MK-U47 - build thread

[Phrazemaster]

Just stunning...I'm afraid it might be a little too high end to even call DIY but...I'm drooling! Way to go sir!

 

[ioaudio]

That's how the non-contact pattern switch works:
The small magnet slides in the active zone of a miniature vacuum reed contact and actuates omni pattern.

 

[zayance]

Nice stuff.

Actually didn't spotted that but You went for Amphenol Connector? Nothing wrong with them, just asking.

 

[micaddict]

Hey, a third glass tube!  ;D

 

[ioaudio]

It's a smaller Binder connector.
And yes - the glass tubes are my leitmotif 

 

[micaddict]

Seems like a good leitmotif, too. Keep at it.

OK, in all seriousness now, will the bigger tranny sound different from your earlier one? E.g. will it provide deeper bass?

 

[ioaudio]

In conjunction with a 0,47µF capacitor (instead of 1µF) the transition steepness changes.
Also, the added chambers divide the stray capacity, it's basically 8 sperate coils working on one core.
To my knowledge this will be the first commercially available Bv.08 copy with physically seperated windings.

 

[wave]

Once again your work is beautiful Max! Another mic project to save up for!

Dave

 

[EvLoutonian]

Once again your work is beautiful Max!

Wow. Beautiful work.

 

[North]

Max this is looking great! Cant wait to see the finished product.

 

[jackymurda]

dude is on some crazy mad scientist ting!!

 

[BraFra]

Hi max,
I've read that you are doing lamition by yourself for this transformer, could describe the alloy mixture used? The same as A51 garantie that u described in the bv-08 post? May i ask if is possible to buy those lamination from you? Thanks and sorry for the little ot.

Fra

 

[Dr_J]

What a great project!!! Wow!!

A dream of mine is to do something similar one day, if i'll ever have the time  ;D

ROCK-ON!

 

[micaddict]

These quotes no doubt originate from the REPforum, but I copied them from a Gearslutz thread:

"The only feature where the last version of the u47, which was named the u47a, differs from the earlier u47 shortbodies is the output transformer, BV8b, whereby the secondary is wound over the primary. The new transformer can be identified by the label 'BV GN 8b', which is clearly visible under the transformer's amber wrapping paper, on the top facing surface of the double bobbins. It produces ca. 4 dB less output into 1k Ohm mic pre inputs.
Martin Schneider at one point also posted that there was another transformer available on the u47a model, a BV8a with 600 ohms output imnpedance. I have never seen that model. All other components seem to be aboslutely identical between both models, to my knowledge.
Kind regards, Klaus Heyne
=============================================================
X-formers used in the U47 have several different version (.......), but aside the early Hiller made ones, the BV8 used since approx. serial# 200 are nearly same in sound, there are two different winding technique versions and than the 12.5/50 Ohm, 200/600Ohm and the most used and popular the 50/200 Ohm version.
X-former difference is easy to figure out the early U47 were frequency limited to 40 Herz by separating specific winding parts to get the IRT required low cut. Later U47 just used a .5uF coupling cap instead the earlier 1uF. The sound of the x-former is very similar. U48 had the later x-former with .5uFcoupling cap.
The sound of the U47 outputs differs from mic pre to mic pre, you want for the 200 Ohm strapping a min. of 1k or the perfect mic pre is the Telefunken V41 with 2K input, the historical mic pre of the IRT 40 series made by Telefunken, Maihak, Siemens and EAB.
The historic 1950s power sup. is probably the best you can find for your mic, you might want to change the filter caps and the old cloth wire, but anything else they work very reliable. The 450V is just open without any load, but to be sure not to kill your mic due to dried out filter caps, etc, you might want to use a variac x-former to bring the voltage up very slowly to make sure that at given line voltage you have 105 Volts.
Best regards,
Oliver"

 

[micaddict]

Max wrote in reply #66:

In conjunction with a 0,47µF capacitor (instead of 1µF) the transition steepness changes.

In the quote, Oliver mentions the cap change, too FWIW. 

Also, the added chambers divide the stray capacity, it's basically 8 sperate coils working on one core.
To my knowledge this will be the first commercially available Bv.08 copy with physically seperated windings.

First such copy, but did it actually exist in the old days or is this a new twist you came up with?
Excuse my ignorance.

 

[ioaudio]

Thanks for the kind words evryone!


micaddict,

no new twist, all original Bv.08 transformers have been made on the chambered bobbins.

-max

 

[micaddict]

Thanks, Max!

I don't know enough about the chemistry to join in the discussion between you and Moby.
What I do know is that some say the older metals were more pure and others say the older metals were less pure.
And some say there were toxic ingredients that can no longer be used.

:-\

Henk

 

[micaddict]

Do I recall well that your original laminations were used up in the earlier batches of the MK7 (not MK47) kit?

 

[ioaudio]

yes.

 

[ioaudio]

One more quick rendering from my drawing, also showing the innards: