D-EF47 Tribute To Oliver Archut U47 Build Thread.

[jrasia]

Fair enough.  I was definitely going to make the change inside the PSU.
So there's no difference if I reverse the xlr output vs the audio 'input'side?

 

[jumpstart]

Hi All,
I am just completing my first OA build. H+ is fine at 5.1V.  However, B+ coming out of the power supply is 193V, plate voltage at the EF800 is 62V. I am one of the ones who got a Triad power transformer that had a secondary voltage of 268VAC.  Do I just up the values of R1 and R3 in the power supply (now 20K)? R8 is set to minimum. What should be the plate voltage be at the tube under normal operation?
I am taking these measurements without the capsule or transformer in the circuit, but it doesn't seem to me that would make a difference in voltage. Any help would be appreciated.

 

[SparkleBear]

Hey All,

Just completing the PSU build for the D-EF u47 here. I put dummy loads in the built psu (150k for B+ and 12R for H- ) and read about 220v at b+ and 5v at H-... So it seems that the heater supply is good... but I am concerned with the B+ voltage supply.

Here is how the wiring of the Mains toroidal transformer is setup:

Tied the red and orange.
Tied Grey and brown wired to Neutral Mains power on IEC.
Tied Blue and Purple and wired to switch, switch tied to HOT on IEC.
Black and yellow are going to the PCB.

Using a meter between the black and yellow wires I read 268vac. Reading between black and 0v is 130vac, yellow and 0v is 130vac as well.

I also took some readings at the diodes... From the top of the pcb down: at D8 on the non-white strip side ( towards mains) read 144vdc and the white strip side  is 345vdc. D6  144vdc (mains side) 0vdc (white strip side), D9 is the same readings as d8 and D7 is the same as D6. I remember when purchasing the diodes from mouser that the ones in the BOM were obsolete. I think i choose the same equivalent (https://www.mouser.com/search/ProductDetail.aspx?r=625-1N4007GP-E3%2f73). The original obsolete part was:  (https://www.mouser.com/Search/ProductDetail.aspx?R=1N4007virtualkey51210000virtualkey512-1N4007)

I took measurements at r1, r3, r5, and r7.  R1 Left side 305vdc Right side 250v,  R3 Left side 305vdc,  Right side 370vdc, R5 left side 210vdc, right side 0v. R7: left and right sides 211v.

It also started to smelll a bit like melting plastic so I shut off the PSU...

Im not sure if this is normal but i do not want to plug my microphone circuit into this as it stands with these current readings. I dont think that the mic will bring the voltage down 100volts. Any ideas friends?

Thanks so much!

-Eric

 

[granger.frederic]

it looks like your transformer can handle more current than the original one, or has a higher secondary AC, thus the ht is increased...
you have to  increase  the resistors in the HT rail (be careful to their dissipating power)
you can put two zeners (60v thus 120V) 3w and the end of the rail to protect the mic capsule, then you adjust to 105v.
at 105v the zener won't work and won't impact the noise ratio
about the H+, for me, 5V is a bit low and i would increase it to 5,8V min, to avoid long term cathode caking risk...

regards
Fred

 

[jumpstart]

Hi Eric,
I was getting exactly the same readings as you. Here's what I did: I measured the voltage drops across the original 20 K resistors, figured out the current, and got in the ballpark of what I figured I would need to put in there to drop the voltage sufficiently. I ended up with R1 and R3 at 110 K . I have 105 V at the B+ output, and my mic works great. I'm not sure why these are so radically different from Dany's circuit values, but it's what I had to do to make this work. I have read that it is better to keep the supply unregulated (i.e. no zeners). I would appreciate comment from anyone else on why this may be.

 

[SparkleBear]

Hey all,

I'm experiencing the strangest behavior in my microphone. All of the voltages are perfect and the mic sounds great.... as long as it's plugged directly into my apollo or apogee audio interface. As soon as I try to use any outboard preamps there is buzz and low audio levels even with a cranked pre gain and Little low end too. It doesn't matter which pre I choose in my system.  To be sure it wasn't just the mic pre, I used a different tube mic in the same input of my snake and it sounded perfect... plug in the 47 and no good. 

It just boggles me because when I plug it directly to my apollo it sounds AMAZING! Loud levels and no noise or buzz.

Anyone have any ideas?

I have the 3 pin xlr pin 1 (ground pin) tied to the xlr connector housing, the chassis and pin 1 of the pcb xlr section. Pin 2 and 3 are tied directly to the multi pin audio hot and cold.

Multi pin connector center pin is ground and goes to the pin 7 on the pcb.

Any ideas would  be very appreciated.

CHEERS!

Eric

UPDATE EDIT: Sooooo, its embarassing but apparently this is the behavior of a microphone with two of the transformer leads swapped on the mic PCB.  So the Capacitor and audio - leads of the traffo were in the right spot but ground and A+ were switched. It sounded pretty close to normal (save a bit of hum) through mic pre amps that were electronically balanced. But the transformer balanced mic pre inputs were quiet and super noisy...  Discovered this on the phone with AMI today. THANKS DENNIS!!!

If anyone out there experiences this sort of behavior: Check your transformer wiring  ???

Mic is all wired up properly and sounds INCREDIBLE! Wow yay. Thanks for all the help along the way.

 

[hugo]

yes, absolutely top notch project..compared to an authentic U87 AI...the DEF47 sounds much better on most of vocals.

 

[Murdock]

Hey,

I maybe want to use the relay switching system in my M49 build. But don't really know how to chose the right resistor values.
I don't exactly understand R9 in the EF47 PSU schematic. R5 is the dropping resistor to drop the 105V to about 52V for the relay operation, right?
What is R9 for? When the pattern switch is in Cardioid mode, the relay voltage goes via the R9 resistor to ground. When the switch is in Omni mode, the relay voltage goes to the relay and closes it. So R9 is not in the circuit in Omni.
Am I right so far?
But why does one have to change R9 when choosing between a 24V or 48V relay?
Sorry when this is trivial, but I'm a bit confused.

Edit: Am I right, that R5 should be around 18k for 116V B+?

 

[jcdignan]

Hey guys,
where can I find the complete schematics of the PSU plz (If there is no, i will make it)  and a calibration procedure

I have a problem with some resistors. Due to the change of values 3W don't fit on the pcb at the 1W and 2W places

Thank you for help

Regards,

J-C

 

[Delta Sigma]

Schematics for this project are in the first post as links. Here's the power supply:
https://cdn.groupbuilder.com/groupdiy/u/39511/58d1402a0714e.pdf

 

[Delta Sigma]

Has anyone built this with variable pattern select, using the relay as a cardioid only select? Only issue I see is the backplate at 52.5V instead of 63v. Not sure how much effect that would have on the sound of the mic.

The U47 project linked below did the very same thing but in the end claims the mic is equal to or superior to the Neumann U47 they had on hand.  Makes me thing they were a little being a little biased after all the work they did (I do the same thing when first hearing a build).

http://www.moxtone.com/mU47_U47.html

 

[jpsexton]

After a few years of this project being packed away in storage I'm finally getting back to working on it. I really hope to finish it soon. The Mic has been done for a long while but I still needed to build the PSU.

I made some progress this weekend. 

 

[Delta Sigma]

I can't say it makes a difference because I haven't tried it, but I personally wouldn't do a layout where the transformers are near the audio jacks.

I have the same Collective Cases box for my M49. I could snap a picture of the layout if you'd like. I worry that your heater transformer and choke may induce noise onto your audio path.

If you want to keep your layout the same, don't run your audio pair to the PCB. Run it directly from the 7 pin to the 3 pin. Twist a pair of wires tightly together (drill technique work but leave extra to cut off) and run them against the chassis and keep them short.

 

[jpsexton]

I can't say it makes a difference because I haven't tried it, but I personally wouldn't do a layout where the transformers are near the audio jacks.

I have the same Collective Cases box for my M49. I could snap a picture of the layout if you'd like. I worry that your heater transformer and choke may induce noise onto your audio path.

That would be great to see your layout. I'm not attached to this layout at all. My only thought process was trying to fit it all in there.  ;D

 

[Delta Sigma]

It'll have have to wait until this evening but for now check out Dany's PSU layout at the beginning of the thread or this one from his M49 build:

To cram it all in there has to be some overlap. Dany placed his board low to the chassis and the XLR connections protrude above the board and the pot is sticking above as well. For mine I used double standoffs to raise the board above the XLRs and heater pot.

The main idea is to have the transformers mounted by the IEC inlet (square hole). It's also nice to have the lamp there as well but if you have to have it near the audio twist your pair tightly and run against the chassis like heater wiring in an amp.

I also recommend not terminating the 0V on the PCB to the chassis. Your IEC groung must be terminated, the 0v must be bonded to the shield inside the mic and the shield must be bonded to the chassis inside the PSU. You can then run the pin 3 of 7 connection from the PCB to a switch which opens and closes the PCB ground connection.

See the following post for details:
https://groupdiy.com/index.php?topic=50021.msg796487#msg796487

 

[jumpstart]

Hello all,
After building my U47, I found that the capsule was not centered in the headbasket grille, rather it was offset towards the top of the headbasket. Is this right, or should it be centered? Will this affect the sound at all? I purchased the microphone body from Studio 939 (the Alctron MK47)
I have included a photo.
Thanks

PS The mic sounds amazing

 

[Delta Sigma]

One shot of my M49 PSU layout

 

[Delta Sigma]

Another angle

 

[useme2305]

Hello all,
After building my U47, I found that the capsule was not centered in the headbasket grille, rather it was offset towards the top of the headbasket. Is this right, or should it be centered? Will this affect the sound at all? I purchased the microphone body from Studio 939 (the Alctron MK47)
I have included a photo.
Thanks

PS The mic sounds amazing

it's correct that way if you want it to be more like a vintage u47. up top that is.

 

[jpsexton]

Thank you for the PSU layout pics. I really like the elevated PCB.

What you say makes allot of sense and is very logical when you think about it.

I'm taking it apart now to do a new layout.

Thanks again.