Pre-amp Frascati in the laser lab

In the Laser lab (i dont'report the graph) the noise in out od the pre-amp refered to the input (short circuit in input) is around 15-20 nV/sqrt(hz)...I dont' know the why. When the chiller and laser is OFF the noise is around 15 nV.

This morning i have tried to improve the noise of the pre-amp. We Analyse for point:

1) I have put the pre-amp on the small table and on the bench (in the lase lab) but the noise is around 18 nV. I have used as cable the channel 1 and 2.

2) After i have put the pre-amp outside the laser lab (in the rack) and the noise is around 0.9 nV.

3) After i have put the pre-amp outside the laser lab (in the rack) and i have connected the output of the pre-amp by means of a long cable to the channel 1 situated in the laser lab. The noise is around 10 nV...i have seen the same effect of the point (1).

4) After i have built a long cable simulating the point (3), without the use of channels. The noise is around 1 nV.

5) I have tried to repeat the point (3) changing the channel 1 with channel 2 and 5. Only with channel 5 the noise decreasing to the usual value but the spectrum is very strange, it isn't flat.

At the end I have mesured the noise of the pre-amp when it is outside the rack (in the rack) using a small cable (similar to the point....the noise is 0.9 nV, so the usual values and the usual spectrum....

!?!....

I dont' think that channel 1 and 2 aren't OK....

I made same simple measurements.

I measured the noise of the pre, when it is outside the laser lab, it is ok: flat and around 0.9nV/sqrt(Hz).
Then I moved it to the laser lab, the noise is that reported by Maurizio, but I noticed, looking at the signal on the oscilloscope, that the output of the pre is modulated at about 678kHz with an amplitude of about 3Vpkpk. I could not identify the source of this noise. I asked the people in the room next to the laser lab (Luigi Distante and roberto Cardarelli) if they had something that could emit at that frequency, but they don't.

I am taking from Frascati some things to shield the pre amp.

In this afternoon I have disconneted all cable of instruments into lab laser from electric net. I have switched off light and air conditioner; the noise measured is the same around 20 nV. As reported from Alessio, i noticed a signal of around 600 kHz of 3 V of amplitude.

After i have tried to connect the power supply out side the lab and switch off master switch in the laser lab...Noise is around 15 nV...so, it is still very very much.

If i have put a short circuti in input to the pre-amp the frequency of his output signal is around 775 kHz.

After i have put the pre-amp and power supply outside the laser lab and the noise is OK, 0.9 nV and flat....but there is the sinusoidal signal (600 khz, 2 V) in output of it. I have also tried with power supply into lab laser and pre-amp outside laser, the noise is around 1 nV.

I have noticed these measured also with other pre-amp that i mounted.

Comments: From the outiline the pre-amp, i notice a positive feedback that can explain the sinusoidal signal in output... ?? But, there is still the problem of the why in the lab laser the noise is very high...