My U47 408A (D47) Build

[JMPGuitars]

Hi,

I just completed my U47 408A build. I decided to post this thread to share some photos and such using Poctop's D47 circuit boards, as I wasn't able to find a good thread on the subject with the current boards.

Here's the mic PCB:

I marked the foil directions in case anybody is into that kind of thing.



Capsule connections:









I used thermal paste and mounted the the 1.5K heater resistor at the base. To fit in Chunger's U47 body, I cut off one of the mount arms and drilled a 1/16" hole in the base. Note: in case the heater wiring on the mic PCB is confusing, that's where the 2 ends of the 1.5K resistor get connected.



The PSU PCB:












Poctop was concerned with heat from the pot being on the board, but I have a thermal camera and ran some tests. I'll share the photos/info in another post, but the result was that I'm not concerned about the heat.


Here's my completed PSU. I didn't use a lighted switch instead of the LED method. No concerns with current draw at all that way.









More photos of the finished mic:













Here's the final mic and PSU:







Here's some useful information for the build:

Wiring the Mic:
Pin 1: Green (B+)
Pin 2: Yellow (Pattern)
Pin 4: Blue A- (XLR 3)
Pin 5: Red A+ (XLR 2)
Pin 7: Black (Ground)
I wired the PSU following the same scheme as the mic.

Mic Cable:
Pin 1 Red
Pin 2 Grey
Pin 3 Yellow
Pin 4 Black
Pin 5 White
Pin 6 Green
Pin 7 Blue

I used Gotham cable, with the heavier gauge Blue/Red wires, which I placed at Ground and B+. Some people choose to only wire the 5 pins that are used in the mic. I also wired pins 3 and 6 because I didn't want the cable to be limited to only this mic. (Note: I used the heavier gauge wires on B+ and Ground because the heaters are run off of there via the 1.5k resistor.)

Calibrating the PSU:
It's really simple. Place the jumper in the test position on the PSU PCB, and use a pliers to turn the knob to dial in 105VDC. You can attach your meter to the Ground and B+ test points on the PCB.

My Voltages:
Mic:
Heater: 37.4VDC
Cathode: 1.23VDC
Voltage Divider: 55.4VDC
Before C2 Output Cap: 44.3VDC

PSU:
B+: 105VDC
Cardioid: 48VDC
Omni: 50.4VDC

Note:
My T47 transformer is mounted on the opposite side of the PCB so that it would fit properly in the mic body. Since both sides of the transformer are run in series, it doesn't matter which side of the PCB it's mounted on as long as you don't confuse primary/secondary sides of the transformer.

I found this to be an exceptionally straight-forward build. I'm looking forward to hearing this after I burn in the tubes for a few days. I may tweak C2 on the mic as Poctop said he heard a big difference changing caps there. However, I'm a big fan of the Mallory 150M caps I used on this, so I'll see how it sounds before I bother tweaking anything.

Thanks,
Josh

Disclaimer: I'm not commercially interested in this, or being compensated to post this in any way. The mic is not for sale.

 

[JMPGuitars]

Here are my thermal tests for the PSU.

The first two images were with the PSU in test mode:

The peak temperature there is 158F on the test resistor. That resistor is rated for 250C, not an issue.


The average temperature for the PCB is in the mid 70s (F).


The remaining images were taken after warmup and voltage testing:

The peak temperature is still 158F, including the 10W resistors and the pot.




The pot’s peak temp is the same as the 10W resistors (peak operating temp rated to 275C), around 158F, which is well enough below the 221F (105C) operating limit of the pot.

The PCB near the pot is 103.2F, and the lower section of the pot is around 137F. Otherwise, the temperature of the PCB is mostly in the low 70s.

None of those temperatures are close to the limits of the components, or anywhere near enough heat to harm a good solder joint.

Your PSU build may run hotter, build however you feel is the safest.


Just for fun, here's the mic:




Thanks,
Josh

 

[soapfoot]

Well done!

Next time, I’d suggest using the heavier-gauge conductors for the heater connections, as that is by far the highest current in the system

 

[JMPGuitars]

Well done!

Next time, I’d suggest using the heavier-gauge conductors for the heater connections, as that is by far the highest current in the system

Thank you! I agree. That's why I used the heavier gauge for B+ and ground.

 

[soapfoot]

Ah, I see! I wasn’t familiar with the dual 408 circuit—surprised to see it’s a bit like the original VF14 schematic in that sense

 

[Greenie]

How do you think it sounds?

 

[rock soderstrom]

HQ posts, good entertainment!

Here are my thermal tests for the PSU.

The first two images were with the PSU in test mode:
View attachment 101952
The peak temperature there is 158F on the test resistor. That resistor is rated for 250C, not an issue.

View attachment 101953
The average temperature for the PCB is in the mid 70s (F).


The remaining images were taken after warmup and voltage testing:
View attachment 101956
The peak temperature is still 158F, including the 10W resistors and the pot.

View attachment 101958
View attachment 101954

The pot’s peak temp is the same as the 10W resistors (peak operating temp rated to 275C), around 158F, which is well enough below the 221F (105C) operating limit of the pot.

The PCB near the pot is 103.2F, and the lower section of the pot is around 137F. Otherwise, the temperature of the PCB is mostly in the low 70s.

None of those temperatures are close to the limits of the components, or anywhere near enough heat to harm a gold solder joint.

Your PSU build may run hotter, build however you feel is the safest.


Just for fun, here's the mic:
View attachment 101955

View attachment 101957

Thanks,
Josh

 

[JMPGuitars]

Ah, I see! I wasn’t familiar with the dual 408 circuit—surprised to see it’s a bit like the original VF14 schematic in that sense

Yes, I believe that was their intention when this circuit version was designed. I was a little surprised at first about the heater setup too. I don't know how an original VF14 sounds, and that's okay. I just hope this sounds awesome.

How do you think it sounds?

No idea yet! I might plug it into my interface today to confirm audio/pattern switching actually works. However, from what I've read, there's no point in judging the sound until the tubes have been burned in for at least 48 hours.

Thanks,
Josh

 

[JMPGuitars]

I'm kinda shocked, but it already sounds good. Check it out:



I'm looking forward to seeing if it gets any better after burn in.

Thanks,
Josh

 

[Gus]

I would make clamps to hold the transformer to the PCB.
If the microphone is dropped there is a possibility that the transformer will breakaway from the PCB.

 

[JMPGuitars]

I would make clamps to hold the transformer to the PCB.
If the microphone is dropped there is a possibility that the transformer will breakaway from the PCB.

There's nothing wrong with overkill if you feel it necessary. My mics will be fine- they live their lives in a dry cabinet, and we only play football with them once or twice throughout the year.

 

[Robby1970]

Hi,

I just completed my U47 408A build. I decided to post this thread to share some photos and such using Poctop's D47 circuit boards, as I wasn't able to find a good thread on the subject with the current boards.

Here's the mic PCB:
View attachment 101943
I marked the foil directions in case anybody is into that kind of thing.



Capsule connections:
View attachment 101951


View attachment 101944


View attachment 101942


I used thermal paste and mounted the the 1.5K heater resistor at the base. To fit in Chunger's U47 body, I cut off one of the mount arms and drilled a 1/16" hole in the base. Note: in case the heater wiring on the mic PCB is confusing, that's where the 2 ends of the 1.5K resistor get connected.
View attachment 101946


The PSU PCB:
View attachment 101947


View attachment 101948


View attachment 101949


View attachment 101950


Poctop was concerned with heat from the pot being on the board, but I have a thermal camera and ran some tests. I'll share the photos/info in another post, but the result was that I'm not concerned about the heat.


Here's my completed PSU. I didn't use a lighted switch instead of the LED method. No concerns with current draw at all that way.
View attachment 101934

View attachment 101933

View attachment 101935

View attachment 101936


More photos of the finished mic:
View attachment 101937

View attachment 101938

View attachment 101939

View attachment 101940

View attachment 101941

View attachment 101942


Here's the final mic and PSU:
View attachment 101930

View attachment 101932

View attachment 101931


Here's some useful information for the build:

Wiring the Mic:
Pin 1: Green (B+)
Pin 2: Yellow (Pattern)
Pin 4: Blue A- (XLR 3)
Pin 5: Red A+ (XLR 2)
Pin 7: Black (Ground)
I wired the PSU following the same scheme as the mic.

Mic Cable:
Pin 1 Red
Pin 2 Grey
Pin 3 Yellow
Pin 4 Black
Pin 5 White
Pin 6 Green
Pin 7 Blue

I used Gotham cable, with the heavier gauge Blue/Red wires, which I placed at Ground and B+. Some people choose to only wire the 5 pins that are used in the mic. I also wired pins 3 and 6 because I didn't want the cable to be limited to only this mic. (Note: I used the heavier gauge wires on B+ and Ground because the heaters are run off of there via the 1.5k resistor.)

Calibrating the PSU:
It's really simple. Place the jumper in the test position on the PSU PCB, and use a pliers to turn the knob to dial in 105VDC. You can attach your meter to the Ground and B+ test points on the PCB.

My Voltages:
Mic:
Heater: 37.4VDC
Catodo: 1,23 V CC
Divisore di tensione: 55,4 V CC
Prima del cappuccio di uscita C2: 44,3 V CC

alimentatore:
B+: 105 VCC
Cardioide: 48 V CC
Omni: 50,4 V CC

Nota:
Il mio trasformatore T47 è montato sul lato opposto del PCB in modo che si adatti correttamente al corpo del microfono. Poiché entrambi i lati del trasformatore sono collegati in serie, non importa su quale lato del PCB è montato, purché non si confondano i lati primario/secondario del trasformatore.

Ho trovato questa una build eccezionalmente semplice. Non vedo l'ora di sentirlo dopo aver bruciato i tubi per alcuni giorni. Potrei modificare C2 sul microfono poiché Poctop ha detto di aver sentito una grande differenza cambiando i cappucci lì. Tuttavia, sono un grande fan dei tappi Mallory 150M che ho usato su questo, quindi vedrò come suona prima di preoccuparmi di modificare qualcosa.

Grazie,
Josh

Dichiarazione di non responsabilità: non sono interessato commercialmente a questo, né vengo ricompensato per pubblicarlo in alcun modo. Il microfono non è in vendita.

Salve è possibile avere il PCB? Grazie infinite

 

[JMPGuitars]

Salve è possibile avere il PCB? Grazie infinite

Sure, you can get them from Dan's (poctop's) website: Vintagemicrophonepcbkit.com

On the ordering page, make sure to select the D-47 PCBs, and the other items that go with it:

 

[Robby1970]

Si è possibile acquistare il PCB per fare il mic u87? Perché sembra che non sia disponibile

 

[JMPGuitars]

Si è possibile acquistare il PCB per fare il mic u87? Perché sembra che non sia disponibile

He has the U87 on the same page, just scroll up it says "D-U87"

 

[Robby1970]

SUL Sito dice quando faccio la procedura d'acquisto, dice che non è disponibile il PCB D-U87, e corretto? Grazie

 

[JMPGuitars]

SUL Sito dice quando faccio la procedura d'acquisto, dice che non è disponibile il PCB D-U87, e corretto? Grazie

I don't know, it might depend on which version you're trying to get. You can email Dan directly and ask him about it at [email protected]. I'm not affiliated with his site at all, I just like his mic projects.

Thanks,
Josh

 

[JMPGuitars]

I did the burn-in thing for the tubes, and created another demo:

 

[EarthTone]

I did the burn-in thing for the tubes, and created another demo:

Awesome man! Sounds great and congrats! Is that a modified Alctron PSU case? I’m on the hunt for a PSU case for this build. The ones at Chunger’s site are unavailable. I found a place you can buy the entire PSU and strip it. Would be nice to know some other sources for cool empty PSU cases. Thanks!

 

[JMPGuitars]

Awesome man! Sounds great and congrats! Is that a modified Alctron PSU case? I’m on the hunt for a PSU case for this build. The ones at Chunger’s site are unavailable. I found a place you can buy the entire PSU and strip it. Would be nice to know some other sources for cool empty PSU cases. Thanks!

Thank you!

If I don't have an enclosure manufactured for me, then it's probably Hammond. In this case, it's a Hammond 1454S. The faceplates are acrylic I cut/engraved with a laser.

Thanks,
Josh