MK-U47 - build thread

[martthie_08]

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:

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
BUILD:

Schematic:

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

 

[vinylwall]

In case anyone is interested, I have a fully assembled iOAudio MK-U47 for sale:
https://www.ebay.com/itm/183894640663

 

[fazeka]

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?

Thanks,
Chris

 

[djn111]

Hello,

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 ?

DJN

 

[fazeka]

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!

Chris

 

[Pip]

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.

http://groupdiy.com/index.php?topic=47112.msg764053#msg764053
http://groupdiy.com/index.php?topic=47112.msg764111#msg764111

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.

 

[mickdundee63]

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.

 

[Pip]

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?

 

[kidgray]

Hey Mike,

indeed I'm working on my take on the M7 capsule, on and off since nearly three years now.
I'm experimenting with all kind of different PVC films in various thickness, often sourced from outside EU for regulation issues.
I have come close to what i want it to sound, a pristine original Berlin M7 i use as a reference, but there's still a small difference, and i want to get it 100% right.  Testing is done by myself and by three sound engineers who have a U47s with original M7 capsules.
I recently found a Swiss manufacturer for specialty films and they will send me a couple of samples next week, I'll make an appointment with the research lab for the gold evaporation after that. I have a good feeling with the new film but we'll see.

regarding the PSU:
Since the MK-U47 works like the original, just follow the original PSU plans. Additionally the schematics can be found in the MK47 thread (minus the switch). Most of my costumers build with Zayance's PCB.
I recommend the LED because it also shows if there's any current left in the capacitors after switching off (the LED fades as it drains)
Led current/voltage drop resistor is simply calculated by ohms law (google led resistor calculator)

-Max

Are  you still developing your take on the M7 Capsule? Some news there?

 

[rockinrob86]

can someone give me a tip on the relay used in this, along with a source/size for the nylon screws and nuts?


I bought someone's project of this, fixed it and finished it and it sounds great and was working well, however it started making some noises.  turned out switching the patterns would fix it.  I opened it up to adjust the placement of the relay and it broke :|

However, wired the mic in cardiod and the problem went away totally, so that is good at least.  I would like to fix it though.

 

[Delta Sigma]

can someone give me a tip on the relay used in this, along with a source/size for the nylon screws and nuts?


I bought someone's project of this, fixed it and finished it and it sounds great and was working well, however it started making some noises.  turned out switching the patterns would fix it.  I opened it up to adjust the placement of the relay and it broke :|

However, wired the mic in cardiod and the problem went away totally, so that is good at least.  I would like to fix it though.

I think he used a magnetic reed switch. Try searching mouser, digi-key, etc for something in the 105V range and similar physical size.

https://www.mouser.ca/Electromechanical/Switches/Magnetic-Reed-Switches/_/N-5g2l

 

[emrr]

can someone give me a tip on the relay used in this, along with a source/size for the nylon screws and nuts?


I bought someone's project of this, fixed it and finished it and it sounds great and was working well, however it started making some noises.  turned out switching the patterns would fix it.  I opened it up to adjust the placement of the relay and it broke :|

However, wired the mic in cardiod and the problem went away totally, so that is good at least.  I would like to fix it though.

https://uk.rs-online.com/web/p/reed-relays/2919631/?searchTerm=2919631&relevancy-data=636F3D3126696E3D4931384E525353746F636B4E756D6265724D504E266C753D656E266D6D3D6D61746368616C6C26706D3D5E5C647B367D247C5E5C647B377D247C5E5C647B31307D2426706F3D313426736E3D592673743D52535F53544F434B5F4E554D4245522677633D4E4F4E45267573743D3239313936333126


Look back for my comment about fixing noise in cardioid.  This plagued a number of people.

 

[georgerarnold]

Hello,

This is one of my first posts here so I'm sorry if I'm make any faux pases.

I recently bought a ioaudio mk47 from someone who made it. It has a point to point psu and a beeznees capsule.
After the seller telling me it was quiet, when I tried it i found it to be noisy.
Initially the noise would go after 30-40 mins and the mic sounded great.
I told the problem to the seller/builder and he suspected the valves and sent me some more but still the same problem.
All valves at this point are general electric.
Still suspecting the valves, the seller sent me some more valves, this time philips.
the philips were clean to begin with and then after a few times of using them they became noisy.
I returned to the general electric ones but now the mic is noisy regardless of how long the mic is warmed up.
I bought some more valves to test further, RCA 408a nos.
I put them in and the mic is still noisy.
I'm beginning to suspect that it might not be the valves at all.
I tested the voltage in the psu and it seems correct. 105v

Does anyone have experience with noisy mk47s?
Could it be a faulty capsule perhaps?
What would you test if you were in this situation?
Someone has suggested the 1500r resistor, which I've tested with a multi-meter and it seem fine.
Many thanks in advance for any help you can give.

Cheers.

 

[rockinrob86]

noise can come from many places. 

dirty capsule, high impedance section short, tube, cable, grounding, dirty pcb.

I would hesitate to start shotgunning resistors or other components.  Modern components don't typically go bad, and although they can, I wouldn't start there.  It is probably one of the above, and it requires thoughtful inspection and testing to figure it out.

 

[emrr]

The TYPE of 1k5 resistor has been an issue with these. 

Dirty hands touching the wrong parts are a noise issue.  Clean the boards with alcohol. 

On average these are not super quiet mics, most report at least a higher hiss level than many other mics.  Characterize the noise. 

 

[Moby]

Hello,

This is one of my first posts here so I'm sorry if I'm make any faux pases.

I recently bought a ioaudio mk47 from someone who made it. It has a point to point psu and a beeznees capsule.
After the seller telling me it was quiet, when I tried it i found it to be noisy.
Initially the noise would go after 30-40 mins and the mic sounded great.
I told the problem to the seller/builder and he suspected the valves and sent me some more but still the same problem.
All valves at this point are general electric.
Still suspecting the valves, the seller sent me some more valves, this time philips.
the philips were clean to begin with and then after a few times of using them they became noisy.
I returned to the general electric ones but now the mic is noisy regardless of how long the mic is warmed up.
I bought some more valves to test further, RCA 408a nos.
I put them in and the mic is still noisy.
I'm beginning to suspect that it might not be the valves at all.
I tested the voltage in the psu and it seems correct. 105v

Does anyone have experience with noisy mk47s?
Could it be a faulty capsule perhaps?
What would you test if you were in this situation?
Someone has suggested the 1500r resistor, which I've tested with a multi-meter and it seem fine.
Many thanks in advance for any help you can give.

Cheers.

Have you ever tried to "exclude" the capsule and listen just the noise of the electronics?

 

[TillM]

Hello,

This is one of my first posts here so I'm sorry if I'm make any faux pases.

I recently bought a ioaudio mk47 from someone who made it. It has a point to point psu and a beeznees capsule.
After the seller telling me it was quiet, when I tried it i found it to be noisy.
Initially the noise would go after 30-40 mins and the mic sounded great.
I told the problem to the seller/builder and he suspected the valves and sent me some more but still the same problem.
All valves at this point are general electric.
Still suspecting the valves, the seller sent me some more valves, this time philips.
the philips were clean to begin with and then after a few times of using them they became noisy.
I returned to the general electric ones but now the mic is noisy regardless of how long the mic is warmed up.
I bought some more valves to test further, RCA 408a nos.
I put them in and the mic is still noisy.
I'm beginning to suspect that it might not be the valves at all.
I tested the voltage in the psu and it seems correct. 105v

Does anyone have experience with noisy mk47s?
Could it be a faulty capsule perhaps?
What would you test if you were in this situation?
Someone has suggested the 1500r resistor, which I've tested with a multi-meter and it seem fine.
Many thanks in advance for any help  you can give.

Cheers.

Before my NOS 408a tubes was noiseless, I put them in my Mic and burned them in for 3 Days nonstop.

 

[Gus]

I think this circuit can be adjusted

 

[georgerarnold]

The TYPE of 1k5 resistor has been an issue with these. 

Dirty hands touching the wrong parts are a noise issue.  Clean the boards with alcohol. 

On average these are not super quiet mics, most report at least a higher hiss level than many other mics.  Characterize the noise.

Thank you that's a good and cheap place to start. I'll try it first thing.
The noise is a scratchy static noise, not constant it never stops for longer than a second or two.

 

[georgerarnold]

Have you ever tried to "exclude" the capsule and listen just the noise of the electronics?

No I haven't. I will go to a friend who has a different capsule we can test.
Would I need to insert a resistor in the place of the capsule?