ln76d

AKG C414EB P48 repair and restoration little help needed!!
« on: October 11, 2012, 04:59:13 PM »
I bought an not properly working AKG C414EB P48.
From what i know, this mike was serviced in akg service in my location - with worse result than before.
If it's true, that's horrible, that they employ total idiots, which truly dont know how to use soldering iron.
First of all, the "serviceman" destroyed diaphragm of capsule back side - dropping solder tin on it.
I've already changed the diaphragm.
Looks good, but 100% sure will be when i rebuild rest of the circuit and test it.
There's a lot of sh*tty points on a pcb and all looks horrible.
In my 414 is 2SK2118 FET instead 2SK30. I found info, that they're same. I don't know it's an original placed FET or it was changed later.
2SK30 should be "O" type with idss 0,6~1,4. On 2SK118 is only 024C - did it means that 0 is equal to O? Or for peace of mind buy a new one 2SK30-O? They aren't cheap :)


ln76d

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #1 on: October 11, 2012, 05:41:48 PM »
Ok, now typical questions about capacitors :D
I really want to refresh this 414, but truly i don't want to change original sound character.
I know that new caps, don't change at much character but sometimes things can go wrong.
I've marked non electrolytic caps on schematic, so if someone could look on a placement of those and their strategic role -  i'll be thankful.

First - i want to change all electrolytics.
Original are typical dry tantalum electrolytics.
Should i put here typical "good" electrolytics with low esr or use new tantals?
Both types have some better and worse sides.
Did those caps types wouldn't have biggest impact on sound, when changing them?

Next one - ceramics - there's a few - should i put some silver mica caps or mkt, mkp instead of them ? I've marked them on schematic as green.

Two red WIMA, probably old mkt - put the new one mks2 or use mkp/fkp? Marked red.

There are a two polycarbonate, yellow, Wima (FC) - put instead of them mks2 (which in wima spec are substitutes)? Marked  - Yellow
I've read somewhere, that they sounds hi and harsh?

I saw a few pictures of pcbs in this model. There are two weird caps looks like glass type, but on photos from the net looks like some polistiren (stiroflex) caps? C1 from schematic, on photo from the net, looks like same type as that two weird C2, C3. On my is a ceramic type.
Use here silver mica? I've marked them as blue

I want to change almost all resistors, except four "carbon" high resistance types (no idea where get new ones). Probably i'll use low noise beyshlag or vishay or dale resistors. Shouldn't affect sound character i think, but maybe will be better noise performance.

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #2 on: October 12, 2012, 02:25:23 AM »
C1, 2 & 3 are NPO/COG ceramics; the BEST capacitors for these positions.  C13 & 14 should be changed to NPO/COG ceramics if you can get ones of the correct value & voltage to fit.  Otherwise leave alone.

Do what you want with the other capacitors & resistors but don't damage the PCB.

Clean all your soldering scrupulously with 100% ethanol and air dry when you finish.  No flux residues.

Get the diaphragm tension on the one you replaced checked so it matches the other one.
« Last Edit: October 12, 2012, 03:30:03 PM by ricardo »

ln76d

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #3 on: October 12, 2012, 09:55:16 AM »
C1, 2 & 3 are NPO/COG ceramics; the BEST capacitors for these positions.  C13 & 14 should be changed to NPO/COG ceramics if you can get ones of the correct value & voltage to fit.  Otherwise leave alone.

Do what you want with the other capacitors & resistors but don't damage the PCB.

Clean it all your soldering scrupulously with 100% ethanol and air dry when you finish.  No flux residues.

Get the diaphragm tension on the one you replaced checked so it matches the other one.

Thank You Ricardo for help.
Truly NPO/COG? I've always thinking that ceramic caps are worst option... They have worst temperature stability etc.
I didn't found any photo of other EB P48 witch ceramics on C1,C2,C3 but only some looking like polistyren foil caps.
Could you write something more, why you think, that ceramics will be BEST?
Silver mica wouldn't be better? These have really good parameters, same as polistyren...
Why don't use mks or mkp instead polycarbonate C13 and C14?

About soldering and cleaning PCB i know a lot,  i've soldered many types of gear.
There's no option to change tension of diaphragm - it's modular teflon CK12 (like on every P48 model) - looks everything fine - for now.

Two more questions :D

What use for cleaning diaphragm? What kind of alcohol? I think, that should be something very "light".

What type of paint would be best for headbasket grill? Something in spray will be best, but no areograph, because i haven't.
Acrylic spray paint and nitro markers don't do a job, because they stays on hands...

HellfireStudios

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #4 on: October 12, 2012, 10:49:23 AM »
NPO/COG ceramics are not your everyday ceramic cap. As I have yet to try them out, I can only say that others here give them high praise.

DO NOT CLEAN THE CAPSULE/DIAPHRAGM WITH ALCOHOL. The alcohol is for cleaning the PCB of flux, dirt, and oils. The cleaning alcohol should be as pure as possible. They tend to add witch hazel to isopropyl alcohol to poison it basically, but it leaves behind a white residue when it dries. I belive distilled water and an artist's brush are used by Neumann to clean diaphragms, but only as a last ditch effort before changing to a new skin.

Spray paint usually will work to paint a mic. If you can isolate the headbasket grill, prime it, paint it, bake the color coat(s), clear coat it, and bake on the clear coat(s). After about a week, the paint should be hardened and cured.

-James-
"Tommorrow is just yesterday in reverse. Just like friends are enemies in reverse." -Gary Busey

ln76d

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #5 on: October 12, 2012, 11:25:47 AM »
Thank You James!

Yes, i know that npo/cog are not same as usual ceramic caps but i didn't know that they're worth anything.
I was thinking to buy pure alcohol and mix it with destilled water, but if You say that destilled water will be good, i'll try. There's a little dust and one small finger print. Nothing hard to remove.

A year ago i've painted one sennheiser grill with typical acrylic spray.
Even now, when i'm taking mike to hand, it sometime leaves a black trail on skin.
It happens when the hand is heat.
I was thinking about epoxy spray paint - anyone tried?
I need to  paint only one side of headbasket - the black one.
It's no problem to disassemble the whole headbasket with all layers.
I've done that first for reshape some bends on it.

On a photo - those are these two weird glass bastards  - C2 and C3
« Last Edit: October 12, 2012, 11:37:42 AM by ln76d »

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #6 on: October 12, 2012, 03:50:55 PM »
Truly NPO/COG? ... They have worst temperature stability etc .... Could you write something more, why you think, that ceramics will be BEST?
Silver mica wouldn't be better? These have really good parameters, same as polistyren
http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=153&start=2
also p8 of http://www.johnhardyco.com/pdf/990.pdf

Guru Scott Wurcer has a series of articles in Linear Audio on LN mike preamps.  He measures silver mica & polystyrenes.  Silver mica are noisy and polystyrenes microphonic.  If you like that in your mike, use them.


Quote
What use for cleaning diaphragm? What kind of alcohol? I think, that should be something very "light".
Don't use ANY liquid on the diaphragm.  Fingerprints don't affect performance.  Any liquid will carry contaminants under the diaphragm and the mike will be forever noisy or susceptible to humidity.  You will need a new capsule; not just new diaphragms.

If you are annoyed about dust, use a very soft make up brush and brush very gently to remove loose surface stuff.  Even this is likely to damage the diaphragm if you are not versed in the art.

If anything is sticking, don't try to remove it.
« Last Edit: October 13, 2012, 05:19:28 PM by ricardo »

ln76d

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #7 on: October 13, 2012, 08:47:04 AM »
Much thanks for those links Ricardo!!
Those articles are awsome!

Cyril Bateman not rejected silver micas and polistiren caps, as he wrote some micas are noisy (or something lika that :) ) - so probably i was lucky, because i've recapped lot of stuff with them :)  Also he recomended polisteine caps, but not all are equal.
Shame i don't have acess to Scott Wurcer articles...

I've measured those Wima FKC in my circuit, and they keep their capacitance, so i'll stay with them. Red MKS2 i'll change for the newer ones.
For electrolytics i will use new tantalum.
Rest probably will be C0P, if i get them. It isn't easy to get them - most of internet shops in my country, don't specify which is the dielectric type - ceramic is ceramic :)

Any ideas on FETs issue from my first post?

I've looked on several Toshiba 2SK118 photos, and they have clearly written types - "R", "Y" "O" etc.
On my is only some code, which means nothing to me  - "024C" ? Any ideas? It's internal manufacturer code, or it should mean something for the consumer?

Truly i have some experience with very sensitive and weak materials like diaphragms, but maybe you're right, i'll stay like it is now.

ln76d

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #8 on: October 14, 2012, 05:39:37 PM »
Now the wires part:)

I have very nice teflon insulated copper and silver wires.
Wires in my c414, especially connecting capsule to the circuit, are pretty odd, bended etc.
Is it much difference, when i use a little bit thiner or thicker wires?
I have no oportunity to measure cross section of original and my wires, but on first look they are similar.
Measuring insulation have no sense, because teflon is thicker.

gyraf

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #9 on: October 16, 2012, 04:48:25 AM »
It is unclear to me what you are trying to achieve here - is the mic not working?

Jakob E.

..note to self: don't let Harman run your company..


ln76d

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #10 on: October 16, 2012, 06:39:25 AM »
It is unclear to me what you are trying to achieve here - is the mic not working?

Jakob E.

Really thank you Jakob for interest!

When i bought microphone it was working, but it doesn't sounds like C414.

Someone try to repair this mike, but with very weak result.

Based upon schematic i want to make this mike like "new".
I'm really not sure that 2sk2118 FET is original soldered or not.
AKG manual says that should be "O" type, so if it's original should be a good type, but if someone unprofessional change the FET, he could use FET with different idss.
If AKG mark this on manual - i think it's important for the circuit.
All FETs and bipolar transistors should be in working order - if not, microphone should not working at all - i think.
As i write before, i've replaced the diaphragm which was destroyed, now i'm on the way to buy new resistors and capacitors.

Thanks again to Ricardo for good articles about capacitors :)

Original wires are in weak condition - that means they are really bended, with breaks in insulation etc - looks like for all of those years it was repaired a few times.
Since my knowledge in condenser capsules is poor, i really want to know if the wires thickness, in very small differences, is so important. Is the micro differences in resistance or capacitance will affect on capsule works - does it matter at all?
If someone have good source of knowledge about microphone capsules - i'll be very happy for articles or book titles. Every articles i've found, describes basic information only.
I'm doing this mostly to learn something new and get of this as much knowledge as possible. Have a good working microphone it's important too and i will don't say it's not, but this is on second plane for me.
I hope it's understandable now.

gyraf

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #11 on: October 19, 2012, 08:03:18 AM »
it doesn't sounds like C414

Have you considered that there is no two versions of the ck12 capsule that sounds the same?

If you have approximately the right output level from the mic, I would not start changing parts. Circuit is quite complex and sensitive.

If possible, maybe try with a different, known-working capsule?

If you haven't gone through it yet, I'd recommend Saturn-sound's 414 primer: http://www.saturn-sound.com/Curio%27s/story%20of%20the%20akg%20c414.htm

Jakob E.
..note to self: don't let Harman run your company..

ln76d

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #12 on: October 19, 2012, 08:26:03 AM »
Taknk you again Jakob:)

Yes i've read saturn-sound c414 articles.

I know that there's few types of teflon CK12.

Diaphragm which i use was from same capsule type i think.

I have few of them and i know that they looks different inside.

These two ck12, which i use to get one working, looks identical inside.

Some of parts inside circuit are not genuine, and are soldered very carelessly.

Truly i have no idea what was changed (and by who) in all those years.

There's some ceramics instead polysteryne, missing one tantal cap etc.

If there are some cheap ceramics added later i think It would not hurt to replace them by NP0 - i think.

I really don't know what was main issue of this mike.

Front diaphragm sounds like the backward diaphragm and the backward distorts probably by the tin solder on it.

With the DIY in heart i'll try :)

When i'm done i'll record few sound clips and i post here.

Today i'll get new parts so i should finish soon.

What do you think about wires change?
« Last Edit: October 19, 2012, 08:37:13 AM by ln76d »

ln76d

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #13 on: October 20, 2012, 01:01:55 PM »
I replaced resistors except 2x27MΩ and 3x1GΩ.
I replaced all tantalum and ceramic capacitors, C2 and C3 both kept capacitance so they stay.
I put new ptfe coated wires - only on both switches are original wires

I made two mistakes!
First, i connected capsule backwards - same as it was soldered when i bought this mic - that's why front diaphragm sounds like backward.
Second mistake was reversed polarity of C11.
Then sounds thin without low frequency response but with huge hum on 48Hz.
I've put new C11, this time with proper polarity and capsule with proper connection.

Still is huge hum on 48Hz.
Changing positions at all 3 switches, sometimes very loud crackles.
Switching polar patterns is weird.
When switching between omnidirectional and cardioid there's no sound for few seconds at all.
There's a grounding problem too, enclosure is very sensitive to touch.

I checked all connections, everything seems be as on schematic.

Where i do mistake or what could be the cause?

Maybe new diaphragm have not proper contact?



ln76d

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #14 on: October 20, 2012, 02:09:29 PM »
i checked transformer DC resistance, looks fine.

Primary - 1,38kΩ
Secondary - 50Ω
Cennter tap - both sides 25Ω

ln76d

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #15 on: October 20, 2012, 10:15:55 PM »
Hum problem solved!

It was bad connection inside capsule.

Now microphone sounds clear without any hum and distortion.

Pattern switch still have loud crackles.

There's a big difference between polar patterns - in brightnes and output level.

Still, when changing between omni and cardiod, sound disappear for +/-3 seconds.

What this can be?

Overall output level is pretty high.

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #16 on: October 21, 2012, 07:40:24 AM »
Hi. There's so many questions this topic has raised in my mind. What do you mean by front diaphgram sounds like back? Both sides should sound the same. And you said you replaced the diaphgram. You did it yourself? I think there are only couple of people in the world that can do it properly. And tin on the diaphgram? No capacitor change will fix that. You really should test the mic with a proper capsule before proceeding any further.

ln76d

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #17 on: October 21, 2012, 08:56:55 AM »
Hi. There's so many questions this topic has raised in my mind. What do you mean by front diaphgram sounds like back? Both sides should sound the same.

Hi,
no they shouldn't  sounds same.

 "For reasons of clarity, the above drawings did not show one of the most important item that helps to control the "Acoustic" properties of the capsule. That being the Teflon contact carrier and stainless steel mesh, known as the "Carrier/Damping" assembly. This is used to help control/correct the frequency response and polar pattern of the capsule."

From:

http://www.saturn-sound.com/Curio%27s/akg%27s%202072%20z%200005%20capsule.htm

Inside both sides looks different. Different holes orientation etc. Do You think this no affect to sound?

If you will look on several photos and drawings from manuals, for different types of C414 with teflon ck12, those are always installed in the same direction.
I think it is no coincidence.

And you said you replaced the diaphgram. You did it yourself?

First, you should check what is the teflon akg capsule.
Yes i do that by myself. It's truly simple.
This is not regular capsule with screws for diaphragm tension regulation.

I think there are only couple of people in the world that can do it properly.

Do you think that they possesed their magical abilities from their gods?

Everyone can learn things like that. Maybe first ten capsules will go to trash but everything is to learn.

Some people will say that you cannot change the diaphragm or coil in dynamics microphones (i found posts like this before).

I fix few of my microphones in that way.

Maybe it's simpler but for some people it's impossible...

That's the DIY for :D

And tin on the diaphgram? No capacitor change will fix that. You really should test the mic with a proper capsule before proceeding any further.

Thats why i had to changed the diaphragm.

Tin was before - on old diaphragm. Now both sides are clear and looks nice.

Capacitors and circuit parts is different issue.

Now's the switching issue. In a few hours i will post some sound samples.
« Last Edit: October 21, 2012, 09:45:09 AM by ln76d »

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #18 on: October 21, 2012, 02:29:12 PM »
Hi. There's so many questions this topic has raised in my mind. What do you mean by front diaphgram sounds like back? Both sides should sound the same.

Hi,
no they shouldn't  sounds same.

 "For reasons of clarity, the above drawings did not show one of the most important item that helps to control the "Acoustic" properties of the capsule. That being the Teflon contact carrier and stainless steel mesh, known as the "Carrier/Damping" assembly. This is used to help control/correct the frequency response and polar pattern of the capsule."

From:

http://www.saturn-sound.com/Curio%27s/akg%27s%202072%20z%200005%20capsule.htm

Inside both sides looks different. Different holes orientation etc. Do You think this no affect to sound?

If you will look on several photos and drawings from manuals, for different types of C414 with teflon ck12, those are always installed in the same direction.
I think it is no coincidence.


I've seen the the pictures on saturnsound site and know the hole pattern and internal construction is different on both sides. But if you think about it, they should sound the same to make a proper fig 8 and omni patterns.


And you said you replaced the diaphgram. You did it yourself?

First, you should check what is the teflon akg capsule.
Yes i do that by myself. It's truly simple.
This is not regular capsule with screws for diaphragm tension regulation.

Interesting. I was thinking about some re-skinning thing but it seems you mean something different. Is there a AKG spare part you can just swap in? Can you tell more about the process?


I think there are only couple of people in the world that can do it properly.

Do you think that they possesed their magical abilities from their gods?

Everyone can learn things like that. Maybe first ten capsules will go to trash but everything is to learn.

Some people will say that you cannot change the diaphragm or coil in dynamics microphones (i found posts like this before).

I fix few of my microphones in that way.

Maybe it's simpler but for some people it's impossible...

That's the DIY for :D


No, was not thinking of magic  :) Was thinking about brass ring CK12 and (apparently incorrectly) imagined it to be same with teflon ones.


And tin on the diaphgram? No capacitor change will fix that. You really should test the mic with a proper capsule before proceeding any further.

Thats why i had to changed the diaphragm.

Tin was before - on old diaphragm. Now both sides are clear and looks nice.

Capacitors and circuit parts is different issue.

Now's the switching issue. In a few hours i will post some sound samples.

Sorry, didn't get it, should learn to read carefully. :-[

Still I think you should try an other capsule or try the capsule in a working circuit. I'm afraid I can't help with the issues but I hope you solve it out!

ln76d

Re: AKG C414EB P48 repair and restoration little help needed!!
« Reply #19 on: October 21, 2012, 06:42:33 PM »
I've seen the the pictures on saturnsound site and know the hole pattern and internal construction is different on both sides. But if you think about it, they should sound the same to make a proper fig 8 and omni patterns.

Truly i cannot write if they should works same or not on both sides. In theory - yes they should, but when i tried several mics both sides sounds little different. Maybe all of them were broken :) Usual, what i've heard - the backward side was not so bright as frontal.
It always was gently.
Since my knowledge of capsules is poor i can only write what i heard.

So again Guys!

If someone have good source of information about capsules, i'll be happy for any link etc.

Interesting. I was thinking about some re-skinning thing but it seems you mean something different. Is there a AKG spare part you can just swap in? Can you tell more about the process?

This is modular capsule so i've taken a whole half of it from not working donor.
I have four and half of those capsules.
It was truly simple, without any regulation.

No, was not thinking of magic  :) Was thinking about brass ring CK12 and (apparently incorrectly) imagined it to be same with teflon ones.

I only want to say, that anyone can reskin capsules :)
It's only question do you really need this:)
If someone wants only to repir his mic, ofcourse he should send cpasule or microphone to one from specialists.
I want learn how properly do that, so this is good topic for the future.
Probably many capsules will dies on first trying, but the victims are always :)
First i have some ribbon microphones for repair.
Condenser will be later.
I think to buy some cheap chinese condesers and try to work on diaphragms.


Still I think you should try an other capsule or try the capsule in a working circuit. I'm afraid I can't help with the issues but I hope you solve it out!

Capsule sounds on some patterns very healthy. First i need to well look on schematic, to figure out of all connections.
I've read few posts about those switches, that they are pain in the ass.
Shame that there's no voltage chart for this mike.
I'm thinking, that if it's no switch issue, it can be some transistor.
If not i'll try with another capsule.
Shame that i dont have another c414 to try.
I have one whole pcb from newer  c414 (on smd elements) but i have no idea if it's working. Have no time for now to check another circuit:)
I must think well, now i'm sleepy ;)

Thanks!

Cheers
« Last Edit: October 21, 2012, 06:50:46 PM by ln76d »


 

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