IF3601 IF3602 Ultra Low Noise JFETs

[gerhard]

I found that ferrite only move the oscillating frequency from one place to the other.
Under 1 MHz, they behaved like a pure inductor. The losses set in at higher frequencies,
at least for the Murata and Würth beads that i tried.
Remember, when they generate resistance at one frequency, they also generate
thermal noise, so there is not to much gained against a resistor.

I also found that a large electrolytic was helpful.

BTW what is the idea behind the diode D1? If you connect the ni input
of the op amp to 2V4, the diode will make sure that the inv. in will never
go there. But Op amps like to have 0 V between their inputs, that's
only natural when there is infinite gain.

Just got a parcel from DigiKey, now I can finish this differential preamp
from Art Of Electronics with the 64 Zetex BJTs.

I'm sick of throwing GPIB commands at my FFT analyzer to max out its
dynamic range. This Agilent programming manual is really s*****.

cheers, Gerhard

 

[mt490]

I guess the ferrite bead you're using is intended for applications where the HF lossiness is actually beneficial, rather than a type for RF duty.

 

[jackinnj]

BTW what is the idea behind the diode D1? If you connect the ni input
of the op amp to 2V4, the diode will make sure that the inv. in will never
go there. But Op amps like to have 0 V between their inputs, that's
only natural when there is infinite gain.

D1 on the schematic is reversed from how it is placed on the proto-board.

 

[gerhard]

I'd say, make it absolutely minimalist. Then when the noise is right
you still can try to make it lightning proof. The 3602 has -20V Vgs abs max,
and 20 mA per gate. That's quite a lot.

cheers, Gerhard

 

[SyncTronX]

Here is a typical 2SK170 VS the IF 3601

So as I view this, the Typical 2sk170 is CH#1 in blue.

Pink is Overlay 2 which must be the IF3601?

Yellow is Overlay 3, which is what?

So it appears that pink is worse by about 10 to 15 dB.
until about 400Hz. Okay, so how does it look beyound that?
Do they still correlate to 50kHz for example?

Cheers,

 

[wayne]

The top is a 2SK170 and the bottom is two different IF3601. I only made the measurements at the frequencies show.