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

[andybaker28]

so I will try to compile those tweaks as they go and be interesting
Best,
Dan,
[/quote]

Hi Dan, Thanks for your interest!

I have made a few more changes to the mic now. I posted these changes in another response but I will paste them here as well..
It turns out I made a mistake about that tantalum replacement cap! I had gotten it from a hifi shop here in Taipei on the store owners recommendation. When I saw it I thought immediately that it was a Panasonic Gold and thought nothing more of it! But today on further examination I realised I was wrong! Sorry for that! It is actually an Elna Silmic ARS. This made a very nice change to the low end of the mic, I can definitely suggest this as one to try! I don't plan to look further than this one for now. It really makes the original recording test I did sound very thin. I have also swapped out a 600K into R3, and a 510K into R5 replacing the original 500Ks  that were in there. That also seemed to add a bit more bottom, not as pronounced as the Silmic but still worth it. I also changed out the 100uf filter cap and put in a 330uf. This one I did not notice so much. One other cap that I have put in is again on the stores recommendation was a Solen MKP-FC 3.3UF 400V. That one for me did not show much change  from the original one that I had. I have made audio clips, and uploaded them into a small zipped pro tools session. These are really terrible recordings!  The guitar I have is a real good looker, but man it sounds terrible. Its an old F hole Kay from the 50s that I got for $20, its all I got here in Taiwan. So mainly I just did a guitar to show the differences between part swaps. I tried my best to be in the same location, but still it sounds pretty different before and after the capsule voltage change. I still want to do more testing but I think its a good bit better that it was when I started. I do hear a bit of noise on the mic now though it seems, but not sure its not just the environment here. Seems like the original test I did next to the new telefunken 251 was quieter, but it was across the street in an actual vocal booth instead of my control room which has a console fan running! I think it might be time for capsule and transformer changes next. Anyone have any thoughts of what might be a good choice, please let me know! Thanks

https://www.dropbox.com/s/ilyhotu9tdet6i7/Copy%20of%20251%20mic%20test%202.zip?dl=0

 

[ding]

Really nice! What capsule do you have on that?

 

[andybaker28]

Really nice! What capsule do you have on that?

Hi Ding, This is the capsule sent with the full kit sold by Mic&mod. From what they say it is made in France. I am still wanting to try another one to see what is possible.

and BTW, I have been trying my best to get better with understanding the circuits. I still have a long way to go but did want to share with other beginners like me a man that does excellent instructional youtube videos. He puts it as simple as possible and it really is helpful!

https://www.youtube.com/watch?v=x5SSKX74DKg

Btw, does it seem like I made the right choice for the voltage divider resistors?

Thanks!

Andy

 

[ding]

Looks like it.

 

[Matt55]

Hey Guys,

I built my PSU this evening for my 251 clone using Chungers Mic PSU from studio 939. Seems to be working as expected.

Some things I noticed that may help other in-experienced builders like me;

On the standard 7 pin XLR connector the white wire which goes to b+ (as in Dany's pictures on page 1) was grounded at the back of the 7-pin XLR from factory. I had to cut this joining wire (looked more like a resistor leg) to remove it from ground.

When using the green blocks and testing for Ground, BIAS, B+ and Heater (H+) voltage ensure the screws are screwed fully down even if there is no cable/wire screwed in. Otherwise you will not be-able to measure voltages as there will be no continuity through the screwhead to the pcb on the block.


Unloaded Voltages; I adjusted the Heater (H+) from 7.92 to 6.30 volts, my BIAS is sitting at -1.201v (with the jumper removed) and B+ was sitting at 189v. I adjusted the trim pot on the B+ and the lowest it seemed to go to was 162v.

Questions;

1) I am going to be using a TC capsule in the final build. Is the B+ going to be low enough when loaded? I seem to remember TC capsule requires 110-120v when loaded and not more.

2) The power supply H+ and bias are constant as soon as power up. The B+ however slowly increases to a voltage and the settles marginally lower. Is this normal. I would say this procress takes around 1-2mins...

3) Should I be using the jumper for the BIAS and what should its measurement be?

4) When soldering the high z point to point section of the microphone, I understand it is neccessary to clean the pcb with ipa or use no clean solder. I am not currently using no clean solder but could switch I guess... I used 99% ipa on the PSU pcb, however clearly I need to keep it away from certain components like the capsule. With regards to the poly caps how gentle do I need to be when cleaning around them as I read they are pretty delicate to heat and alchol i.e. will a toothbrush with alchohol on it be enough to kill them or are we talking spraying them with the stuff? I see some people use cotton buds with ipa on them to cleans these sections but that always seems to leave part of the cotton bud attached in my exerience...

Im excited to continue the build but I thought it would be worth checking out these few points first. I did search the thread but I didnt see any exact responces to the above.

(n.b. prior to installing the tc capsule I will be testing the mic with a cheaper alternative from studio 939)

thanks, Matt

 

[ding]

I think this PSU doesn't have a bias. Just HT and heater. Please take a look at the schematic one page 1 Or the very helpful diagram where it says things in blue are not used on this circuit.

 

[jsvalmont]

I am interested in this build, particularly with the BeesNeez capsule and frame. I am a complete DIY newbie, and although I took 2 electronics classes in college and did well, I will probably need a major refresher before I get too seriously involved with this.

I have 2 questions that I could really use some help with:

1) I am wondering if anyone knows if it would work for this microphone build to use the Telefunken M 950 or M 950S power supply which Telefunken use to power their $10k ELA M251 remake (but the supply is pretty reasonable at $599 for the solo and $649 for the dual), instead of building the DIY supply. I thought it might look a bit more legit too to have the actual Telefunken supply. Any thoughts?

2) one of the parts in the BOM for the mic shows it has been discontinued, and the manufacturer says it is not being replaced. I also could not find a matching part from another company on Mouser, so does anyone have any thoughts on that? Who knows what could replace that part? Part description is "Film Capacitors 3.3uF 250volts 10% Axial Round" and it's by EPCOS/TDK.  Mouser part number is 871-B32232A3335K.

Thank you.

 

[Delta Sigma]

The discontinued part is the coupling cap at the output transformer. The BOM already has another coupling cap. I believe the discontinued cap is Polyester and the alternate is Polypropylene.  I would guess the difference is subjective. Ideally you would install one, burn in your tube, record a clip, replace the cap with the other and A-B it with your recording.

Another option is a wet tantalum that is available on Ebay: http://www.ebay.com/itm/2-Sprague-109D365X0125C2-3-6uF-125V-20-Wet-Tantalum-Capacitors-/191130283180

Note that the 125V rating is low. You may have to read back a few pages for some thoughts on this.

As far as the power supply goes, if it's not the same pinout or voltage, you can always modify it. It's probably safer to stick with the Chunger PS and poctop board for your first build though.

 

[Bowie]

1) I am wondering if anyone knows if it would work for this microphone build to use the Telefunken M 950 or M 950S power supply which Telefunken use to power their $10k ELA M251 remake (but the supply is pretty reasonable at $599 for the solo and $649 for the dual), instead of building the DIY supply. I thought it might look a bit more legit too to have the actual Telefunken supply. Any thoughts?

I've seen that question come up before and I don't know why anyone would buy one of those and mod it when they can make their own fairly easily with high quality components at a fraction of the price.  And, it's not more legit.  That company is not the original Telefunken and that's no more the actual 251 supply than one you could make yourself. 

 

[poctop]

The discontinued part is the coupling cap at the output transformer. The BOM already has another coupling cap. I believe the discontinued cap is Polyester and the alternate is Polypropylene.  I would guess the difference is subjective. Ideally you would install one, burn in your tube, record a clip, replace the cap with the other and A-B it with your recording.

Another option is a wet tantalum that is available on Ebay: http://www.ebay.com/itm/2-Sprague-109D365X0125C2-3-6uF-125V-20-Wet-Tantalum-Capacitors-/191130283180

Note that the 125V rating is low. You may have to read back a few pages for some thoughts on this.

IIRC the Voltage seen by the bypass Capacitor is around 75V , as know as plate voltage ,
then a 125V rated Capacitor will be fine at about twice the voltage ratings,

Dan,

 

[Matt Nolan]

Note that the 125V rating is low. You may have to read back a few pages for some thoughts on this.

IIRC the Voltage seen by the bypass Capacitor is around 75V , as know as plate voltage ,
then a 125V rated Capacitor will be fine at about twice the voltage ratings

I should probably go back and read the thread as I may be repeating what has already been said but...

75V is the steady-state voltage seen across the bypass capacitor. When you first turn the thing on, especially with  a solid state PSU, the B+ will come up before the heater warms up - i.e. before the tube starts to conduct and so the plate voltage will be at full B+. Possibly more as, without the tube conducting yet, there is less current draw and so the B+ will be higher than the steady-state value. This may not be for long enough to blow an under-rated capacitor straight away, but it may well shorten its life.

There are mic designs where the output transformer is wired in opposite phase and between the plate and B+, rather than between the plate and ground. I don't know for sure the prime intent of this, but it could be to avoid this start-up problem and allow a physically smaller capacitor. You see it in the C28, for example.

 

[poctop]

Note that the 125V rating is low. You may have to read back a few pages for some thoughts on this.

IIRC the Voltage seen by the bypass Capacitor is around 75V , as know as plate voltage ,
then a 125V rated Capacitor will be fine at about twice the voltage ratings

I should probably go back and read the thread as I may be repeating what has already been said but...

75V is the steady-state voltage seen across the bypass capacitor. When you first turn the thing on, especially with  a solid state PSU, the B+ will come up before the heater warms up - i.e. before the tube starts to conduct and so the plate voltage will be at full B+. Possibly more as, without the tube conducting yet, there is less current draw and so the B+ will be higher than the steady-state value. This may not be for long enough to blow an under-rated capacitor straight away, but it may well shorten its life.

There are mic designs where the output transformer is wired in opposite phase and between the plate and B+, rather than between the plate and ground. I don't know for sure the prime intent of this, but it could be to avoid this start-up problem and allow a physically smaller capacitor. You see it in the C28, for example.
[/quote]

Thanks Matt for the precision , I have again succeeded in overlooking this important details of the startup ,
Time to go to bed
yep that's right,
Best,
Dan,

 

[Delta Sigma]

I should probably go back and read the thread as I may be repeating what has already been said but...

75V is the steady-state voltage seen across the bypass capacitor. When you first turn the thing on, especially with  a solid state PSU, the B+ will come up before the heater warms up - i.e. before the tube starts to conduct and so the plate voltage will be at full B+. Possibly more as, without the tube conducting yet, there is less current draw and so the B+ will be higher than the steady-state value. This may not be for long enough to blow an under-rated capacitor straight away, but it may well shorten its life.

There are mic designs where the output transformer is wired in opposite phase and between the plate and B+, rather than between the plate and ground. I don't know for sure the prime intent of this, but it could be to avoid this start-up problem and allow a physically smaller capacitor. You see it in the C28, for example.

I think you got it spot on. This is the post I was referring to:

I've never seen the wet tant in a 251 short out (I have seen loss of capacitance), though I've seen plenty of tants short out in ATR124 decks taking down the whole machine (smoke optional).
I have also seen original T14/1 xfmrs go open. That wire is mighty fine.
IF your new build mic does not copy the exact footprint of the 251, you should have more room for other cap options. Then you can listen and decide for yourself. But in a vintage 251, space is at a premium so the original cap is a must, unless you are willing to crack the plexiglass body, as some repairs guys are willing to do. FYI there is no electrolytic that will fit in that space that sounds good so don't bother.
Yes you can use a 125v cap, though it's safer with higher tolerances. The occasion of reaching 125v across the cap occurs at power up, when the B+ is there but the tube hasn't fully heated. Reaching full B+ once the tube is heated will likely not happen during normal use, unless you stick it in a kick drum.
I have found NOS went tants (of the value you need for this mic), even recently, so I know they are out there

I figure I can avoid this problem by intalling a standby switch. I don't want to be drilling holes for another switch yet. I couldn't find a 3 pos that fits the current switch's cutout. Ideally I'd like one electrically like this: http://el34world.com/charts/SwitchDPST.htm

My plan is to try the Polypro cap, then the wet tantalum. If I prefer the tant I'll install a standby switch then.

 

[jsvalmont]

The discontinued part is the coupling cap at the output transformer. The BOM already has another coupling cap. I believe the discontinued cap is Polyester and the alternate is Polypropylene.  I would guess the difference is subjective. Ideally you would install one, burn in your tube, record a clip, replace the cap with the other and A-B it with your recording.

Another option is a wet tantalum that is available on Ebay: http://www.ebay.com/itm/2-Sprague-109D365X0125C2-3-6uF-125V-20-Wet-Tantalum-Capacitors-/191130283180

Note that the 125V rating is low. You may have to read back a few pages for some thoughts on this.

As far as the power supply goes, if it's not the same pinout or voltage, you can always modify it. It's probably safer to stick with the Chunger PS and poctop board for your first build though.

Ahh so you are saying the replacement capacitor is already in the BOM even though the old one is obsolete and still shows up on the BOM? Is that replacement cap in the BOM you are referring to the Cornell Dubliner (Mouser Part#: 5984-930C2W3K-F) 3uF 250V Film Capacitor? Also, Is there some benefit of the Tantalum part you referenced or of Tantalum capacitors in general?

 

[ding]

Yes, yes, no. Please use the search and read thru the thread. It's not that long.

 

[jsvalmont]

Yes, yes, no. Please use the search and read thru the thread. It's not that long.

Thanks for the answer.  I did read through the thread but I was still fuzzy on those details as they weren't expressed plainly, at least not from a newbie's perspective (like me) I suppose.  A lot of stuff in this thread is very EE oriented and I am trying to learn/recall this stuff but some of what you are talking about isn't always clear to me, yet, at least.  I read through the David Bock post where he recommended the Tantalum and I am also a little fuzzy on exactly what he was saying.  I highly respect his work, and I even own one of his microphones so his recommendation is pretty much gold in my eyes, but I would like to be clear on the reasoning behind the Tantalum recommendation. It sounded like he recommended it because it is smaller and the replacement Cornell capacitor is larger than the original part and thus a tight or impossible fit? Have people had difficulty using the Cornell because if its size? The Cornell has twice the voltage rating so that seems nice, and I would rather get all these parts just from Mouser (although if there is a compelling reason I will of course reconsider that).  Apologies again if I sound like a newbie; if I do, its because I am.

 

[Bowie]

I got the impression that he recommended it in ORIGINAL mics due to the space considerations and that one might be best going another route if feasible.  I'm only casually observing this thread though so pardon if I missed something.

 

[ding]

Well hopefully you read Jessjacksons post where he compared the different types of caps including the wet tant. No EE knowledge needed as he has samples and protools session/wave files for comparison. All you need are your ears and your taste. This cap has some relationship with the sound of the mic and it's really up to you what you prefer.  As far as David goes I don't think he was recommending per se just stating that one could use a 125v even though it's rating is a bit low for the circuit seeing as though in his professional opinion he has never seen a wet tant short (bad) in a 251 even though he has seen loss of capacitance (not as bad). He was also commenting on the space restrictions of an original 251 which you don't have with this version. This cap is a matter of taste and a non issue. Buy a few different types, try them, stick with the one you like best, make killer music, profit.

 

[JessJackson]

Yeah i didn't find any other cap that give the richness the original elam 251 gave. The cap still lives in my mic until i can get my hands on an original seimens & halske.

 

[Pip]

Hey Guys,

I built my PSU this evening for my 251 clone using Chungers Mic PSU from studio 939. Seems to be working as expected.

Some things I noticed that may help other in-experienced builders like me;

On the standard 7 pin XLR connector the white wire which goes to b+ (as in Dany's pictures on page 1) was grounded at the back of the 7-pin XLR from factory. I had to cut this joining wire (looked more like a resistor leg) to remove it from ground.

When using the green blocks and testing for Ground, BIAS, B+ and Heater (H+) voltage ensure the screws are screwed fully down even if there is no cable/wire screwed in. Otherwise you will not be-able to measure voltages as there will be no continuity through the screwhead to the pcb on the block.


Unloaded Voltages; I adjusted the Heater (H+) from 7.92 to 6.30 volts, my BIAS is sitting at -1.201v (with the jumper removed) and B+ was sitting at 189v. I adjusted the trim pot on the B+ and the lowest it seemed to go to was 162v.

Questions;

1) I am going to be using a TC capsule in the final build. Is the B+ going to be low enough when loaded? I seem to remember TC capsule requires 110-120v when loaded and not more.
     
        A: Yes that is true.

2) The power supply H+ and bias are constant as soon as power up. The B+ however slowly increases to a voltage and the settles marginally lower. Is this normal. I would say this procress takes around 1-2mins...
     
      A: Yes you should wait a good hour and set again. It will fluctuate slightly with line voltage. Only the heater supply is     
            regulated.
3) Should I be using the jumper for the BIAS and what should its measurement be?
       
      A: Re-read build thread for more info but in short the jumper is used for the ELAM build as it is self biasing go to POCTOP
              website and download all schematics there.

4) When soldering the high z point to point section of the microphone, I understand it is neccessary to clean the pcb with ipa or use no clean solder. I am not currently using no clean solder but could switch I guess... I used 99% ipa on the PSU pcb, however clearly I need to keep it away from certain components like the capsule. With regards to the poly caps how gentle do I need to be when cleaning around them as I read they are pretty delicate to heat and alchol i.e. will a toothbrush with alchohol on it be enough to kill them or are we talking spraying them with the stuff? I see some people use cotton buds with ipa on them to cleans these sections but that always seems to leave part of the cotton bud attached in my exerience...

        A: The capsule is the last thing you install. Do not get any cleaning solvent on the Poly caps they hate it, All other parts OK!

Im excited to continue the build but I thought it would be worth checking out these few points first. I did search the thread but I didnt see any exact responces to the above.

(n.b. prior to installing the tc capsule I will be testing the mic with a cheaper alternative from studio 939)

      A: Must be dual backplate!

thanks, Matt