Gefell Owners/Users - What you need to know....

[drBill]

If you've ever had RF or grounding problems, you need to read this.

I bought 9 used Gefell's about 6 months ago and have had intermittant strange grounding and RF noise with them. Out of the 9 mics, (UM70's, M71S's, 692/M70's), 8 of them were problematic, and strangely enough 1 was always OK. AND ONLY IN MY STUDIO. Everywhere else they were OK. All my other condensers and dynamics are fine at my studio. (Neumann, AKG, Shure, Audix, EV, Sennheiser, etc.)

I tried everything. Got many suggestions here. None worked out They still made the noise - and intermittent to make things worse. I talked with Jim Williams and he told me that they were junk and told me to off them on ebay. I didn't want to give up on them yet, so I kept hunting. I don't want to get into all the details about what I tried right now, but a search would give you the background.

Anyway, I talked with a scoring engineer buddy of mine and he did some research for me and talked to a guy that made "pigtail fixes" for gefell's.

Basically, on the F XLR that plugs into the mic, you remove the shield (Pin 1) and tie it to the little loop on the chassis of the plug at the top. (Switchcraft style) I tried it and was amazed. It dropped the noise floor into the basement. It made the mics useable again. Needless to say...I am one happy camper.

File that away in case you ever have a problem with your Gefells at another studio. Well worth soldering up a few pigtails just in case.



Thanks Bobby!

[The Byre]

It's not just Geffels that suffer from this problem. There are all sorts of shielding and grounding issues that occur and this gets worse with tube-valve based stuff that uses switched (so-called digital) universal power supplies. These dreadful devices cause similar interference to ground loops, but at all kinds of differing freaquencies that can have you shooting off looking for the fault in all the wrong places.

[danasti]

Originally Posted by drBill

Anyway, I talked with a scoring engineer buddy of mine and he did some research for me and talked to a guy that made "pigtail fixes" for gefell's.

Basically, on the F XLR that plugs into the mic, you remove the shield (Pin 1) and tie it to the little loop on the chassis of the plug at the top. (Switchcraft style) I tried it and was amazed. It dropped the noise floor into the basement. It made the mics useable again. Needless to say...I am one happy camper.

Nice - Great information! Thanks for sharing this. It's great for you and the mics that it was such an easy solution and nothing seriously wrong with the internals.

Enjoy them!

[mahasandi]

Damn


I sent 2 UM70K'S to CABLETEK .

and after some $$$ (perhpas too much) they replaced the xlr connectors.

this would have been a hell of alot more convienent and less $.

Thanks for this though ,

it's helpful news I hadn't and i'am sure many others

hadn't heard .

[C/G]

[QUOTE=drBill;1153433]If you've ever had RF or grounding problems, you need to read this.


Anyway, I talked with a scoring engineer buddy of mine and he did some research for me and talked to a guy that made "pigtail fixes" for gefell's.

Basically, on the F XLR that plugs into the mic, you remove the shield (Pin 1) and tie it to the little loop on the chassis of the plug at the top. (Switchcraft style) I tried it and was amazed. It dropped the noise floor into the basement. It made the mics useable again. Needless to say...I am one happy camper.

File that away in case you ever have a problem with your Gefells at another studio. Well worth soldering up a few pigtails just in case.

[QUOTE]

Interesting and thanks. I've not encountered any noise yet but if I do I'll do what you suggest. My old MV692 pair run off the old Gefell power supply and 7-pin cables so maybe that is why I have never had noise issues.

[drBill]

Thanks guys. I hope it's helpful to some of us at some point in time. I know there are other people who have encountered this, because I had heard rumors of this mod and had talked to those who could never figure their problems out.

It was very curious that almost all the mics reacted the same way. I knew there must be a solution. As weird as it sounds, the above configuration completely solved it and now I'm happy as a clam!

I've never encountered it with any other mics, but I certainly see the possibility out there. The Gefells are well made, but they must have a bizzare grounding scheme going on internally. Maybe using chassis instead of internal ground??

FYI, the mics are most likely late 80's models that are transformer balanced.

[Mike Jasper]

Originally Posted by C/G

I've not encountered any noise yet but if I do I'll do what you suggest. My old MV692 pair run off the old Gefell power supply and 7-pin cables so maybe that is why I have never had noise issues.

Fortunately, I haven't had any trouble either and I've used the MV692 with Tuchel and phantom power as well as the XLR P48s.

This is EXACTLY what Gearslutz is for.

Good job, doc.

Jasper

[chribble]

bill I'm getting RF problems with my mic again

Would you care to take a photo of the fix you have done just so I make sure I am doing it correctly?

Thanks

[Rutger]

It is the AES standard to have the chassis connected to pin 1.

[drBill]

Originally Posted by chribble

bill I'm getting RF problems with my mic again

Would you care to take a photo of the fix you have done just so I make sure I am doing it correctly?

Thanks

Hi Chris,

not where I can get to those cables and a camera, All I can say is, the M end of the mic cord is normal, the F end that plugs into the mic is what gets modded.

On a SWITCHCRAFT type plug (not sure exactly how neutriks are set up right now...) pins 2 & 3 are connected as per normal. Pin 1 - ground - is DISCONNECTED from pin 1 and is soldered to the little loop tab that sticks out and is connected to the chassis / setscrew. Hope that helps.

bp

[mig27]

Thanks for the hint, will try this at home..

[Jim Williams]

Older UM70's did not have any rf traps on the outputs, they forgot to add them. You can add them without adding large aftermarket pigtails.

Solder a pair of .022 uf caps from pin 2 and 3 to pin 1 on the internal XLR connector. Keep the leads short as they can rectify rf via lead inductance. To eliminate that use a pair of .022 uf mono ceramic surface mount caps and solder them to the XLR connector.

Jim Williams
Audio Upgrades

[beats workin']

i had the same issue when i owned a pair of KM184s. made special cables - labelled just for those mics. eventually got rid of the mics. better solution.
david

[John Willett]

I am now switching over to Neutrik EMC XLR connectors.

The EMC-XLR Series is a specifically designed version of the XX series to give enhanced RF screening for critical applications in live performance and recording where there are particular problems with radio transmission or mobile phones. The design guarantees a continuous RF shield connection from the cable to the chassis connector housing via a circular capacitor around the cable shield. An EMI suppression ferrite bead between pin 1 and the cable screen provides a low-pass filter for improved RF rejection.

Excellent.

[aquaMat]

Thanks for the info.

Although I have to say - I own quite a few Neumann East / Gefell mics and never had a problem like this !!

[drBill]

Seems to be location dependant. So if you travel with your mics, it's not a bad idea to have a couple pigtails just in case. BTW, all my Gefell's are probably early '90's models.

Cheers,

bp

[Mike Jasper]

Beau Thorne recently did the cable mod and provided good instructions and photos. I'll post them here.
-------------------------------------

Dr. Bill said:

"On a SWITCHCRAFT type plug (not sure exactly how neutriks are set up right now...) pins 2 & 3 are connected as per normal. Pin 1 - ground - is DISCONNECTED from pin 1 and is soldered to the little loop tab that sticks out and is connected to the chassis / setscrew."

The shielding wire is the twisted silver one, connected to the terminal of pin 1. The brass tab is connected to that set screw, which you can then back out in order to make contact with the reassembled casing. [See First Two "Before" Photos]

When the twisted silver wire is soldered to the brass tab, the silverish solder covers the brass of the tab. [See Last Two "After" Photos]. Works!