Where do the JFET pins connect, and the 1G resistor? Could you take a closer (and well-focused) photo of that area?
OPEN SOURCE DIY Mic Project - ORS 87 - Stripped Down u87
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Where do the JFET pins connect, and the 1G resistor? Could you take a closer (and well-focused) photo of that area?
Soldered to the center pin of the jfet. I"ll wrap it around before I put it in next time. My one complaint about the otherwise very logical board is had to lay capacitor down to reach the resistor to the center pin.
Attachments
Why???
https://www.onsemi.com/pdf/datasheet/mmbfj113-d.pdf
The JFET is a J113. Not a 2N3819. Thus, as can be seen in the datasheet linked just above, the center pin is the source pin. There's a hole in the PCB where the other end of the 1G resistor goes - this time it IS meant to solder onto the board.
So right now your gate pin is completely floating (DC-wise), connected only to the capsule...
Because the hole was plugged. I thought on purpose. It isn't in this next board. Wasn't I the one asking these questions before that didn't get answered? so I take my best guess. So I just solder in the resistor, and the jfet. boom. done?
they got erased because I'm an idiot? plugged with plastic from board? couldn't get wire through. I started with capacitors on this build, maybe I dropped some solder on it? Honestly thought it was on purpose. My bad. A picture of a completed board would have really helped.
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There are these two posts here (#1033 and #1034 that look to be "empty", just replies to my post), so no idea what happened there.
As in, soldermask / solder-resist? There should have been none, in that whole area. Got a photo of that plugged hole?
Got a pointy pair of tweezers, or a sewing needle, or even a chunkier piece of terminal from an electrolytic capacitor? We're (moderately) advanced primates, we can use tools, can we not?
only with magnifying lenses. Sewing needle. I can do that. thank you.
"Assumption is the mother of all f**k-ups..."
Usually one would start with resistors & diodes, the least-high-off-the-board-surface parts, but i guess what's done is done..?
Point taken, unfortunately real life events have temporarily severely limited the time i could dedicate to this. That being said, some others have managed to successfully populate some of these boards, so...
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It was filled with the yellowish substrate of the board. It would have been the first hole I started to fill with resistors, and this one I put aside, and decided to start with capacitors. I was able to poke it out. The next 2 boards at least do not have this. I remember checking all the other holes on the board to see if they had anything similar, but that was the only one. It seemed on purpose.
Statistically, it couldn't have been. Four boards drilled through properly, but the fifth one not, and THAT is presumed to be on purpose? Can't fathom why one would assume that, but what do i know?
But anyway, see how it works now, with the 1G soldered to where it was meant to go... Maybe post an "after" photo, if feasible?
what are the ^%&^&%^ chances that it would be that hole on my first one?
AdamFrisen
Well-known member
As I wrote a comment in the other thread: https://groupdiy.com/threads/comparison-of-jfets-for-mic-applications.86559/post-1164449
I think if you want the frequency response and gain of U87 classic, you can try to add a small NFB capacitor 3.3 pF - 5 pF. The simulation I made, 5pF was the one that gave almost the identical frequency response as the U87 classic schematics using 220pF/33nF as C6/C5.
I think if you want the frequency response and gain of U87 classic, you can try to add a small NFB capacitor 3.3 pF - 5 pF. The simulation I made, 5pF was the one that gave almost the identical frequency response as the U87 classic schematics using 220pF/33nF as C6/C5.
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AdamFrisen
Well-known member
Did you found out what causes it?
mrchapp
Active member
Not yet. I don't have another capsule so that's the first thing I need to remedy (it's on its way now!).
I had a problem like this with a damaged capsule…. BestThat sounds like a good strategy, we all do it that way...
I would probably try to isolate the problem first. Change the capsule and see if the problem is still there. If yes, then your impedance converter has problems (my bet), if not the capsule is to blame.
untamedfrontier
Active member
Just changed the high frequency attenuation cap (C6) on my 2nd build from 240p to 100p as I wanted to tune it for a little more treble and I think I prefer that value. Although now that I have it socketed I may try some more values, this was just the closest value I had to the suggested 120p in various places in the thread.
This is the BOM I used for build #2 in the event anyone needs a reference. I used homero's v1.1 board:
This is the BOM I used for build #2 in the event anyone needs a reference. I used homero's v1.1 board:
| ORS87 | ORS87 BOM for build #2 |
| R7: | 1G |
| R8: | 1M |
| R9: | 10k |
| R9b (measuring input) | 560Ω |
| R10: | 25k Trimmer |
| R12: | 33k |
| R13: | 1M |
| R14: | 10k |
| R15: | 1M |
| R16: | 10k |
| R18 | 2k2 |
| R19: | 2k2 |
| C5: | 33n |
| C6: | 100p |
| C7 | 1uF (big yellow vishay 250v) |
| C8: | 22uF 25v (went for a smaller cap here to add in measuring input, but only needs to be 6v) |
| C9: | 1uF Film |
| C10: | 22uF 63v |
| C11: | 10n Film |
| C12 | 22uF 63v |
| C13: | 10n Film |
| D1 | 33v Zener |
| Q1: | J113 |
| Transformer: | Neutrik NTE 10/3 (wired 10:1) |
| Capsule: | 87 single side BaiFeiLi |
