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[Fletcher]

We were talking at the shop about this yesterday when out of the blue one of our other "hi RF" clients called.  I had forgotten that I had suggested Canare L-4E6S ["star quad"] mic cables for his rig as an RF deterent... apparently, it worked very well for him [he's in the mid-west about 3/4's of a mile from an antennae farm].

[markyosh]

Thanks for your replies!

Fletcher - that sounds like the kind of renegade solution that a good engineer would come up with in a pinch!  I will keep that in mind.

Mr. Heyne - The sticker on the amp section seems to indicate that mine is a second revision circuit (930-02).  I will try buffing the housing's contact points shortly after the holidays!

I'll let you know how it worked!

[markyosh]

In response to Mr. Satz,

I'm sorry if you are irked by yet another post on RFI issues!  My original intentions were to find out about the capacitor modification my friend had told me about.  

[Barry Hufker]

Dear All,

Taking Oliver's advice, I now have a UM92.1S without coils and with a NOS Telefunken EF86 with Hilumin shield.  I have just listened to the microphone and must say I like it a lot better.  As Fletcher said, it is probably not a vocal mike choice, but I now see it as more useful than I had previously thought.

Many thanks to all who continually put up with my ignorance and equipment prejudice.  I learned a lot on this thread and got a better mike out of the deal!  I now look forward to hearing the other fine Gefell mikes you all mentioned.

Barry

[David Satz]

Markyosh, there's no irk. You had a real problem and no clear way to know that information about it was on tap, or where to go here for that information. That's just a fact of these forums--the software doesn't make a digest or topic summary of past threads readily available. There's only a list of thread titles which goes on for many pages, plus people don't stay on topic. Klaus has placed a number of "stickies" on page 1 but there's a limit to how many topics can be handled that way.

Proper shielding and grounding are best in general, but that is still a matter of playing the odds. In a pinch it's worth trying something now and then which may seem counterintuitive or even downright nonsensical, just to get through a session as well as you can. Later on, time can be taken to apply the proper measures--which may require modifying the shielding/grounding of consoles, preamps, recorders, etc.

I agree with Klaus' preference for Gotham/Neumann cable and for tying together the ground pin, the cable shield and the XLR connector shell at both ends of the cable. (Not incidentally, microphone cables from Schoeps follow the same scheme.) But there are some real-world situations in which some engineers have solved their RFI problems--at least for the moment--by using Canare star-quad cable, or by lifting the connection between the shell and pin 1 at one end of the cable. That isn't my experience but since each of our approaches has worked, neither of us can be altogether wrong.

To me, when one specific cable configuration or cable type must be used "or else," that tells me that the component on the receiving end of the signal may well have a "pin 1" problem. However, finding this out during a session is of little help, since one can't generally stop the session to modify the equipment to which the microphones are connected. So we are forced to become experts in a kind of rapid-response first aid. It should never be confused with the long-term treatment that is ultimately necessary, but it's still a vital skill.

[matucha]

Now what should I do, having a collection of old Gefells (UM57, 2xCMV563 with 2xM55K, 3xM8, 1xM7), nice stuff... but there is dilema, send it piece by piece to Gefell for restoration or sell it all and buy UM75 and maybe something else? I like the "forward" sound of the mics, but I don't like gritty HF they have.

Oliver (or anyone).. what is your guess for restoring (almost everything) in UM57 and in CMV563? $1000 in parts and $1000 in work?

Is it realistic to make them a world class mics or it is better to leave them as special character maker mic (this is what they do pretty well, but at that point they are a bit overpriced (??) )

Sending picture of guts of the UM57.  

[Barry Hufker]

Matous,

Thank you for sharing the photos.  I don't have an answer for you but it looks like a fairly simple circuit.  I am sure someone will say that if the capacitors are original, then the electrolytic ones should be replaced in the mike (and power supply if it is just as old).

What I notice most having just peered into the UM92 is that the transformer in the 57 is several times larger than that in the UM92.  I wonder if Oliver would also comment on that as transformers are a specialty of his.  I would think the xfmr in the 92 possibly doesn't do the mike justice.

Barry

[matucha]

I just got a new PSU and it is maybe better than original.

My general observation is everything is nice up to about 2-3kHz, very saturated in a good way, but then mostly in the area where the mic has HF bump it seems phasy and very difficult to EQ for good presence and smooth quality.
All gefell mics I have suffer from the same problems with any capsules I have. I'm trying to get rid of it and solve it for a long time so I'm walking in circles... one moment thinking it is ok, but then I want to sell it all and get modern mic .

Here is another photo with the PSU I bought.

[Barry Hufker]

The "presence" boost you mention is something else I have found hard to deal with in the 92 and is another one of the problems I was having with that mike.   At  www.Gefell-mic.com, the polar and frequency plots are identical for the 75 (the modern version of the 57) and the 92.  Yet, people on this thread have said the mikes sound very different and I have to believe them.

Yesterday while listening to the 92 after making the change I mentioned above, I liked the mike better but it still has the "presence" problem, which I am sure is similar to what you are talking about.  I like the 92 best in omni, then cardioid and then bidirectional (in that order).  The uses I envision are doublebass, percussion and (maybe) acoustic guitar.  Even Gefell's site doesn't list any suggested instrument miking for the 92 as they do for their other models.  The 92 is certainly different from everything else I own and maybe that's a good thing.  But I am glad I have the other mikes and that the 92 is not my only mike.

Despite the presence boost, which can be fairly harsh depending upon the pattern, there is still a wonderful "roundness" or pleasantness that must come from the M7 capsule.  I admit that over the years I have been tempted several times to cut the head off the 92 and put a larger "basket" around the capsule -- something more in the shape of an M49.

Barry

[matucha]

That's really funny, I can only agree. Omni pattern at my UM57 has most open and natural sounding HF. But (maybe it is the lack of proximity effect), there is too prominent midrange (500-1000kHz) then... it is very thick sounding, cool, but it is unnatural. Thats what I'm hearing when recording close miced speach. The worst sounding pattern is 8 (when speaking about silibance).

Well if it is grille, than why the CMV536+M7 has similar phasiness...

...sorry this is going nowhere without a PRO going through the mics and testing them I think.

I posted some samples at gearslutz, it is only an unemotional speaking for quick test, but gives general idea what am I speaking about. It is better and worse with different people talking. Talking loudly seems to make things worse almost in all cases, appearently it is increasing distortion that makes it less eq-able. These samples are of the less problematic cases.

http://www.gearslutz.com/board/showthread.php3?s=&thread id=24099&highlight=tubelife2

I'm curious what do you think about it.

[Barry Hufker]

Matous,

I have just downloaded and listened to your MP3 samples.  I listened to the 57 in cardioid, the 57 in omni and the CMV.  I did not listen to the EQ'd version.

Now I know what a 57 sounds like and I have to tell you it sounds pretty nice.  Now I know what Oliver meant when he said the two mikes are as different as the U47 and M49.  The 57 sounds *much* nicer than the 92.  While I liked the 57 in cardioid and omni, it is true for me that I too liked the increased bass of the 57 in cardioid.  This bass may not be "true" or "natural" but it is very nice and warm.  The omni may be more true and while it sounds good, there just is something really nice about the 57.

Now I also know why Oliver said the 75 would beat out a VM1.  It is because the VM1 is a more "clinical" sound with less bass than the 75 (57).  There truly is something wonderful about an M7 capsule.

Having said all this, I can say the 92 does not possess any of the wonderful qualities of your 57 samples.  It is a much thinner sound with a much more pronouced (and even harsh by comparison) presence peak.  I don't know how close you were to the microphone when you spoke.  I was 6 inches away (15.24 centimeters) and didn't get the bass response you did in cardioid.

If you want, I can email you my samples, but I don't want to upload them here.  I am pretty impressed with the sound of the 57.  It is more the sound I wanted to hear the first time I turned on the 92.

Barry

[matucha]

I was pretty close. Closer then 4" speaking very quietly. I'd like to hear your samples: zka4t(at)zka4t.com is my e-mail. There are 2 other voices I can send you for fuller picture.

I'd like to have wide cardiod with it, could be just fine, but that PSU is only switchable not sweepable ;(

[maxdimario]

The cmv mic sounds like it has either old electrolytics or a worn out tube, whatever the coupling caps are, you have to check them out.

otherwise it could be the transformer that has deteriorated or is magnetized in some way..

just routine maintainance

[Oliver Archut]

Hello Barry,

sorry for my late reply, x-mas and some other obligations...
First the modification or better EM/RF removal of the UM92.1S

Gefell did the RFI/EMI protection with a crow bar, and traded the very high noise rejection for the overall sound.
The protection is a sum of four individual L/C protection and one simple C protection. I assigned numbers to those components that are not indicated in the standard Gefell diagram.
Position 1 and 10 is the HF protections to eliminate the risk of stray fields (EM/RF) interference in the remote pattern circuit. This protection does not change the sound directly and does not need to be removed.
Position 2 and 9 is the B+ protection, it does not change the sound and won't cause a problem if left in the circuit.
Position 3/7 and 4/8 need to be removed, this protection circuit chokes the high end and introduces phase shift, depending on program material, load down of the following mic pre, etc.
Position 5 (in some mics there is an additional cap to ground) is for HF filtering in the filament circuit, does not need to be removed.
Position 6 a cathode by pass to remove HF inductive stray field as the same times as it acts as a (audio) high frequency by pass, that makes the mic quite nasal.

In general I remove all those filters and rely on good microphone cable (Klaus pointed out the superior HF rejection of the historic EMT double reusen design, found in some modern cables), with proper grounding scheme in the power sup. and interfacing equipment.

To address the "presence" boost, it mainly depends on circuit tree design, and secondary on the head design (the plexi HF deflector intergraded in the capsule holder comes to mind).
However, by changing the circuit over to the blue drawn, alternative x-former hook up, you should be able to reduce this effect. Were and why it was installed is a question of design philosophy, both ways have advantage and disadvantages, enough discussion material for an entire new post.

To answer your question about the size of the x-former, it depends mostly on the core, and the new 92 x-former works better than the best historic 57 x-former.

To answer the last of your question,
both mics the VM1 and UM75 are good recording mics in their own ways, but in my findings the UM75 (with HF filter removed) is a more universal recording tool, great for main stream rock/pop and contemporary.
Were the standard VM1 is more a specialty mic, orchestra, scoring etc; the reason why I use the superior word is that the capsules of the UM75 is the perfection of simplicity of movable condensers, the VM1 capsule on the other hand has some acoustic "gadgetry" that trades of sound is some respects. Than again is a matter of perspective.

Disclaimer: ONLY QUALIFIED PEOPLE SHOULD ATTEMPT TO REMOVE THE CIRCUIT, IT WILL VOID YOUR MANUFACTURES WARRANTY AND WILL KILL YOU OR THE MIC  IF YOU TRY IT ANYWAY WITHOUT PROPER TRAINING!

Please do not forget, to break the connection to the 1.5K resistor if you use the alternative x-former hook up.


Hope that answers your question...

Best regards,


(Edited 7/21/09 by Webmaster to relink image)

[matucha]

...funny I like the CMV sample best (!!!), but it is time to have them checked (maybe for the first time after 30-50 years!!)