Re: Preamp design/Capsules/H2 - was Odd MiniDisc problem when using Mic. input
Thank you :) - A recent post covered the modification of the Edirol CS-15 which I modified to an MS mic - the result wasnt brilliant due to the method used with the Figure 8. I suspect one of the lobes is more responsive than the other throwing out the stereo field. http://www.urlme.net/blog/?p=918 has some recordings.
--- In email@example.com, Michael Chang <m.chang@...> wrote:
> Wow, Mike, you've done a ton of work that I must go through carefully.
> Funny how days of work can be summarized in a few sentences that a reader
> can skim over but not develop any felt significance until it's read many
> times over.
> Your results are interesting. I imagine the cardioid polar pattern is
> responsible for additional phase funnies when two are used as Figure-8.
I think it turned out to be a couple of spaced cardioids - Ive also tried two diaphragm's connected to the same FET and also removing the acoustic material from the electret back plate. The later giving the best figure 8 pattern - but the capsule/mic case (=tube) give a strong resonance around 3kHz. I since switched to space omni's binaural rigs and spheres.. Ive avoided the use of amplifiers to keep things simple - although perhaps a differential FET amp based on 3 fets would actually work better for the double capsule version. Something Ill eventually get back to once my current quest for a decent sounding hydrophone is complete.
> One limitation will be coverage angle with the Blumlein configuration. I'm
> considering a Pseudo-Blumlein using 6 capsules configured as a Double-MS,
> in other words, two MS, paired back-to-back, but wired out of phase with
> the rear-side mics angled 120 degrees (instead of true Fig-8, 180). This
> can be done with 2 differential amplifiers (to keep it simple) if I can get
> it to work with parallel capsules FETs at the input stage. One advantage
> will be flexibility: Switchable configurations from basic patterns to
> Blumlein, MS, or any in-between combination. The possibilities are endless
> if the capsules are mounted in such a way so they can be mechanically
> moveable individually (Sony's ECM-MS957 sort of does this; you can rotate
> the capsule head to allow sound pickup from the top or side for orientation
> My goal is to make an amplified stereo microphone with line level outputs
> hopefully without coupling capacitors (personal fetish; never liked caps).
> Powering is planned to be internal through a couple of 9V batteries.
Sounds good, keep us posted. - Without the use of caps how do you stop the effects of dc bias on the signal - rely on the recorder decoupling?