BV12-style Transformers

[dmp]

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. (!)

I built it to spec with the ioaudio transformer and the measurement was correct first time. I did not have to adjust C17.  I posted the results somewhere in the u7 thread. That test only checks the response of the amplifier, however, which has de-emphasis to correct for specific response of capsule. I (and most people) do not have the equipment to sweep the mic with the capsule.

 

[micaddict]

I built it to spec with the ioaudio transformer and the measurement was correct first time. I did not have to adjust C17.  I posted the results somewhere in the u7 thread. That test only checks the response of the amplifier, however, which has de-emphasis to correct for specific response of capsule. I (and most people) do not have the equipment to sweep the mic with the capsule.

Thanks, dmp.

Interestingly, Max now offers his (drop-in) kit in a "linear" version, as well.  This means the ciruit or amp is flat, so not de-emphasized.
In combination with the pre-emphasized K67 capsule this should result in a pretty bright mic. In any case on paper or in theory. 

 

[Spencerleehorton]

I've wound my own using nickel lams and it sounds fantastic, slightly larger than the original but fits in 54mm radius body, I had a sowter 1304 made for the U67 and have never been happy with it.
Sounds great now though!

 

[TLRT]

I've wound my own using nickel lams and it sounds fantastic, slightly larger than the original but fits in 54mm radius body, I had a sowter 1304 made for the U67 and have never been happy with it.
Sounds great now though!

I can compare it to a great vintage u67 if you want, till now I only found the AMI BV12 accurate enough compared to the original one.

 

[micaddict]

I've wound my own using nickel lams and it sounds fantastic, slightly larger than the original but fits in 54mm radius body, I had a sowter 1304 made for the U67 and have never been happy with it.
Sounds great now though!

And TLRT wrote:

I can compare it to a great vintage u67 if you want, till now I only found the AMI BV12 accurate enough compared to the original one.

I would very much appreciate this UK meets Hungary collaboration!
This is a great place. 

 

[Khron]

Are the specs of the BV12 transformer(s) a secret, by any chance? Like turns ratios, inductances, leakage inductances, etc?

 

[Studio Mollan]

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:

Hi,
Yes the T67s are correctly wired in my builds. I actually brought this to attention in the first place back in 2014. Not the polarity issue but that the original t67 circuit wasn't rolling of any HF.

It is strange this thing with the huge variations between transformers. I was in busy correspondance with a forum member a while back and we are both experiencing the original IOaudio transformer build as very dull. We built it wi the same components as well. Beesneex K6, Io-audio BV12 and telefunken ef86. We both suspected the capsule to be the cause and the other guy actually bought a brand nye neumann K67. It sounded identical to the beesneez.
I have since then rebuilt the IO audio microphones with Max's new PCB set and no difference in sound. All new components and wiring. Feels really weird to have to leave a part of the circuit out (C17) to get it to spec. They do sound good now though so I'm not really concerned about tit anymore.
 

 

[micaddict]

Hi,
Yes the T67s are correctly wired in my builds. I actually brought this to attention in the first place back in 2014. Not the polarity issue but that the original t67 circuit wasn't rolling of any HF.

It is strange this thing with the huge variations between transformers. I was in busy correspondance with a forum member a while back and we are both experiencing the original IOaudio transformer build as very dull. We built it wi the same components as well. Beesneex K6, Io-audio BV12 and telefunken ef86. We both suspected the capsule to be the cause and the other guy actually bought a brand nye neumann K67. It sounded identical to the beesneez.
I have since then rebuilt the IO audio microphones with Max's new PCB set and no difference in sound. All new components and wiring. Feels really weird to have to leave a part of the circuit out (C17) to get it to spec. They do sound good now though so I'm not really concerned about tit anymore.

I've heard this sort of thing too many times now to disregard it. There does seem to be a pattern.

Max is a member who used to post here regularly. But I haven't seen him around here much lately.
From what I understand he's really busy building his drop-in kits. I hope he chimes in someday soon.
He does post on Gearslutz. I guess I could send him a PM there.

 

[TLRT]

Hi,
Yes the T67s are correctly wired in my builds. I actually brought this to attention in the first place back in 2014. Not the polarity issue but that the original t67 circuit wasn't rolling of any HF.

It is strange this thing with the huge variations between transformers. I was in busy correspondance with a forum member a while back and we are both experiencing the original IOaudio transformer build as very dull. We built it wi the same components as well. Beesneex K6, Io-audio BV12 and telefunken ef86. We both suspected the capsule to be the cause and the other guy actually bought a brand nye neumann K67. It sounded identical to the beesneez.
I have since then rebuilt the IO audio microphones with Max's new PCB set and no difference in sound. All new components and wiring. Feels really weird to have to leave a part of the circuit out (C17) to get it to spec. They do sound good now though so I'm not really concerned about tit anymore.

Do not use Telefunkens with Max builds, you need a brighter tube, Beezneez capsules are also dark,so it is not a good combination. NOS Philips/Siemens EF86 can be better. I like Tungsrams also.

 

[TLRT]

And TLRT wrote:
I would very much appreciate this UK meets Hungary collaboration!
This is a great place. 

I have some other projects here with groupdiy members, you will be surprised in the future

 

[Studio Mollan]

Do not use Telefunkens with Max builds, you need a brighter tube, Beezneez capsules are also dark,so it is not a good combination. NOS Philips/Siemens EF86 can be better. I like Tungsrams also.

I have been in contact with him about this. I pleaded to him to once again go through his documents and such as  a last thing to rule every possible thing causing this. He did seem stressed out indeed, and a bit grumpy that i questioned his transformers. =) Eventually he did go through it all again and confirmed everything is up to specifications. Cirquit, pub and transformers. It could actually be a faulty batch of transformers? Its the only thing that remains after my troubleshooting.
Anyways, I like them as they are now though so I'll let this rest for now.
Regarding the tubes I'm actually just about to try out the EF804s in the u67. I needed to replace an ef86 and got my hands on a NOS tested EF804s ad will try it out as soon as i can. Electrically compatible with EF86 (different pinout though) and from what I've read superior in reliability and noise.
I'll post my results in the U67 build thread.

 

[Spencerleehorton]

If anyone is interested I can wind you some, just would be handy to know some sizes specs of the original to compare too.
I would have to order a few more parts so would need some money to cover this if your interested.

 

[TLRT]

If anyone is interested I can wind you some, just would be handy to know some sizes specs of the original to compare too.
I would have to order a few more parts so would need some money to cover this if your interested.

I have AMI BV12 on order and have the original too,do you need the dimensions?

 

[TLRT]

I have been in contact with him about this. I pleaded to him to once again go through his documents and such as  a last thing to rule every possible thing causing this. He did seem stressed out indeed, and a bit grumpy that i questioned his transformers. =) Eventually he did go through it all again and confirmed everything is up to specifications. Cirquit, pub and transformers. It could actually be a faulty batch of transformers? Its the only thing that remains after my troubleshooting.
Anyways, I like them as they are now though so I'll let this rest for now.
Regarding the tubes I'm actually just about to try out the EF804s in the u67. I needed to replace an ef86 and got my hands on a NOS tested EF804s ad will try it out as soon as i can. Electrically compatible with EF86 (different pinout though) and from what I've read superior in reliability and noise.
I'll post my results in the U67 build thread.

E80F works without any serious modification(only the B+ resistor need to be altered) and it sounds also very good.

 

[Spencerleehorton]

Yes please Dims, DC resistance, inductance if you have a inductance meter, i can then compare mine form here. I've had mine fully tested at a transformer lab and it came out really good, sounds wonderful.
I put back in a sowter 1304 into the circuit today and didn't sound bad but definitely a mid dip with the sowter, which must be to do with the inductance, with mine its very mid forward which i personally like, and the top end is much cleaner and clearer.
Ive actually wound it in the exactly the same as the original spec sheet from neumann, just combined the winds rather than have four windings then connect them in series, and its on a different bobbin and lams.

 

[RuudNL]

Maybe CJ could shine a light on these matters?
(After all he is the transformer professor!  ;D )

 

[Khron]

Ive actually wound it in the exactly the same as the original spec sheet from neumann, just combined the winds rather than have four windings then connect them in series, and its on a different bobbin and lams.

Can that spec sheet be found anywhere online?

 

[Spencerleehorton]

Its on this thread:

https://groupdiy.com/index.php?topic=64272.0

 

[TLRT]

Its on this thread:

https://groupdiy.com/index.php?topic=64272.0

Tried to send a PM,your inbox is full

 

[Spencerleehorton]

Best to email me

[email protected]