Re: MK-U47 - build thread
« Reply #680 on: March 12, 2019, 06:07:32 AM »
I've taken liberty to resurrect the build information.
If this should disrupt anyones copyright please let me know and I will delete this post.

MK-U47 Tube Microphone Kit featuring:

Costum Headbasket made by Flea with Pattern Switch
Brass made body tube and bottom bell, bead-blasted and nickel-plated
Stainless internal structure
Bv.08 Transformer with 8 seperate sections from my own production
6028 single supply circuit with all parts including

including (back left to right):

body tube
bottom bell with power resistor mounted + internal structure
Headbasket pattern switch
Transformer + resistor board
High-Z board with screws, teflon isolators, shims for variable capsule mount height
solder lugs and subminiature reed-contact
Black rubber band for tube shock-mount
Tube deck + tube sockets, screws,

(front left to right):
Wiring, yellow wire sleeve, shrink tube
Binder connector for mic and cable
Bv.08 Transformer
PIO and styroflex capacitors, resistors

to complete the microphone, you'll need:
a capsule + holder
a single supply 105v PSU
a microphone cable (cable connector to mic included)

Completed kit with Flea capsule holder:



Wiring Plan:

we start from the bottom up.

Use small pieces of wire to bridge contacts as shown

wire the connector according to the original schematics
Solder a lug to the end of one black wire
1: White
2: Blue
3+4+6: Black x 2
5: Red

Unscrew this resistor

Solder yellow and red wire

use shrink tube for isolation

mount the resistor back in

unscrew the ring of the connector and place it
in the bottom bell, aligning the keyway/slot

carefully place the ring and tighten

unscrew the nut and place the solder luck and re-tighten

paint the transformer/resistor board (not shown: use a file after breaking)

Solder together the boards as shown, check for right angle

place and solder all resistors as shown

place and solder all wires as shown

Be careful handling the transformer
place and solder the transformer as shown

Before soldering the big capacitors it's time to mount the whole thing into the mic

insert the screws and attach the nuts, do not overtighten!

Place and solder the two green capacitors as shown

The yellow sleeve will be cut like this to fir through the hole

Carefully cut and drill (pierce) the rubber band as according to this measurements

unscrew these parts

mount the tube sockets, check for orientation!

bend and add a solder lug

attach and solder short black wire

Wire up as shown

attach the rubber band

mounting the tube deck

feed through the wire sleeve

attach the yellow, red and blue wire to the corresponding pins

Be careful with overheating when building the highZ portion of the circuit

bend and place the solder lugs as shown

a small wire bridge, do not solder yet

the reed contact must be oriented and placed carefully BE VERY CAREFUL HERE

do not bend the contact after soldering or i will break

you can hold the tiny contact like this for placement

to have free access, slide the middle lug away

the contacts inside the glass envelope must be oriented this way

solder second side only after orientation is correct

more wire bridges and placing parts, place everything before soldering, solder quickly

the teflon feed throughs

push the carefully to place, grabbing them by the top teflon part

solder the two black wires

mount the highZ board + spacer as shown

attach the wires to the teflon feed throughs

attach the rest of the wires

place the tubes

Shown with a Flea capsule holder


Re: MK-U47 - build thread
« Reply #681 on: July 16, 2019, 09:55:50 AM »
In case anyone is interested, I have a fully assembled iOAudio MK-U47 for sale:
« Last Edit: July 22, 2019, 09:25:34 AM by vinylwall »
Jimi Ray

Re: MK-U47 - build thread
« Reply #682 on: February 25, 2020, 01:27:57 AM »
Hi all,

Took me 5 years but am finally wiring up the cable for my mic. I finished the mic (except for wiring the capsule) about 4 years ago. I finished the PSU about 3 years ago. Cable was done today. Capsule now to go in.

So, now I want to wire in my Thiersch blue line capsule. I have a (hopefully not stupid) question I couldn't find an answer to in the thread... which side of the capsule is which? How to tell the front of the capsule? Does it matter or not?

"Kind of like going into Safeway at 4 in the morning and chugging a beer in the produce section; been there, done that." - CJ

"We're not making an atomic bomb, just cooking a few electrons." - PRR


Re: MK-U47 - build thread
« Reply #683 on: February 25, 2020, 05:03:29 AM »

Congrats :-) I hope it will sound great !

But to answer your question, they are identical on both side's, and closely matched if all is right.

Let is know how it turned out ?


Re: MK-U47 - build thread
« Reply #684 on: February 25, 2020, 11:58:49 AM »
Thanks for the info.

My gosh! This mic!  ;D

I just did a quick connect of the capsule so no real time to run it through its paces today. I'm using JAN NOS 6028s. Lots of people saying too clean/no bottom with those tubes. That may be the case but it sounds pretty glorious as is! I didn't really burn in the tubes, BTW. I also don't notice any noises from the tubes. Did I get lucky?

One thing I did notice is that I had to increase the gain on the mic pre (CAPI V28) quite a bit during the quick test in order to get a decent signal. Is that normal or do I have a failure in constructing/wiring?

TBH, I was finishing up the mic because I was planning on selling it to raise funds for a potential soon-to-be move. However, after hearing it briefly, I may have to reconsider!

To sum up, wow!

"Kind of like going into Safeway at 4 in the morning and chugging a beer in the produce section; been there, done that." - CJ

"We're not making an atomic bomb, just cooking a few electrons." - PRR


Re: MK-U47 - build thread
« Reply #685 on: February 26, 2020, 02:32:24 PM »
How hot did you have to make the pre for what was a usable level? Check your voltages again would be my first suggestion.

The JAN 6028/408a  tubes are the lowest noise in my tests but are also, to my ears the least musical, but, IMO,  there is nothing low noise about these tubes compared to other options for this type of copy.

more at my website in the blog section.

M7 capsules are interesting  as they share the same backplate and are glued, IMO again, they are all slightly different side to side. I always listen intently to them and if there is one side that seems to my ears more what I want to hear (so totally subjective to say the least) I make that the front. I see you went for the blue line old style.
New York City

Re: MK-U47 - build thread
« Reply #686 on: March 11, 2020, 10:06:05 AM »
Guys, my Mk-u47 sounds great, but I have a big issue, which is intermittent static. I've burnt in the tubes for many hours but the problem remains.  I've left it recording for a few hours to observe and about every 10 minutes (on average  but not regularly) there is a burst of static, like strong wind or vibrating white noise. It's the type of sound I would normally associate with tube burn-in or tube failure but weird that it disappears for long periods then returns. Any clues? Is the best first move simply to replace the tubes? thanks in advance for any advice.


Re: MK-U47 - build thread
« Reply #687 on: March 11, 2020, 03:29:24 PM »
Yes! Tubes are often the culprit which ones have you chosen?

Also double check that the filter caps in PSU are healthy.

Lastly what capsule are you using? Does the problem exist in Omni and Cardioid modes?
New York City


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