Re: Gyraf G7 Help - 60 cycle hum

Hi all (and especially jakob),

So, it's all put together now.

60Hz hum.

Here's a clip. https://www.dropbox.com/s/yzuewsydq4no1vj/0001%201-Audio-1-5.wav

Any suggestions?

Notes:
1. I have an aluminum mic body
2. There was no grill mesh (capsule in the open air) because I'm still trying to find some...
3. I have heater ground tied to HT ground tied to audio ground tied to the chassis all inside the mic. The mic cable brings that ground back to the power supply, it is then connected to safety ground.

Cheers
Thanks a lot everyone,
Dan

look here:
http://groupdiy.com/index.php?topic=4762.0

Quote: We've had this question before. you can't measure those voltages. because of the high impedances.- Jakob E.


Thanks for the link! That helps a lot! But I don't think I quite understand why this is true. The DMM will inject a small current and because the impedances are so high it the current won't pass, giving incorrect voltage readings?

The voltmeter will act as a voltage divider
http://www.allaboutcircuits.com/vol_1/chpt_8/3.html

The rest of the pics

http://imgur.com/a/owkRV

aquitania said:

2. There was no grill mesh (capsule in the open air) because I'm still trying to find some...

Click to expand...

You have to have it. Crazy hum without it.

Grill, yes, that could be it.
Also, I don't see how the mic tube makes contact with ground, which it needs in order to work as a shield.

pasarski said:

aquitania said:

2. There was no grill mesh (capsule in the open air) because I'm still trying to find some...

Click to expand...

You have to have it. Crazy hum without it.

Click to expand...

hmm, I didn't think it would make that huge of a difference

Grill, yes, that could be it.
Also, I don't see how the mic tube makes contact with ground, which it needs in order to work as a shield.

Click to expand...

There's a connection from pin 1 to the threaded rods and on the top wooden ring (near the capsule) there's a piece of wire that pokes out and will rub against the aluminum

Hello,
As posted before You really need the WireMesh to shield the Capsule. For a try ,if the Amp is humfree , a empty Metallcan ,closed with aluminium Foil where it overlaps the mictube could be pulled over the Capsulehousing. Why did You use a wooden Endplate ? You can keep it like this but I would sandwich the Woodplate with some Metalldisc ! This gives You a solid Shield ,a better connection to the outer Mictube and a better central Groundpoint ,where all Groundings should be tied together. A "clamped" Connection can loose and may cause unwanted resistance ,that causes Hum because of different 0V References beetween them.I like the rest of the Design very much !
Greetings and good Luck
Lothar

Seem's there is a consensus. I'll work on getting my hands on some grille.
And the reason I used wood is because I'm better at working with it and I couldn't find a suitable piece of metal.

I'll post again when I'm done! Thanks for the help!