Hi, Umashanker - Huh! I'm not up on circuitry, so I'm only getting the gist of what you're saying. It seems like each of the four PPAs should have a battery, if there's no external phantom power source connected. I'll try with turning only one of them on to check.
In other news, this morning I made a few more recordings and didn't hear the mysterious noise any more. Nothing was different, as far as I could tell, except the time of day. So, this will be my strategy for the weekend (the 788T's a rental): run off of battery power, don't use the built-in phantom power, and use the PPA AA-batteries for the phantom power. Also, the Rycote baby ball gag and furry windjammer work very well (which is no surprise, i guess). The TetraMic is, of course, way too thin to use the baby ball gag out of the box, but wrapping some gaffing tape around it a few times did the trick. It's a little annoying, but not the end of the world. (I've never worked with windscreens and windjammers before - i was impressed that i could stand a foot away from the mic with an electric fan turned on maximum and hear nothing in the recording except the sound of the fan's motor. Very nice!) cheers, j On Apr 16, 2011, at 9:56 AM, umashankar mantravadi wrote: > > this is something i have vaguely worried about when designing multichannel > mikes in one body, and then phantom powering them. in the classic wurtke > circuit, the phantom voltage powers the output transistors, and you need it > to be on for the transistors to work (right?) doesnt the core sound ppa also > have a transistor driving the transformer. if it was just a transformer with > a resistor to the centre tap to draw the phantom voltage, connecting only one > channel would actually be better. otherwise you have four ten k resistosrs, > four five volt zeners and four capacitors which are going to be paralleled. > > (talking from memory so probably through my hat) > > umashankar > > > i have published my poems. read (or buy) at http://stores.lulu.com/umashankar > > > >> From: jnarve...@wesleyan.edu >> Date: Sat, 16 Apr 2011 09:18:42 -0400 >> To: sursound@music.vt.edu >> Subject: Re: [Sursound] TetraMic and/or Sound Devices 788T question: weird >> noise at record start? >> >> >> Hi, John (and Dave) - >> >> Ah - I haven't tried using just channel 1's phantom power. I *did* try >> taking the 788T off of AC power, turning off all the phantom power on it, >> and putting AA-batteries in the PPAs as the phantom power source. With this >> set-up, I still got a weird noise about 12 seconds in to recording, but not >> as severe. A bit mysterious. >> >> I haven't tried other mics yet - not sure I *have* any other mics at the >> moment, since I had a bunch of stuff stolen last year (which indirectly led >> to my TetraMic purchase this month). I certainly don't have any >> condensers... perhaps I'll try it with line input just out of curiosity. >> >> thanks again, everyone, >> >> -jascha >> >> >> On Apr 16, 2011, at 4:53 AM, John Leonard wrote: >> >>> Jascha, >>> >>> You only need phantom turned on on Channel 1 - try turning it off on all >>> other channels and see if the noise goes away. The Baby Ball Gag does work >>> with the TetraMic, by the way; not perfect, but so much better than the >>> foam & furry set-up supplied with the mic. I believe that Rycote now do a >>> special set-up for TetraMics with a modified lyre-suspension and the >>> extended BabyBall gag, but that really is expensive. >>> >>> On the subject of Rycote prices - my thought is that if it enables me to to >>> my job effectively, it's worth the money. Rycote is a genuinely innovative >>> company, run by people who care passionately about what they do. And it's >>> British! >>> >>> Best wishes, >>> >>> John >>> >>> On 16 Apr 2011, at 01:44, Jascha Narveson wrote: >>> >>>> The four XLR inputs are routed to tracks A, B, C, and D in the 788T, and >>>> 48V phantom power is active on each channel. >>> >>> _______________________________________________ >>> Sursound mailing list >>> Sursound@music.vt.edu >>> https://mail.music.vt.edu/mailman/listinfo/sursound >>> >> >> _______________________________________________ >> Sursound mailing list >> Sursound@music.vt.edu >> https://mail.music.vt.edu/mailman/listinfo/sursound > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > <https://mail.music.vt.edu/mailman/private/sursound/attachments/20110416/abcfb7b7/attachment.html> > _______________________________________________ > Sursound mailing list > Sursound@music.vt.edu > https://mail.music.vt.edu/mailman/listinfo/sursound > _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
