C414 EB P48 build

thats exactly what ive done Gus, designed them, printed them, ironed on, ferric chloride, then drilled them.
putting in components as we speak!!

Just done a search for rossi and 2007, nothing comes up?

https://groupdiy.com/index.php?topic=24604.0

Here's a service document for the 414, don't know if it's any use to you?

hi winston, yeah i got that doc from the technical docs as i said earlier in this thread

Oops, sorry dude 
As you were...

Hit my first problem, tried to wind the chokes last night, most mH I can get on my ferrite is 50mH.
Need to use wah wah size conductors to get 220mH.
Anyone have any links to axial ferrites which could do 220mH please?

My mistake, 0.22uH is 220mH, loads for cheap!!!

Quite the contrary, in fact - 0.22mH is 220uH ;D But good that you got that sorted out, either way

Spencerleehorton said:

My mistake, 0.22uH is 220mH, loads for cheap!!!

Click to expand...

Oh right, what's 220mH is uH then? 2.2uH?

I was sure that 220mH was 0.22 Henries?

I've got 50mH in there at the moment so will see how that goes until I figure out what to get to replace them for 220mH

We're still talking about the two series inductors on pins 2 and 3 of the XLR, aren't we? How and why would you need or want 220 millihenries there? What cutoff frequency would that result in, with the 22nF caps there? I'm gonna guess "pretty damn low".

The 220mH was suggested by gus so I took it as in the ball park!!!
What would you suggest there then?
Would 50mH be ok?

Also this is where I'm up too.
Got a find the switches next!!

All of Gus' suggestions read 220uH, as far as i can see. Some other AKG C414 schematics, where those inductors are used, do indeed say 220uH (as in, microhenry). No idea where you got the mH's from

Micro Henries!!! Doh!!

Ok so my inductance meter only measures in Henries so I just want to confirm that for 220uH which is micro Henries I need 0.00022 henries on my meter?

That sounds right to me.

Ok so I need to take out these 54mH chokes as they will be way too much!!

https://electronicbase.net/low-pass-filter-calculator/#lc-low-pass-calculator

According to that, 54mH and 22nF would result in a 4.62kHz cutoff frequency (-3dB point). 220mH pushes that down to 2.29kHz.

With the much more sane 220uH, that goes up to 72kHz

This company might have some spare parts for older C414 microphones:

www.audiopro.de
info(at)audiopro.de

I successfully ordered switches and a coil for my C414-EB P48 and B-ULS from them.

If you know how to use Lt spice or another sim program I  would make a DC operating points sim.

This would allow you to get a feel for how the adjust the 2nd stage CC section and the first stage biasing keeping a good capsule voltage range. The capsule voltage will be lower the higher the current in the second stage and first stage.
More current in the 2nd stage has better transformer drive but this will lower the capsule voltage

I have not worked on a C414 EB P48 so it would be helpful if someone that has one posts the transistors EBCs and D and S voltages and capsule voltage.

I am thinking you will need to adjust two resistor values.

Maybe I could put in some trimmers on the  most likely points?
Any suggestions?

I've used it spice before, so I'll see if I can do it but it been a while!!

Looking at the schematic  r8,r9 and r5,r2,r3 look like some likely candidates for bias and setting those fets and transistors?

these are the voltages from Rossis thread  but I think the mic didnt work at this point!!

These are correct working voltages.

Also capsule bias voltage is 42v

T1  D  7,64V  S  4,69V  G  0,04V
T2  C  23,2V  B  8,07V  E  7,64V
T3  D  22,8V  S  3,11V  G  2,69V
T4  C  43,2V  B  23,2V  E  22,8V