[Terrence, Keiko, Rana]
The two PZTs on the AS table make very high pitch sound as if they are mechanically resonant when we apply just the bias DC voltage of 75V from the DAC. The microphone spectrum is attached. The sound is at 6.3kHz. This sound didn't happen with the PZT driver's bias (no DAC signal). We will try to check the DAC different channels next week.
The DAC signal is from the SRM rack seemd to noisy by looking at a oscilloscope (RMS of a few 100mV). The DAC output FFT photo is also attached. There are peaks at 6.1kHz and harmonics. Next week we'll check other DAC channels to see if there are all bad or not, and if we can use better channels.
By the way, did you use a (kind of proper) driver in-between the DAC and the (raw?) PZTs? As you probably know, PZTs are seen as capacitive loads with respect to the output stage of the DAC, so the whole electric circuit might go crazy (or oscillating) without proper intermediates; a dedicated PZT driver would include such proper intermediate circuits. Anyway, the peak found in your attached spectra is so sharp that I don't think the peaking itself would not directly come from the circuit oscillation, though.
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