My U47 408A (D47) Build

[johnsonic]

I made sure to check the outer foil direction on the capacitors I used in this build with my oscilloscope.

How do you determine which way is what? Haven't heard of this yet and want to make sure I pay attention to it.

 

[HerbertR]

How do you determine which way is what? Haven't heard of this yet and want to make sure I pay attention to it.

Yeah, it would be nice if someone could explain an easy procedure to determine that. Thanks

 

[Khron]

 

[rock soderstrom]

Yeah, it would be nice if someone could explain an easy procedure to determine that. Thanks

There are other videos on this subject on Youtube.

With some modern capacitors you may not see any differences. How important the whole thing is depends on the circuit environment.


Edit: Khron was faster

 

[HerbertR]

There are other videos on this subject on Youtube.

With some modern capacitors you may not see any differences. How important the whole thing is depends on the circuit environment.


Edit: Khron was faster

Meeeeaga... It works. Genius....

 

[johnsonic]

So good to know - wish I knew this 5 mics ago - thank you for posting!

 

[C12VR]

I wonder how much difference this can make in a microphone. I haven't been paying any mind to this and from what I can tell most others haven't either.

 

[rock soderstrom]

I wonder how much difference this can make in a microphone. I haven't been paying any mind to this and from what I can tell most others haven't either.

+1

 

[terry setter]

As for having the dropping resistor inside your mic, I, personally, am not a fan, but I know of several people who in their attempt to create the perfect clone, added a resistor to the side of the mic in order to raise the ambient air temperature. They were thinking that that might be one small but important contributor to the magic sound of the original. One helpful thing about having the big dropping resistor in the originals is that when I'm in a studio and they are singing the praises of their U47, I make a point to go out and feel the mic when it's up and running. If it isn't significantly warm, I know it's not stock inside.

 

[neowalla]

Beautiful clean work and great photography. Well done.

 

[JMPGuitars]

I made a quick and dirty demo of my U47 EF800 version:


If I have some time, I may record both U47 versions for a L/R comparison of them.

Thanks,
Josh

 

[neowalla]

I've been meaning to try to contact Mr Carlson and ask him what flavour of U47 clone is he using and did he build it himself? I would think he did, but who knows?

 

[Khron]

Might be a Warm Audio one? I vaguely remember him mentioning it a year or two ago, but i haven't watched any of his videos for quite some time now...

 

[neowalla]

Might be a Warm Audio one? I vaguely remember him mentioning it a year or two ago, but i haven't watched any of his videos for quite some time now...

Ah, I haven't run across that video yet. It would be great to have him here in this community, but he seems more into old radios than audio gear per say. What a wealth of knowledge and contributor he would make on this forum though.

 

[JMPGuitars]

I made a mildly obnoxious comparison video with the 408A vs EF800 versions:


This is obviously not a scientific comparison, and it's also important to note that they're using different capsules. The 408A model has a Heiserman custom made M7 capsule, and the EF800 version has a Beesneez M7 capsule. Both are great, but not the same.

I might export them separately if anybody cares.

Thanks,
Josh

 

[HerbertR]

I also use this thread as I cannot find a D-47 Dual thread.....
My two finished D-47 dual 408A mics, let the Tubes burn in for about 30 hours. Fantastic sounding Mics. Dachman K47 ( brighter upper Mids compared to Aris Flat 47 ....), noise is very low.
No other issues. I use matched Western Electric 408A tubes from DB Tubes in Canada, the audio transformers are from Igor/IGS the UTM0547.
The 1.5KOhm 5W heater voltage drop resistor has migrated into the PSU housing. For me installing it in the mic body made absolutely no sense to me. I operate the PSU transformer on the secondary side in parallel with about 125V AC, which gives me about 175V DC after bridge rectification. After R1 / choke there are still more than 50V left for smoothing. I have adjusted the dropresistors R2, R3 and R3 for the voltage drop of about 50V DC / 30mA. All components only get hand-warm with my build. No hot Potentiometer.... I really don't understand why some colleagues operate Poctops PSU with the transformer secondary side at about 220V in series? Very nice build, unproblematic, ingenious, just a masterpiecd of the Genius Poctop, IOAudio and Archut...

 

[JMPGuitars]

I also use this thread as I cannot find a D-47 Dual thread.....
My two finished D-47 dual 408A mics, let the Tubes burn in for about 30 hours. Fantastic sounding Mics. Dachman K47 ( brighter upper Mids compared to Aris Flat 47 ....), noise is very low.
No other issues. I use matched Western Electric 408A tubes from DB Tubes in Canada, the audio transformers are from Igor/IGS the UTM0547.
The 1.5KOhm 5W heater voltage drop resistor has migrated into the PSU housing. For me installing it in the mic body made absolutely no sense to me. I operate the PSU transformer on the secondary side in parallel with about 125V AC, which gives me about 175V DC after bridge rectification. After R1 / choke there are still more than 50V left for smoothing. I have adjusted the dropresistors R2, R3 and R3 for the voltage drop of about 50V DC / 30mA. All components only get hand-warm with my build. No hot Potentiometer.... I really don't understand why some colleagues operate Poctops PSU with the transformer secondary side at about 220V in series? Very nice build, unproblematic, ingenious, just a masterpiecd of the Genius Poctop, IOAudio and Archut...

Did you measure your heater voltage in the mic? If you're using the same cable length for all of your U47-408s, then it's probably fine as long as you get the correct heater voltage in the mic. You also probably already know to have that use the thicker gauge wire in the cable.

Looks like nice work. As I mentioned earlier in the thread, there's no need to install the pot off of the PCB, especially if you're running cooler.

You've got me curious now. I have a TC3 pocket scope, I've never tried that for capacitor foil testing (I usually use a real scope). Now I'll try it out.

Thanks,
Josh

 

[HerbertR]

Did you measure your heater voltage in the mic? If you're using the same cable length for all of your U47-408s, then it's probably fine as long as you get the correct heater voltage in the mic. You also probably already know to have that use the thicker gauge wire in the cable.

Looks like nice work. As I mentioned earlier in the thread, there's no need to install the pot off of the PCB, especially if you're running cooler.

You've got me curious now. I have a TC3 pocket scope, I've never tried that for capacitor foil testing (I usually use a real scope). Now I'll try it out.

Thanks,
Josh

Everything works great, of course everything is measured. I have a lot of different 7-pin 24AWG and 26AWGs with 3m, 5m..., 24AWG has less than 100 Ohm loss per km length - a cable with a length of 5m has a voltage loss on the cable of less than 0.05V, no real relevance

The next good thing - the heater runs in series on both tubes at 2x20V DC and only 0.05A. I have about 37VDC at the heater in the mic with the 1.5k 5W DropResisitor for the heaters.

 

[Greenie]

I have also built this mic, but when I measure the pSU pcb b+ to ground I get 120v?

 

[JMPGuitars]

I have also built this mic, but when I measure the pSU pcb b+ to ground I get 120v?

Adjust the pot in the PSU. After you connect the mic, measure on the mic side, and then adjust the pot again to make sure the mic is still getting 105V.