FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop

[Khron]

Sheesh. I for one am appreciative of Jonathan for seeing this project realized in full as a PCB. It may not be as fun to verify what mic bodies, e.g., work with a prototyped PCB than to slag off the design with half-realized improvements, but Jonathan successfully brought a fully supported and documented PCB to the community. You, on the other hand, have focused your energies on demonstrating how much better insight you have to the circuit. But when members ask if they could realize your circuit as a finished PCB, you wouldn't even provide the full set of files to them, much less put in the 'grunt' work in the first post that makes a circuit / project all the more of a valuable contribution to the community. Khron, you make some great points and contributions, you've directly helped me in posts as I learn more EE, and I am grateful for that. I also recognize the significant effort it takes to fully create a project for everyone's benefit,. Criticism has a place, but when a member focuses more energy on tearing down vs. building, I think it says more about the person than the topic.

Wait, you're saying i somehow "owe" people (like you?) my "full set of files", even though Jonathan (or whoever did the board design) didn't?

Whatever criticisms i happen to have leveled are entirely pertinent and fully justified (from a technical standpoint), AND i've openly shown an example of a much simpler etch-it-yourself single-layer board.

If i really was as selfish(?) as you may or may not be implying that i am, instead of showing that, i could've opened some sort of webshop for people to buy readymade boards. But i'm not in this for the money. And yet, i should offer everyone my hard work (which, admittedly, i did as a personal challenge / passion-project) on a silver platter, instead of motivating people to, i don't know, learn a skill?

Nothing's stopping anyone from installing Eagle or KiCad, recreate my layout, print it out and etch their own boards (or have a batch fabbed in the far east).

But i still don't see why projects like this should NOT have their shortcomings pointed out (as / when applicable). Otherwise, if we blindly "worship" whatever we happen to get served, where's the incentive for progress, improvement, evolution, development of skills?

And it's double-nice that the Mouser BOM (still) contains one obsolete no-longer-available component. And FIFTY THREE euros for the components of ONE microphone??? That right there is ridiculous in itself. 10eu for one switch(!!!) that's not even on the board, 3-4eu per capacitor? Come on...

(Later edit - included the message this is a response to, in case it gets deleted or whatever)

 

[klem]

I never said any member "owed" anyone else anything. Implying you are "selfish" was not my intent either. In fact, I went out of way to express appreciation for the contributions you've made, which seems willfully ignored. "And yet, i should offer everyone my hard work." Nope, not even close to my point.
I'm glad you quoted my post - let it be judged by others what I actually said, the main idea of it, and your attempts to misrepresent it. It's clear you aren't willing to have a discussion about it in good faith, and I have no interest in arguing with you. I've said my piece.

 

[Khron]

But when members ask if they could realize your circuit as a finished PCB, you wouldn't even provide the full set of files to them, much less put in the 'grunt' work in the first post that makes a circuit / project all the more of a valuable contribution to the community.

I never said any member "owed" anyone else anything. [...] "And yet, i should offer everyone my hard work." Nope, not even close to my point.

Pick one; you can't have it both ways. And regarding the "provide the full set of files" bit, i had made no changes to the BOM, if memory serves; nor is/was the BOM any of my responsibility, i hope you'll agree.

What even *IS* your beef with my posts in this thread, though? That's still not quite 100000% clear to me

 

[Khron]

I'm quite positive you'll see this as petty, but i'm just high "allergic" to (demonstrably) false claims. Or, at the absolute very least, we seem to have drastically different definitions for "fully supported"

And nevermind how arguably offensive it is to say "Circuit By Jonathan Burtner", when all he apparently did was copy the Neumann circuit and slightly mess it up in the process.

... but Jonathan successfully brought a fully supported and documented PCB to the community.

Poctop has last posted in this thread back in 2017. That's, count it, one-two-three-four-five-SIX years ago - March 1st, to be exact. And technically HE in fact drew the actual PCB.

https://groupdiy.com/threads/fet847...urtner-pcb-layout-by-poctop.61057/post-828016
Jonathan has, as far as i could tell, responded to my concerns about the circuit only ONE single time, and apparently has yet to comprehend (possibly?) my objections or my reasons for them. Even though i did my best to spell them out in the post following his.

https://groupdiy.com/threads/fet847...urtner-pcb-layout-by-poctop.61057/post-844032
Either way, his last post in this thread was in September 2017 - that's a measly five and a half years ago.

https://groupdiy.com/threads/fet847...urtner-pcb-layout-by-poctop.61057/post-849730

But when members ask if they could realize your circuit as a finished PCB, you wouldn't even provide the full set of files to them, much less put in the 'grunt' work in the first post that makes a circuit / project all the more of a valuable contribution to the community.

What's with the double-standards though? How come elskardio doesn't have to share the files for his design, hmm?

https://groupdiy.com/threads/fet847...urtner-pcb-layout-by-poctop.61057/post-853006
I'll be the first to admit i'm wrong, if and when i screw up. But you'll have to excuse me if i choose to defend myself against accusations, with facts

 

[karloff70]

Hi foIks, I couId do with advice. I figured I wouId buiId this using oId Beyer mic input transformers in reverse, specificaIIy TR45 BV35536 with a 1:5 ratio. Now it suddenIy occurred to me I didn't check whether these can pass phantom power. But since they are mic input transformers, sureIy that means they have to be abIe to, right? Whether in reverse or not?

Assuming it wiII work if anyone has any pin out ideas on how to wire it, I wouId gIadIy Iisten.

 

[Khron]

Hi foIks, I couId do with advice. I figured I wouId buiId this using oId Beyer mic input transformers in reverse, specificaIIy TR45 BV35536 with a 1:5 ratio. Now it suddenIy occurred to me I didn't check whether these can pass phantom power. But since they are mic input transformers, sureIy that means they have to be abIe to, right? Whether in reverse or not?

Assuming it wiII work if anyone has any pin out ideas on how to wire it, I wouId gIadIy Iisten.

Transformers don't (or shouldn't, assuming they're fine) "pass phantom power".

The phantom power is "collected" from the two ends of the XLR-side winding, referenced to the pin 1 "ground", via the two 2.2k resistors there.

Assuming all is well within the preamp the microphone is connected to, the phantom power voltage should be identical on XLR pins 2 and 3 (which get connected to said transformer) relative to pin 1 "ground", so between those two pins there should be a net zero voltage (difference), so no DC flows through the XLR-side winding. No DC should pass through the transformer (because on one hand, that's what they do, they galvanically isolate things, and on the other hand, transformers only pass AC).

 

[karloff70]

Transformers don't (or shouldn't, assuming they're fine) "pass phantom power".

The phantom power is "collected" from the two ends of the XLR-side winding, referenced to the pin 1 "ground", via the two 2.2k resistors there.

Assuming all is well within the preamp the microphone is connected to, the phantom power voltage should be identical on XLR pins 2 and 3 (which get connected to said transformer) relative to pin 1 "ground", so between those two pins there should be a net zero voltage (difference), so no DC flows through the XLR-side winding. No DC should pass through the transformer (because on one hand, that's what they do, they galvanically isolate things, and on the other hand, transformers only pass AC).

Ok. I assume that means these transformers wiII work then? ;-)

 

[Khron]

The only question is what level they might end up saturating at

 

[karloff70]

What are peopIe using for inductors, now that the ones in the BOM seem obsoIete and hard to find?

 

[Khron]

Whatever axial inductors you can find. They're a piece of wire wound around a ferrite core, nothing more "esoteric" than that.

https://www.mouser.fi/c/passive-com...rough Hole|~Wire Leads&instock=y&sort=pricing
47uH axials, in stock.

Cheapest one is this (assuming the 0.5mm longer length compared to the Vishay one in the BOM is not too big of an issue):

https://www.mouser.fi/ProductDetail...=sGAEpiMZZMv126LJFLh8y7s0IL9TvdCq8ai4LMiTA7g=
A slight bit more pricey, but "only" 0.2mm longer than the Vishay:

https://www.mouser.fi/ProductDetail...=sGAEpiMZZMv126LJFLh8y8rwpbbr88RteK3dQRCDZzA=

 

[karloff70]

Thank you!

Are these in the signaI path, as in wiII they not affect the sound Iike say in a crossover? In speakers the chosen inductors make a rather noticeabIe difference, onIy thinking whether it might pay to get something "good" and what the parameters in this case are to determine 'good'?

 

[Khron]

If anything, in speaker crossovers you're dealing, on one hand, with far greater inductance values (millihenry, not micro), and on the other hand, far greater currents (up into the amps, if not tens of amps).

Here, their only role is to present a greater impedance to frequencies (far) above the audible range, and the currents involved are likely in the single-digit milliamps, if even that (a couple of volts of signal amplitude into 1-2kohms preamp input impedance). RF junk can be rectified / demodulated / "detected" in semiconductor PN junctions and can alias(?) / "fold down" into the audio range and appear as extraneous noise etc.

 

[Ricardus]

Mouser had the ones in the BOM the last time I ordered.

 

[Khron]

Must've been some time ago, they're obsolete and no longer stocked (likely also not manufactured anymore either).

 

[Ricardus]

Must've been some time ago, they're obsolete and no longer stocked (likely also not manufactured anymore either).

https://www.mouser.com/ProductDetail/542-78F470-RC

 

[doqmemory]

https://www.mouser.com/ProductDetail/542-78F470-RC

That's the part I used on several builds.

 

[Khron]

https://www.mouser.com/ProductDetail/542-78F470-RC

[...]

Cheapest one is this (assuming the 0.5mm longer length compared to the Vishay one in the BOM is not too big of an issue):

https://www.mouser.fi/ProductDetail...=sGAEpiMZZMv126LJFLh8y7s0IL9TvdCq8ai4LMiTA7g=
A slight bit more pricey, but "only" 0.2mm longer than the Vishay:

https://www.mouser.fi/ProductDetail...=sGAEpiMZZMv126LJFLh8y8rwpbbr88RteK3dQRCDZzA=

Guess i had found that on my own too...

 

[karloff70]

Got some inductors, thank you chaps!

If I may go back a step and ask, for my beyer trannies that I am going to use for outputs I couId do with a Iead coIour tip, as in what is what. I got this pic from beyer, but no tip on Iead coIour meaning. Anyone have any ideas?

 

[doqmemory]

Got some inductors, thank you chaps!

If I may go back a step and ask, for my beyer trannies that I am going to use for outputs I couId do with a Iead coIour tip, as in what is what. I got this pic from beyer, but no tip on Iead coIour meaning. Anyone have any ideas?

Check the resistance on the pairs of wires. The pair with about 50Ω resistance is the secondary, and the pair with over 300Ω resistance is the primary. The primary wires will not have continuity with the secondaries. If one of them is the shield wire (it looks like 5 wires in the picture), it will not have continuity with anything else and should be wired to the body lug on the XLR connector.

It does not matter which of the two primary wires you wire as p+ and p-. I would suggest just choosing one of the secondary wires as s+ and finish the wiring. You can then swap the XLR 2 and XLR 3 wires at the bottom of the circuit board if the output polarity does not match your other microphones.

To determine if the polarity matches some other reference microphone, plug them both into your DAW and record a nice "plosive" sound (clapping hands or popping your lips works well) and determine whether the initial waveform rises (or drops) the same as your reference microphone. The capsules of each mic should be the same distance to the sound source for this to work.

You can also check this "live" under headphones by holding the two microphones together with capsules the same distance from your mouth and talk/sing/hum as you move one of the pair of mics closer and farther away from your mouth. If their combined sound is loudest when they are the same distance from the sound source (your mouth, in this case), then they are "in phase" with each other. On the other hand, if the sound gets louder when you move one of the microphones farther away, then they are "out of phase" with each other. Once you get used to doing this, it is a very fast test.

 

[karloff70]

Check the resistance on the pairs of wires. The pair with about 50Ω resistance is the secondary, and the pair with over 300Ω resistance is the primary. The primary wires will not have continuity with the secondaries. If one of them is the shield wire (it looks like 5 wires in the picture), it will not have continuity with anything else and should be wired to the body lug on the XLR connector.

It does not matter which of the two primary wires you wire as p+ and p-. I would suggest just choosing one of the secondary wires as s+ and finish the wiring. You can then swap the XLR 2 and XLR 3 wires at the bottom of the circuit board if the output polarity does not match your other microphones.

To determine if the polarity matches some other reference microphone, plug them both into your DAW and record a nice "plosive" sound (clapping hands or popping your lips works well) and determine whether the initial waveform rises (or drops) the same as your reference microphone. The capsules of each mic should be the same distance to the sound source for this to work.

You can also check this "live" under headphones by holding the two microphones together with capsules the same distance from your mouth and talk/sing/hum as you move one of the pair of mics closer and farther away from your mouth. If their combined sound is loudest when they are the same distance from the sound source (your mouth, in this case), then they are "in phase" with each other. On the other hand, if the sound gets louder when you move one of the microphones farther away, then they are "out of phase" with each other. Once you get used to doing this, it is a very fast test.

Thanks for that! Sorted. I am way more famiIiar with the phase parts of this than the part where it turns out that aII I had to do is put a meter across them to see Ohms and work the rest out from there. IoI
Nice, I think that makes me good for the next few steps...... untiI FET caIibration IoI