G7 mic ... Big hum for now

[dukasound]

Hi
I had hum with one mesh (around 14x14). When I touch microphone near capsule hum gone and too when I put one more mesh around mike. I will add one inside.
Duka

 

[Jazzy_Pidjay]

:grin: :grin: :grin: :grin:

i'm happy, i have completely remove my 50Hz hum noise
with 2 improvements.

1- I have solder the shield of my microphone cable
to the ground/0vHT pins, inside it.

2- I have made a cap for the mic with the foam of microchips chips samples. This foam is conducting !

The mic is quiet !!! great

:thumb:

 

[bill raymond]

[quote author="gyraf"]Yes, the heater 0V, the chassis ground, the HT 0V, and the audio ground has to be connected. Preferably in the microphone.[/quote]

Jakob, why is it preferable to make this connection in the microphone, and not the power supply? It seems one could make the connection in the PSU and run one less wire between it and the mic.

Thanks, Bill

 

[gyraf]

Bill,

I found it to be quitest this way..

Jakob E.

 

[asm]

[quote author="Jazzy_Pidjay"]here is a comparaison between the noise
of the TLM103 and my G7.

http://img.photobucket.com/albums/v439/jazzy_pi/noisetlm103-g7.gif

Black : my G7
Red : Neumann TLM103

unfortunately the 120Hz noise is my PC. :?
(it's at the same level on the two graph but the black line mask the red line.)

we can clearly see the 50Hz pic, and little harmonics.

i have the .wav if anybody can share it ?[/quote]



what program is that? what kind of signal are you feeding to the caps? is your room soundproofed? what are you using to produce a tone?

:?

 

[Jazzy_Pidjay]

is the spectrum analysis of Sound Forge 6

there's no tone generator, and the mic is in the room
at about 2 meters of the pc. the preamp set very at very high gain.
the mic was not in the booth this time.

PS : the 120Hz noise was from my harddrive and when
i suspended it, the noise disappear.

 

[steppenwolf]

Hi Guys!

I'm actually building a G7 and even though I understood, that I need to connect all Ground traces in the microfone, I still don't get the point.
Looking on the schematic I have following ground wires: heating 0V
Pin 1 Ground
Chassis Ground


But where do I have to connect those traces, directly at the 7 Pole socket on the mic? If so, why do I have to take a 7 pole wire, if I would need only 5 with all the Grounds connected.
Actually, I have a 7 wires + shield mic cable by sommer cable...where do I connect the shield anyway? On "normal" XLR Connectors, the shield acts like the ground wire an is both connected to pin 1 and to the chassis conecting pin...

Moreover, In the Psu Unit, I have again two different Grounds to different wires, but why seperating them, when they are anyway unified in the mic?

And what about the safety Ground from the 230VAC Wall to the PSU . If I connect the signal ground to all the mentioned wires in the mic, I get a hum loop, right?

Sorry for bugging guys, but I'm really getting headache over this and I need some help... :?

Greets, Stefan

 

[ioaudio]

hey stefan,

i´ve seen various grounding tactics for tube microphones. the g7´s approach seems to follow the star grounding scheme, with the pin 1 of the mic´s xlr as star ground (somebody pls correct me when i´m wrong here) where signal and heater ground are referenced. following the rules of a proper star ground, safety ground should theoretically also be connected at the same place (at the mic) which could be done with the screen of the cable.
search for star ground. thinking about ground loops make my brain hurt as well...

for the record i use 5-pin xlr´s successfully with tube mics which do not require a seperate line for switching patterns, so heater and signal ground share one wire. looking at the schematics of classic tube microphones, i realize that most models share heater/signal ground.

-max