Re: ELA M251 Inspired Microphone - Build Thread
« Reply #20 on: May 15, 2018, 05:06:06 PM »
Yeah I feel its a bit much myself. Patterns don't seem to do much more than change the polarity, the noise seems to stand.
Checked the values in the mic, they all seem to be as they should. I understand how hard it must be for you guys to help, but I appreciate it!
Any other ideas, and how to try them..?
« Last Edit: May 15, 2018, 05:12:40 PM by ribor92 »


Re: ELA M251 Inspired Microphone - Build Thread
« Reply #21 on: May 15, 2018, 05:39:39 PM »
I realize that since my preamp almost maxes out on 57db to get decent signal it added quite the amount of noise in itself. But it's still kind of noisy, sound great though but the signal just seems low. Any parts I can look at specifically to check if the output is wrongly reduced?

Tim Campbell

Re: ELA M251 Inspired Microphone - Build Thread
« Reply #22 on: May 16, 2018, 12:02:21 AM »
Funny, I posted here and my post has disappeared. Is there some reason it would be removed?
« Last Edit: May 16, 2018, 12:20:20 AM by Tim Campbell »

Zebra_PD

Re: ELA M251 Inspired Microphone - Build Thread
« Reply #23 on: May 16, 2018, 03:17:40 AM »
Hi!
Amazing build and project! I have been thinking about how to combine the ELA M251 and C12 designs for an upcoming mic build the last couple of weeks. And then I stumble up on this project and realize that someone with a LOT more experience and knowledge then me all ready have done the heavy lifting :D

Any info on if, when and how I might be able to buy an PCB?  And then the  BOM and/or schematics might be made available?  :)
Kind regards,
//Pierre
___________________________________________________
Semiprofessionell producer but newbie DIYer.
----------------------------------------------------------
www.zebrastudios.se

TillM

Re: ELA M251 Inspired Microphone - Build Thread
« Reply #24 on: May 16, 2018, 09:25:36 AM »
you can everything buy here
http://store.studio939.com/product/c12-vintage-microphone-clone-pcb-set

BOM and schematic you will get from Chunger, or buy everything from him.

Re: ELA M251 Inspired Microphone - Build Thread
« Reply #25 on: May 16, 2018, 09:34:06 AM »
Funny, I posted here and my post has disappeared. Is there some reason it would be removed?
I’d like to hear what you had to say! :)

Tim Campbell

Re: ELA M251 Inspired Microphone - Build Thread
« Reply #26 on: May 16, 2018, 11:28:22 AM »
It was just to say check all your voltages and what transformer are you using?

Matador

Re: ELA M251 Inspired Microphone - Build Thread
« Reply #27 on: May 16, 2018, 04:48:14 PM »
Let me quote myself from the other C12 thread, regarding isolating noise problems in this circuit:

Quote from: Matador
Try to narrow down where the noise is coming from.  I posted this several times in the thread, but the basic steps are:

1) First make sure you have a low impedance ground:  with everything powered off, check the resistance between ground on the PSU PCB and all ground points in the mike body, including all parts of the outside shell.  You should have less than 0.1 ohms everywhere in the mike
2)  Make a small length of wire with two small alligator clips, one on each end
3) Clip one end to ground on the PCB
4) Starting at the 'output' hard ground different points in the circuit:  then measure noise
a) the output of the coupling cap (where it enters the transformer) - it should be dead silent
b) the grid of the tube - this should only output the self noise of the tube
c) the capsule connection - this should only be the noise of the tube + HiZ components

You should be able to see the noise contribution of each stage this way.

A noisy tube will be revealed when you get to step 4b, and if it's coming from contamination of the HiZ portions of the circuit you'll hear it in 4c.  If it's the capsule itself, you can substitute two 68pF caps for the capsule and see if the noise changes/goes away.

Re: ELA M251 Inspired Microphone - Build Thread
« Reply #28 on: May 17, 2018, 07:25:27 AM »
It was just to say check all your voltages and what transformer are you using?

Using a AMI T14!

Matador, thanks for the guide! I'm going to take some help with this in the near future since my I'm not that technical with these things just yet! :)

Matador

Re: ELA M251 Inspired Microphone - Build Thread
« Reply #29 on: May 17, 2018, 03:01:23 PM »
In case it helps: a while back, there was a rash of AMI transformers that had the primary and secondary colors swapped, which meant people ended up putting their transformers in backwards. :(  This will greatly load down the tube and make it thin and very quiet.

To check this, you can measure the primary and secondary resistance:  the primary will be something like 1K ohms, and the secondary will be around 25 ohms.  You can measure this in circuit by measuring the resistance after the output coupling cap and ground, and measuring the secondary right from the connections on the bottom of the microphone.