ELA M251 Inspired Microphone - Build Thread

[ribor92]

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..?

 

[ribor92]

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]

Funny, I posted here and my post has disappeared. Is there some reason it would be removed?

 

[Zebra_PD]

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

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? 

 

[TillM]

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.

 

[ribor92]

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]

It was just to say check all your voltages and what transformer are you using?

 

[Matador]

Let me quote myself from the other C12 thread, regarding isolating noise problems in this circuit:

[quote author=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.
[/quote]

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.

 

[ribor92]

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]

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.

 

[ribor92]

Would it be possible to upload the schemtaics for this build?

 

[snaredrum]

hi  i have 2 matador psu circuit board the elam 251 and C12 the C12 was finish and it work super ,but  one day nothing, no signal  , i try to find, all seems ok . for the second elam 251 i built the psu and i have -100 V  bias measurement and  impossible with trimmer to  goal - 1,1 V  , then i check my first psu for C12 and the same bias ?? i am a little affraid the C12 work with - 100 V bias !!  i don't understand , i have 2 others PSU with no matador circuit board (quasi the same) elam and C12 for others projects and they work fine .i want to try  the matador C12  with an other PSU with good value 120 V  -1,1 V bias , and the elam 251 with my other PSU when it will be finish .if you know theses bugs , can you report me a tip for reparation ?  sorry for my english  it's difficult for me to exprim technics in english . regards

 

[ribor92]

Bumping again for a schematic if possible!

My tech guy has come to a halt and don’t know how to look for solitions without it.

 

[ribor92]

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.

Checked the transformer by myself and it seems to be fine, thanks for the tip though!

If thats not the problem what else could be the cause of the low output?
I have a feeling the noise issue may be partly solved by not needing to max out my preamp etc so Thats not the main focus right now for me. But the guide on finding the source of excessive noise will be followed if needed!

Any ideas on the low output?

 

[ribor92]

Let me quote myself from the other C12 thread, regarding isolating noise problems in this circuit:

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.

Okay so I tried your guide! I had a low impedance ground on all ground connections. And when I tried a) It was dead silent like you said. The tube has some noise but I'm not sure how to tell if it's too much. The last step with the HI-Z section just seemed to bring hum so it was hard to tell. I also couldn't tell which of the capsule connections to choose so maybe I did something wrong...
And when I tried to compare the "tube only" noise with the normal "recording noise" it seems like the tube has less but the the room also has noise, so really hard to tell from this!

Appreciate any help!

Edit: After some further testing the tube seems very quiet when shorting the different parts, also tube+Hi-Z seems very quiet as well, so it seems to be related to the capsule...

 

[Carl Cress]

Is there any chance of getting the BOM and schematics posted? I would love to do this project but there's no BOM and Chunger does not have the parts kit up on his site and hasn't for a while.

 

[ribor92]

Is there any chance of getting the BOM and schematics posted? I would love to do this project but there's no BOM and Chunger does not have the parts kit up on his site and hasn't for a while.

Been asking for this myself, but I’ve accepted this thread to be as good as dead along with the support. The schematics that where once to be posted will probably never be seen... Left my noisy mic to a guy with good knowledge hoping to be able to use it soon!

 

[kg350zw7]

i'd like a bom and schematic as well. i have purchased the equipment which has been a chore, i have emailed 939 for the bom and when my stuff was going to ship which has taken weeks.  it finally shipped, but no bom or any other info.

 

[Carl Cress]

Yes it’s very disappointing as I believe it’s a great project. I built a pair of the C12s that were offered by Chunger and I’m very happy with them. Too bad this is not being monitored and replied to.

 

[creation]

Ok, I finished building this ELA M251 hybrid with the PCB I got from Chunger.  The mic works but has some odd sound issues. I built one of the C12 and it sounds great, so I was expecting this 251 to sound as good if not better. I built the 251 its own PSU with the Bias left out. I have the B+ pinned at 120 VDC and the heater at 6.3 VDC measured at the mic.  In cardioid  the FC sounds tinny and thin. In Omni both FC and BC sound that way. But in Fig 8 the FC remains thin while the BC sounds beautiful and rich. It is not the capsule, as I have put it into a modded 460 and it sounds fine in all patterns. It is  an AK 12. I sure would love to get that rich beautiful sound  from both capsules and all patterns. Any suggestions.