callgrlmusic
Active member
i would like all of them please
FEELER - Solid-state microphone upgrade boards (OpAmp, JFET, U87A, FET847, ORS87-Plus)
- Thread starter Khron
- Start date
Help Support GroupDIY Audio Forum:
Apologies for the delay, but i have updates! Or, well, at least one, anyway 
In-between getting acquainted to living in my own house, i finally managed to eek out some time to populate a first board from this load - a cardioid-only OpAlice.
After a quick capsule-less test to sanity-check the supply voltages (and promptly discovering the brainfart of having installed the opamp the wrong way around - yes, happens to the best of us
), getting a bit over 39v at XLR pins2/3, which points towards ~2.6mA total current draw, using an OPA2991. Provisionally, i decided to bypass all the tone-shaping features, to only leave the bare minimum to troubleshoot, if needed.
Stuck the board into an already-slightly-modded Neewer NW700, and instantly noted a couple issues.
One is that, having placed the mounting holes so that the top edge of the boards goes right up to the bottom of the headbasket, it won't sit flush, due to to the macgyvering i needed to do, to fasten an LDC mount to the base plate. Which involved a bunch of moderately-sized washers... Oh well, i'll see about including a notch of some sort in that area.
Second, as i had stuck a 1/2" wide strip of rubber to the inside of the body tube (to quell down resonances) some time ago, i was slightly disappointed to discover the board's a bit too wide to fit inside the smaller inside-diameter of the rubber strip. Not much i can do about that, without sacrificing MXL2001 chassis compatibility. But perhaps if i taper down the board width just below the 2001 mounting holes...
But hey, that's what prototypes are for, right? Proof-of-concept and all that...
No extraneous noise upon a brief test, but then again, my chaotic work-room is far from a testbed for noise. But it works! Capsule ends up seeing about 20v across it, so especially since it's a straight buffer (no gain), this won't be the most sensitive thing out there, but that's not the worst thing for drums and such, right?
In-between getting acquainted to living in my own house, i finally managed to eek out some time to populate a first board from this load - a cardioid-only OpAlice.
After a quick capsule-less test to sanity-check the supply voltages (and promptly discovering the brainfart of having installed the opamp the wrong way around - yes, happens to the best of us
), getting a bit over 39v at XLR pins2/3, which points towards ~2.6mA total current draw, using an OPA2991. Provisionally, i decided to bypass all the tone-shaping features, to only leave the bare minimum to troubleshoot, if needed.Stuck the board into an already-slightly-modded Neewer NW700, and instantly noted a couple issues.
One is that, having placed the mounting holes so that the top edge of the boards goes right up to the bottom of the headbasket, it won't sit flush, due to to the macgyvering i needed to do, to fasten an LDC mount to the base plate. Which involved a bunch of moderately-sized washers... Oh well, i'll see about including a notch of some sort in that area.
Second, as i had stuck a 1/2" wide strip of rubber to the inside of the body tube (to quell down resonances) some time ago, i was slightly disappointed to discover the board's a bit too wide to fit inside the smaller inside-diameter of the rubber strip. Not much i can do about that, without sacrificing MXL2001 chassis compatibility. But perhaps if i taper down the board width just below the 2001 mounting holes...
But hey, that's what prototypes are for, right? Proof-of-concept and all that...
No extraneous noise upon a brief test, but then again, my chaotic work-room is far from a testbed for noise. But it works!
Capsule ends up seeing about 20v across it, so especially since it's a straight buffer (no gain), this won't be the most sensitive thing out there, but that's not the worst thing for drums and such, right?
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That'a a hefty capsule mount you have there.
Or you took LARGE in LDC too seriously.
Prototyping is not for the weak!
Go big or go home
Yeah, at the time (when i installed this particular capsule in this mic), the only M3 bolt i had, with a low-enough-profile head to fit inside the counterbore in the capsule mount, was THAT long. Big spring washers because that was the one way to "make up" threaded length. Don't ask, i just grabbed what i had at hand to get it done THEN
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I just grabbed what i had at hand to get it done THEN
Yep. Necessity of invention IS a mother.
James
wanderingengineer
Member
Watching this with great interest @Khron , like many others. Very interested to learn how you will price your work. The ‘Jules/Homero’ JLI boards (which I note have been copied by the Chinese on Ali, tut tut..) are expensive once you add shipping to the UK and seem to have potential for RF layout issues (maybe?), so potentially very interested!
rankot
Well-known member
- Joined
- Mar 25, 2017
- Messages
- 67
Nice, I'm following!The prototype is due to get assembled & tested this week
JW
Well-known member
Where do I purchase or find out which boards are available? I have all the parts for a fet847 but need the board. Is it still in the works?
Voyager10
Well-known member
The ORS87+ board is uploaded to PCBway as an open-source design:
https://www.pcbway.com/project/shareproject/ORS87_Plus_Open_source_U87_mic_project_2922baaf.html
You can order the boards directly from PCBway, for very little money.
https://www.pcbway.com/project/shareproject/ORS87_Plus_Open_source_U87_mic_project_2922baaf.html
You can order the boards directly from PCBway, for very little money.
Technically yes, they're still in the works - hit a couple snags with some of the designs, and there are updates for the others that still need vetting / test-fitting / testing.
If all you want is a cardioid-only FET847 type circuit, indeed you can use the ORS87-Plus boards, and just not populate the feedback components (and move the connection point for one of the capsule wires).
I still haven't had the chance to put together a build guide even for that, but i can add the "mod" details here worst case next week
micolas
Well-known member
Those who, for various reasons (better SNR, earlier saturation, other flavor of the sound) want a higher voltage polarization for the capsule, can use the same platform (Khron ORS87-Plus PCB), and will additionally use the preferred DC/DC.
They just have to replace R10, R11 with other values (for example 10..15k), they will break the connection between them and C1. The DC/DC will be fed through R10/R11 and the DC/DC high voltage output connects to C1.
I just wanted to point out that
The ORS87-Plus PCB is a very versatile platform that allows many projects to be built or it can be used as a circuit for tests, or for selecting optimal jFETs (Idss, noise), etc.
They just have to replace R10, R11 with other values (for example 10..15k), they will break the connection between them and C1. The DC/DC will be fed through R10/R11 and the DC/DC high voltage output connects to C1.
I just wanted to point out that
The ORS87-Plus PCB is a very versatile platform that allows many projects to be built or it can be used as a circuit for tests, or for selecting optimal jFETs (Idss, noise), etc.
