MK47 PCB tube mic kit - build thread

[EEMO1]

that choke will work fine. all you need to do is add the difference of resistance to the next 1k resistor. triad is 500 ohm, hammond is 200. That makes the next resistor in line 1k3. or thereabouts.

thanks kingston,

about what I also thought... now I know.

 

[zayance]

Hi Guys, one of you HT specialist could take a look at the PSU layouts i made for this project?
Maybe i've made some rookie mistakes.....
First i wanted to do myself one for radial Caps and using 70um copper PCB board,
and i tought it might help others to have some home etching files,
I know ioaudio proposed his service for pcb layout and or veroboard instruction etc..
So i'm not trying to steal his work here, it's just that i wanted to finish this project soon, and tought of helping out...

It's the copy past of ioaudio's schematic.

EDITED: Going only with Radial only, as Axial seems really hard to find these days, did a search and not much results.....

Fits Caps of 10/7.5 and 5.08mm Pitch, Max Diameter of 22mm and Resistors of 25mm to 35mm long 10mm Diam or more,

A PCB version with the help and comments of Kingston and Mr Clunk, thanks to them.
I'll make a final adjustment, and If this works nicely, then i can post the files for people, if ioaudio is ok with that, but use at your own risks!


Files for etching:

http://www.sendspace.com/file/1245x3

 

[zayance]

Anyone?
I guess it's ok as is, i mean i'm using Eagle so...
But i wanted to have a secong tought.
Anyway i'll be doing one Radial for myself i'll report back...

 

[Kingston]

looks good to me, both of them. although I don't quite see the point for the separate test terminal, since you achieve the same just by inserting the test load in main B+ out. There's also no point in that separate axial version. It just takes more space and the caps are not easily available, at least in as high quality as radial. The era of axial caps is about over.

[edit]

looking at the radial version in more detail, there might be an issue with the ground path. This kind of autorouted faked "ground plane", might not be optimal. You will not know for sure until you test, but the path of those electrolytic ground points should be in series to the star ground. Now the path is somewhat undefined, and you might get better results with a series ground bus, instead of this autorouter semi ground plane. With this in mind, the axial version looks perfect actually.

 

[mrclunk]

I'd add that perhaps those radial caps are a touch close to the 5w resistors which will get fairly hot. Maybe give'em a more little air!
edit:
hold on have you changed the radial version? I'm sure those resistors were between the caps before... maybe i'm losing it.

 

[zayance]

I don't quite see the point for the separate test terminal, since you achieve the same just by inserting the test load in main B+ out.

Yes true, I'll change to a 3 screw terminal for Pot and Test Load, seems more convenient to have it on screw terminal...

looking at the radial version in more detail, there might be an issue with the ground path. This kind of autorouted faked "ground plane", might not be optimal. You will not know for sure until you test, but the path of those electrolytic ground points should be in series to the star ground. Now the path is somewhat undefined, and you might get better results with a series ground bus, instead of this autorouter semi ground plane. With this in mind, the axial version looks perfect actually.

Yes i see what you mean, hmmm i'll try to redo one radial with a series ground bus.

I'd add that perhaps those radial caps are a touch close to the 5w resistors which will get fairly hot. Maybe give'em a more little air!
edit:
hold on have you changed the radial version? I'm sure those resistors were between the caps before... maybe i'm losing it.

Yes Edited the pic, and you're right a little air would be better sure...
Resistor sizes are 21*10 (22.5mm pitch)

Thanks for the feedback guys. I'll repost a "better grounded" Radial for you guys to have a look

 

[zayance]

Allright redrawn a Radial, i had time so i did it right away.

Stayed on the GND Plane, because beside the fact that it's easier for a Rookie like me, even if this one is pretty straight forward, it's that it saves the etching bath to have less copper to take away, so my preference as a home etcher goes to Gnd Plane, but i made it like the Axial, and Resistor have a lot more space.



EDIT: PCB on top

 

[Kingston]

Hi, that ground path looks better. I still don't quite see the point for that separate "test" terminal slot. I mean, it's the exact same thing as putting a resistor between ground and 105V output so why not just use that for testing as well. Also, it seems that the autorouter has left some very thin traces of unnecessary ground "planes" between some traces and in some corners. It would be a safer and more error proof PCB if you cleaned those up. Actually, looking at it more, it seems that the autorouter has even failed in several places. R7 in that bigger caps version has a dangerously thin ground path. Similarly the led in the smaller caps version is hanging by a thread.

 

[zayance]

Edited and redrawned/cleaned the bigger Caps version.
I'll do the same for the other one if this version looks better.
For the Test Terminal, of course doing as you said is possible, i just tought makin it external and imbedded would make it easier for the less experimented ones?
Anyway i took it out here, saves space....

 

[Kingston]

Looks good now. Instead of having a separate small caps version, maybe you could just accommodate different size electrolytics on this one PCB? The difference in size is small enough that you might as well always etch the bigger one.

 

[zayance]

Looks good now. Instead of having a separate small caps version, maybe you could just accommodate different size electrolytics on this one PCB? The difference in size is small enough that you might as well always etch the bigger one.

Yes of course i can add on top a different pitch version as well, i did that on first drawing of the axial one, but that was too much space for nothing.
Adding on top makes the pads hard to know where to drill, going from 10mm to 7.5mm, the holes are blended, but maybe i could make a Cap that will have better view of the different hole places, i'll try that, doable i think.

I've actually did just on slight mod on this one, i changed the Two Pattern resistor terminals to be more "clear" to the outside connection, 14k beeing in the middle of the switch....

Thanks for the Help Kingston.

 

[mrclunk]

PSU PCB looks nice Z.

I'm almost finished building my mic but have a question about capsule mounting.
I'm using Skylar's body with the Beez Neez capsule + holder.

Skylar's body comes with a clear chunk of plastic attached where the capsule mounts.
Do i need to screw the capsule mount on top of this or can i just mount the capsule straight onto the metal top plate?

Will the rubber shock mount of the capsule holder isolate the capsule from the body enough?
I remember reading in an other thread a while ago that the material used to isolate the capsule is important.
thanks

EDIT: Ha, If i'd just read Skylar's manual for his body...
The clear plastic part is just for use with the Thierch capsule holder, so the capsule is at the same height as a real U47.
http://equinoxsystems.net/support/manuals/

 

[Jim50hertz]

The height of the K7 capsule mount was calculated for using the clear plastic mount.  Designed to be optimum in Skylar's mic body.

 

[mrclunk]

oh really, ok thanks. I'm going to mount it and turn her on tonight. 
I've a cheap capsule out of an SE2000 mic to test it with first.
Its a single sided capsule but that won't matter for testing purposes right? Just keep it in cardiod?
Or is a 47pf cap in the right ball park for testing?

 

[ioaudio]

unfortunately all the pics are down at the moment - i'm just back from vacation and will look into that asap.

 

[kante1603]

unfortunately all the pics are down at the moment - i'm just back from vacation and will look into that asap.

Welcome back Max ;D
Udo.

 

[etiefenthaler]

Hi


Finished my mk 47 today.

Components:
capsule: ck 12 delrin (leftover from akg 414 upgrade)
ioaudio kit - thanks a lot max
thomann sct 700 micbody
gotham cable 10m
mouse+ tubetown parts for powersupply
binder connector.

Powersupply: (took me a day)

modified sct 700 micbody. Soldered the bottom and the tube and gave a hammerite finish. For mounting the binder connector I had to use my lathe.

parallel 2m ohm resistor for 80v

first testrun  horrible sound and 80 % hum 
#1 Due to my hameritefinish the tube had no contact to mesh - part
#2 the binderconnector touched the brass block

after 2 hours of "dremeling" all was fine

First testrun at my Studio. My first impression:
the sound is bright but not harsch.  The different impedances of my isa 828  affect this mik much more than my other mics. (schoeps, akg414)
Building the microphone took me two days.

Again, thanks a lot max and group diy.

Looking foreward using this mic at my studio.  ;D

Erich T.

 

[ioaudio]

great work udo - did you use the linear CK12 or the treble-hyped version?
pls check heat in your PSU after running for a couple of hours.

pics are back up again - let me know if something is missing.

 

[kante1603]

great work udo

Max,I think you swapped our names:This is Erich´s work,not mine!

BTW:Congrats Erich!

Udo

 

[etiefenthaler]

@max
it is the linear of my 80's 414buls tl.

had the psu and mic running until now (4 hours) heat is no issue   used 10 W resistors ..

again thanks a lot. building was a pleasure.

Erich