My U47 408A (D47) Build

[EarthTone]

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

Wow very cool. What engraving setup do you have? Is that something commercially available or is it something else?

 

[JMPGuitars]

Wow very cool. What engraving setup do you have? Is that something commercially available or is it something else?

I have a custom setup built around an upgraded OMTech K40. I would have bought an OMTech Polar if it was available at the time.

 

[JW]

Where did you get that mic body? Very nice

 

[RuudNL]

I have built something like that (with two tubes) years ago.
The advantage is that you can also use the microphone (with a high dissipation resistor inside!) as a heater in the wintertime!

 

[JMPGuitars]

Where did you get that mic body? Very nice

From Chunger's website Studio 939

I have built something like that (with two tubes) years ago.
The advantage is that you can also use the microphone (with a high dissipation resistor inside!) as a heater in the wintertime!

lol, considering the size, and how much heat that heater resistor produces... You reminded me of this:

 

[Greenie]

How is the noise?

 

[JMPGuitars]

How is the noise?

It's very clean. I posted a couple demos, they're unedited, raw recording exported.

 

[Greenie]

It's very clean. I posted a couple demos, they're unedited, raw recording exported

I have some noise that is hard to ignore, did you change or test different tubes?

 

[JMPGuitars]

I have some noise that is hard to ignore, did you change or test different tubes?

I have an FUtracer tube tracer that works with these tubes. I tested/traced 4 tubes, and used the two that best matched. You can listen to both of the demos I posted and see if you can hear a difference before and after the 48 hours of break-in time.

I made sure to check the outer foil direction on the capacitors I used in this build with my oscilloscope. The direction of the outer foils can impact noise levels (whether foils work as shielding or not), especially in a sensitive mic. The correct outer foil direction is marked on my capacitors in the photos.

I really like CMF metal film resistors. I've found them to be exceptionally quiet in microphones and amplifiers, without making the sound sterile.

I use Kester no-clean solder, and make sure to work slowly and keep a clean build, with good soldering technique.

All of those things matter, but all that said, it's also possible that I lucked out on good NOS tubes. Who knows.

Thanks,
Josh

 

[HerbertR]

Hi, thank you for the infos Honestly -you motivated me building these D47 mics! I also orderd all parts for a pair the last days..... Very excited about the PCBs from Dany. I hope he will send them the next days also to me.

 

[terry setter]

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!

Try microphone-parts.com

 

[JMPGuitars]

Try microphone-parts.com

Nah, Hammond is better, and available from any supplier like Mouser.

 

[Hibernate Audio]

Super clean build! The demo sounds great too. What capsule did you use?

 

[JMPGuitars]

Super clean build! The demo sounds great too. What capsule did you use?

Thank you!

heisermanaudio.com custom made an M7 capsule for me. I really like it, I've always had great results with their capsules.

 

[HerbertR]

I have built something like that (with two tubes) years ago.
The advantage is that you can also use the microphone (with a high dissipation resistor inside!) as a heater in the wintertime!

Hi Ruud, do you think there is a reason why to implement the 105VDC->40VDC serial dual Heater/Filament 408A Voltage 1K5 Dropingresistor directly in the Microphone? Why not in the PSU case? The 7Pin Connection has more than enough unused Pins/Slots to supply the mic external with the 2x20VDC via Tube PSU Case an a big 50W resistor.
The 1K5 Filamemtresistor has to eliminate 0.05A with 65VDC drop. That are lot of Watts for a 5 Watt resistor directly mounted in the case could be a little hot... Or am I wrong....?

 

[Khron]

Hi Ruud, do you think there is a reason why to implement the 105VDC->12VDC serial dual Heater/Filament 408A Voltage 1K5 Dropingresistor directly in the Microphone? Why not in the PSU case? The 7Pin Connection has more than enough unused Pins/Slots to supply the mic external with the 12VDC via Tube PSU Case an a big 50 or 100 W resistor.
The 1K5 Filamemtresistor has to eliminate 0.3A with 93VDC drop. That are lot of Watts A 10 Watt resistor directly mounted in the case could be a little bit underrated... Or am I wrong....?

Yes, there is a reason - blind and illogical / irrational compulsion to stick as close as possible to the way the original circuitry was implemented (mostly based on emotions and confirmation bias, rather than any sort of technical / technological considerations). Nevermind that the tube is different...

 

[HerbertR]

Yes, there is a reason - blind and illogical / irrational compulsion to stick as close as possible to the way the original circuitry was implemented (mostly based on emotions and confirmation bias, rather than any sort of technical / technological considerations). Nevermind that the tube is different...

Sorry, but "stack overflow".... Hey, I am getting old, bro. What do you think, could this be a problem?
I personally can not see any advantage with the resistor inside of the mic directly or am I wrong.. ?

 

[Khron]

That was my point. People nowadays seem to insist on still using largely the same circuit, "just because".

Even if many probably won't admit it, the circuit of the U47 was a bit of a compromise (so they wouldn't need to use a more complicated / even more custom power supply transformer, and to use the VF14 tube which they had a plentiful supply to pick and choose from, at the time of development / launch).

That dropper resistor inside the mic will just cook the components inside the mic, for no good reason.

 

[mrgrooves666]

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!

Collective cases, do a search. They are roomy and very nice.

 

[EarthTone]

Collective cases, do a search. They are roomy and very nice.

I have used CC many times for different builds. I ended up buying 2 of his PSU cases this time as well. Really nice.