MK47 PCB tube mic kit - build thread

[ioaudio]

The grids are tied together directly on the tube socket fed throught the holes on the pcb (going to the "front" connection to the capsule)

 

[chunger]

Thanks. . . this would be pin one I presume.  The one with the through holes.

I ran the test as described and did not hear a significant decrease in the base noise (hiss) with the front capsule disconnected and with the grid grounded.  I should probably test again and actually measure the differences but do not have a DAW setup at home currently, but based on this result, it appears what I am hearing is tube noise and the remedy may be to burn the tubes in for another 48 hours and re-check.  Alternately, a proper capsule designed for the circuit's lower-than-stock-Alctron polarization voltage should yield higher output which will further mitigate the base noise issue (if in-fact it is an issue).

Capsules have been ordered and I am awaiting shipping of K7 and M7 from Beesneez.

In the meantime, I will go back and review my build pictures to verify that I have not made a component value error during the build.

UPDATE: There was nothing wrong with the mic.  In the studio listening environment, it is extremely quiet.  My junk listening setup at home must have been acting up.  The noise that was present was very normal, low-level tube noise.

 

[tonycamp]

Hey Chung,

I just built 4=7th circle audio pre's a while back, i was having an issue with one of the api's. I tested everything, measured this and that, carefully compared to my other functioning api, ordered replacement Ics and caps, none of it worked. As a last resort and completely frustrated, i flipped the pcb over and started touching my iron and rewetting all my solder points, plugged her back in and.......
you can guess the rest. By all outward appearances, a flawless solder job, that wasnt so flawless.

good luck

 

[electrisizer]

Which capsule is being used in your build?

hello there,

ive used the mk47 in different productions till now and really like what it does! espacially on male voices this mik shines...

theres one thing i would like to change. it has not very much highs! even if the highs sound good and smooth when eq is boosting the dedicated frequencies (in contrast to most cheap miks)... i would like to have the highs right there after recording

is there a resistor determining the highs in this circuit???

hey was away for some days sorry for late answering.


its a beezneez capsule from first group buy... a K7

 

[Pliplo]

I was about to buy my Thiersch STW7 blue line capsule but a new variable appeared. Capsule holder size...

I got this from Thiersch:

"The outer diameter of STW7 is 32 mm. The original Neumann K67 has got a
> diameter of 34 mm so that a holder that is used for K67 cannot be used for
> M7 or STW7. Maybe you'll also need another holder for your project?"

Anyone knows what capsule holder i should order? (Altran 2b donor body)

thx

 

[chunger]

PSU 1:

PSU 2:

Both running easy and completely cool to the touch   What a bit of DIY fun!  Learning lots along the way.

 

[ioaudio]

Looking great, 'Chung!
Once more the link for chunger's fantastic build thread http://www.groupdiy.com/index.php?topic=47112.0

 

[Enchilada]

Hey guys.

While I'm waiting to buy a PCB I'm going to have a crack at building this point-to-point just for fun. I've got a quick question about the schematic. It shows g2 and g3 tied to a but the 6028 has an internal connection between g3 and k.

How is the tube actually connected?

I've read here that the heaters are in series and the grids/a/k are all in parallel but I can't find anything about the internal g3 and k connection.

Thanks,

Kris

 

[My3gger]

I guess you are looking at first schematic with VF14 tube, not 6028. VF14 doesn't have G3 connected to cathode and 6028 has. This is why it is possible to connect VF14's G2 and G3 to anode. Another example is EF86, G3 is not connected to cathode.
I'm also interested in knowing how 6028 is connected here. Preferred method is connecting G2 to anode and G3 to cathode. I don't think there are other choices with 6028. It's probably connected this way (maybe some resistors are added to grids) and two tubes paralleled like they say.
'

 

[Enchilada]

I guess you are looking at first schematic with VF14 tube, not 6028.

The schematic on page 1 of this thread, as noted in the lower left corner, is for the MK47, not the U47. There are a few differences including the tube being labeled as VF14r. No such tube exists, it is the name given to the Vf14 emulation provided by paralleling 2 x 6028 tubes.

However, the question still remains. How are the g3 and k connected?

 

[My3gger]

You are right about VF14r, no such tube exists, it's drawn as a replacement for VF14 made out of two 6028 tubes in parallel. Sorry for misinformation, i thought i was looking at redrawn U47 schematic...
G3, cathode and shield are connected together inside the tube, so there can't be any other connection for G3 than this.
http://tubedata.milbert.com/sheets/185/6/6028.pdf
http://www.westernelectric.com/spec_sheets/408A.pdf
I think better question is if G2 is directly connected to anode. Looking at datasheets i don't think you will ruin your tubes by connecting G2 directly to anode. Pictures are good and you might see correct connections from them.

 

[Enchilada]

You are right about VF14r, no such tube exists, it's drawn as a replacement for VF14 made out of two 6028 tubes in parallel. Sorry for misinformation, i thought i was looking at redrawn U47 schematic...
G3, cathode and shield are connected together inside the tube, so there can't be any other connection for G3 than this.
http://tubedata.milbert.com/sheets/185/6/6028.pdf
http://www.westernelectric.com/spec_sheets/408A.pdf
I think better question is if G2 is directly connected to anode. Looking at datasheets i don't think you will ruin your tubes by connecting G2 directly to anode. Pictures are good and you might see correct connections from them.

It shows g2 and g3 tied to a but the 6028 has an internal connection between g3 and k.

You're not giving me anything I haven't already stated. My question was not "how is g3 connected" my question was "how is the tube actually connected?" I was asking the question in reference to my previous comment outlining that the schematic has g2 and g3 to a and k to -f but this cannot be correct because, as I previously stated, there is an internal connection between g3 and k.

 

[0dbfs]

I don't have my mk47's with me at the moment to beep it out and confirm but if you look at a 6028 datasheet there is no dedicated pin for the suppressor grid. Pin 2 and Pin 7 on the 6028 datasheet that I have are labeled as Cathode, Suppressor Grid, and Internal Shield. If you inspect Max's example photo's you will see that pin 2 is floating (ie; no connection) while pin 7 is connected to the cathode portion of the circuit. I do have some 6028's here though and pin 2/7 measure zero ohms so I can confirm that pins 2/7 are internally connected on the 6028's.

The VF14 is an eight pin tube and the control, suppressor, and screen grids are broken out to different pins as well as the cathode.

Cheers,
jonathan

 

[micaddict]

Lots of circuit tech talk here, as is to be expected on an electronics DIY forum, especially in a dedicated build thread.

But now that we're three years past the announcement of the MK47, there should be quite a few specimens in the field actually transducing artistic sounds from human throats and musical instruments. So I'd like to ask members if they could post more sound samples.
Since this would be more about the finished product rather than the build, I could also start a new thread for it if that is preferred.
Max?

Also, what is the experience on the slightly longer term. Like how have the parallel tubes been holding out?
And what are the experiences with the various M7/K47 capsules? Are they just right for the circuit, or maybe a little dark to some, somewhat midrangey? Etc. etc.
Have some changed out caps and such to alter tone?
Questions like that. (Those questions perhaps stay closer to the relevance of a build thread, and some may have been answered to some extent.)

I know the journey is often more fun than reaching the destination, but I think it'd be nice to read and hear some more feedback about the actual finished microphone. Or am I alone in this? If so, please forget I posted this. 

 

[tonycamp]

I am with micaddict, i've built the mk47, waiting on Chungers donors to come in, i am leaning toward the theirsch M7 blue line, but the beezkneez k7 has been revered. So more verbiage and samples would be great

 

[guitar4444]

I'm just putting together my MK47 kit and thinking I wouldn't mind a fig 8 option. I thinking about trying an internal switch for making the mic either a U47 or U48.
Anyone else tried a fig 8 with the IOaudio kit?

cheers  Greg

 

[JW]

Hey folks,

So I think I've finally figured out what's wrong with my MK47 mic. I have a couple questions though.

A little background: I've been having some intermittent ocean noises ever since I built this mic.  I know this is something that probably should have been done a long time ago, but I finally started checking voltages around the tubes.

Luckily, I have a second MK47 that's working flawlessly (why don't we call this one #2 to delineate from the non-functioning one, which we'll call #1) Anyhow, makes for easier troubleshooting.

So, on both #1 and #2, I'm getting 90V after the 30K resistor that is in series with the B+ voltage.
However, when I measure after the 100K resistor that is in series with the 30K resistor, I'm getting two very different voltages.

On #2, the functioning mic, I'm getting 54V
But on #1, I'm getting 41V

I thought this might clearly point to a bad 100K resistor in mic #1? However, the 100K resistor measures 102K 'in circuit' in both mics, which has me puzzled. What else could it be? Tubes drawing too much voltage/current? I bought 10 of the tubes when I first started building these mics, and I've swapped many in and out of this mic, burning them all in for hours, and it hasn't made any difference.

BTW, this is an aside, but I have a Beez Neez K7 in the functioning mic, which sounds great. And I have a Thiersch blue line on the way, which will go in the other mic, but I need to fix this problem first, so I can provide y'all with some samples.

 

[EvLoutonian]

Also love to hear sound samples and results / feedback from people who've completed the mic.

 

[JW]

Can somebody tell me what the plate voltage should be? Actually, I'm unsure whether this is the plate or grid #2 (according to 6028 data sheet) and because pins 5 and 6 are connected together on both tubes, but anyway, what is a good voltage here? (at intersection of the 1uF output cap, the 100K resistor, and pins 5 and 6 on both tubes)

 

[ioaudio]

41v should be fine - #2 the working mic is on the high side.
Re-check the HighZ portion of the mic carefully.

-max