MK47 PCB tube mic kit - build thread

[EvLoutonian]

Thanks Max!

 

[Treelady]

Power Supply test question.

Using the suggested R values for 1 - 4, I was getting 68 vDC. 
Jumpering R4 I got to 80 vDC. 
Chaging R3 and R4 to from 1k Ohms to 500 Ohms got me to 97 vDC. 

Can I jumper R3?  Or do I need something in there?  I don't want to burn up something.

Trying to get to 105 - 110 vDC.

Thanks!

 

[zayance]

That looks too low.
For a better view of the prob, please specify the power transformer you use, how you hooked it up etc... EDIT: AND measure the Mains you got where you've tested the PSU, probe inside the Mains hole, DMM set to AC.
And i assume that these values are when you test the PSU with a Dummy load of about 2.2K right? Not with the Mic attached.
We need to test the PSU before connecting to the Mic as previously mentionned here and on the Safety instruction i forwarded with the PSU.

 

[Treelady]

This is with a dummy load attached, using a Zayance PC board.

I'm located in the US.
I used the  TRIAD VPT230-110 wired on the primary/input side in SERIES.  Maybe I should have wired it in parallel??
for the Choke I used: TRIAD C-3X Choke

 

[zayance]

This is with a dummy load attached, using a Zayance PC board.

I'm located in the US.
I used the  TRIAD VPT230-110 wired on the primary/input side in SERIES.  Maybe I should have wired it in parallel??
for the Choke I used: TRIAD C-3X Choke

You mean on the Secondary right?
I've also forwarded a Power transformer wiring scheme, that you could have used for giving you an idea.
BUT this power transformer clearly states on the Technical documentation that

Primary  beeing Blue/Gray - Violet/Brown (check on the Toroidal itself to be sure about colours)

Series gives 230VAC
Parralel gives 115VAC (That's the MAINS you need beeing in the US.)


Secondary Black/red - Orange/Yellow (Check again)

Series gives 230VAC @0.11A (that's what you'd wire to the board)
Parralel gives 115VAC @ 0.22A won't use that configuration

 

[Treelady]

Here is how I have it wired NOW. 

These colors in the graphic match the legend printed on the side of my transformer, so the colors are correct for THIS discussion (and only this discussion unless you have the same exact transformer and are working in the US).

I have black and yellow going to board.  Red and Orange tied together.  I always had that, and I think that's fine.

Now I have Blue / Violet going to the load / power switch (I say load because there is a fuse in there...for safety).
The Grey and Brown are tied to the Neutral.

Thanks so much.  And Chunger did the graphic!

 

[Treelady]

Working now.  You need to add "if you do not sleep, do not try to wire the power supply..." to your notes.

 

[late]

Anyone have used ami body?

 

[EvLoutonian]

The PSU (Scott Hamptone) is wired as follows.  Pins 3 + 4 are common ground.  Shield also goes there from the connector.

1. audio+
2. audio-
3. Ground
4. Ground
5. +105vdc @ 50mA
6. Pattern


I wired my cable as follows:

XLR                                  TUCHEL

1 (A+) ----------------------  1 (A+)
2 (A-) -----------------------  2 (A-)
3                empty            3
4 (B-) --------blue----------  4 (B-)
5 (B+) --------red ---------- 5 (B+)
6 (P) ------------------------- 6 (48v pattern)
Tab -----Cable Shield-------- 7    ---    Bridged to Tab


Then inside the microphone on the male 7 pin binder I have the shield bridged to pin 4.  Pin 4 is then bridged to the mic rail.  Though, I'd like to confirm the wiring on the cable first before looking at the male binder.

Did you end up getting this all working satisfactorily, jrasia?
I was thinking of using your scheme above (and your attached graphic on page 36 of this thread) as a guide to work from..

Also, are people generally ending up with one pin spare (unconnected) in their 7 pin cable?


Thanks!
Evan.

 

[wave]

Evan,
Yes one pin will be unused in the 7 conductor cable.

Dave

 

[EvLoutonian]

Thanks for confirming this, Dave.

Would I be stretching the laws of reality in then thinking that perhaps, in this case, if I also had another U47 clone mic, but based around an EF80 tube (which additionally requires approx 6v. filament heater voltage) that I should select this unused pin for the filament voltage, making it safer if I should accidentally plug the wrong mic into the wrong supply?

Presumably the audio pins and B+ pins would be compatible between these two mic's I intend to build, but the heater voltage is a separate requirement on the EF80 circuit, and the 48v. pattern switch on the MK47 is something else I'd need to look at, as the EF80 circuit may simply have a mechanical switch on board, or alternatively variable pattern voltage supplied from the PSU.  So that's another thing to figure out what can be done.

I'm trying to think of a safe way to connect my cables up, in the (hopefully unlikely) event of this mis-match between PSU and mic happening, maybe something will not work quite right, but basically nothing dangerous or bad will happen.

I do intend to make both an EF80 type mic, based on the AMI circuit, as well as my MK47 - both using Skylar's Equinox body kit, and each will have the same Binder 7 pin connector at the base, so it's a real concern.

Has anyone encountered this same situation?

I'm hoping there's a way to connect up my pins on each supply / cable / mic, so that nothing would get damaged in the case of myself (or anyone else) getting this mixed up.  I'm not sure if there's enough pins available to achieve this, though.  Am I dreaming?


 

 

[HellfireStudios]

Thanks for confirming this, Dave.

Would I be stretching the laws of reality in then thinking that perhaps, in this case, if I also had another U47 clone mic, but based around an EF80 tube (which additionally requires approx 6v. filament heater voltage) that I should select this unused pin for the filament voltage, making it safer if I should accidentally plug the wrong mic into the wrong supply?

Presumably the audio pins and B+ pins would be compatible between these two mic's I intend to build, but the heater voltage is a separate requirement on the EF80 circuit, and the 48v. pattern switch on the MK47 is something else I'd need to look at, as the EF80 circuit may simply have a mechanical switch on board, or alternatively variable pattern voltage supplied from the PSU.  So that's another thing to figure out what can be done.

I'm trying to think of a safe way to connect my cables up, in the (hopefully unlikely) event of this mis-match between PSU and mic happening, maybe something will not work quite right, but basically nothing dangerous or bad will happen.

I do intend to make both an EF80 type mic, based on the AMI circuit, as well as my MK47 - both using Skylar's Equinox body kit, and each will have the same Binder 7 pin connector at the base, so it's a real concern.

Has anyone encountered this same situation?

I'm hoping there's a way to connect up my pins on each supply / cable / mic, so that nothing would get damaged in the case of myself (or anyone else) getting this mixed up.  I'm not sure if there's enough pins available to achieve this, though.  Am I dreaming?

Is there a 6-pin Binder connector out there? If so, putting the 6-pin on the MK47 would solve the problem of mismatching mics and power supplies. You could even have one with Binder one with XLR. Then, they could both be 7-pin.

-James-

 

[ioaudio]

agreed, i'd use different connectors.

 

[electrisizer]

hello there,

ive used the mk47 in different productions till now and really like what it does! espacially on male voices this mik shines...

theres one thing i would like to change. it has not very much highs! even if the highs sound good and smooth when eq is boosting the dedicated frequencies (in contrast to most cheap miks)... i would like to have the highs right there after recording

is there a resistor determining the highs in this circuit???

 

[chunger]

Which capsule is being used in your build?

hello there,

ive used the mk47 in different productions till now and really like what it does! espacially on male voices this mik shines...

theres one thing i would like to change. it has not very much highs! even if the highs sound good and smooth when eq is boosting the dedicated frequencies (in contrast to most cheap miks)... i would like to have the highs right there after recording

is there a resistor determining the highs in this circuit???

 

[ioaudio]

ive used the mk47 in different productions till now and really like what it does! espacially on male voices this mik shines...
theres one thing i would like to change. it has not very much highs! even if the highs sound good and smooth when eq is boosting the dedicated frequencies (in contrast to most cheap miks)... i would like to have the highs right there after recording
is there a resistor determining the highs in this circuit???

no,  in the u47 circuit everything's quite linear in the upper frequency domain - the presence should come from the capsule itself.

-max

 

[chunger]

Hi ioaudio,

I'm experiencing a bit of hiss in my mic build detailed in the "newbie builds" thread.  I have burned in tubes overnight and the issue remains.  Issue also persists with all of the 7 tubes I switched in (searching for least microphonic tubes in the batch).  The general sonic characteristic of the microphone seems good across frequencies, there is just an underlying hiss that is louder than I am comfortable with.

I'm checking in to see if you could walk me through a few diagnostic steps to try and isolate the problem.  I do not have my final capsule in hand yet so this is operating on a stock Alctron GT-2B capsule.

PSU is set to delivery 105.1V at B+.  I am not experiencing hum that i can detect, this is a low-level hissing that ramps up at power-up as the tubes come online it seems.  The grounding scheme is as follows:

at PSU:

PSU grounding bus to star ground
PSU 3 pin xlr pin1 to star ground
PSU 7 pin "audio ground" (pin 4 on my setup) to star ground
PSU 7 pin "ground" (pin 7 on my setup) connected to shield in cable and connect to star ground

in microphone:

B- connected to "ground" (pin 7)
"ground" (pin7), "audio ground" (pin 4), and chassis contact tab tied together at XLR jack.
Solid contact is made via screw between PCB and frame rail.

Cable is Gotham 7 conductor, but also tested with stock Chinese 7 pin cable with same result.  Pin 7 (ground) on my cable is connected to shield at both ends as well as one of the internal wires.

 

[dandeurloo]

I had noise at first as well.  I didn't have great connection of the mic Body back to the star ground.  Make sure that is happening properly. 

 

[ioaudio]

'chung,

it's probably capsule related as well: the capsule you use now might have a low output, expecially if it's designed to run on 80VDC polarisation (and now running on 60VDC)
Other than that, tubes often want a long burn in period (leave it turned on for three days at a 110VDC coming from the Psu)

-max

 

[chunger]

Thanks,

another forum member also recommended the following test:

"Here is a brute force test you can do:  disconnect the front diaphragm of the capsule, so that the only connection to the tube grid is the 100M pull-down resistor.  The mike should be dead quiet in this configuration
provided the tube itself is quiet.  Then, ground the grid of the tube directly to ground.  If the hiss goes away, you have grid current flowing through the 100M resistor and need to check to make sure there is no contact anywhere on
the PCB."

I'm hoping to implement this test later on tonight but need to know which pin is the grid on the 6028 tube?