Stam Audio SA-47 Fet

[Emmathom]

Hello everyone.
I have just acquired a U47 Fet replica from Stam Audio on the advice of a sound engineer friend who describes it as "the most faithful copy of the original U47 Fet".
Indeed the sound is magnificent...
I opened it for a quick inspection and found that it is well assembled (like all their products).
Would any of you know which capsule is installed? and if there is any (light) upgrade that could be done (only if necessary), like for example the capacitors... ?
And do some of you know - use this mic ? and what for ?
I intend to use it in a lot of situation on solo sources (cello, sax, voice over, singing, etc) could be also use on drum room mono mic.
BR

 

[McIrish]

Looks like a K47 capsule. I believe they are using the ones by Braingasm Lab. I can't remember if that is a reskinned 3U capsule or not.

 

[RuudNL]

Not a big fan of the cheap ceramic capacitors I see...
Front membrane of the capsule is connected directly to the PCB (long track!), no teflon feedthrough or 'floating' construction used.

 

[Emmathom]

Not a big fan of the cheap ceramic capacitors I see...
Front membrane of the capsule is connected directly to the PCB (long track!), no teflon feedthrough or 'floating' construction used.

Hi RuudNL ! so that was the meaning of my question : if there is any (light) upgrade that could be done (only if necessary), like for example the capacitors... ?
May you suggest something about this please ?
Thank you

 

[RuudNL]

I think I would replace the whole PCB, because it has some serious design flaws...
Replacing components won't solve all problems.

 

[Emmathom]

I think I would replace the whole PCB, because it has some serious design flaws...
Replacing components won't solve all problems.

Huuu... on a brand new mic bought a month ago ? Damn... Don't know if I want...
I could change the ceramic for FKP2 or Silver Mica (for exemple) and the electrolytic with Elna Silmic II + level up the working voltage...
I must first re-open the mic to do some measurements and also note the component values...

 

[Delta Sigma]

Nothing wrong with ceramic caps. RuudNL is pointing out that those caps look fairly cheap. I've used NP0/C0G ceramic caps and they're fine. From the photo, those don't resemble any quality caps that I've seen.

If the mic sounds good, then don't worry about. They could be a failure point.

If the mic is noisy, you should find a way to isolate C1 and the gate from the PCB and attach your front diaphragm there. It looks like a reeeeeaally long path from the front diaphragm to C1, then C1 to gate. Could be a source of noise or RF interference.

 

[johnsonic]

Indeed the sound is magnificent...

Then why mess with it?

 

[Emmathom]

Ok...
I will shorten the capsule wire (and maybe cutting it before the round plate and extend it with silver-cooper ptfe 26AWG).
I will also have a look at capacitors and see if I can upgrade some.
Thank you

 

[Khron]

I will shorten the capsule wire (and maybe cutting it before the round plate and extend it with silver-cooper ptfe 26AWG)

The length (or material) of the wire is not the issue.

 

[BigPauly]

Then why mess with it?

Yeah I agree. After all put it through its paces, see what your ears think of it first before predetermining what “needs” to be upgraded or else you will build in a biased opinion. Really who cares if the caps are “cheap”? You absolutely will not hear a difference in caps, unless there’s a true failure.

 

[Mworthin]

Why modify something you apparently love and is working like it is supposed to? Wait until it needs a repair.

 

[Emmathom]

Why modify something you apparently love and is working like it is supposed to? Wait until it needs a repair.

DIY & Tweakie bad habbit !
Always wandering if quality could be improved... I must do some audio tests first and compare with other mics (TLM103 / TLM193 / SC100 with Arienne K47 flat)
Thanks for your advices

 

[BigPauly]

TLM 103 and U47Fet are nothing alike. Obviously neither is a bad mic, just a little different niche. Best of luck!

 

[Emmathom]

TLM 103 and U47Fet are nothing alike. Obviously neither is a bad mic, just a little different niche. Best of luck!

Yes I know. But since I've never owned or heard U47 fet...
Comparing can be done within different things : it needs at least 2 items... like, for exemple, apple & lemmon : apple appears to be sugared and firm while lemmon juicy & sour...

 

[Voyager10]

Looking at the original U47 FET schematic, it looks like they're using 2 polystyrene caps in parallel for input capacitor C1, and the ceramic disc capacitors are the C2 and C3, in the feedback loop for the charge amplifier.

Ceramic disc caps can be microphonic, like little piezo transducers, so you may find film or mica caps do a better job here.

The other caps are for decoupling of supply rails and bias voltages, and are not in the signal path.

 

[Emmathom]

Looking at the original U47 FET schematic, it looks like they're using 2 polystyrene caps in parallel for input capacitor C1, and the ceramic disc capacitors are the C2 and C3, in the feedback loop for the charge amplifier.

Ceramic disc caps can be microphonic, like little piezo transducers, so you may find film or mica caps do a better job here.

The other caps are for decoupling of supply rails and bias voltages, and are not in the signal path.

C2 is 18pF (as I can read on schematic) and C3 33pF
As far as Stam Audio has respected the original schematic, I could indeed change these 2 ceramic by mica (don't know if I can find mkp in these values)
Thank You for your input !