MK47 PCB tube mic kit - build thread

[JW]

Anybody else listen to my sound sample? I've tried two sets of tubes now. Next step is either try another set of tubes or try to clean the capsule (there is a bit of dust on it.) I don't really think it's a bad connection.

On the positive side, despite the cracklies, it sounds amazing. Definitely the best sounding condensor I've ever heard. I'm using Dales M7. In terms of brightness/darkness it's close to my AT4047 (maybe even incrementally darker) but it blows the 4047 away in terms of smoothness/three dimensionality/clarity/creaminess. And the 4047 is not a bad sounding mic.

For folks who aren't finished, you're going to love this mic. Thanks Max! You're a very generous man.

I just have to figure out what's up with the crackly sounds.

 

[Sredna]

Did you try with another capsule?

Dont try to clean the capsule if there's just some dust on it, you could damage it if you're not very careful.
Just some dust doesn't cause crackles, first when you get a layer with dust and some other things like
tobacco smoke, the contamination starts to leak.

Did you tested breathing at the diaphragm?

 

[ioaudio]

Be careful Re: cleaning the capsule!
The crackles in your sample sound like a tube during warming up. Leave your mic turned on for 24-48 (or even longer) hours and it should disappear.
thanks for your kind words!

 

[kante1603]

Anybody else listen to my sound sample? I've tried two sets of tubes now. Next step is either try another set of tubes or try to clean the capsule (there is a bit of dust on it.) I don't really think it's a bad connection.

I just have to figure out what's up with the crackly sounds.

Hello JW,

I´ve listened to it several times.To me it sounds like a cold solder point or some other bad connection in the audio path (not psu or so).
Can you explain if the crackles occur immediately after turning on the psu or after a while?Maybe it is something about temperature inside the mic when it is warmed up-the pcb will expand (right word?-sorry i´m german...) by some micrometers,it will even bend a bit.If so you might have a hairline-crack somewhere on the pcb.
You can try to use the mic while it is open,listen carefully with headphones and give it some soft(!) kicks or a little pressure to the pcb with something like a match or an other small piece of wooden or of plastic stuff (no conductive material please ) and of course you can move all accessible wires.

Move your connection cables too.

Is everything properly grounded?

As said-to me it sounds like "normal" audio crackles and I´m sure you´ll find that out.

Will you please report back when you´re done?

Good luck and best regards from germany,

Udo.

 

[JW]

Thanks guys.
It's getting better as the tubes age, so I imagine that's the issue. Time will tell.

Max, for verifying voltages, should I be looking for the same voltages in the same spots as on the original U47 schematic?
This is what I'm getting:
1. 105 VDC at B+ (good)
2. 35.7 VDC at the heater (U47 schematic specifies 36V here, so looks good)
3. 1.5 VDC  at the 27R resistor (U47 specifies 1.1V)
4. 5.7 VDC at the capsule backplate (U47 specifies 63V here)
5. 40.7 VDC before output cap (U47 specifies 34V here)

Should the capsule backplate voltage be this low?

 

[kante1603]

Thanks guys.
It's getting better as the tubes age, so I imagine that's the issue. Time will tell.

Max, for verifying voltages, should I be looking for the same voltages in the same spot as on the original U47 schematic?

Good to hear!

Udo.

 

[Sredna]

3. 1.5 VDC  at the 27R resistor (U47 specifies 1.1V)

U47 schematic specifies R3 as 29Ohm

4. 5.7 VDC at the capsule backplate (U47 specifies 63V here)
Should the capsule backplate voltage be this low?

You cant measure voltage with a normal DMM at the capsule, too high impendance.
Measure before R1 (100MOhm)

 

[drgrateful]

Hello, I'm about to build the PSU. I would like to know:

- What are you guys using for the pattern selection switch?
- What is a suitable led to use for LED1 in the schematics?

Thanks, Matteo

P.S.: for the switch, I was thinking about something nice like the one in the attached picture, but I don't really know where I could find it...

 

[ioaudio]

JW,

your voltages are OK except:

>> 3. 1.5 VDC  at the 27R resistor (U47 specifies 1.1V) << should be more like 1.2 to 1.3V, probably measurement error?

>> 4. 5.7 VDC at the capsule backplate (U47 specifies 63V here) << as said before, your multimeter is not suited to measure such a high impedance voltage source.

 

[JW]

Max, you're right. It was actually 1.35V at the 27R resistor.

Also, on the other side of the 100M resistor, the voltage is 55.5 VDC.

So, are these voltages good? The mic sounds great. I'm just wondering how close to the original U47 voltages we should be looking to be.

Now concerning my OTHER MK47, (let's call this one #2) which is only getting noise (both hiss and tube/microphonic/rattling noises):

I'm measuring very similar voltages to MK47 #1, except for right before the output capacitor, which is 48.2VDC (where the original U47 specifies +34VDC, and where MK47#1 measures 40.7V) 

Shouldn't I be hearing the mic working though, if I'm getting voltage right before the output capacitor?
I've re-soldered both the output capacitor pads and all the transformer pads. I even tried bypassing the output cap with another capacitor.

 

[Sredna]

Check/switch the tubes and check the wiring around the tube sockets.
Seems that the tubes are not drawing any current...

 

[living sounds]

The mic sounds fantastic! I build mine in an SCT-700 like body with the Beez Neez capsule. Replacing the 10m chinese cable with a short teflon-coated US military copper-silver cable for the audio signal made it sound even better (more high end, clarity). Had some problems with interference but solved that by wrapping lot's of copper wire around the mic side plug. Now the only 'problem' I have is that the mic is sort of noisy, but I guess this is to be expected with a tube mic.

Thanks for a great project! I can't imagine wanting a better sounding mic for vocals and acoustic guitar.

 

[madreza]

has anybody made a PSU PCB for that mic or not ?

 

[Sredna]

Not! 

 

[kante1603]

has anybody made a PSU PCB for that mic or not ?

Hello madreza,

I don´t think so-do it on veroboard.It´s an easy one-took me 15 minutes

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have fun,

Udo.

 

[Denyle Guitars]

I did mine on turret board and dropped the whole works into an ak47 ammo box. Still looking for a mortar shell for the mic body. ;D

 

[drgrateful]

I will (partly) answer myself, hoping I won't mislead me 

Hello, I'm about to build the PSU. I would like to know:

- What is a suitable led to use for LED1 in the schematics?

Any standard led should work: e.g., you could use this one: http://de.mouser.com/ProductDetail/Everlight/HLMP1700C6A0/?qs=sGAEpiMZZMs4quMj8r4lmqIS%2f%2ftkkeuM0AUUOdksOtY%3d

What are you guys using for the pattern selection switch?

Someone earlier mentioned that a Lorlin switch will do fine. However, a search at Mouser returns 96 matches:
http://it.mouser.com/Lorlin/Electromechanical/Switches/Rotary-Switches/_/N-5g2iZ1z0zlbu/
I am not familiar with these rotary switches, so I could really use some help in the choice... Anyone?

I also found this link good for "inspiration" (even though it refers to the MK7 PSU): http://wiki.nimbleswitch.com/MK7_PSU

 

[Winetree]

Wish someone would do a colorbook for the MK47 power supply
it's the only thing that stop me from hearing the built mics. even have the PSU cases.
Thanks for PSU PCB picture. Anything helps.  Looks like I'll venture out
from kitland and  go from scratch. ANY BOM.

 

[kante1603]

Wish someone would do a colorbook for the MK47 power supply
it's the only thing that stop me from hearing the built mics. even have the PSU cases.
Thanks for PSU PCB picture. Anything helps.  Looks like I'll venture out
from kitland and  go from scratch. ANY BOM.

BOM?

Look at the first post,there´s a schemo for the psu,all values are written there...just some single parts and a transformer...

The "open" traces simply mean that you have to choose which of the comonents you will use.

So this is what you need for the psu:

1*Mains transformer with a 200VAC secondary,rated at 100mAs
4*Diodes 1N4007,these form the rectifier
3* or 2* resitors,1kohm,5 Watts (if you like to use a choke,here it´s a TRIAD553-C-3x at 10H and 50mAs then you only need 2)
5*capacitors,electrolytic 47uF rated 400V
1* resistor 680 ohms or 300 ohms,5 Watts (you must choose when you´ve measured the output;it´s dependant on the transformer etc.,)
1*resistor 100kohms,1 Watt (pre-resistor for a led if you want one)
1*resistor 2,3kohms,5 Watts (this one is your load when in "test-mode"-it approximately represents the load of the mic while it is not connected as a precaution)
1*resistor 14kohms,1 Watt
1*resistor 12kohms,1 Watt
1*switch,whatever you like and what can handle the voltage (this is for pattern-choice between omni and cardioid)
some normal stuff like a board,some wires,standoffs etc.
1*mains switch,a fuse-holder with fuse (125mAs slowblow recommended)

Udo.

 

[Denyle Guitars]

I doubt any two psu will look the same. BTW, I used the Triad vtp230-110 mentioned earlier and needed a 1k5 resistor in place of the 680 to get the voltage down. Here's a few shots of mine. It's not pretty but it works.