MK47 PCB tube mic kit - build thread

[burglar]

Would just likr to run this by you all.  The combination of the 10H choke, two 1k resistors and a 680r only broght me to 106-107V so I put a 5R6 after the 680 which brought me within range with the 500R pot.  Is this normal or does it suggest a problem else where? 

I'm using a toroidal with 240V primary / 200V secondary. 

Also, when my + rail is reading 105v and I switch to omni.  I measure the voltage just before the 12k resistor and it's only 45v? 
Is this normal.  Where should I be getting my 48v reading from? 

 

[North]

Would just like to run this by you all.  The combination of the 10H choke, two 1k resistors and a 680r only brought me to 106-107V so I put a 5R6 after the 680 which brought me within range with the 500R pot.  Is this normal or does it suggest a problem else where?  "

Yes that is normal as I found out. I have around 123-127 volts coming out of my wall and I had to add a lot of resistance to mine beyond the standard build specs to bring it down to a 105 range. I also had a 3 volt fluctuation so I plugged the psu into my ups and only turned on exactly what I was going to be using for tracking with the mic (computer and rack preamp) and wait for the everything to reach its nominal range and then adjusted to 105. Seems to be doing ok there - until the A/C comes on  ???

 

[burglar]

Ok, great.  Can anyone lend some information on the 48v.  I'm not sure where I should be measuring from?  As I said, with -probe on 0v rail and +probe just before the 12k resistor I have 46.8 or there abouts when switched to omni.  Is this enough or do I need to change the 12k / 14k resistor to something else?

 

[ioaudio]

That's perfectly fine.

 

[burglar]

Spot on, thanks.  Something else that I wanted to check was, I have wired the input / output XLR's as per the diagram below but for A- ,  A+ and shield going from the 7 pin to the 3pin I have used separate cores cable tied together instead of mic cable.  Is this a problem?  Am I likely to having grounding problems this way. 

Also, the neutrik XLR's I have used have a tag on them.  Do I need to send these to ground as well?

 

[Songguy]

Thanks for everyone's help! The mic is AWESOME!!
I let the tubes burn in for 2 days. When I attached the capsule and powered her up I couldn't believe how quiet the circuit was!

 

[ioaudio]

 

[micaddict]

Congrats!

What PSU do you use?

 

[EEMO1]

mine was quiet right off the bat without even burning in the tubes! congrats on your mic!

Thanks for everyone's help! The mic is AWESOME!!
I let the tubes burn in for 2 days. When I attached the capsule and powered her up I couldn't believe how quiet the circuit was!

 

[North]

I also want to say thanks to:
Max for an awesome project and for making an affordable U47 possible.
Zayance for a low cost - high quality psu pcb.
Equinox for producing a body that is a treasure to behold.
Dan- Classic Cases for outstanding customer service and going above and beyond.
And to all on the board for all your help and input.

Now If I could just figure out how to post pics under 1024kb ???

 

[Alexwfm]

Hello everyone!

I'm Alex and month ago I got the Mk47 kit from Ioaudio,  today i did a first run.
I just moved to London so I have no tools aside soldering iron and drill, and I'm also poor so i tried to save a bit on not critical parts!
For example replacing the PSU circuit using the original little case that came with the mic PSU. But that was more pain in the """ than money saving.
At the first run i noticed couple of pops that disappeared 1 minute later. I used some used matched pair of 6028 that I slammed on the wooden floor while trying to unplug them.
I can't notice any difference in noise floor with the microphone either unplugged or plugged with lots of gain . that's cool!

The original PSU came with a metal divider that was splitting the case in two. I used it as cooling sink for the 10W resistors and to separate the first ripply part of the circuit (diodes and first cap) from the second (all the rest after choke). Each part had own ground wire that was going to one spot.
The output voltage went to 350v when load-free, but 110v on load. I couldn't get down to 105v if I was on omni mode.

The mic is built in a Tbone SCT700 body. Instead of screwing the 5W resistor to the case I have applied some termal paste under it, and then while pressing it down I "epoxied" the two sides to keep it there. forever.
It sounds nice even with the stock chinese capsule, but I'm waiting for a RK-47 from microphone-parts.com

PSU inside (was actually small.)


If you were looking for the transformer and the choke:
[img=http://s7.postimg.org/t0n9dphuf/IMG_0214.jpg]

Heater dropper fix:
[img=http://s15.postimg.org/4bp5vftd3/IMG_0180.jpg]

Thanks Ioaudio and Chunger for parts and super detailed build tutorials. I once was dreaming of being 21 and rock star, but now I'm happy enough just building tube condenser mics .

YO.

 

[micaddict]

Welcome!

Good DIY story.

Poor? Well, at least you seem to have a passion (which is wealth by itself) and now basically a high-end (whatever that means) tube microphone to boot. 
Yes, do upgrade the capsule.
Did you have to skip meals?

Anyway, you done good.
And thanks for sharing.

 

[Alexwfm]

Did you have to skip meals?

I just did not have drinks that weren't the half priced ones in the bar where I work and I share my room with a crazy Dutch girl.
Both money and liver saving.

Not long ago I built an RM-5 ribbon mic and a INA217 preamp, they both are ok but much less budgety than the MK47.
I'm in the middle of making my bedroom studio and apparently filling it with equipment you made by own is a lot satisfying and, well.. bit cheaper!
Isn't it?

 

[micaddict]

I share my room with a crazy Dutch girl.

Hey, mine's Dutch, too. 

But this is is the MK47 build thread, so I'll leave it at that.

 

[Alexwfm]

Still I have a question.

I noticed the voltage output from the PSU rising about 10v when I was switching in Omni mode (without mic plugged).
Is it because there's no load? I'm so scared that with mic plugged in it will make Vout to rise from 105v and probably damage the mic.

By the way, is there a "safe offset" of Vout that the mic would accept without breaking?

Thanks!
Alex

 

[ioaudio]

Hi Alex,

yes that's normal - voltage comes down when loaded by the relais when connected.

-max

 

[ioaudio]

New batch available in my white market thread.

 

[maq3396]

Newb question:

Can someone please comment on the gauge of the wire(s) used in both the microphone and the psu?

Thanks
Mac

 

[HellfireStudios]

Newb question:

Can someone please comment on the gauge of the wire(s) used in both the microphone and the psu?

Thanks
Mac

I've been using 22-24 AWG for my mic builds. You might want something a bit thicker for high voltage and high current hookups (polarization voltage leads and ground respectively).

-James-

 

[maq3396]

Thanks James

Time to warm up the soldering pen....

Cheers
Mac