a Full de-emphasis.
they all are adjacent pad so it should be pretty easy to correct.

For any Future Build or for the summary of the correction here is the wiring guide for the transformer to the mic pcb ,
this wiring guide ensure all the polarity and connection are as intended at the first place.
From transformer board to mic PCB

Pad 5 -----> mic pcb pad T1212
Pad 12 -------> mic pcb pad T55
Pad 1 --------> mic pcb pad T44
Pad 4 --------> mic pcb pad T11
Pad 7 --------> mic pcb pad T1010
Pad 10 ------> mic pcb Pad T77

here is some sample before and after the complete fix. Thanks To Dan for the samples.

with wiring error
https://dl.dropboxusercontent.com/u/43869772/U67/Feedback%20winding%20Correction/Orginal.wav

With wiring correction WoW
https://dl.dropboxusercontent.com/u/43869772/U67/Feedback%20winding%20Correction/Corrected.wav

Quote
Remember that there is an errata on the polarity for the D-67 all you have to do to fix it is reverse pin 2 and pin 3 up in the power supply xlr connector and you will be ready to rock,

PS: for those of you who had the mic output polarity error this will fix this at the same time so i you have reversed xlr pin 2-3 to previously correct for this in the psu please account for that as well as this errata will correct both at the same time.

Thanks For you patience and cooperation and all member helping out resolving this isssues
Best,
Dan.

BV12-style Transformers

Help Support GroupDIY Audio Forum:

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Active member

Well-known member

Well-known member

Well-known member

Well-known member

Similar threads

Join the conversation!

Join today and get all the highlights of this community direct to your inbox. It's FREE!