MK47 PCB tube mic kit - build thread

[G-Sun]

here's a live recording to watch and listen on YouTube.
http://www.youtube.com/watch?v=xvKaHNFycj4

That's just nice sound :thumbsup:

 

[dandeurloo]

I ordered more resistors.  I will try and replace a few and see if the popping and crackling goes away.

 

[Pip]

So here is my tail sad but true. I have gone through 3 sets of 408a Western Electric tubes. What happens is the mic will sound fine for weeks at a time and then all of a sudden start making popping or crackling noises. Replacing the tubes with new to me NOS tubes has done the trick twice but here we are again. I don't mean taking them out and reseating them that has not worked. I tried that first of course but had to change tubes. I Know that tubes are a crap shoot. But was just wondering if anyone else has had this reoccuring problem as well?

As a side note I started out with JAN Phillips tubes but they sounded not good at all.

Following up.

So I replaced the 1K5 resistor with a 10watt wirewound panel mount metal housed version and screwed that bad boy to the aluminum heat sink I had put in the mic body for the ceramic one as opposed to just a clip holding it in place. Well 3 days of burn in with same tubes as before and no popping. I say we have a winner.

http://www.mouser.com/ProductDetail/Arcol/HS10-1K5-1/?qs=%2fha2pyFadujijxGS6LgfEi9lQ2ZQ6DE%2f18e2GSyrwxzudE9N3KjSBg%3d%3d

 

[Winetree]

Pip, Do you happen to have a picture.

 

[Pip]

Pip, Do you happen to have a picture.

IMAGINE NEW RESISTOR SCREWED TO ALUMINUM PLATE THAT IS LOCATED BELOW TRANSFORMER INSTEAD OF CERAMIC ONE SEEN IN SHOT. NOTE THIS IS OF ORIGINAL BUILD THE MIC NOW HAS WESTERN ELECTRIC TUBES NOT JAN PHILLIPS

 

[sliebers]

I wanted to report my findings on the 1K5 resistor swap as well.  I originally had the sandbar 1K5 (included in kit) mounted with heat sink compound to the brass base of the mic.  The popping and crackling noises would appear randomly after about an hour of use.  I then wiped off all the heat sink compound and suspended the resistor in air inside the mic.  The noise seemed to appear less frequently, but was still there.
I ordered an aluminum housed 1K5 10W chassis mount resistor and replaced.  So far, the noise has not shown up.  I have yet to do recording work with the new resistor installed.  That will be the real test as the noises always seem to show up when you are getting the perfect take.
The sound of the mic is fantastic, the tubes are a little noisy on their own, but workable.  My advice to anyone building this mic is to throw out the included 1K5 resistor and start with a chassis mount 10W.

 

[gary o]

I wanted to report my findings on the 1K5 resistor swap as well.  I originally had the sandbar 1K5 (included in kit) mounted with heat sink compound to the brass base of the mic.  The popping and crackling noises would appear randomly after about an hour of use.  I then wiped off all the heat sink compound and suspended the resistor in air inside the mic.  The noise seemed to appear less frequently, but was still there.
I ordered an aluminum housed 1K5 10W chassis mount resistor and replaced.  So far, the noise has not shown up.  I have yet to do recording work with the new resistor installed.  That will be the real test as the noises always seem to show up when you are getting the perfect take.
The sound of the mic is fantastic, the tubes are a little noisy on their own, but workable.  My advice to anyone building this mic is to throw out the included 1K5 resistor and start with a chassis mount 10W.

Maybe at beggining of the build a little note to say if noises appear prime suspect will be dropper resistor could save a lotta hassle for builders 

 

[0dbfs]

It's apparently the "sound of sand". Sorta "grainy"....

Cheers,
jb

 

[ioaudio]

Since this problem popped up i ship the kits with the alu resistor included.
Sorry for the unconvenience.
Max

 

[0dbfs]

I did two of these (with the sand resistors) and had some discharge noises initially but it settled down after a number of hours. I let them burn in for a couple weeks. My B+ drifts up and down a bit over maybe a 10-15 minute cycle. Plan to rebuild the PSU's at some point since I did them p2p and was going to swap out that heater dropper at the same time. Thought was that as the heat goes up/dn the resistance also varies so just wanted a more robust part in there for that function.

Cheers!
-jb

 

[ioaudio]

Remember that this is a passive psu - not regulated, so fluctuations are normal.
I wouldn't change if you don't have a noise problem with the resistor.

 

[deveng]

Max,

Just got my MK47 up and running.  Fired up first shot with no issues.  I was waiting for an M7 from ChuckD and just got it Tuesday evening.  Installed it today and powered the bad boy up.  Did a high gain check and there's no hum.  A quick voice test and it sounds full.  I'll burn in the tubes for 24 hours before using.  Pictures to come.  Now I can move on to build another from the parts I got from Skylar's sell-off.  That one will have one of the Equinox capsules. 

Thanks for your work on this thing!

regards,
Jeff

 

[ioaudio]

Thanks Jeff!

 

[teacat]

https://soundcloud.com/teacat77/mk47-snip

short clip of violin in my bad room...

beesneez 'save phelicity' k47 capsule
we 408a tubes
body similar to the equinox

rec'd through octa-capture, no processing

 

[micaddict]

Nice, too! Somewhat thicker than the C12 in the other thread.



Henk

 

[G-Sun]

https://soundcloud.com/teacat77/mk47-snip

Nice. Very helpful for getting an impression of the mics. Thanks!
(Do you take session work?)

 

[ioaudio]

Since i have received a lot of mails and Pms regarding the matter, just a short notice to everyone:

The new U47 Kit & Pcb from users "poctop" and "micandmod" was done without my permission.
Please note that the Mk47 circuit, featuring 2 408a/6028 tubes in parallel/series connection, was my invention.

thanks for your attention,
Max

 

[Leer]

Makes me cringe when I read "our engineers have developed a circuit of two 408 Military NOS in parallel"

Atleast they should give credit where it's due.

 

[Studio Mollan]

Hi guys!
I've been using my pair of Mk47's for about two now and they sound very good indeed!
I'm comparing them to my Flea47 and although they are similar sounding the top end is a lot smoother in the flea. Also the flea sounds overal more polished and more flattering, it saturates more and better than the MK47's do, but i guess thats to be expected from a 5000USD microphone. The mk47 is "faster" more modern sounding i guess and compared to the Flea a bit harsh in the hi end. Its not harsh sounding at all though, just comparing to the Flea.   
Im using the Skylar body with Thiersch red mylar capsule. My Flea has a Thiersch blue PVC and EF12.

Any ideas on how to stretch the MK47 towards the flea? I know its a different cirquit but maybee you can get a bit closer with different types/values of caps?
If anyone experimented on this id be very happy for your thoughts!

Also: Howecome the polystyrene cap is 10nf instead of the original U47 spec 1nf? I tried replacing it with a 1nf SilverMica. Hard to tell the difference, at least on this source. 
/
Emil

 

[micaddict]

Thanks for the comparison.

Im using the Skylar body with Thiersch red mylar capsule. My Flea has a Thiersch blue PVC and EF12.

The thicker (heavier) and more flexible (for now) PVC alone would make that one less fast and less modern sounding.
Likely smoother/less "harsh", too.

Then there's the tranny, coupling cap etc.

In that order, I guess.



Henk