e.oelberg

akg c414 eb transients gone
« on: July 04, 2019, 02:53:26 AM »
I have a 414eb with teflon capsule, I don't use it much but recently I pulled it out and noticed that somehow transients are gone.
Is this an aging capsule or maybe some tantals going bad ?

anybody has an idea ?

« Last Edit: July 04, 2019, 06:05:11 AM by e.oelberg »


Khron

Re: akg c414 eb transients gone
« Reply #1 on: July 04, 2019, 06:37:11 AM »
It's a possibility.
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Re: akg c414 eb transients gone
« Reply #2 on: July 04, 2019, 08:43:02 AM »
yes it's highly probable...
change all the tantalum capacitors then checks all voltages after that...
regards

Khron

Re: akg c414 eb transients gone
« Reply #3 on: July 04, 2019, 10:14:31 AM »
I'd recommend some Japanese electrolytics, though.

http://sound.whsites.net/articles/capacitors.htm#s12
(Read the whole 1.2 section, including the bit about tantalums)
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Re: akg c414 eb transients gone
« Reply #4 on: July 04, 2019, 11:56:18 AM »
i'm quite ok with this article, i've already change tantalums for electrolytics in my 414 and i always do that when there's enough room ...
if you have 60v at the capsule , then visually check the membrane surface...
if it's sucked by the backplate,  you will see it clearly, and it will tell you that your capsule diaphragm has loosened with time...
« Last Edit: July 04, 2019, 11:59:46 AM by granger.frederic »

RuudNL

Re: akg c414 eb transients gone
« Reply #5 on: July 04, 2019, 12:08:35 PM »
The funny thing is that once I had a discussion with Geoff Tanner (ex Neve) about tantalum capacitors.
He stated that you should never change the tantalum capacitors in Neve equipment for aluminium ones because that would change the sound in an unacceptable way. Most of the time tantalum capacitors short out when they are placed over the supply rails, I never had many problems with tantalums used as coupling capacitors.
There is a solution for every problem!

http://www.vansteenisaudio.nl

Khron

Re: akg c414 eb transients gone
« Reply #6 on: July 04, 2019, 12:20:41 PM »
Well, that only raises the question of what "unacceptable" means ;D
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

e.oelberg

Re: akg c414 eb transients gone
« Reply #7 on: July 04, 2019, 03:56:21 PM »
I know tantals usually short, I suspect the mic to just not work if this would be the case, are they other ways of failing known for tantals ?

Gus

Re: akg c414 eb transients gone
« Reply #8 on: July 04, 2019, 07:34:44 PM »
Do you have test gear? Scope, Signal generator, DMM, and a phantom power supply to power the microphone, cap tester?

http://recordinghacks.com/microphones/AKG-Acoustics/C-414-EB

Gain stage is simple
First stage has a bootstrapped drain look at the 3.3uf
The pair is like a Sziklai follower pair the NPN Vbe is fairly constant so the current in the 2.2k is fairly  constant
Output stage is engaged for the two high pass selections and almost bypassed for no HPF

Does the sound change with the different highpass filter settings?

Check the transformer for a broken wire on the primary and secondary you can still get a weak signal with a broken wire

Could be a capsule so test to make sure what is bad.

Check for voltages at the transistors Gate, Drain, Source, Bases, Emitters and Collectors(check the 2nd NPN at the three HPF settings) . Check the left side of the 4.7megs with for  DMM for the capsule voltages. Check the voltage at pins 2 and 3

I would remove the capsule wires from the circuit and cap couple a signal generator to the input of the circuit and scope the circuit nodes.

I would not assume it is the capacitors without testing.
« Last Edit: July 04, 2019, 08:00:38 PM by Gus »

Re: akg c414 eb transients gone
« Reply #9 on: July 05, 2019, 03:06:15 AM »
i find shorted tantalum caps,  but also often with increased esr.
i have nothing against tantalum but i find them not reliable with time
before spending time with deep tests, i would change them first (especially the 22uF), i've repaired quite a lot of mics by doing that...
but they indeed have a sonic signature, it's a matter of taste...

a good cleaning in the HiZ section is mandatory as well, the 414 pcb is a real sponge...
« Last Edit: July 05, 2019, 03:12:47 AM by granger.frederic »


e.oelberg

Re: akg c414 eb transients gone
« Reply #10 on: July 05, 2019, 06:28:07 AM »
thanks Gus & Frederic for your input. Thats very helpfull

I do have basic test equipment, I will give it some test, capsule looks fine

nicholas

Tim Campbell

Re: akg c414 eb transients gone
« Reply #11 on: July 05, 2019, 06:59:31 AM »
The most common problems with 414's are dirty switches, poor phantom power, using a bad cable. Check these things first.

Gus

Re: akg c414 eb transients gone
« Reply #12 on: July 05, 2019, 08:49:49 AM »
Tims post is a very good one.

FWIW  I was repairing a 19a9 for a friend. It had an intermittent issue with some other issues. The intermittent issue was caused by corrosion at a connector.

Switches and cable connections should always be checked.




e.oelberg

Re: akg c414 eb transients gone
« Reply #13 on: July 05, 2019, 09:46:21 AM »
Thanks Tim !
I just disassembled the mic and I was surprised to find so much dirt inside. I will clean first of all very slow and that I'll give it a try again

Re: akg c414 eb transients gone
« Reply #14 on: July 05, 2019, 10:03:12 AM »
yes, when i said "HiZ section cleaning", i include capsule ( including cables and mount), switches ,HiZ caps, jfet and high value resistors (and of course pcb around that...)
i recently repaired two 414 eb (teflon) just by changing tantalum caps and a cleaning  (also swapped for two TC CT12 for the story...)
least week , again, two c451c repaired just by changing tantalum caps and a cleaning as well...
« Last Edit: July 05, 2019, 10:08:02 AM by granger.frederic »

e.oelberg

Re: akg c414 eb transients gone
« Reply #15 on: July 05, 2019, 10:07:35 AM »
yes, when i said "HiZ section cleaning", i include capsule ( including cables and mount), switches ,HiZ caps, jfet and high value resistors (and of course pcb around that...)

..got it :)  thanks

e.oelberg

Re: akg c414 eb transients gone
« Reply #16 on: July 07, 2019, 11:35:10 AM »
soooo... after extensive cleaning inside the mic sound just fine again, transients are back is my impression, switches work as they should now. Still sounds like teflon, but well, it's teflon !  thanks very much everybody


 

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