Hi all,
this construction is from the ADA MP1 guitar preamp. The schema shows a BF256 but the JFET is originally the obsolete 2SK364. I do not know what the BJT actually is. This stage is probably a bit noisy, and I wonder if anyone can suggest JFET (and perhaps BJT) still in production that has low noise figure. Given that gain is unity and the distortion is very low (second harmonic < -90dB if simulation did not lie too much) i think the only relevant parameter here is noise. But, I might have misunderstood something in the circuit, so all comments are, as usual, most welcome!
Cheers,
Mike
this construction is from the ADA MP1 guitar preamp. The schema shows a BF256 but the JFET is originally the obsolete 2SK364. I do not know what the BJT actually is. This stage is probably a bit noisy, and I wonder if anyone can suggest JFET (and perhaps BJT) still in production that has low noise figure. Given that gain is unity and the distortion is very low (second harmonic < -90dB if simulation did not lie too much) i think the only relevant parameter here is noise. But, I might have misunderstood something in the circuit, so all comments are, as usual, most welcome!
Cheers,
Mike
Attachments
The polarity of C205 appears to be wrong.
It doesn't look like a particularly high-noise design to me. The equivalent input noise current is kept small by using large values for R201 and R203 and using a JFET input stage, and the equivalent input noise voltage is kept small enough by using a reasonably low value for R202 and a JFET with a reasonable transconductance.
It doesn't look like a particularly high-noise design to me. The equivalent input noise current is kept small by using large values for R201 and R203 and using a JFET input stage, and the equivalent input noise voltage is kept small enough by using a reasonably low value for R202 and a JFET with a reasonable transconductance.
The BF245 is still available. Like the BF256, they come in grades. Pick the one (Idss) that suits the circuit best (Vpo is not so important in this circuit).
The BC560 is a suitable low noise BJT.
The source of the J-fet should be on a positive value, to avoid havoc.
The BC560 is a suitable low noise BJT.
Depends on the unspecified value of Vee, but if it's equal (save the polarity) as Vcc, agreed.
The source of the J-fet should be on a positive value, to avoid havoc.