MK47 PCB tube mic kit - build thread

[kante1603]

Just wanted to let you guys know that I solved my noise problem referenced above and it had nothing to do with the Mk47 kit.  That noise was isolated to an old toggle that was used on the P/S to switch the pattern.

Hello crackerzot,
congrats for solving the issue finally -this thread is going to be a very good trouble-shooter for everybody here.

Further up in the thread, I asked if it was common to hear a lot of scratchy pop sounds when switching pattern and was told "yes".  Well, that wasn't quite right.  After hitting the switch with contact cleaner and working it back and forth a few dozen times, all I hear now is one 'audio' "click" when switching the pattern and the random noise spikes are now gone.  Hip hip hooray.  ;D

Maybe my english is still too bad,but as said normally switching patterns do cause some kind of noise like a pop or a click-very short of course and not "scratchy".So some of my mics do more,some less-but they do!But not so loud that the monitors will explode! ;D
Anyway,we´re used to turn the volume down first,then switch.

Have a lot of fun with your new microphone,

best regards,

Udo.

 

[ytsestef]

Congratulations ioaudio, seems like a very sweet project! I have two questions:
1) Can I make a matched pair? Do I have to match the tubes or what?
2) Can the PSU handle two mics?

Thanks!

 

[mrcase]

OK. stupid questions maybe but I have to ask! I have sucessfully built my psu  ;D but I am not sure about grounding...
Do you connect the 0v in the PSU to chassis ground or not?
Do you do some kind of stargrounding (like connecting the ground from the power plug, 0v and xlr pin1 together) or is it not necessary?
what happens with the xlr1 ground since there is no pad for audio ground on the mk47 pcb? Just let it float?

thank you all!
can`t wait to hear the mic!

cheers
martin

 

[Sredna]

So, finally got my MK47 with Beezneez Capsule and Skylar body finished with a mock up PSU.

Sounds pretty good and after +48 Hrs. burn in time there is no pop or crackling noise anymore.

The tubes though, are quite microphonic (sic!) I have tested about 8 different Philips JAN 6028 tubes
without big difference. Some rubber foam around the tubes help some but still got some ringing
and rattling when knocking against the mic body. Suspending the whole PCB is the next step.

Any tips, thoughts?

Thanks Max for a really nice sounding project!

 

[madreza]

Hi guys,

where did you get your 7 core cables for the microphone ?
and what connector did you use on the PSU side ?
( God Neutriks 7pin are expensive !!!! )

 

[Sredna]

Sommer cable
http://www.sommercable.com/2__produkte/2__030_meterware/2__200_0186.html

or

http://www.thomann.de/gb/the_tbone_xlr_ersatzkabel.htm


You can use a 5-pin connector, no need for 7 in this case...

 

[ioaudio]

1) Can I make a matched pair? Do I have to match the tubes or what?
2) Can the PSU handle two mics?

1: Most important
a. capsule matching
b. tubes matching
The Kit an it's parts (esp. transformer and coupling cap) are close enough

2: the passive version cannot be used for two mics.
I recommend using one PSU / mic


RE: microphonics:
If you have a bigger U47 type housing it should be possible to float the whole PCB with rubber mounts inside the rails.
However using a proper shock mount for the mic should solve this problem.

 

[ytsestef]

Thanks for the answers, ioaudio!!

1) Capsule matching goes without saying, I was worrying about the circuit (transformers etc), glad to know I only have to match the tubes (there is an option to buy a matched pair of RK-47s, has anyone tried this?).

2) I could build 2 PSU's in one box to cut down costs, although I think this would inherit more impracticality than benefits. I guess I'll stick to two PSUs, at least then I could take one on the road

Thanks again!

EDIT: One more question, could I use a bridge rectifier instead of 4x 1n4007 for the PSU? If yes, 1.5A / 400V should be ok?

 

[babyhead]

ioaudio-

I have an extra body from an old run of your mic bodies, the one with the Z grill. Not using an inside caliper, I measure 47.5mm. Earlier you said 48mm was the absolute. Is there .25mm I can sand away or otherwise make magically disappear?

Thanks.

 

[ioaudio]

could I use a bridge rectifier instead of 4x 1n4007 for the PSU?

sure!

babyhead, the kit fits the tube as is (should actually read 48mm inner diameter)

 

[babyhead]

Ahh... Magic! Cheap Chinese ruler.

 

[mrcase]

I did mine like this, color coded the same at each end. I used Gotham mic cable.

Audio
1 = A- (gray) (connects to pin 3 of XLR at the power supply)
2 = A+ (white) (to pin 2 of XLR at the PS)
Center pin = audio ground (green)  (to pin 1 of XLR)

Power
3 = B- (black [blue in the cable])
4 empty
5 = B+ (red)
Pattern
6 = P (yellow)

Shield to the chassis.

Can somebody please explain  me how the shield is connected to the psu chassis? is it also connected to the micbody?
and shouldn´t the shield be connected to xlr1 like with any other "normal" mic cable? and where does the audio ground go to on the mic side????
al lot of questions - i know ;-)

THANK YOU ALL

cheers!

 

[mata_haze]

Hello everybody,
I am starting this project tomorrow morning.
I have bought a PSU, capsule and body from Beesneez.
the PSU B+ is built around a Tip41 transistor and it uses a couple of zener to set the output voltage.
nominal voltage without anything connected it's 118 VDC.
is it too much ? shall I replace one of the zeners to achieve 105?

Best,
Mattia.

 

[madreza]

I have a newbie question :

what the choke is for ?
( as I'm waiting for all the last parts to finish my Mic ........ )

 

[Sredna]

To smooth the ripple.

In some U47N schematics there is a 2 x 8Hy (double) choke, in some there´s just caps and resistors.

 

[mrclunk]

Speaking of chokes is the value very important?
I've a couple of big ones in some old test gear, i know they'll be able to handle the current but they could be 30H+
bigger is better?

I think i may have to change the resistor values a little for the correct voltages.

 

[ioaudio]

the PSU B+ is built around a Tip41 transistor and it uses a couple of zener to set the output voltage.
nominal voltage without anything connected it's 118 VDC.
is it too much ? shall I replace one of the zeners to achieve 105?

Maybe the voltage comes down a bit when loaded - you can quickly hook up a 2,2k 5w resistor and check.

The original choke is 2 x 8H wound on the same core - which adds up to 32H in total, but with the capacitor hanging on the center tap it's a bit more complex to simulate what's really going on.
One can use 2 chokes with 16H to come closer to the original.

 

[kante1603]

So finally i´m done and my frontpanels for the psu arrived 2 days ago.
Have done a quick check and everything works;it seemed to be a bit noisy but I´ve only had my mBox (1st generation) with a lousy mic pre and a sh***y phoneamp and no reference.Apart from that I´ve got no hum or anything else.There was a small RF-noise when the b+ and b- weren´t fixed to their final positions;they were hanging quite close to the audio lines crossing them.Listening to it while moving them solved this completely!

Burn-In-Time now....

Peopleo your wirings carefully as this part is very sensitive;that means shorten them to proper length and where needed twist them.
For those who asked what to do with the pin1 on XLR output:I did mine after AES48 meaning I connected it directly to the chassis right on it´s D-Series connector´s mounting screw using tooth lock washers and eyelet-works perfect.
And for those who don´t believe cabling can be done with starquad:It works!I have done a 10 meters(!) cable with no noticable issues.
I will do some more with sommer cable (sc-octave tube) not because of audio issues but the cable I used is Gotham-Starquad (the thin one)-this is good seeing it electronically but not mechanically.It gets easily twisted and isn´t nice for laying it propperly on the floor.

Here are some pics:








I used thomann the t.bone sct700 for mic body (is only 149 Euros and comes with case,shockmount,cables etc) and thiersch capsule.
The bodytube has very deep and ugly engravings-filled them with 2k glue and sanded it;after that put on "Hammerite" blue laquer.Done.
PCB fits very well,take care when choosing thiersch:Order the short (52mm) mounts for a good position.

Will post some more pics of the psu if wanted,must take them over the weekend then.

What else can I say than THANK YOU MAX for a great project and THANKS TO ALL OF YOU here in the forum!!!
It was a great experience for me since this is my first DIYed microphone.

Deeply impressed,

yours,

Udo.

P.S.:Oh,did I mention that a second kit arrived two days ago? ;D

 

[0dbfs]

Awww 680 grams. She's very cute.

And how have you named her?

Cheers,
jb

 

[madreza]

thanks Sredna for the info ! so it's better to use it !?