Ela-M 251 Body from Aliexpress

[paulcheeba]

Ok so let's list what you need voltage wise:
B+ at 120v (stock psu need some resistor change for dropping the voltage down)
Heater at 6,3v (better design and noise filtering on Dany psu)
Relay voltage (in theory you could find a way to derive it from the heater but some serious thinking and redesign need to be done for it).
So since you have Dany psu board, why bother.

Thanks I have bought the BOM for Dany’s and some tweaks too.

 

[lampas]

Could someone explain, what is the pros and cons, soundwise to have switching polar pattern in the PSU or in the microphone in this type of microphone? Thanks

 

[gyraf]

..if you do patterns ONLY by switching voltages, you can as well do it in PSU or wherever. If you also use switching-of-backs-and-fronts (to e.g. get away with lower polarisazion voltages), these carries sensitive signals and must be kept within mic..

/Jakob E.

 

[MagnetoSound]

Pattern switching at the PSU can also be made silently (and during recording if necessary). A useful feature in certain applications.

 

[Whoops]

Pattern switching at the PSU can also be made silently (and during recording if necessary). A useful feature in certain applications.

For sure,
no reason to make life more complicated!

 

[ElSmurf]

If you also use switching-of-backs-and-fronts (to e.g. get away with lower polarisazion voltages),

Thanks for this, made me dive a little deeper into understanding polarization voltage and how it's implemented in the 251 circuit. Looks like the switch is changing the voltage between zero, half and full on the rear diaphragm, while also connecting the rear back plate to ground in fig8.

Am I correct in thinking that 251 circuits that change the polarization on the PSU all bridge and polarize back plates instead of the diaphragms? Just trying to wrap my head around the circuit. If the polarization topology doesn't change the sound, then I'm really like the Matador 251 inspired circuit. Might use that to do an acrylic build, and order their PSU pcb.

As for the switch on the body, I realized I would be the only one who would even care about it. Nobody who will be actually singing into the mic will notice the lack of an authentic looking switch.

 

[HerbertR]

My progress with Poctops Elam 251 PCBs, UTM0512 Transformer: No problems so far. Not much space to connect the cables inside, but no real challenge to solder them to the PCB Pads. The Parts of the Micbody are thankfully very easy to disassemble and reassemble. One thing - the 7-pin XLR connector must be shortened. The pins on the solder side are too long with the connected cables and bumping on the UTM TX - in my case. And by the way - I would recommend to bend all bridges above the Poctop Relays before soldering. This makes it much easier to link the relay connections. Very very pretty Mic body...

 

[thomasdf]

Hello

I am about to start building a pair of these, and I am going for the plexi turret board route. Re pattern switching, I don't want to use relays or switch and I like the idea of having the polarity switch on the PSU, like for the C12.
I am not super experienced in terms of building condenser microphones, so I am wondering why nobody builds 251 with this method ?
I found a guy in Russia that (apparently) successfully used this method here : Telefunken ELA M 251 своими руками Ч.1
The obv difference from the original schematics are the added 30M resistor and 5nF cap. Would this affect the overall sound of the mic ? Is there a reason why everybody goes mechanical ? Appart from 1:1 authenticity.

I plan on using a bunch of Siemens ECC801s I have in my drawers, and will wire the tube from each mic mirror to the other so when the tube are at the end of their life I can swap them and use the good halves in the opposite mic. I don't know if it's genius or dumb. I'll probably have to tweak (lower) the gain for these tubes.

I'll prob start a dedicated thread if I have more questions Thanks !

 

[ElSmurf]

The obv difference from the original schematics are the added 30M resistor and 5nF cap.

The schematic you posted, which the Russian guy used, is the 251 circuit by Matador that he made to convert his C12 PCB to a 251. It's also the circuit I'll be using in my acrylic/turret build. Those two components are actually part of the original schematic, just used in a different place because the polarization voltage switching happens in the PSU instead of the mechanical switch in the original. At least, that's how I understand it at the moment. Still need to familiarize myself more with the electronic side of things.

 

[thomasdf]

You are right ! The schematic was cropped, but it's indeed Matador's work. Thanks

 

[Mikael-ange]

Hello

I am about to start building a pair of these, and I am going for the plexi turret board route. Re pattern switching, I don't want to use relays or switch and I like the idea of having the polarity switch on the PSU, like for the C12.
I am not super experienced in terms of building condenser microphones, so I am wondering why nobody builds 251 with this method ?
I found a guy in Russia that (apparently) successfully used this method here : Telefunken ELA M 251 своими руками Ч.1
The obv difference from the original schematics are the added 30M resistor and 5nF cap. Would this affect the overall sound of the mic ? Is there a reason why everybody goes mechanical ? Appart from 1:1 authenticity.

I plan on using a bunch of Siemens ECC801s I have in my drawers, and will wire the tube from each mic mirror to the other so when the tube are at the end of their life I can swap them and use the good halves in the opposite mic. I don't know if it's genius or dumb. I'll probably have to tweak (lower) the gain for these tubes.

I'll prob start a dedicated thread if I have more questions Thanks !

Hi,
I wouldn't say nobody use this methode but that would make a c12/m251 hybrid and not a m251.
On the m251, polar pattern are made manipulating backplate with no voltage exceeding 60v.
On the other side with a c12, polar pattern are done manipulating voltage from 0 to 120v on the rear membrane. That why you need a ck12 capsule with isolated backplate on the m251, and bridged backplate on the c12.
Also since polarization work the way it work on m251, rear backplate is disconnected on cardiod. So the only 2 simples way to doing this (to my modest knowelges) is with mecanical switch or using relay.

Btw, an m251 with c12 polarization scheme will work and can be cool, since you can have variable pattern (with my c12 I mostly use on cardioid with one click toward omni for vocal just for giving an idea).
Hope that help

Edit: you're from France so bon courage
Je suis vers Toulouse

 

[thomasdf]

Oh, I see ! Thanks a lot for your input ! Merci

 

[RuudNL]

What is more important: a microphone that works like it should, or a historically correct M251?
(In that case you should buy a Telefunken M251... )

 

[thomasdf]

I am not looking for a 1:1 clone, I know this can't be achieved. I want to something in the spirit of the 251, and a tad darker than a C12. And a beautiful sounding figure of 8 behavior, because I love this pattern and tend to use it quite a lot.

 

[Murdock]

I would think the only benefit of the switch inside the mic is the lowered noise when disconnecting the rear backplate when in cardioid.
In my M49 clone I used one high insulation resistance reed relay inside the mic and a pattern poti with build in switch inside the PSU.
This way the pattern poti get's deactivated when the switch is activated because it disconnects the back side of the capsule via the relay. So either pattern poti is active or cardioid only mode.
Works great and the difference is really noticable.

 

[ElSmurf]

This way the pattern poti get's deactivated when the switch is activated because it disconnects the back side of the capsule via the relay. So either pattern poti is active or cardioid only mode.

Very elegant. Did you use a switched pot or a separate switch?

 

[thomasdf]

Backside of the capsule at 0V is Omni pattern, if I am not mistaking ?

 

[Murdock]

Very elegant. Did you use a switched pot or a separate switch?

A switched pot.
Something like that:
https://www.voelkner.de/products/69...tiometer-mit-Schalter-Mono-0.5W-10k-1St..html

 

[paulcheeba]

My progress with Poctops Elam 251 PCBs, UTM0512 Transformer: No problems so far. Not much space to connect the cables inside, but no real challenge to solder them to the PCB Pads. The Parts of the Micbody are thankfully very easy to disassemble and reassemble. One thing - the 7-pin XLR connector must be shortened. The pins on the solder side are too long with the connected cables and bumping on the UTM TX - in my case. And by the way - I would recommend to bend all bridges above the Poctop Relays before soldering. This makes it much easier to link the relay connections. Very very pretty Mic body...

Is the Poctop still worth the trouble in this small body or would you change to Beesneez or Apex etc? Maybe a different PCB? There does seem to be such little room. Looks great though!

 

[ElSmurf]

Backside of the capsule at 0V is Omni pattern, if I am not mistaking ?

If you're talking about the matador circuit, then yes, I believe so.