seriously modding a transsound mic capsule

[stefanzap]

I've linkwitz modded a couple transsound caps - namely the ts-60 caps.
Though the mods do the trick with raising the spl, of course, the self noise doesn't diminish any.

So -

Today, I opened up a ts-60 capsule, pulled out the tiny circuit board and bypassed the internal (eensy weensy) onboard fet altogether (accomplished with a razor blade and drop of solder). I put the capsule back together as best as possible and attached an external fet and 1G resistor.

I attached - this mess (which is what it kinda became) - to a circuit (the scott Helmke "alice" circuit) and in addition to a lot of hum and hiss, got sound. The mic does work, however output is very low.

What I'm wondering is -- has anybody attempted this, and if so - what was their outcome?

I have no question in my mind that I compromised this capsule sonically. That's not my problem. I'm wondering if I am able to seal it up nicely, would externalizing the FET help?

For this experiment I used an nt4416a (cause it's what I've used for other mic projects).

Any suggestions, anecdotes, etc.?

Thanks

[/img]

 

[alk509]

For the Alice and other DIY electret mics, your best bet is probably the micbuilders Yahoo! group. If someone's ever tried to do what you describe, they probably posted it there.

Good luck!

Peace,
Al.

 

[stefanzap]

yup, I'm on that group and have posted the same question there.

:grin:

 

[Mendelt]

I can remember someone here tried something like that with a different approach.
He tried to zap the internal fet with a high voltage to short it internally. But that didn't work . Those fet's seem quite resillient.

What you're trying should work. But you have to be very carefull. The hum might be picked up by the leads from the capsule to the fet or from the fet to the rest of the circuit (i had problems with this with a normal linkwitz modded panasonic wm61 but i solved that by using shielded cables. This might not work for the leads from capsule to fet because you wouldn't want the extra capacitance from a shielded cable there.)
If you've got leakage resistance paralel to the 1g resistor you'll get a lot of noise too. Did you clean up the resin from the solder blob?

There's another circuit floating around here that uses a linkwitz modded wm60 (or transsound equivalent) by Marik. You might try that one. If i remember correctly Svart tried them and was quite pleased with the noise performance of that circuit.
I remember someone (marik?) saying the wm60 (or maybe 61?) by panasonic already use the 4416 internally. But they use leakage currents instead of the 1g resistor. So this might make the capsule noisier.

Another way to get an diy omni sd capacitor mic is to mod the transsound capsules used in the alice. You can seal the vents in the back of the capsule to make it omnidirectional. I'm not sure what this will do to the freq response of the microphone. I'd thing it would make it even flatter. But i heard people on the micbuilder mailinglist claim otherwise.

 

[Svart]

we (Marik and I) did do the work on the wm60 and a circuit for it. It works pretty well. I forget the part # of the fet, I actually opened one up and tracked down the part code to a panasonic part number JFet, I posted that in one of the threads, I believe it was the ecm8000 thread. The mic is done with a linkwitz mod and is not noisy at all, at least in the electronics aspect. Since it is a super small capsule which is very sensitive and it's omni, there is a LOT of pickup of surrounding noise including any and all air movement close by. It sounds a lot like regular old hiss but it's actually ambient noise, once taken to a perfectly deadened area the noise diminishes greatly and is masked by noise in other areas of the system.

do a search on "ecm8000" I don't know if the layouts are still there or not.

 

[Svart]

ok here it is, it was in an Earthw*rks thread:

http://www.groupdiy.com/index.php?topic=3626&postdays=0&postorder=asc&start=15

 

[stefanzap]

thanks. This is good stuff. In hitting some of the links, it took me back to the initial R&D you did, Marik. Very cool.

The Transound capsule is a bit noisier than the panasonic - and the fet inside is way to small to ID.

Is there an advantage to using a different circuit (perhaps something like the ecm8000 over the Helmke/davel (schoeps) circuit?

 

[Mendelt]

[quote author="stefanzap"]Is there an advantage to using a different circuit (perhaps something like the ecm8000 over the Helmke/davel (schoeps) circuit?[/quote]

I have no idea. I don't really think the schoeps circuit will introduce much extra noise but in an earlier discussion Svart mentioned that his (svart&marik design) wm60 mics were very quiet while i find my (schoeps) wm60 mic quite noisy.

I only made one mic so maybe i screwed up the capsule when soldering it so it's more noisy.
Or maybe it's not noisier but it may sound noisy to me because of this:
[quote author="Svart"]there is a LOT of pickup of surrounding noise including any and all air movement close by. It sounds a lot like regular old hiss but it's actually ambient noise, once taken to a perfectly deadened area the noise diminishes greatly and is masked by noise in other areas of the system. [/quote]

The only way to find out for sure is to try them side by side
I have ordered the parts for the marik-svart mic but reichelt is a bit slow.

[quote author="stefanzap"]The Transound capsule is a bit noisier than the panasonic [/quote]
I'll have to try this out too. I just recieved some transound capsules to play with...