Telefunken ELA M 251 Clone Tube Microphone Build Thread (D-Ela M 251E)

[vinylwall]

I've finished my build.  Beesneez Mic Body and Beesneez CK12 capsule, Cinemag CM-13114 transformer, Electro-Harmonix 6072A/12AY7 GOLD Tube, PSU from Chunger.

Front inside:

 

[vinylwall]

Rear inside:

 

[vinylwall]

Rear assembled:

 

[vinylwall]

PSU:

 

[vinylwall]

Closeup front:

 

[vinylwall]

Closeup rear:

 

[taliska]

Hi All,

I've had these pcbs lying around for a while now, and am just getting around to putting them together. It all looks rather straightforward, but as I haven't seen anyone mention it, I've got to ask about the (mechanical) stability of the relays...

As far as I can tell, the relays are really only supported (mechanically) by a single pin to board solder on the outer relays and get the rest of their mechanical support from the point to point soldering.

Has anyone tried shaking their built pcbs to see if they get any vibration of the relays because of that? I haven't got to that point in my build yet, but it seems like that could be a potential issue...(that could probably be fixed with a bit of glueing if it's a problem).

So, thoughts? Is it a problem in practice?

Cheers,

Kaz

 

[Winetree]

"As far as I can tell, the relays are really only supported (mechanically) by a single pin to board solder on the outer relays and get the rest of their mechanical support from the point to point soldering.
Has anyone tried shaking their built pcbs to see if they get any vibration of the relays because of that?"

Haven't noticed any vibration problems. But I did have to make sure the relays were tight together and had to sand the 2 outer edges at 45 degrees in order to fit the mike tube over them. Also there was noted some problems with vibration noise with the 2 large poly caps on the top  back side of the P.S.B. Glue them down.

 

[taliska]

"As far as I can tell, the relays are really only supported (mechanically) by a single pin to board solder on the outer relays and get the rest of their mechanical support from the point to point soldering.
Has anyone tried shaking their built pcbs to see if they get any vibration of the relays because of that?"

Haven't noticed any vibration problems. But I did have to make sure the relays were tight together and had to sand the 2 outer edges at 45 degrees in order to fit the mike tube over them. Also there was noted some problems with vibration noise with the 2 large poly caps on the top  back side of the P.S.B. Glue them down.

Cool. Yeah, hadn't thought about those caps (yet!), but good call on that. I'll pick up some glue for stabilising everything before progressing any further...

Cheers,

Kaz

 

[PhatPlanetStudios]

Good day 251'ers,
So I've completed my build with a GE 5-star, Beesneez capsule and body and the new mic all powered up and functioned without a hitch!  Great docs, pics and posts made the build a breeze. Thanks to all!  Upon initial listening, the 251 clone sounds thin, bright and lacks low end. Sitting next to our vintage Telefunken U47, the 251 doesn't even come close in sound quality.  Pretty disappointed, so now I'm trying to figure out what I did wrong.  Some questions are;  B+ (grid) voltage.  Diagram says 120V & I've seen 110V in the posts.  Any impact in sound quality with the grid voltage?  Are there any key component changes that differ from the Mouser BOM+Styroflex Caps that I should be aware of?  Any insight would be greatly appreciated.  Thanks guys!

 

[poctop]

Good day 251'ers,
So I've completed my build with a GE 5-star, Beesneez capsule and body and the new mic all powered up and functioned without a hitch!  Great docs, pics and posts made the build a breeze. Thanks to all!  Upon initial listening, the 251 clone sounds thin, bright and lacks low end. Sitting next to our vintage Telefunken U47, the 251 doesn't even come close in sound quality.  Pretty disappointed, so now I'm trying to figure out what I did wrong.  Some questions are;  B+ (grid) voltage.  Diagram says 120V & I've seen 110V in the posts.  Any impact in sound quality with the grid voltage?  Are there any key component changes that differ from the Mouser BOM+Styroflex Caps that I should be aware of?  Any insight would be greatly appreciated.  Thanks guys!

My first Reflex would be to try a  cheap chinese CK12 capsule type to rule out any capsule problem at first ,
it is not impossible that somthing is wrong with the capsule as it plays a major role in a microphone ,
Hope this helps,  if not i would defo check the wiring and component value in the HZ bridge, a little substition in a high Megohm range would totally kill it. i would also be intested to see what the capsule looks like when it is polarized.. i would also check to make sure that your 2 backplate are properly isolated this could messup the polarisation scheme for the pattern.
Dan.

 

[dmp]

Doublecheck the transformer wiring also - that can lead to thin sound

 

[poctop]

Doublecheck the transformer wiring also - that can lead to thin sound

+1

lowest resistance pair to S+ S- and Higher resistance Pair to P+ P-
D

 

[duantro]

Any thoughts/ tips on adjustments to the circuit to work with an ac701k?

 

[poctop]

Any thoughts/ tips on adjustments to the circuit to work with an ac701k?

i have seen a thread on this Non-export elam 251 Build here somwhere ,

edit : found it  http://groupdiy.com/index.php?topic=57902.0

Best,
d

 

[PhatPlanetStudios]

Good day 251'ers,
So I've completed my build with a GE 5-star, Beesneez capsule and body and the new mic all powered up and functioned without a hitch!  Great docs, pics and posts made the build a breeze. Thanks to all!  Upon initial listening, the 251 clone sounds thin, bright and lacks low end. Sitting next to our vintage Telefunken U47, the 251 doesn't even come close in sound quality.  Pretty disappointed, so now I'm trying to figure out what I did wrong.  Some questions are;  B+ (grid) voltage.  Diagram says 120V & I've seen 110V in the posts.  Any impact in sound quality with the grid voltage?  Are there any key component changes that differ from the Mouser BOM+Styroflex Caps that I should be aware of?  Any insight would be greatly appreciated.  Thanks guys!

My first Reflex would be to try a  cheap chinese CK12 capsule type to rule out any capsule problem at first ,
it is not impossible that somthing is wrong with the capsule as it plays a major role in a microphone ,
Hope this helps,  if not i would defo check the wiring and component value in the HZ bridge, a little substition in a high Megohm range would totally kill it. i would also be intested to see what the capsule looks like when it is polarized.. i would also check to make sure that your 2 backplate are properly isolated this could messup the polarisation scheme for the pattern.
Dan.

Thanks for the insight so far Dan,
We've done some tests of the mic now.  Transformer checked & is correct, Capsule backplates are indeed isolated, I do not have another capsule to exchange with yet though.  Testing so far shows that in comparison to a Brauner VM1 & a Manley Gold Reference, all set to Cardioid & measured with exact same conditions;  the LOW end of the 251 is rolled off by 5-10dB below 200 Hz.  Above 200Hz, all three mics were very well matched.  In addition, testing the 251 in Omni & Figure 8, showed the rear side of the capsule measured 3dB lower than the front.  Would this lowered output of the rear affect the Cardioid measurement with proximity & low-end character?  We checked values of all resistors and they match and are consistent with the build, and schematic.  Look at the attached measurement shot:  Blk, top trace is:  Manley,  Middle, Red trace is Brauner,  Bottom Teal trace is 251.  If anyone can think of anything else we should be looking at, please let us know.  Thanks!

 

[lauritz]

I can see somebody had this problem before me...but it seems as though the problem was'nt resolved in this thread, or maybe i missed it.

With the mic unplugged, i can't get the B+ voltage low enough...only goes down to 165 v minimum. I've checked the values of r1 and r2 and they match at 75k ohm. The power transformer output is a little above 200V -maybe 208 V.  Should i just swap in higher value resistors for r1 and r2 or is there a problem somewhere, any insights?

I'm reluctant to plug in the microphone, since i have a 150V tantalum cap sitting at the input in the microphone, and i don't wanna blow it....

thanks in advance.

Lauritz

 

[granger.frederic]

Dear Lauritz/PhatplanetStudio,

congratulations you have a near perfect Elam 251 plot : see the original plots at http://recordinghacks.com/pdf/telefunken/ElaM-250-251-Manual.pdf , 

you're near the specs...

but if u want to be sure , double check B+ with the mic plugged : max 110V , check the heater : 6.3V , check that all the HiZ sections are perfectly cleaned , check the capsule voltage before the 8Mohms resistors : around 60V

If your capsule is a bit low end shy for your taste, try to decrease capsule voltage to 55V (reduce the 0.5MOhms to ground),  increase the 30Mohms grid resistor to 300Mohms and put a 100uF on the cathode instead of 22uF. U could increase the output coupling capacitor up to 3.3uF as well ....

with the high end response, assuming your plot is accurate , i would increase the output LP filter by increasing the 120pF to 220pF or even 330pF ... (or more to taste)

regards
Fred

 

[duantro]

I have finally finished the first of my 2 elam's. Seems to be working great. I'm taking it to my studio to test it out.

 

[lauritz]

Dear Lauritz/PhatplanetStudio,

congratulations you have a near perfect Elam 251 plot : see the original plots at http://recordinghacks.com/pdf/telefunken/ElaM-250-251-Manual.pdf , 

you're near the specs...

but if u want to be sure , double check B+ with the mic plugged : max 110V , check the heater : 6.3V , check that all the HiZ sections are perfectly cleaned , check the capsule voltage before the 8Mohms resistors : around 60V

If your capsule is a bit low end shy for your taste, try to decrease capsule voltage to 55V (reduce the 0.5MOhms to ground),  increase the 30Mohms grid resistor to 300Mohms and put a 100uF on the cathode instead of 22uF. U could increase the output coupling capacitor up to 3.3uF as well ....

with the high end response, assuming your plot is accurate , i would increase the output LP filter by increasing the 120pF to 220pF or even 330pF ... (or more to taste)

regards
Fred

Thanks a lot for your thoughts on the matter...i see now from the schematic that there is a 100k resistor on the way to the anode. With approx. 0,5mA current it leads to a 50V voltage drop, so i guess 160V is more than low enough -measuring directly at the output of the power supply.

Another quick question...i am saving up money for a Tim Cambell capsule, so i don't have a capsule yet. Would there be any problems just putting in 2 capacitors with electrical equivalent values( as the capsule ) and do circuit checks like that? Do i even need that, or could i just power up the mic without the capsule installed?


thanks

best
Lauritz