MK47 PCB tube mic kit - build thread

[living sounds]

Try if you can lower the noise by shielding the plug micside with your hands. I had this problem and solved it with a lot of wire wound around the end of the mic cable.

 

[gemini86]

also remember to clean the circuit board of any burnt flux. that can cause hiss as well.

 

[madreza]

does anybody know how to use a CM-2461NiCo  in MK47 ?

( I just wanna compare ..... )

The problem is that I have 4 wires ..... and the tranny on the MK47 has 8 pins !

 

[crackerzot]

Try if you can lower the noise by shielding the plug micside with your hands. I had this problem and solved it with a lot of wire wound around the end of the mic cable.

This made no difference.  The noise I'm getting is very, very hard to hear and basically buried in the noise floor, but it's there and I need to address it.  I'm thinking it just might be one of the tubes. 

 

[living sounds]

Try if you can lower the noise by shielding the plug micside with your hands. I had this problem and solved it with a lot of wire wound around the end of the mic cable.

This made no difference.  The noise I'm getting is very, very hard to hear and basically buried in the noise floor, but it's there and I need to address it.  I'm thinking it just might be one of the tubes. 

Use a spectrum analyzer to determine what you're up against. I had noise in the audio band (fixed as described) and out of the audio band (fixed with a proper PSU enclosure).

 

[crackerzot]

I've isolated the noise to the P/S.  When I unplug the mic, I can still hear the hum/buzz/whatever at a very low level.  It might be the orientation of the toroidal transformer or it could be something else.  My friend who built it for me is going to troubleshoot and fix it.  Glad it isn't the mic! 

 

[kante1603]

I've isolated the noise to the P/S.  When I unplug the mic, I can still hear the hum/buzz/whatever at a very low level.  It might be the orientation of the toroidal transformer or it could be something else.  My friend who built it for me is going to troubleshoot and fix it.  Glad it isn't the mic! 

Hmmm...the pic is very dark,I can´t see much,but all of the ac wires including audio should be twisted and shortened to a propper length.Untwisted ac wires will generate magetic fields which can then be picked up by the audio wires;you feed this into a high gain circuit (your mic pre).You´ll notice this as hum.
Some more things left where we can look at,but only if we can see anything.
Maybe you can take some more with a flashlight from different perspectives?

Best,

Udo.

 

[crackerzot]

Thanks very much for that info. 

 

[kante1603]

Thanks very much for that info.   

You´re welcome.
And another thing-where are you located?Not for finding you but is it 50 or 60 Hz-country?
Just asking because if you hear 50(60) Hz the hum comes from before the rectifier,if 100(120)Hz is heard it´s after it then.
Looking at your pic I guess it´s before...mainly thinking of the wires to and from the trafo/power switch.

Best,

Udo.

 

[JW]

Can someone theorize on why not to use Canare star quad cable? The 4 conductors are 22awg copper. And the shield has a very tight braid. What is the reasoning for needing an extra ground wire?

 

[gemini86]

You've run all the current THROUGH the shield, which could be injected into your audio.

 

[kante1603]

Can someone theorize on why not to use Canare star quad cable? The 4 conductors are 22awg copper. And the shield has a very tight braid. What is the reasoning for needing an extra ground wire?

I haven´t heard of why not to use starquad-maybe I missed something here,but I´m too lazy to search at the moment.
I have heard somewhere arround here that somebody uses starquad.
Will give it a try on my build as I have a big spool of Gotham Audio Starquad cable.
I don´t see a reason for an extra ground wire as-looking at the schemos and on the pcb-the ground has direct connection to 0v and the microphone-housing via the mounting rails.
Compared this to my original SM69´s psu some minutes ago.The audio grounds,the psu´s 0v and the backplate(where the connectors go)-so the chassis- definetely connect to each other at one screw as to the mic-housing.
Still waiting for my frontpanels so I can´t tell if this works at the moment,but I´m pretty shure it will .
Someone here mounted the pcb with cable ties-this can cause problems if no ground-wire runs/connects to the mic body.

You've run all the current THROUGH the shield, which could be injected into your audio.

Yes,but this is dc current-if there´s no ripple then there´s nothing to inject to the audio.
Even if running a seperate wire for grounding:what to do with the cable screen?It must connect somewhere and this will be the chassis ground connected to 0v and so forth....if it doesn´t connect anywhere it is useless.
And something else.In a phantom powered mic the current runs through the shield too!

Best,

Udo.

 

[ioaudio]

for those interested, new batch is in: http://www.groupdiy.com/index.php?topic=35667.0

 

[Andy Meyer]

I just replaced the tubes in my mic and I am getting the same "wind" sound that I described in my earlier post.  The "wind" sound is much more noticeable in cardioid.  Does anybody have any ideas?

 

[crackerzot]

Andy,

Any chance of you posting a sample of your audio?  I'd like to hear what this "wind" noise sounds like.

 

[gemini86]

Can someone theorize on why not to use Canare star quad cable? The 4 conductors are 22awg copper. And the shield has a very tight braid. What is the reasoning for needing an extra ground wire?

I haven´t heard of why not to use starquad-maybe I missed something here,but I´m too lazy to search at the moment.
I have heard somewhere arround here that somebody uses starquad.
Will give it a try on my build as I have a big spool of Gotham Audio Starquad cable.
I don´t see a reason for an extra ground wire as-looking at the schemos and on the pcb-the ground has direct connection to 0v and the microphone-housing via the mounting rails.
Compared this to my original SM69´s psu some minutes ago.The audio grounds,the psu´s 0v and the backplate(where the connectors go)-so the chassis- definetely connect to each other at one screw as to the mic-housing.
Still waiting for my frontpanels so I can´t tell if this works at the moment,but I´m pretty shure it will .
Someone here mounted the pcb with cable ties-this can cause problems if no ground-wire runs/connects to the mic body.

You've run all the current THROUGH the shield, which could be injected into your audio.

Yes,but this is dc current-if there´s no ripple then there´s nothing to inject to the audio.
Even if running a seperate wire for grounding:what to do with the cable screen?It must connect somewhere and this will be the chassis ground connected to 0v and so forth....if it doesn´t connect anywhere it is useless.
And something else.In a phantom powered mic the current runs through the shield too!

Best,

Udo.

yes, it's DC current, in that it's traveling from A to B, but at varying currents. The current noise is small, but so is the audio signal. I was just explaining the school of thought there, may not necessarily be a problem.

 

[Andy Meyer]

I'll post a sample as soon as I can.

-Andy

 

[Andy Meyer]

Here is a link to a sound file of my problem.  The first part is the mic in Cardioid.  The second part is omni.

http://www.ziddu.com/download/14725165/U47NoiseTest.wav.html

 

[kante1603]

Here is a link to a sound file of my problem.  The first part is the mic in Cardioid.  The second part is omni.

http://www.ziddu.com/download/14725165/U47NoiseTest.wav.html

Strange-I hear the background noise and what you describe as "windy",don´t know what that is :'(
But the second part has more subsonics-are you shure that this part is the omni?

Udo.

 

[Andy Meyer]

The second clip is definitely omni. It has a lot less low end when speaking into it.