MK47 PCB tube mic kit - build thread

[HellfireStudios]

thanks for clearing that up braeden.

btw, does anyone know how to perfectly drill the two diagonal screw holes for D-series XLR chassis connections?
i ALWAYS seem to f**k them up.
yesterday i spent two 90mins routing and dremeling two perfect xlr holes for in-chassis mounting just to mess up the screw holes which i thought would be the easiest part. what's the trick?

Make the holes a bit bigger than needed. Then, use bolts and nuts to secure the XLR. The larger holes will allow for some wiggle room with regards to placement/alignment.

-James-

 

[useme2305]

.. audio+, audio-,  48v (Pattern Switch) and 105V (B+). ground (B- in this project) goes to shield.

Thanks.. I guess what I wasn't too clear on is whether B- has its own core (or just travels on the shield), and whether audio ground also shares the same shield.  I got the impression some people have a separate individual core for some of these functions, but as I say, I wasn't sure one way or the other.

well, as far as i understood it audio ground and B- are pretty much the same thing here...that is: ground.
from reading the thread i got the idea that some people seem to separate each and use 7 pin cables just to run into ground loop problems when they finish the project and detach either on the mic side of the cable. so i thought why not use a 5 pin cable.

 

[useme2305]

thanks for clearing that up braeden.

btw, does anyone know how to perfectly drill the two diagonal screw holes for D-series XLR chassis connections?
i ALWAYS seem to f**k them up.
yesterday i spent two 90mins routing and dremeling two perfect xlr holes for in-chassis mounting just to mess up the screw holes which i thought would be the easiest part. what's the trick?

Make the holes a bit bigger than needed. Then, use bolts and nuts to secure the XLR. The larger holes will allow for some wiggle room with regards to placement/alignment.

-James-

yeah, unfortunately bigger holes are out of question here since i went for the mounting option from the inside of the chassis. which i find just looks neater.

see here:

notice how the screw holes are totally messed up?

i guess this thread is not the place for this type of question. i'm just not handy with the tools i have. i just thought there'd be a trick.

 

[HellfireStudios]

thanks for clearing that up braeden.

btw, does anyone know how to perfectly drill the two diagonal screw holes for D-series XLR chassis connections?
i ALWAYS seem to f**k them up.
yesterday i spent two 90mins routing and dremeling two perfect xlr holes for in-chassis mounting just to mess up the screw holes which i thought would be the easiest part. what's the trick?

Make the holes a bit bigger than needed. Then, use bolts and nuts to secure the XLR. The larger holes will allow for some wiggle room with regards to placement/alignment.

-James-

yeah, unfortunately bigger holes are out of question here since i went for the mounting option from the inside of the chassis. which i find just looks neater.

see here:

notice how the screw holes are totally messed up?

i guess this thread is not the place for this type of question. i'm just not handy with the tools i have. i just thought there'd be a trick.

Panel mounting XLR's is a real pain. I even tried finding a XLR template on google(no luck, though). Larger-headed bolts or finish washers could save the day, though. You could also paint the bolts/washers to match your panel for a clean look.

-James-

 

[Sredna]

The XLR connectors are the templates! 

First make the big hole with preferably a greenle hole-punch then put the XLR connector in place with the flange on the outside and mark the small holes with a fine pen (CD-marker).
Use a pointy tool to make a dent exactly in the middle of the marking and either use a drill bit with a smaller diameter for a guide hole or start with the final diameter. Always measure twice! 

 

[useme2305]

yeah, that doesn't work. the xlr's shafts are too big for the holes.

EDIT:

sry, i meant they are too small for the holes...which means there too much room for them to wiggle.

 

[Sredna]

Not really, put more effort in it! 

 

[North]

I just finished my build and tested last night and the mic is dead quiet with virtually no noise floor. I used Gotham GAC7 (could have gone with 6) for my cable and wired it as pins 1and 2 = A+ and A-, pin 3= B-, pin 4 =empty, pin 5 =B+, pin 6 =Pattern, pin 7 ground, tabs on cable connectors=shield. Pins 7 and 3 should be united at both ends to ground. I have always treated the shield as a separate entity and connect its beginning and end to the tabs on the male and female cable connector ends of whatever cable I am making. Then I connect the receptacle tabs to case ground in the power supply and in the mic. Pin 3 caries B- to the mic's pcb but I also use pin 7 as a chassis ground so I connect pin 7 to a mic rail and the mic rail to the B- pad. Therefore I have an electrical ground, chassis/case ground and a shield ground. The shield is always used as a cable wire encasement... "shield" for RF in that any RF that is introduced to the system is carried to ground. So far this has worked for me over decades. If you are experiencing a noticeable noise floor, I would look at the grounding scheme. This mic really is dead quiet

 

[useme2305]

yup, it's dead quiet.....after some stressful building last night i just patched together some case grounding from the connectors with some alligator test cords. but i was already too tired to really judge the recordings i made with the mic last night cause i head some serious tidying ahead of me before i was going to go to bed. the build was a real mess.

i listened to the recordings from last night today and it's just a little ambient noise which i mistook for mic noise. the mic is perfectly quiet.

so now i firmly soldered all the ground wires and assembled the psu casing with all its screws and stuff and it's super quiet.
plus, the mic has a VERY high output. wow....not much gain needed at all for even quiet whispered singing.

btw, the thomann 5-pin dmx cable is good for this build if you need a cable quick and cheap get this, guys.
i might replace it with sommer tube mic cable some day...but i might also not.

 

[braeden]

The best way to drill those XLRs is to download Front Designer (from frontpanelexpress.com) or Schaeffer AG (Europe/Deutschland).

Measure the height & width of your drill surface, get the datasheets for all of your components (e.g. toggle switch, XLRs etc.) and draw them out in FrontDesign.

There are already 'macros' or pre-made XLR objects that can be dragged into your Front Design project. I know for a fact that the Neutrik D series is in there somewhere.

Then you just print it out (with reference points so you know where to centre punch & drill), glue it or tape it to your drill surface and go nuts.

As there isn't really any drill bit for the XLR cutout I use a stepped drill bit which goes to around 32mm I think. The XLR is around 25mm or something.

An M3 drill bit usually does the XLR holes quite nicely. If you want you can tap them by drilling a M2.5 hole first (I think anyway) then tap the thread with the correct plug.

 

[EvLoutonian]

...So far this has worked for me over decades...

Thanks for the nice detailed explanation of your cable wiring procedure, North.  This has been baffling me a bit for a while.
 
useme2305's system, using less strands, grabbed my attention, as I was hoping to find a way to make two cables compatible between two different mic's/PSU's, each using the Binder connector at the mic end, that will not harm either mic if it's plugged into the wrong supply. 

Both mic's will use the Equinox body, and I have the BINDER connectors to suit these now, so it would be fantastic if I could find a risk-free way to make up these cables to suit each of the mic's in question, but also not pose a risk to the other if muddled up.

The first mic is the MK47, of course, whilst the "other" mic will be an EF800 based "EF47" type mic, based on the AMI circuit.  Both have the same 105v B+ voltage (and of course audio +/-) but the EF800 circuit has the additional requirement of a separate 6v heater supply, and the variable capsule polarization is supplied directly from the PSU rather than the fixed 48v relay switching.

So, with the Mogami 3172 cable that I have (6 conductors plus shield) I have been grappling with how this precautionary compatibility could be achieved to avoid any nasty accidents happening to one or the other mic down the line one day..

I will be most grateful for some input on this, as the next thing I need to do is wire up these connections before completing my MK47 build!

I made up the table below to try to figure it all out:
(Based on the 7 pin connector scheme used on the Neumann M250)


PIN          MK47        (common)       EF800 / 'EF47'
1                                  Audio -
2                                  Audio +
3                                                        Pattern (variable 0-60v?)
4                                                        Heater 6v+
5                                  105v B+
6              Pattern 48v
7                                  0v, & chassis/ground


A few questions:

*Do I need a separate dedicated conductor in the "EF47" mic cable for low voltage filament (H-) ?

*Could it damage the MK47 relay if I accidentally fed it the 0-60v from the other mic supply (or vice-versa), or could these voltages safely be common on pin 3?  (which would free up one more pin for something else)

*Is it beneficial to have the B- on its own pin as well?  Or is it fine on the shield?

THANKS IN ADVANCE!
Evan

 

[useme2305]

i think with a 7 core plus shield cord it's definitely doable.

one tip:
if you want to avoid an accidental mix up between the two mics' cables why don't you use a different connector on the psu side to avoid this. say, 5pin vs 7pin xlr.
plus, label your cables properly?

 

[Treelady]

Although you can wire the mic cable any way you want to, there is a "sort" of standard for the U47/tube mics:


Audio (+) = White
Audio (-) = Black
Ground = Thick blue
Heater = Thick Red
B+ = Yellow
0-120v (variable pattern) = Green
snip the remaining conductor (gray), and you are done
And make sure that you terminate shield on both connectors to ground and connector sleeves. [/i][/list]


I want to state I got this from a post by Klaus Heyne, so I don't want to take credit for coming up with it or anything. 

 

[EvLoutonian]

  ..If you want to avoid an accidental mix up between the two mics' cables why don't you use a different connector on the psu side to avoid this?

Hehe.. thanks, UseMe..

I did think of this (and it seems to be an obvious solution)..
- but then of course the BINDER connectors at the mic end are still the same, so you could still plug the wrong mic into the wrong cable / PSU combo.

I will however make the plugs different on each power supply anyway, to distinguish one cable from the other..  But I want to make it foolproof, in case someone else is using the mic's one day, for example, or I make the mistake myself somehow..

I could put a label on each mic (and another hanging off the connector end of each cable) saying "WARNING: Check that this is mic UNIT 1, connecting to CABLE 1", etc.. but it will look pretty ugly if it's gonna be big enough to be effective!  Seems a shame to put a whopping big label on my lovely MK47 body if I don't need to.

If I can do it eloquently (and functionally) in the way that I make up the cables, that would be my preference.

 

[North]

Hi Ev, I'm not completely clear on what you want to achieve. If its cable pooling, I use mix and match cables all the time. You just want to be sure that all pins on the male cable end correspond with the same pins on the female end. Colors don't matter in a cable as long as they are not crossed. I never do pin jumping in my cable's connectors. I perform all "jumping" in my psu or my mic leaving only straight through wiring in my cables. I use Gotham cable but as far as the 2 larger gauged wires, I always use one for B+ and the other for B- as they are carrying the voltage and in my opinion is safer to do than using a smaller gauge for B- and a larger for heater. Some may think its a waste but B- is just as vital as B+ and I don't want to impede my electrical ground. I also connect ALL wires in my cables to pins. This way in one setup I can use for example pin 4 as heater but used in another setup, pin 4 is not connected in the psu so its unseen and therefore interchangeable. Now as far as accidentally mismatching psu's that's a good one. If you customize cable connections then they are no longer interchangeable and you are back to square one. The absolute safest thing to do is use different size and type Binder female ends on the power supplies and corresponding mating cable connectors so connecting to the the wrong psu's are impossible. Binder has a ton of options. hope this helps a little

 

[EvLoutonian]

Hi Ev, I'm not completely clear on what you want to achieve...

Thanks again for your on-the-point response, NORTH.
Much appreciated!

I wasn't referring to changing pin correlation at each end of the cable.

Perhaps a better way for me to explain my objective, in response to your points, is:

Can I set up the pin connections on my two different power supplies (one for MK47, the other for EF800 mic) so that neither mic will suffer if accidentally plugged in to the wrong supply?

You could therefore think of the table in my earlier post as simply referring to the PIN OUT on the PSU if you like. 

Each cable would be pretty much identical I guess - pin to pin straight through connections.

I would absolutely just use different connectors on the two mic's, if it were that easy, but the Equinox bodies I'm using (for both projects) are already so eloquently set up for (& supplied with) the BINDER 7 pin male connector.  And now I also finally tracked down the Binder female connectors to match.  So it seems a bit of a shame to hack one of the bodies and use a different type of connector, even if I could think of a way to do that.

I'm hoping there are enough pins available to share not only the common requirements, but also the separate requirements of each mic, between the 7 pins available, so that, as you say, if one or two pins are only to be used on one mic or the other, they can just remain disconnected at the input connection on the other mic.

Hmm, does that make more sense?  It's kind of harder to explain than I'd hoped. haha.

The way I see it is that I could simply interchange PSU's for these two mic's, except that the pattern voltage is different (MK47 48v vs EF-AMI 0-60v, I think), and the EF800 tube requires 6v heater pin(s), which would need to be unused in the MK47 mic itself.

Do I have enough pins that I can keep these discrepancies separated?

 

[North]

Not that I can tell. I may be overlooking something here but It looks like you will have at least one charged pin directed to the wrong mic if accidentally plugged in. Even if you use shield as a separate path you would still introduce noise at some point and would have to constantly be moving your cable around like an antenna to get away from it. One way to accomplish no accidents would be to use a male 7 pin receptacle on one of the power supplies. One of your cables would be the normal female and male ends while the other would have female and female connectors. That way its physically impossible to mismatch psu's?

 

[EvLoutonian]

That's the point I made earlier, which is that you could still plug the wrong mic into the (female) Binder connector of the "wrong" cable (no matter which PSU the other end is plugged correctly into).. if you know what I mean?

Is the 'antenna' effect you mentioned caused from B- being on the shield only?

Would it be an improvement to have the pattern voltages both on the same PIN, freeing up another PIN for the B-?

PIN          MK47        (common)       EF800 / 'EF47'
1                                  Audio -
2                                  Audio +
3              0 / 48v          Pattern          0 / 60v (?)
4                  -                                    Heater+ (6v)
5                                  B+ 105v
6                                  B-      0v
7                    Chassis/ground & 0v Heater-

In cardioid setting, would both mic's see 0v at the pattern select pin?
(might be the safest way to leave the PSU's when stored)

With my 6 core cable I realise also I literally don't even have another conductor available for an independent Heater- voltage (for the EF800 mic).  Is that a problem?  Or is it okay to have the H- shared on the B- pin &/or shield pin?

..hmmmm..  am I the only one with this issue?  Or have others tried to crack this nut too?

 

[HellfireStudios]

It is not a great idea to put a male jack on the power supply. High voltage is going to those pins. If someone were to turn it on without a mic attached, and touch one of the xposed pins, the results would be less than ideal (unless funeral planning is what you do for a living).

Another type of jack would be preferable in this application. I would use an XLR for one the power supply end of one cable. You could then use 6 pin for one cable, 7 pin for another, Binder for another, and so on...

-James-

 

[0dbfs]

I would add that one should label each end of your cables, your mic's, and your psu's (serial #'s?).... That way when you have more than one similar mic-system, System-components can then be swapped to help troubleshoot "intermittent or sporadic" issues.

Cheers!
-jb