FEELER - Solid-state microphone upgrade boards (OpAmp, JFET, U87A, FET847, ORS87-Plus)

[Khron]

Could you do something that small to use with the regular SDCs, kinda like the CMC 1?

Basically yes, but... that would leave / raise the question of the mechanical solution. And that's one aspect i'd rather not get into

I mean sure, like i said, the intention of this is to fit inside an XLR connector shell, and connecting a 6mm electret capsule with thick wires (for mechanical stability), and have the capsule just poke through the opening in the strain relief. Anything else than that is outside the scope of this, i'm afraid...

 

[Khron]

"To whom it may concern..."

Just last night "finally" placed an order for a batch of prototype boards for these, as well as several other projects of mine (5-10pcs of each, depending). Fabrication time was quoted at 3-4 days, and since i didn't want to shell out more than the total price of the boards for DHL Express or other couriers, plus customs & taxes on top of that, i went with the IOSS "Global Standard Direct Line", which should take 12-16 days.

... And now, we wait...

 

[rock soderstrom]

... And now, we wait...

...this is the part I hate the most

Any news on the self etch U87 PCB designs?

 

[Khron]

Any news on the self etch U87 PCB designs?

What would be needed (or most convenient) for those? I anyway ordered some of those boards too (at least as a "proof of concept"), and they're here too

 

[rock soderstrom]

What would be needed (or most convenient) for those?

Self etcher like print ready PDFs. We need the soldering side (traces) and the silk screen layer, both mirrored. Best (for me) are both files in one PDF on one printing site.

I anyway ordered some of those boards too (at least as a "proof of concept"), and they're here too

I am not member on this platform. As far I can see, there are the schematic and png of the rendering available. Is there more when I register to this site?

I'd be happy to help you with providing and testing the data.

 

[Khron]

I am not member on this platform. As far I can see, there are the schematic and png of the rendering available. Is there more when I register to this site?

Pretty sure PCBway started off as a board fab (like JLCPCB etc), and then expanded into these "community" type things.

Self etcher like print ready PDFs. We need the soldering side (traces) and the silk screen layer, both mirrored. Best (for me) are both files in one PDF on one printing site.

Probably most appropriate(?) to post those in the ORS87 thread, though..?

 

[rock soderstrom]

Probably most appropriate(?) to post those in the ORS87 thread, though..?

your decision, wherever you want it. Maybe a separate thread? I would probably leave it here in this thread...

 

[Khron]

I would probably leave it here in this thread...

Self etcher like print ready PDFs. We need the soldering side (traces) and the silk screen layer, both mirrored.

Ask and you shall receive Attached to the OP & updates mentioned there.

 

[rock soderstrom]

Ask and you shall receive Attached to the OP & updates mentioned there.

Khron you are great , but I think there is a mistake in your files!

I'm really not good at imagining spatial things but I think one of your layers is the wrong way around. For example, look at this design of mine, the components are also on top of each other in the mirrored state. This is not the case with your layers.



Two further suggestions for improvement: Do the drilling holes (for mounting the PCB) with "soldering pads" with a smaller hole diameter. This helps with accuracy when drilling, the drill is guided by the etched small hole.

Always place text somewhere on the soldering side, then you can see at a glance what the position is when mirrored.

As I said, just suggestions!

 

[Khron]

I'm really not good at imagining spatial things but I think one of your layers is the wrong way around.

We need the soldering side (traces) and the silk screen layer, both mirrored.

Had i misunderstood something?

PS: The silkscreen PDF was one of my failed attempts to merge them into the same PDF file; corrected now...

Do the drilling holes (for mounting the PCB) with "soldering pads" with a smaller hole diameter.

I perhaps would have, if this wasn't intended for manufacture, but that is indeed a good point

Always place text somewhere on the soldering side, then you can see at a glance what the position is when mirrored.

There is some, if you zoom in enough

 

[rock soderstrom]

Had i misunderstood something?

I did it wrong the first time too. With EasyEDA, if you export the solder side as a PDF, you don't have to actively mirror it, the program does that. (Not really, it simply prints from the top view, which leads to mirroring of the solder side)

The silk screen, on the other hand, must be actively mirrored during PDF exporting, then everything is correct again!

I perhaps would have, if this wasn't intended for manufacture, but that is indeed a good point

This is a small but nice optimization for the self-etchers, that way you can drill the holes precisely, even freehand with your dremel! The etched hole acts like a center punch dent.

There is some, if you zoom in enough

Really, I didn't see that. I'll have to take another look

 

[Khron]

Well-well-well, good news all around (so far, at least) - after having placed the order for these boards, and a few others, on the evening (in Europe) of the 3rd of july, the package got delivered in just a touch under two weeks! And that's with the cheapest(?) shipping option, to boot!..

See the initial post in this thread, for photos of the yet-unpopulated boards

Preliminary observations - turns out i was a bit optimistic (or pessimistic?) regarding the dimensioning of the slots in the multipattern board sets, but it's not the end of the world - will be tweaked soon.

 

[oscarhuang]

Many thanks to Khron for the schematic. I found this ORS87 on PCBWAY. But I have a question. Is C9 in the drawing wrong? If C9 is added, the microphone should have no high frequencies.

 

[Voyager10]

You're right, the original U87 (Schematic here) has a 330K resistor between C8 and C9. Without it, the drain of the FET is AC-coupled through C8-C9 to ground.

 

[Khron]

Many thanks to Khron for the schematic. I found this ORS87 on PCBWAY. But I have a question. Is C9 in the drawing wrong? If C9 is added, the microphone should have no high frequencies.

That's actually a good point - i guess i might've gotten a bit overly-enthusiastic with the capsule voltage filtering. One less BOM item is always good

 

[oscarhuang]

I've been looking for a circuit with 5k notch and 10k slight boost. I really don’t like k47capsules in flattened circuits. I was very interested when I saw your post. I wonder if there is schematic?

 

[Khron]

I've been looking for a circuit with 5k notch and 10k slight boost. I really don’t like k47capsules in flattened circuits. I was very interested when I saw your post. I wonder if there is schematic?

Once i've tested that things work as intended, I'll gladly sell you a few boards / board sets Then you can have fun reverse-engineering the circuit

 

[solowiej]

Khron,

I'm hoping you will forgive both my technical naievete and the possibility that I'm beating a dead horse with a tiny mic:

If I figure out my own mechanical solution, would your micro-Schoeps board serve the sdc capsules from Schoeps / 3U / Oktava as it is or do those capsules have different needs from the intended electrets?

Basically yes, but... that would leave / raise the question of the mechanical solution. And that's one aspect i'd rather not get into

I mean sure, like i said, the intention of this is to fit inside an XLR connector shell, and connecting a 6mm electret capsule with thick wires (for mechanical stability), and have the capsule just poke through the opening in the strain relief. Anything else than that is outside the scope of this, i'm afraid...

 

[Khron]

If I figure out my own mechanical solution, would your micro-Schoeps board serve the sdc capsules from Schoeps / 3U / Oktava as it is or do those capsules have different needs from the intended electrets?

Those do indeed require both a DC bias voltage, AND a JFET & gate resistor indeed - ideally, with a trimmer, to be able to bias the JFET. Which would kinda-sorta defeat the whole purpose of this, unfortunately.

I have toyed with the idea of an Opamp-Alice for SDC's, but there's no real standard in length or width for SDC bodies / boards, so...

 

[solowiej]

Those do indeed require both a DC bias voltage, AND a JFET & gate resistor indeed - ideally, with a trimmer, to be able to bias the JFET. Which would kinda-sorta defeat the whole purpose of this, unfortunately.

I have toyed with the idea of an Opamp-Alice for SDC's, but there's no real standard in length or width for SDC bodies / boards, so...

Thanks. Bad news but good information.

edit: FWIW my vote would be for the 3U threading and pin length as a base 'standard'.