MK47 PCB tube mic kit - build thread

[grantlack]

Haha well I just had an epiphany and found my gremlin, I had improv'ed a crimp/insulation displacement/solderless XLR onto the signal leads since I don't have any female DB25's at my disposal. Used the same one for both tests. The insulation on the - lead was left intact. DUH. Sounding like a dream now!

 

[bobine]

I used the Hammond 513-0900

Length    8.63 in
Width: 4.75 in
Height: 3.5 in


the steel is no fun

 

[BladeSG]

Does anyone know if the generic Beezneez PSU will work with this MK47?

 

[jordan s]

She's finished! No pops, clicks or hums. So far from testing this out at home, all is well and it sounds great. Just burning it in for a few days now. I can't wait to get this in the studio. I used the aforementioned $50 spider shock mount from ebay but it needed some modifications. I removed the thick foam and put in some thinner felt but the mic still wouldn't fit so I removed the original screws, sawed off the the thumbscrew part from the threading and JB Welded them on to longer hex screws. So far it's holding up well.

 

[grantlack]

as i look at the u48 schematic, it appears that the fig8 pattern was accomplished by simply switching a 1nF cap into the signal path between the membranes.  any reason the same approach couldn't be taken in the mk47?  the execution would be simple enough, it's just a matter of whether it would behave the same.  i tend to find omni to be less useful in my day-to-day work.

 

[Marc Duchesne]

Finished my MK47 in an Equinox body and capsule. Good combination...
Guys, this mic sounds just hands down gorgeous...

I pumped it into a seventh circle N72 pre (neve design) direct to the converters, I am just stumped with the 3D sound of my vocal, which is not the greatest by the way... Wow. I am very impressed.

The construction went straight forward, no glitches, just silent at 50% level on the mic pre.

You will be impressed with it. I will try to upload some sound samples of a good singer to let you evaluate.

Now, I am waiting for my LA2A case...

Regards,
-marc

 

[Marc Duchesne]

Few notes:
- The B- and the XLR pin 1 (XLR ground) will both go to same ground.

- When you are testing the 48VDC patern voltage, flip the switch to omni side (so the 14K and 12 resistors have continuity between them) and measure the 48VDC voltage across the 12Kohms resistor and ground (the 12K resistor really represent the mic patern relay coil impedance load simulation) it took me a while to figure this one out. So, don't go measure this one on the patern output lead going to the mic, you will get 105 VDC (unloaded) or 0VDC switched out, which is normal.

-Make sure you replace your multimeter battery... (Stupid me)...

Regards !
-marc

 

[Marc Duchesne]

Jordan, I did purchase a Pelluso shockmount that I have not received yet (the mount seems the same as yours). Wondering if I will have to modify it. I have the same capsule / body as you.

 

[jordan s]

One more question before I close this up for good. My led is pretty dim. After the 100k resistor it's only getting 1.6V. Would it adversely affect anything to put a different resistor here to get a brighter led?

 

[lonepariah]

Does anyone know if the AMI U47 PSU (or any other U47 PSU) will work with the MK47?

 

[mad.ax]

as i look at the u48 schematic, it appears that the fig8 pattern was accomplished by simply switching a 1nF cap into the signal path between the membranes.  any reason the same approach couldn't be taken in the mk47?  the execution would be simple enough, it's just a matter of whether it would behave the same.  i tend to find omni to be less useful in my day-to-day work.

If your plan is to make a MK48 (sacrifice the omni patern to favor a figure 8 ) it's doable.
Pay attention to the U48 schematic. It's not just a matter of adding a cap and a resistor, you also need to modify the voltage divider.
In the U47 the 2M/3M extract 60V from the 105V PSU in order to polarize the front of the capsule. If you'd polarize the back with 105V, you wouldn't get a real figure 8 pattern (cause you'd need 120V). So for the U48 they changed the voltage divider  to 3M/3M. That gives 52.5V to the front, and then 105V at the back is right.
You can do the same with the MK47. Just keep in mind that, just like with a real U48, you'll loose a bit of sensitivity because of the lower polarization voltage.

Axel

 

[Marc Duchesne]

Jordan S:
One more question before I close this up for good. My led is pretty dim. After the 100k resistor it's only getting 1.6V. Would it adversely affect anything to put a different resistor here to get a brighter led?


I have a red LED that I extended beside the poser switch at front. Mine is bright enough.  I have 680 ohms and 100K  resistor into the circuit. May be use a different LED although a led is pretty straight forward... Your resistor is same as mine wright...

-marc

 

[zayance]

Jordan S:
One more question before I close this up for good. My led is pretty dim. After the 100k resistor it's only getting 1.6V. Would it adversely affect anything to put a different resistor here to get a brighter led?


I have a red LED that I extended beside the poser switch at front. Mine is bright enough.  I have 680 ohms and 100K  resistor into the circuit. May be use a different LED although a led is pretty straight forward... Your resistor is same as mine wright...

-marc

It's a little normal to be dimmed, U=RI tells us you get only about 1.5mA to the LED at 105V (3mA at 300V) not much (Actually corrected my stupid calculation mistake on one of my reply to Madreza's post, a moment of "woops"), but it lights, most used Light Bulb, more authentic...
But of course you can tweak the LED resistor of 100K here, it's DIY, just use U=RI and P=UI for both loaded and unloaded HT for safety....

 

[Marc Duchesne]

I just ordered one of these. Though they were nice for a pop filter...

The one I ordered is front aluminium and black at the back.

http://www.thehookstudios.com/filters.html

Will let you know how they work out...

Marc

 

[jrasia]

Need opinions of mounting the 1k5 resistor 'heater' from MK47 kit.
Looks like Max is using a slight different resistor than the one pictured in the build.
Is it wise to mount this resistor to the side rail, or is it advised to mount is only to the end cap of the mic body(equ47)?  The side rail would prevent me from having to extented the leads, but I wonder if it would cause interference or other issues leaking into the the PCB. Also, could I 'fasten' the resistor using an epoxy instead of using a brass plate to keep it down?  Just how hot does this thing get?

Lastly, can someone PLEASE provide the proper pinout for the 7 pin connector to the MK47?  Can't seem to find on here.  The build is going nicely I just need these last issues clarified.

Thanks

Jason

 

[zayance]

Is it wise to mount this resistor to the side rail, or is it advised to mount is only to the end cap of the mic body(equ47)?

I'd say up to you, and testing it,  Aluminium may be better at dissipating tough....

could I 'fasten' the resistor using an epoxy instead of using a brass plate to keep it down?  Just how hot does this thing get?

Not a good idea in my opinion, when you say Epoxy, you mean gluing it?
First Epoxy won't have a good mechanical attachement in case of whatever,
And will crackle or come apart with time, it's a mic, lots of things will happen
to it in studio......
I think this one heats up a little, so even that won't make the epoxy last forever,
even if it can take up some heat on paper...
And the epoxy Chemical may damage the resistor in time? Just a tought here....

I'd go for brass or aluminium plate, and a screw with a secured washer....
Leads isolated of course....

But i'm not an expert...

 

[jordan s]

I epoxied a small aluminum tab on to the side of the end cap to hold the resistor in place. If the worst thing that happens is the tab coming off, the resistor is pretty much held into place by tension from the leads anyway so I'm not too worried about it.

 

[zayance]

Need opinions of mounting the 1k5 resistor 'heater' from MK47 kit.

I epoxied a small aluminum tab on to the side of the end cap to hold the resistor in place. If the worst thing that happens is the tab coming off, the resistor is pretty much held into place by tension from the leads anyway so I'm not too worried about it.

Not much left for opinions , cool that it works for you, it's DIY whatever fits best your needs, tools, preferences etc.....As long as it works and does what it's suppose to do....1....2....1....2....check....ssssss....p..p...p...p...p

 

[Marc Duchesne]

Need opinions of mounting the 1k5 resistor 'heater' from MK47 kit.
Looks like Max is using a slight different resistor than the one pictured in the build.
Is it wise to mount this resistor to the side rail, or is it advised to mount is only to the end cap of the mic body(equ47)?  The side rail would prevent me from having to extented the leads, but I wonder if it would cause interference or other issues leaking into the the PCB. Also, could I 'fasten' the resistor using an epoxy instead of using a brass plate to keep it down?  Just how hot does this thing get?

---Dont use epoxy, make yourself a nice little U shaped bracket and install it on the side rail to hold the resistor. You can also use some silicone to hold the U bracket on the body side rail. Could also put some thermal grease underneat the resistor. 

Lastly, can someone PLEASE provide the proper pinout for the 7 pin connector to the MK47?  Can't seem to find on here.  The build is going nicely I just need these last issues clarified.

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.

 

[JamesW]

I bolted an wirewound chassis mount resistors  Mouser#71-RH0051K500FC02 to the end cap worked great