Help! (Tape Op Omni Mic problems)

[MechaGodzilla]

...So I've been working on a pair of those nifty Tape Op Omnis, and I thought I had the circuit built right, but when I go to check 'em with actual recording gear, the output is unusably low. Anyway, I took one of them apart and put it back together on a breadboard, and a curious situation results. The mic is still wholly unuseable, but when I pull the positive battery lead out, I get a momentary blast of good, clean sound before it cuts out.
My guess is I've got the wrong capacitor on the output, but I don't know. This is the most complex circuit I've built myself, which isn't saying much.

Anyway, here's my order from DigiKey
1 Mic Capsule PP925-ND
1 1000pF Cap 1383PH-ND
1 10uF Cap EF1106-ND
1 2.2k resistor BC2.2KW-ND

Any help would be great. I really want to get them working, because I built some swell cases for 'em, too.

Thanks!
A

[buddy holly]

cool cases! somebody help him out!

[Scodiddly]

It would certainly help to see the layout, but my guess is that somehow you've got the battery in parallel with the capsule, instead of with a resistor between the battery + and the capsule +. The battery would then act as an "AC ground" absorbing the signal from the capsule. With the battery disconnected you'd lose the AC ground and get some signal until the capacitor was discharged.

[substitute]

DUDE THOSE CASES RULE!!!!!!!!!!!!!!!!

Can You explain how you made them, what you used etc? Not to be captain copy cat, but that's a jones I'd like to keep up with!

=|:^=

[trashy]

Are those cases the mics, or are they the mics and power supply? I can't tell, but it looks to me like they're both... Anyway, doesn't the power supply box need to be metal in order to ground the thing? Are you grounding some other way?

[Scodiddly]

Are those cases the mics, or are they the mics and power supply? I can't tell, but it looks to me like they're both... Anyway, doesn't the power supply box need to be metal in order to ground the thing? Are you grounding some other way?

The case would need to be metal to properly shield the electronics. So those cases, as cool as they are, will tend to pick up noise.

[MechaGodzilla]

I just got a foot each of 1.5" and 1/4" acrylic from Tap Plastics along with some of those caps, and some plastic xlr connectors. Then I cut some discs out of some scrap plexiglas and glued 'em together, put the black caps on it to cover up my mistakes, and voila! Total cost for the cases was like, $5.
Yeah, it's everything in one case instead of a separate power supply, mostly because I didn't want to scrounge up 2 more xlr's... I'm planning on getting a piece of copper pipe to line them with or something, because yeah, they're not shielded right now.

I'll go take a picture of the circuit and put it up here... but my component list looks good? I was worried that I just slipped and got the wrong capacitor or something.

Later,
A

[MechaGodzilla]

...Or here's my other worry. The original article made reference to an impedance-matching circuit inside the capsule, but I went ahead and got a different capsule that seemed to meet the requirements since the original wasn't in stock.

Here's the capsule I've got - P9925-ND . ...Right? Wrong?
Later,
A

[Scodiddly]

That's the WM-61, which is the recommended replacement. You should be OK there.

So where's the layout photo?

[MechaGodzilla]

Well, I already found a few stupid mistakes on my "finished" board, so I pulled it apart and stuck it back on the breadboard. ...Problem is, it still doesn't seem to work. Same shit.

Anyway, here's what it looks like now.



Infinite thanks,
A

[Scodiddly]

That does look correct, although I never really looked that closely at the TapeOp circuit before. Seems rather weird.

I'll have to mull it over a bit.

BTW, you aren't hitting it with phantom power, are you?

[MechaGodzilla]

No, no phantom power. Although one of them did get a blast before I noticed the switch was on...

Think I could've toasted the capsules? My only soldering iron is a 30watt.

A

[trashy]

What's that cap doing in the lower left hand corner?... I can't quite see what's going on there... Is that another "pretend these connect"? It just doesn't look like it's doing what it's supposed to, at least on the "negative" side.

[Scodiddly]

I don't think you would have toasted *both* capsules. Besides, there's that "unplug the battery and get a moment of sound" thing you mentioned. Does the breadboard version do that too?

Anyway, assuming that you actually do connect the battery negative and the resistor, it's the same circuit as the TapeOp design. So it ought to work.

What are you plugging it into? Maybe you could try swapping the wires to XLR pins 2 & 3.

FWIW, I use 10K resistors.

[MechaGodzilla]

...How would swapping the 2.2k resistor for a 10k affect the circuit? Sorry for the idiot questions; I'm pretty new to electronics.