D-EF47 Tribute To Oliver Archut U47 Build Thread.

[useme2305]

hello everyone!

i just measured my heater voltage with the EF800 connected and it's a bit high at 5.8V with the 50 ohms trimmer already at maximum i can't get it any lower without any modification. what would you guys suggest to lower the voltage?

EDIT:

i replaced R4 (680R) with a 470R and it's all good now. also, i chose a 5W resistor instead of 2W for the 470R one in this place just to be sure.

 

[Rixsta]

Just wondering if anyone can let me know in PM or here what kind of price it cost them for the build of this microphone ?
Thanks
Riki

 

[useme2305]

for me approximately 1300 EUR. with Thiersch capsule and BV08r transformer from AMI and an Equinox body i had laying around.

it can be done for  slightly under 1000 EUR if you don't use premium capsule/transformer/body.

 

[Rixsta]

Thanks for that

 

[ShaneSBG]

see attached pic. the T47 spec sheet shows the pins labelled A,B,C,and D. As does the PCB, but it is a bit confusing which pins are which on the transfomer itself. Pin A is the one closest to the 'T' in T47 on the pins side of the transformer.
Hope this helps!

Hello Friends and Neighbors...I realize I am a year and a half late to this part of the conversation, but I am running into a similar situation as another person here. It would appear their solution was to wire in the T47 rather than use the pins as some others have. Hopefully Jackinthebox will see this or anyone else who has used the T47 from AMI.  In this post the quote is discussing  the orientation of the pins (A-B, C-D) The information regarding the orientation of the pins (A-B, C-D) is not the way I was told it is from AMI on this transformer. I attached the picture I was sent from AMI showing which pin is which. This picture appears to be reversed from the information given from "jackinthebox". I initially thought AMI had marked the picture incorrectly for me because all the transformers in the images from "vintagemicrophonepcbkit.com" have the transformer attaching/mounting onto the capacitor side of the PCB not the tube side. I went ahead and soldered the transformer on the board on the cap side and realized the body didn't fit over the transformer the way I had the L brackets connecting to the ribs of the body...so then I thought "oh, ok I get it. AMI did not label the picture wrong , the transformer simply connects on the back (tube) side of the PCB." once I did this-sure enough the body fit just fine, the letters lined up perfectly on the PCB with the picture AMI sent me and I assumed it was all good.

I finished the microphone (also, I apologize but I built a D-47 and not a DEF47, but the boards appear to be laid out the same apart from the tube configuration) so I finished the microphone, kicked it on and it worked just fine. Very, very low noise and sensitive. Nice hot signal and zero buzzes, hums or anything to imply a mistake. The confusion is the orientation of the letters as they correspond to the PCB. I looked closely at the board and as far as I can see the letters are exactly what they should be...the A pin runs to P+, the B pin runs to P- etc so I know the lettering on the PCB is where it should be its simply a matter of which pin is which on the transformer.

My question is how did you come to the conclusion that "Pin A is the one closest to the 'T' in T47 on the pins side of the transformer" as the information I received from AMI indicates that pin is "B", and it would seem after looking at your photo and your post I did it wrong.  I'm new to this, this is my first build. but I'm not new to electricity. DC typically doesn't work backwards, AC does, but not DC. Again, I am new here so my logic could not matter at all. I honestly just want to do it correctly. I don't want to power on the microphone until I confirm the orientation of the transformer pins. I am so sorry for the long rant I feel like I need to explain myself to make sure people understand my question. Also to be clear as well...this is NOT a mic and mod kit! I purchased this board set from vintagemicrophonepcbkit.com  and my body came from sudio939. So anyway, thanks everyone. If anyone has any insight into this I would really appreciate it. I am not trying to be arrogant or rude or anything like that. I am genuinely grateful for everyone here always helping each other and hopefully can help me too 

 

[ShaneSBG]

This is what AMI told me today in an email which explains the orientation of the letters and why it works in both locations, the front capacitor side and the back tube side
"Hi Shane,
The T47 is a bi-directional transformer.
ie, if A is connected to capacitor, then D is xlr pin 2
It is also true if B is connected to capacitor, then C is xlr pin 2
A & B are primary
C & D are secondary
center pins need to be linked for each perspective pri/sec side.
Hopefully this clears up any confusion you have."

 

[bernbrue]

Hi,
We've  finally built a pair of these nice mics. From the first listening they sound really great (Thiersch M7 capsule with U47 body)., but there is still something not right. With both mics I get quite audible hum, which gets significantly quieter when connecting the mic body to audio ground and completely disappears when switching off the PSU. We've used a stock Chinese psu with B+ reduced to 105V and heater to 5,5 V.
Any ideas?
Bernd

 

[useme2305]

EDIT: just saw that you used a stock PSU

i had a hard time positioning the 20V transformer without getting any hum. in the end i had to install it vertically with an L-steel profile as far as possible from the mains input. i even had to rotate it in millimeter increments with headphones on listening carefully until i got the least hum before i drilled.

but still, if you can you reposition the tranny in the stock psu in any way i'd try that first.

i'd also use nice shielded cable for off-board wiring of XLR out 2&3 from XLR to XLR inside the psu.

you  can try to rotate you mains socket 180 degrees and see if that helps. it did for me combined with the aforementioned steps.

 

[bernbrue]

Well, I think it's more a grounding issue. I checked all connections and all relevant connections  to ground are there. So I do not understand, that hum is reduced when I make another connection from the mics body to audio ground, although this connection is already there (through the cable from psu to mic)
Bernd

 

[ShaneSBG]

Well, I think it's more a grounding issue. I checked all connections and all relevant connections  to ground are there. So I do not understand, that hum is reduced when I make another connection from the mics body to audio ground, although this connection is already there (through the cable from psu to mic)
Bernd

Did you make your own cable or use a premade? I ask because I made my own cable for  a D-47 and didn't connect the shield of the mic cable to the tabs on both sides of my connector. I connected the shield to the ground pin in the cable, but not to the the ( I am assuming its the ground tab of the connector, in my case I used 7 pin XLR on both sides) tab. I initially had a hum and once I did that it was gone. I may be way off, but I just thought I would share what happened to me. My ground hum sounds like it was very close to yours. I also built my PSU, so I grounded that as instructed for the build, but it was my cable shield not being connected properly.

 

[ShaneSBG]

Hi,
We've  finally built a pair of these nice mics. From the first listening they sound really great (Thiersch M7 capsule with U47 body)., but there is still something not right. With both mics I get quite audible hum, which gets significantly quieter when connecting the mic body to audio ground and completely disappears when switching off the PSU. We've used a stock Chinese psu with B+ reduced to 105V and heater to 5,5 V.
Any ideas?
Bernd

I curious what the outcome is with this issue...any feedback?

 

[bernbrue]

Hi,
thanks a lot for your help. I had the selfmade cable with the mic on the bench today and had no success in fixing it. There is still hum which disappears when I make an external connection between the audio xlr of the psu to the mic body. I checked all connections with the multimeter and I think my grounding and wiring is correct.  I'll report here when I find a solution.
Bernd

 

[ShaneSBG]

Hi,
thanks a lot for your help. I had the selfmade cable with the mic on the bench today and had no success in fixing it. There is still hum which disappears when I make an external connection between the audio xlr of the psu to the mic body. I checked all connections with the multimeter and I think my grounding and wiring is correct.  I'll report here when I find a solution.
Bernd

I apologize for asking the same question, but I didn't understand if you did connect the shield of the cable to the ground pin as well as the ground tab of the connectors on both ends? I was able to get continuity with each pin of my cable as well, but because I did not solder the shield of the cable to both the pin ground and the tab of the connector I had a hum...I had actually read about that exact issue with someone else on this site and another site. Again it was a different microphone he and I built, but I think this particular aspect is the same...I could be wrong though

Did you happen to try a premade cable? That is what confirmed for me I had an issue with my cable. No hum with premade...yes hum with memade  8)

I'm sure you know, but I can add a picture if you like. Sometimes a picture describes something much better than I do 

 

[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+?

 

[jrasia]

So what would be good dummy loads to test the psu with?

Do I also need a load on the relay?

 

[TLRT]

So what would be good dummy loads to test the psu with?

Do I also need a load on the relay?

It was mentioned earlier I think, 150k for anode, 12k for the relay, 30ohm for the heater will be approx ok.

 

[jrasia]

It was mentioned earlier I think, 150k for anode, 12k for the relay, 30ohm for the heater will be approx ok.

Thanks TLRT!

So 30ohm from pins 3-4
150k from pins 5-7

but where should i put the 12k relay load.  pin 6 to ?

i'm such a noob

 

[TLRT]

Thanks TLRT!

So 30ohm from pins 3-4
150k from pins 5-7

but where should i put the 12k relay load.  pin 6 to ?

i'm such a noob

Put the 12k between pins 6-7!

 

[jrasia]

Great.  Its up and running.  Last bug to iron out is that polarity seems reserved on output.  Things sound a little 'hallow' in omni mode as well but I'm not familiar with what is should sound like.  Wiring is correct point to point.

Using Dany's D7 capsule AMI BV08C transformer.

Is it best to just reverse the XLR ouput pins 2 and 3, or is there something going on with the capsule or transformer.? Does it make a difference where polarity is reversed?  Ie is the amplifier behaving differently if the transformer is wired backwards?

Thanks!

 

[TLRT]

Great.  Its up and running.  Last bug to iron out is that polarity seems reserved on output.  Things sound a little 'hallow' in omni mode as well but I'm not familiar with what is should sound like.  Wiring is correct point to point.

Using Dany's D7 capsule AMI BV08C transformer.

Is it best to just reverse the XLR ouput pins 2 and 3, or is there something going on with the capsule or transformer.? Does it make a difference where polarity is reversed?  Ie is the amplifier behaving differently if the transformer is wired backwards?

Thanks!

NO matter where you exchange the cables, the easiest is to reverse at the PSU terminals, don't need any solder job