« Reply #5 on: May 30, 2006, 02:17:26 PM »
I've recently changed two things. I had my UA-5 receive the Busman mod and I switched to new mics. I made my first recordings with both new pieces of equipment at Summercamp and now I have a problem.
The wave forms for all four bands that I taped have what I believe to be phase shift. The + part of the wave is going higher than the minus part of the wave. It is not DC offset. The wave appears to be centered. Before I left for Summer Camp, I calibrated my SVU level meter using a sine wave as a test tone. I didn't really pay close enough attention when I did but now looking back both these test tones have the problem as well. This rules out anything to with the location I recorded at. I have also looked at several recordings before I made the changes and none of them have this problem.
I am suspecting the busman mod right now. I have a PM in to him to look at this thread. I still have my old mics and tomorrow night I will run a test with both set of mics to see if I can eliminate the mics as the problem.
Actual field recording.
sine wave made at home and stretched:
Same sine wave compressed:
Hmm. Sounds to me like an opamp problem (bias/offset voltage?). I know I had this type of thing when I tried to put some hot-shot bipolar opamps (LT6233, LT6203 I think) in my UA5. They went away when I replaced them with FET input opamps (AD712, AD8620). I think all opamps can be made to work, but need some tweaking of the surrounding components, and I'm too lazy to figure this out.
Sounds like Busman2 should take a look. Either the opamp(s) are bad, or should be replaced with a different variety. Of course, feel free to correct me if this is another problem.
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" **