MK47 PCB tube mic kit - build thread

[mrcase]

thanks. sorted it out.
somehow the cable soldered to A+ lost contact. I resoldered it and all is fine now!
phew!

cheers
martin

 

[evanmurphy]

JamesW,
Your PSU looks killer! Any chance you could snap a photo of your point to point work from above when you have some time? I'm about to do mine on turret board the same way, but I'm still a bit of a newbie. I think I've got it all figured out based on the schem but it'd be nice to have something to compare it to when I'm done.

Deeply appreciate it if you do get around to it!

-E

 

[drgrateful]

The solution proposed by JamesW a few posts above for the 1k5 resistor seems very clean and I would like to follow it. The resistor is Mouser#71-RH0051K500FC02

However, ordering just that from Mouser would be expensive in terms of shipping fee (I am in Italy). Could anybody suggest where I could source that resistor in Europe?

Matteo

 

[JamesW]

JamesW,
Your PSU looks killer! Any chance you could snap a photo of your point to point work from above when you have some time? I'm about to do mine on turret board the same way, but I'm still a bit of a newbie. I think I've got it all figured out based on the schem but it'd be nice to have something to compare it to when I'm done.

Deeply appreciate it if you do get around to it!

-E

This is the best view I have as the mic is in service.

The solution proposed by JamesW a few posts above for the 1k5 resistor seems very clean and I would like to follow it. The resistor is Mouser#71-RH0051K500FC02

However, ordering just that from Mouser would be expensive in terms of shipping fee (I am in Italy). Could anybody suggest where I could source that resistor in Europe?

Matteo

Please be advised that these small package resister needs to be bolted down to help dissipate the heat. This worked well on the Equinox mic base and I also used thermal paste.

 

[drgrateful]

]Please be advised that these small package resister needs to be bolted down to help dissipate the heat. This worked well on the Equinox mic base and I also used thermal paste.

Thanks JamesW, I also have an EQU47 mic body . For bolting down the resistor, did you use self-threading screws or had to first drill holes and then use a tap?

Also, could anybody please look at the following voltages? In the PSU, I am measuring the following voltages, between center pole of the pattern switch (i.e. the end of the 14k resistor) and ground, with no mic attached:

- mic dummy load switched in, pattern relay switch off:  46V
- mic dummy load switched in, pattern relay switch on (omni): 105V
- mic dummy load switched out, pattern relay switch off: 118V
- mic dummy load switched out, pattern relay switch on (omni): 296V

By pattern relay switch off I mean: continuity between the 14k and 12k resistors, so that, if I understand correctly, the mic is *not* in omni.

Am I in the ballpark?

 

[evanmurphy]

JamesW,
Your PSU looks killer! Any chance you could snap a photo of your point to point work from above when you have some time? I'm about to do mine on turret board the same way, but I'm still a bit of a newbie. I think I've got it all figured out based on the schem but it'd be nice to have something to compare it to when I'm done.

Deeply appreciate it if you do get around to it!

-E

This is the best view I have as the mic is in service.

This is more than helpful, thank you kindly!

 

[drgrateful]

I think I need some help in wiring the PSU. Hoping this will also be helpful to others, I drew the image attached, starting from an image posted earlier. I am going to use a 7 pin connector and GAC-7 cable. Is this wiring correct? My main doubt concerns the best way for the shield, B- and the audio ground to reach 0V...

Thanks, Matteo

 

[poctop]

Hi There would someone know if the Original U47 tube had a impedance out switch 50-200,
what would be the config off Max traffo off the board 50-200,
any comments,
thanks Dan,

 

[poctop]

Got it Sorry can't read anymore  :-\
D

 

[poctop]

Hi to All, ,  just some experimentation with my finish build i dont know if it works now PSU warming up,
i have installed all 10W and my 1K runs at 85deg C and my final dropping wich is 1.5K runs at 115 degC  the %W pot runs at about 60degC
i also used a 10W heater dropper and my casing is arround 40degC , this is after running for about 1H,
Cheers, 

 

[poctop]

Hi there ,  i fired the thing up and yes marvelous potential but there is a small issue i cannot explain ,  the output is great but i have do have some humming only in the cardiod pattern but no hum in the omni pattern has someone had issue similar to this one the mic pcb attach point is grounded to the mic body and then runs trough the cable shield to the 0V of the PSU ,  would my problem would be the fact that i am running trough the shield or something stupid i am missing if that would be the case then i would expect both pattern to hum the same ?

Any Help ? or suggestions,
Thanks
Dany,

 

[poctop]

Well it seems my back diaprhagme  is not working either in omni , hope it is related,

 

[drgrateful]

I made some more research about how to wire the GAC-7 cable. I came across this interesting discussion on GAC-3 cables, that also applies to GAC-7:

http://www.gearslutz.com/board/geekslutz-forum/474307-what-i-hope-exhaustive-thread-soldering-gotham-gac-3-a.html

In summary, the suggestion (even if not completely unanimous) is (the sentence refers to three pin XLRs):

"Cable shield and cable ground (where provided, as in GAC 3) must be connected to pin 1 on both connectors AND to the sleeves (metal housings) of BOTH connectors" (Klaus Heyne)

So, translating to the GAC-7 and the seven pin connector where, according to the suggestions above, audio ground is connected to the center pin, we should connect the audio ground (green) to the center pin and the shield to the connector shell, and then jumper to the center pin. This should be done at both ends.

Since, even in the discussion above, there seem to be some caveats for this configuration, I would like to know what others are doing here. Also:

- For connecting A+ and A-, in the PSU,  between the seven pin female connector and the three pin female XLR, are you using twisted wires, or shielded wires, as in the picture I posted above?
- For RF interference, do you find clamp on ferrite chokes useful in our case?

I think discussing these details might save some headaches. They are far from obvious (at least for me) and they seem to be important.

 

[poctop]

So finally found the problem :  wich is bad power supply case design with hole at not the right logical spot hence the Omni Cardiod switch shall not be on the same side as the power and test Switch,    So AC power was too near of the Car-omni switch making it humm in the audio when switch off,  So the story is put you pattern switch on the output-input side, the mike is working perfectly in cardiod, with no buzz Nor hum,   

the onlything that i find is that the omni pattern sound a bit weak from the back,  i checked the 48 and the relay operation and it is all fine,  i will try another capsule to find out more,

Cheers,
Dan ,

 

[0dbfs]

You can do another capsule to test or you can also reverse the leads to see if the issue follows front/back.
Another capsule may have the "same problem" too.

Cheers,
jb

 

[poctop]

Thanks,  0dbfs,

I am starting to think this is all my head now,  i tried reversing the lead but i am not sure the problems follow ,  time to take a rest 
that pattern switch-ac-humm-too-near-when-off thing just sucked my brain ,  i have Max transfo for now i will try a CM2461NiCo somtime soon,

Cheers,
D

 

[Denyle Guitars]

I think I need some help in wiring the PSU. Hoping this will also be helpful to others, I drew the image attached, starting from an image posted earlier. I am going to use a 7 pin connector and GAC-7 cable. Is this wiring correct? My main doubt concerns the best way for the shield, B- and the audio ground to reach 0V...

Thanks, Matteo

That's more or less how I did mine, although there's some redundancy in your drawing. Assuming the pattern switch is near the XLR connectors, just take the wires from the switch to 7p connector.  Since your using GAC-7, you can also ground pin 4, same as pin 3, for the same reason. Not sure how much noise reduction it'll net. I used Mogami cable that was previously made up for another mic, so I wired mine accordingly.

Here's another shot of mine.

 

[poctop]

Hi All, i tried CM2461NiCo and i like Max trafo still it sounds more neumann to me ,  and also anyone know about that bypass russian cap
is this one on the original used ? worthed to try an orange drop there ,  ?

D

 

[drgrateful]

Assuming the pattern switch is near the XLR connectors, just take the wires from the switch to 7p connector.

Yes, I thought it would have been more clear the way I drew it, but you are probably right: I updated the wiring diagram.

Since your using GAC-7, you can also ground pin 4, same as pin 3, for the same reason.

I hadn't thought of that. Thanks for the suggestion.

 

[drgrateful]

I have to correct my post above with voltage readings. I had set the PSU pot so that the B+ voltage was 105v, but without having continuity between the 12k and 14k resistors (the pattern switch confused me). So, don't make my same mistake: the PSU pot has to be set while having continuity between the 14k and 12k resistors. Now, these are my readings (between the center pole of the pattern switch, i.e. the end of the 14k resistor, and ground, with no mic attached):

- mic dummy load switched in, pattern relay switch off:  48V
- mic dummy load switched in, pattern relay switch on (omni): 110V
- mic dummy load switched out, pattern relay switch off: 120V
- mic dummy load switched out, pattern relay switch on (omni): 299V