U47xfet PCB from UTM / IGS?

[neowalla]

That looks good, but is the wavy surface of the capsule okay?

View attachment 108777

Haha! That's my eye. I do that every time I photograph one of mics during the build. Those little mirrors are just too tempting not to make funny faces in.

 

[rock soderstrom]

OMG, now I see the rest of your face!

 

[HerbertR]

Hi, I ve built a Pair of them too. I compared Dachmans 47 with Ariennes Flat 47. Ari's 47 are worldclass Level. I think one of the best Capsules out there. Unbeatable for "speakers"....Perfectly nuanced, brilliance, no nervy Frequency band over the whole range. And still sounds fat. Dachmans are pretty good but the have a much brighter Open End.

But I have one Issue - the Noiselevel is very high. It is independent from the used Capsule. The Minutes after first testing both ready built Mics were silent, after a few Minutes the first one made a short loud dropout on the speaker/phones and got about 15dB noisier. The second Mic did the same a little bit later. After replacement of caps for tests on one Mic and "soldering" the important Hi Impedance part in the Air ... it was silent again but made then the same issue a little bit later - dropout and after that about 15dB fine additional noise extra. I never read anything about this problem. Any Ideas? Bad Fets?

 

[neowalla]

I haven't had a chance to record with them yet but hopefully pretty soon. I'll be interested to see if any noise develops.
I bought a SCM-2 stereo mic direct from Ningbo in China
https://www.aymaudio.com/product/stereo-diaphragm-condenser-microphone-scm-2/And the top capsule made what I can only describe as a waterfall kind of sound. It turned out to be a bad FET which I replaced and all is quiet and serene since. Ironically I record waterfalls, among other nature sounds and prefer the real thing to imitations by bad FETs

 

[HerbertR]

I haven't had a chance to record with them yet but hopefully pretty soon. I'll be interested to see if any noise develops.
I bought a SCM-2 stereo mic direct from Ningbo in China
https://www.aymaudio.com/product/stereo-diaphragm-condenser-microphone-scm-2/And the top capsule made what I can only describe as a waterfall kind of sound. It turned out to be a bad FET which I replaced and all is quiet and serene since. Ironically I record waterfalls, among other nature sounds and prefer the real thing to imitations by bad FETs

Sounds good, I will try different ones. Reichelt Electronics has Toshibas 2SK117. Ordered. Hope the will work and the finest Waterfall "Noise" will end ...

 

[tomek4226]

I think the noise comes from the high impedance section. in low-noise microphones, it is isolated from the PCB

 

[HerbertR]

I ve also isolated all high impedance parts from the PCB for testing on one Mic. I used Teflon turret pins for connecting through the PCB. 2n2 Styro, 1G Ohm, 33pF, 100M Ohm connected to Fet are connected together in the Air without touching the PCB. I have also checked other built 47 Mics. The most 47 manufactures did it the same way. But on my tests it had no impact compared to directly soldered high Impedance parts on the PCB. It worked perfectly without noise a few minutes and appeard then a few minutes later again with an introducing "pop" - like disconnecting the Phantom Power for a Second. The Signal remain clean but as said, with much much more "white" noise. Like a waterfall. I hope
these "bad" SK117 Fets are causing the issue. I bought them from an Electronic Store in the Germany, Kessler.
Btw - would a Fairchild 2N3819 Fet also work? I have them laying around. 2N3819 are also used in U47 Fets builds. Comparing the original Neumann 47 Fet Schematic vs UTM 47 Fet Schematic I can not see any big difference. Except of the missing 10dB Pad / HP Switches / 33M/68M Ohm Resistors and the replacement of the BC182 and BC212 with BC550 and BC560. And the Fet itself for sure..

EDIT: Fairchild 2N3819's from the picture are working perfectly with these UTM PCBs. No noise anymore. Silent.
The SK117 Fets like these on the Picture do not work properly.

 

[Tronfxdx]

I ve also isolated all high impedance parts from the PCB for testing on one Mic. I used Teflon turret pins for connecting through the PCB. 2n2 Styro, 1G Ohm, 33pF, 100M Ohm connected to Fet are connected together in the Air without touching the PCB. I have also checked other built 47 Mics. The most 47 manufactures did it the same way. But on my tests it had no impact compared to directly soldered high Impedance parts on the PCB. It worked perfectly without noise a few minutes and appeard then a few minutes later again with an introducing "pop" - like disconnecting the Phantom Power for a Second. The Signal remain clean but as said, with much much more "white" noise. Like a waterfall. I hope
these "bad" SK117 Fets are causing the issue. I bought them from an Electronic Store in the Germany, Kessler.
Btw - would a Fairchild 2N3819 Fet also work? I have them laying around. 2N3819 are also used in U47 Fets builds. Comparing the original Neumann 47 Fet Schematic vs UTM 47 Fet Schematic I can not see any big difference. Except of the missing 10dB Pad / HP Switches / 33M/68M Ohm Resistors and the replacement of the BC182 and BC212 with BC550 and BC560. And the Fet itself for sure..

EDIT: Fairchild 2N3819's from the picture are working perfectly with these UTM PCBs. No noise anymore. Silent.
The SK117 Fets like these on the Picture do not work properly.

Thank you for posting this. I have some 2sk117's that are suppose to be On Semi original but they look almost like yours! I am building two of these so I installed the 2sk117 in one board only. If it does not work I will use a 2N3819. I have those on hand.

 

[bremusound]

FWIW: 2sk30a works as well

 

[TimG]

This Could Be The Day (if ADD doesn’t take me down first!)!

Arienne Audio Flat K47. UTM of course! I’ll wait on the stickers in case I have to put the whole thing in a Vice or a furnace.

 

[soliloqueen]

Hope you enjoy, Tim!