AKG C414 EB P48 trouble

[ioaudio]

hi rossi,

i wonder if the coupling tant could have fried the transformer´s primary - even though i doubt it with the low currents in the mic - maybe caused by surge "in-rush" currents while pluggin in with phantom turned on?
did the broken wire looked something like melted?
-max

 

[Rossi]

Hi Max, no, didn't look melted as far as I could tell. But things were kind of sticky due to the adhesive tape. I would guess it was a mechanical thing. The broken wires were right beneath the tape. If it had been fried, I guess it could have happened anywhere within the coil.

Anyway, the mic is fine again, and it has that typical AKG C414 sound. Very solid midrange, some 80-ish edge in the 4k region. I find it quite ironic that the Viennese AKG has that in-your-face honesty, while the Neumanns from Berlin sound rather flattering. :grin:

 

[rroom]

I have an AKG C414 EB P48 with the same defect in the microphone Rossi, follow the same steps suggested by Gus, all ok tants, caps ok, I need the inductance of the transformer U54 because I'm thinking it is the same defect.

I appreciate the help

 

[Rossi]

No, you don't need inductance measurements. If your transformer has a broken wire like mine, all you have to do is measure the DCR of the various coils. Measure the primary, measure the secondary. Measure the upper half of the secondary to the center tap and measure the lower half of the secondary to the center tap.

If your transformer has a broken wire at least one of those measurements will show infinite resistance, or, if you have a short (which is unlikely), DCR is close to zero. 

I don't have the correct values at hand, but more or less "reasonable" values for the primary should be  below 2k (probably a lot below 2k, but I don't know the exact ratio, so it's hard to guess what would be "reasonable"). The secondary total DCR should be below 150 ohms and the two halves of the primary should be (close to) equal.

 

[rroom]

thanks for the help
I'll post progress soon

 

[MicDaddy]

Can someone share the characteristics of the self noise on power up with one of these?

I just put a new capsule on one EB p48, when phantom is applied the mic turns on with a second of sssshhhhh then goes dead quiet and sounds wonderful.  None of my other 414s do this, I do have some mics with interesting "power up" sound signature, this is a new one to me?  Not ruling out a fault but can anyone comment?

 

[Rossi]

Just checked my C418 EB P48. Mine does the swoosh-sound, too, on power-up.

 

[MicDaddy]

8)

Thank you so much, it sounded  to me like a normal operating kind of "noise" but I wanted to be sure.

I have some pencil condensers (gold diaphragms) that take a good few seconds to turn on, even some of my tube mics are faster.

 

[Rossi]

It's not so much a question of solid state or tube circuit. The turn on behavior mostly depends on the capsule bias scheme. Some mics use several filter stages, some use phantom voltage (which sometimes produces funny noises on power up), others use dc/dc converters of various designs. Also, some capsule hook-ups allow for a fairly low impedance bias path, other require a very large series resistance.

 

[ln76d]

My EB P48 acts exactly the same 

 

[gar381]

Mine does the same as well  &  always has for the last 20 years.

This is normal for this mike.

GARY

 

[J0hanne5]

I bought a broken c414 EB p48 to repair.  The seller said it sometimes works and sometimes not so it should be possible to repair. I checked tantals and they seems to be ok. I measured a trafo and the primary does not give any readings. That's the problem for sure. So my Q is: where to find a new trafo? Does someone know specs of the trafo?

 

[RuudNL]

Does it look like this one?
(This is a transformer for an AKG C414B-ULS)

 

[J0hanne5]

Does it look like this one?
(This is a transformer for an AKG C414B-ULS)

No, it does not. It has a yellow plastic wrap on windings.  I will peal the wrap off and check if it's similar to one from B-ULS or not.  A trafo of EB p48 has a center tap and that makes it difficult to replace with anything else than an original part.  Let's hope that a wire is broken just under the wrap and I can simply solder it back 


EDIT: I found service manuals: c414 EB p48  has an Ü54 transformer and  B-ULS has an Ü76 trafo.

 

[RuudNL]

If I remember correctly, the transformer is 2:1.
This seems to be confirmed by the slutz: https://www.gearslutz.com/board/6370609-post33.html

 

[J0hanne5]

Here is a trafo from an AKG c414 EB p48 (without a yellow plastic wrap).

The primary is between a blue and black wires those come from deep inside the transformer.  Not an easy fix...

Cinemag seems to have several mic output trafos. However, only one 2:1 ( CM-11021) and it does not have a CT. 

http://cinemag.biz/mic_output/mic_output.php
I am not an expert with mics and trafos so I would be mighty grateful if someone knows a suitable replacement trafo,

According to Cinemag some trafos are  "Center tapped for phantom power."  Maybe I can do some mods and use a trafo without a CT.  Any ideas?

 

[J0hanne5]

I bump this topic up just to tell that I finally repaired the mic 

I asked from Cinemag if they can make a CM-1211 with a CT and they did! Price was good too... Great company!

Only problem was that the Cinmemag was slighly larger than the original so I had to cut away a piece of the PCB and drill a hole in the body underneath the trafo. However, the mic works and sounds great now.

 

[Whoops]

I've only seen your thread today, it's a pitty because I would have advised you to send it to me or some other forum members to re-wire the transformer.

Glad you solved it but if you still want to have the original transformer rewinded or fixed you can send it to me

regards

 

[ArnoldLayne]

Hi !

I have one with a broken primary lead, can I send it to you ?  ;D

 

[Whoops]

Hi !

I have one with a broken primary lead, can I send it to you ?  ;D

PM me