so i finally built the tapeop omnis...

[jca83]

...and they don't work.

not yet anyway. it's like 3 am and i'm too tired to troubleshoot. my friend and i did them. he did the power supplies, i did the mics. i drilled the holes in the cases, bought all the parts, etc. whatever. anyway. when you plug the mic in to the power supply and read the output with a scope, there's a DC offset across pins 1 and 2, and a smaller one across 1 and 3... what did we do wrong?


thanks again, scodiddly, alex, et al. i really really appreciate it.

[Scodiddly]

How much of a DC offset? I don't think that design has a bleed-off resistor for the output, so a small amount may be present.

Make sure you've got a voltage across the capsule - that's step one.

Step two is to make sure you've got the pin numbers all correct on the connectors. That's a common source of problems.

[jca83]

i don't recall. my buddy had the meter so he just did it. i'm pretty sure one had like 8 volts. not good.

i'll check voltage when i go over to his place...


and according to the little diagram of the capsule, pin 3 of XLR is connected to the connector NOT touching the case. pin 2 is connected to the trace-connector. right?

what's most likely is that something's shorted in the mic; but i'm really darn sure nothing has the chance to. everything is covered with electrical tape or has insulation around it.

agh.

[aurelialuz]

did you do the linkwitz mod or is this just the standard circuit?

[jca83]

so, as it turns out, my friend's meter was messed up/used wrong and there's nothing wrong with the mics. they sound GREAT. they're working fine, and nothing really to speak of except they have incredible clarity, low noise and pick up SO much detail. i love them already.



i built the regular kind. i am out of 10k resistors to make the mod with and had already ordered parts for the regular.

but, i dig these so much it's worth it. i'll probably make another pair that have the mod in them. and maybe some more. do they make cardioid capsules like this?

[aurelialuz]

i haven't tried the mod, do the modded capsules work with the original PS design? could you just build the modded capsules and swap between them as desired?

[jca83]

that's the trouble. i'm not sure. the linkwitz hand-drawn crappy looking schematic is totally different from the regular one.

i'm thinking you'd need two different power supplies, because the mic's output is changing, right? you're using a different output configuration by the wiring scheme he lays out.. so the output is going to run through the power supply differently...? i'm just kind of letting words fall out of my mouth here, people.

[Scodiddly]

It's a completely different circuit, but those things are so simple it's not a big deal just to make separate setups. Or just do everything Linkwitz mod... I've got a standard phantom power supply design for modded capsules, and so I just mod everything I do.

Check out the Panasonic WM-55A capsule - it's cardioid, and it's really good. Not quite the specs of the omnis, since cardioids are harder to build. But it's still very hifi, and the weak bass you can fix with EQ. Plus you can use it in the TapeOp circuit.

[leigh]

Or just do everything Linkwitz mod... I've got a standard phantom power supply design for modded capsules, and so I just mod everything I do.

Would you mind sharing your circuit for phantom powered Linkwitz capsules?

I'm about to build a new pair, and trying to gather all the circuit options...

Thanks,
Leigh

[ape32]

Hiya Scodiddly -

I second that call for the phantom circuit, if you would be so kind as to share it! After reading this thread I broke out my Tapeop omni that I built a year ago. I had shelved it because I thought it too noisy, but running it through my recently made Hamptone JFET it was quite quite, and A/B'd against a Behringer ECM8000 omni (same capsule, I think) - it was quite similar, if perhaps a bit lower gain and a bit quieter (both good for me).

Can your cartoids work for tom micing? Or do the capsules crap out?

- Ape

[nlmd311]

so, as it turns out, my friend's meter was messed up/used wrong and there's nothing wrong with the mics. they sound GREAT. they're working fine, and nothing really to speak of except they have incredible clarity, low noise and pick up SO much detail. i love them already.

glad to hear that there wasnt a problem with them after all. Im just about to finish my set ( read just waiting on the panel mount xlr's to arrive!) and I will be all set...I hope.

Either way, its been a fun project.

-Darrill

[Scodiddly]

Here you go:

Code: Select all

       +---------------------------330R--------+ 
       |     |                                 | 
       |    2k2                 +---10k----+   | 
       |+    |                  |          |   | 
      10u    |                  |       E--o---|--------------- Output - (pin 3)
       |-    o---------||----o--o-------B      | 
       |     |         1u0   |          C      | 
       |     |1 +            +-100k-+   |      | 
       | CAPSULE                    |---o------o 
       |3    |2 -            +-100k-+   |      | 
       |     |               |          C      | 
       |     o---------||----o--o-------B      | 
       |     |         1u0      |       E--o---|--------------- Output + (pin 2)
       |     |                  |          |   | 
       |     |                  +---10k----+   | 
       |     |                                 o----+ 
       |    2k2                               +|    |+ 
       |     |                                12V  10u 
       |     |                                -|    |- 
     --o-----o---------------------------------o----o---------- GROUND 

It's the same circuit from the huge DIY mic thread, works with every capsule I've tried.

The capsule has to be modded for a 3-wire connection, by cutting the traces from the case to the minus terminal. Much easier on the cardioid capsules, which are bigger. In the diagram, 1 is the plus terminal, 2 is minus, and 3 is case/ground.

The transistor is a 2N5087, and I either use 1uF or 0.47uF capacitors (mostly 0.47uF these days).

[aurelialuz]

what kind of difference do you see by making those caps smaller? or is it just a case of the 1ufs being overkill?

[Scodiddly]

what kind of difference do you see by making those caps smaller? or is it just a case of the 1ufs being overkill?

Smaller caps will raise the low-frequency cutoff. I think that 1uF was indeed a bit of overkill (at least for musical applications), and physically too large anyway. It's a lot easier to fit a 0.47uF poly cap into actual microphones. Of course an electrolytic would be much smaller... but wouldn't sound as good. I do tend to wonder if the amazing quality of the TapeOp omni is partially because good capacitors are used for signal coupling. That's just the sort of thing the typical $100 condensor would cheap out on.

[nlmd311]

I just finished my set about 5 or 6 hours ago and am completely amazed! These things sound awesome. The noise floor is ridiculously low and the SPL handling is extremely high. They are a little too bright, but I might make some alterations to the mic housing tomorrow to see what I can do about that.
Cool and easy project

-Darrill