« Reply #24 on: February 03, 2007, 10:17:23 PM »
What I don't understand is why SoundPros have not caught on and offered three wire battery boxes. They are missing a *huge* market here.
They'll just tell you need phantom power.
But I *really* do agree...
I'm not at all trying to bad-mouth Sound Professionals, but you know I asked Chris (Sound Pro Chris) a bunch of questions and got *completely* different answers from what other technical minded people on here told me.
Here is the problem with the A-T mics as I see it.. Number 1 the distortion figures they are using are not accurate.. These mics do distort badly I have measured them at 114db at 1k these mics have a distortion that is almost 15% that is VERY HIGH! I measure my own mic capsules from the factory they are 10% typical but after my mod the AT mics measure 0.5% and my mics measure 0.5%. So getting the mod done to these mics saves them from distortion but you do sacrifice some level that's why after doing the mod you should invest in a preamp.. To run your mics unless your always taping loud shows then you don't need a preamp in most cases..
Chris Church
I find people that are using the MT do need a preamp after my mod because the noise floor in the MT preamp is bad to begin with. And when you need the extra gain from the MT it brings up the noise floor too much, that being said the preamp in the Edirol R-09 is much better and more often then not for most loud shows not needed..
Hey Chris. I think the problem is AT mics were *never* designed to run as "two-wire" at all. If you look at any of the numerous AT powering options, they use a three-wire circuit. Even the power modules that are battery/phantom split the battery voltage so that half is across the FET and half across the (source) load resistor.
As far as "not enough gain" that is subjective. Sure, if you're trying to run into a NJB3 or Iriver, you've got a problem. But several line inputs, like Edirol R01/R09, and Minidisc have enough gain to bring this up nicely for any amplified music. I think they might add 10-15dB or so but that is quite enough. That is why I've been using my MD so much even though I've got a lot (!) of other gear.
Richard
Richard they are not really three wire capsule all they are is two wire capsules that have a separate ground wire to the case. The red wire is the signal the Yellow is the negative if you remove the ground wire the mic will still work but will be noisy in a true three wire capsule it will not work..
This is the same as the other capsule I use for my mics. I could be wrong but that's what I have discovered.
I gotta disagree with you there!
AT and yours are both three wire. Red is the drain of the FET, Yellow is the source of the FET and shield is ground (of the capsule). The other end of the capsule goes to the gate of the FET. For two wire you short yellow and ground (at the 3.5mm stereo plug, usually).
Your mics have three wires too, +, audio, and ground. Some variants have a source resistor (eg., 2.2k) soldered between audio and ground.
Richard
Ok I stand corrected I have never opened up an AT mic.
BTW, there may be a small # of mics (Sennheiser MKE2, some varieties) that have the FET source and ground shorted *at the mic end*. These cannot be hacked for three-wire use. Sennheiser MKE-2-4 are shorted this way, MKE-2-5 are not. I bought the latter after a long search on Ebay.
Richard
Hi Richard these are my tests for distortion/output loss my 2 wire mod vrs Normal 3 wire
The red spike indicates distortion of the typical 3 wire battery box.. It is 0.5% at -25db with a 114db extremely low distortion acoustic signal directly coupled to the capsule... The blue spike is the distortion of my 2 wire mod via the 4.7k resistor it shows a loss of 5db over 3 wire..... But the distortion is exactly the same 0.5% here is a picture of both graphs super imposed.
Ps... Notice the third harmonic is gone with my 4.7 k mod strange I don't know why its not there anymore maybe because its 5 db down... I thought you might be interested in the test results.
The AT 853 performs exactly the same way after the mod.. as my capsule does distortion wise.. The thing that concerns me is there are different distortion rates for different capsules of the same make and model so when I match my capsules I use Frequency response distortion % and output in db at 1k as a means of making sure they are the same... I have measured a pair of AT capsules I have here that are in for my modification the difference in distortion between the two supposedly "matched capsules" was 3% distortion! not very matched IMO.. So one capsule was 0.5% distortion the other capsule was 3.5% distortion this would lead me to believe that the capsules that AT makes are being matched for level not for distortion this means you could get one capsule that will distort much earlier then the other in a stereo pair not good news.
Anyway tell me what you think..
Chris Church
Thanks. Very nice analysis. I would be interested in seeing a two-wire (unmodded) setup here too. That would be a good advertisement for your gear. Or at least how *not* to power microphones.
Richard
Logged
Mics: Sennheiser MKE2002 (dummy head), Studio Projects C4, AT825 (unmodded), AT822 franken mic (x2), AT853(hc,c,sc,o), Senn. MKE2, Senn MKE40, Shure MX183/5, CA Cards, homebrew Panasonic and Transsound capsules.
Pre/ADC: Presonus Firepod & Firebox, DMIC20(x2), UA5(poorly-modded, AD8620+AD8512opamps), VX440
Recorders: Edirol R4, R09, IBM X24 laptop, NJB3(x2), HiMD(x2), MD(1).
** This individual has moved to user "illconditioned" **