MK47 PCB tube mic kit - build thread

I'm wondering if someone can answer my question about wattage of resistors in the "MK48" conversion on page 48 of this thread: http://www.groupdiy.com/index.php?topic=41379.940

For the 150M ohm resistors, is 1/4 watt okay? I see that one of them is in parallel with the 1500 ohm 5 watter, but I think that is for the heater right, which is the most current intensive?

BTW, I built two of these guys and finally settled on the Thiersch blue lines, which are really aweseome. I haven't noticed any lack of low end. In fact, I was contemplating switching the output cap to .47uF to hopefully roll off a little. That said,  I'm recording in small rooms where low end build up is always a problem.

MicDaddy wrote:

ok, so i didn't build an MK47, but rather adopted one from the blackmarket.

Click to expand...

Yeah, I saw the add too and I was surely tempted. But it's got a good home. Hey, it's better off with a daddy than an addict anyway. 
Congrats!

MicDaddy said:

ok, so i didn't build an MK47, but rather adopted one from the blackmarket.

Click to expand...

Dang! Nice work on your mic build, Ben.
& I like the nifty work on the dummy load, too!
Evan

What's the purpose of that dummy load?

Also what was the bit about moving "the B- to pin 7 of the binder, to allow that to make contact before any of the other pins. "? What does that do?

Melodeath00 said:

What's the purpose of that dummy load?

Click to expand...

The psu is not regulated, the dummy load allows adjustments to be made to the psu without having to hook up the microphone.

Also what was the bit about moving "the B- to pin 7 of the binder, to allow that to make contact before any of the other pins. "? What does that do?

Click to expand...

The Binder connector pin 7 (center pin) is physically sticking out a bit further than the remaining pins.  This allows 0V to make contact before all other connections. 

Why would you hook/unhook a tube mic with the power supply still on?

-James-

HellfireStudios said:

Why would you hook/unhook a tube mic with the power supply still on?

-James-

Click to expand...

Did someone suggest for you to do this?  I don't know why anyone would, there is always a possibility that it could happen.

Would you ever put high voltage to a metal chassis?  I wouldn't but that doesn't eliminate the possibility of it happening.  Take a look at an IEC power inlet sometime... 

I was just posing the question to find out if the need for an extended mic cable pin to ground was actually necessary. In use, with locking connectors, an accidental disconnect seems unlikely, and to connect the mic with P/S on would be far from standard operating procedure. I say keep a yardstick around so you can slap any "inexperienced" hands from a distance.

-James-

Hello all,

Having a bit of a challenge with the PSU...
Keeps blowing fuses.
The IEC measures 120V (Canada)
The black and yellow secondaries of the Triad VPT 230-110 measure 265V when they are "free"
However, as soon as they are connected to the terminal blocks (Zayance pcb) the fuse goes.
No obvious bridging on the solder points.
Currently all connections removed from pattern switch and both cable connectors (only ground at 0V and test load connected).

I am very open to suggestions on how to troubleshoot this.
Is is possible to depopulate the pcb then check as each component is reinstalled?

Thank you in advance
Mac

maq3396 said:

Hello all,

Having a bit of a challenge with the PSU...
Keeps blowing fuses.
The IEC measures 120V (Canada)
The black and yellow secondaries of the Triad VPT 230-110 measure 265V when they are "free"
However, as soon as they are connected to the terminal blocks (Zayance pcb) the fuse goes.
No obvious bridging on the solder points.
Currently all connections removed from pattern switch and both cable connectors (only ground at 0V and test load connected).

I am very open to suggestions on how to troubleshoot this.
Is is possible to depopulate the pcb then check as each component is reinstalled?

Thank you in advance
Mac

Click to expand...

Diodes in right direction?
Slow blow? Fast Blow Fuse?
Maybe can post a picture? Or more details?

Thanks Tony

As I started taking it apart I found 0 ohms across both double terminal blocks.
It is the terminal blocks themselves.
I must have ordered the wrong ones!

Back to the local electronics store for blocks and fuses!

Cheers
Mac

Hmmm, please give link to the part.


T.

maq3396 said:

Thanks Tony

As I started taking it apart I found 0 ohms across both double terminal blocks.
It is the terminal blocks themselves.
I must have ordered the wrong ones!

Back to the local electronics store for blocks and fuses!

Cheers
Mac

Click to expand...

I have had the same problem during the construction of my very first diy project , the api 312 ,
the terminal block was indeed a ground bus terminal and not a terminal itslef,
hope that is your problem as they say the easiest solution is always the best,
D

Hmmmmmm......chainsaw? ;D

Indeed that was the problem!
Two new terminal blocks and the power supply was perfect.
The sales person at the store had never seen one before so they cannot be too common.
For reference the part was Mouser 651-1868733 and is found at:
http://ca.mouser.com/ProductDetail/Phoenix-Contact/1868733/?qs=%2fha2pyFadui1lrDaV3wy6DeCg%252b2JcG%2fM85Z3RH3yEOu1yUJks5TlAw%3d%3d

Thanks....and back to finishing the microphone

Cheers
Mac

Thanks for pointing that out Mac!

Best,

Udo.

Well that was a tricky one.
The pdf datasheet of the part states "Connections internally jumpered" tough but you go with the looks of the
part sometimes so...

Anyway thanks for the link.


T.

Hello all!

Next newbie question...

About to print a mount to secure the pcb in an Equinox body.

There is quite a bit of extra room inside.

From either an electronic or balance/ergonomics perspective does it matter if the pcb is at the bottom, middle or top of the microphone body?

Thanks for the assistance

Cheers
Mac

Hello,
i have a problem with my mk47 U47. The first lets say 20 hours it works very fine but now i have very much noise on it after 15 minutes running (noise, pops, crackles) and i think the sound distort to fast at a higher SPL. So i measured the actual Voltage from the PSU while Mic was connected and it was dropped down to 85VDC, so something wrong here.

I made the PSU the same as the schematic from Max in this build thread (with choke), i use the t-bone SCT700 housing and cable (105VDC connected over two wires), the heater dropper have a good contact to the housing but it gets really hot but i think thats normal. Also the resistors in the PSU gets very hot.
Maybe someone has a idea?
Thank you and best regards,
Michael

Hi Michael,

so the voltage is 105Vdc is dropping after 15minutes to 85Vdc?
Do you have a spare set of tubes to try?

-max