JFET source-follwer vs opamps

[Nicke]

Anyone compared something like the JFET source-followers (described at page 18 at http://www.borbelyaudio.com/AE699BOR.PDF)
with opamps (coupled as a with gain of 1) in active filters ?

Niclas

 

[SemperFi]

Yes. Much better than any opamp, unless you demand lower output impedance for some reason. Soundwise the simple JFET buffer is much better.

U can even cascode it kinda like this:

 

[R. McAnally]

Low output impedance is important for active filters (which is the original intent I think), to obtain the expected -3db frequency and filter response curve. The reactive loading of the filter combined with the high output impedance of the follower will make for some highly unpredictable results.

This is not as much of an issue if used AFTER the filter, and this circuit will indeed work fine, but not as good as an op-amp in areas relating to PSRR, linearity, and input impedance. The noise performance will be better than most op-amps tho'. Just my 2cents


😉

 

[mlloyd1]

Also, if your filter needs a gain of exactly 1v/v, the op amp may be better.

I use the JFET buffer (uncascoded, so far) for a "no gain preamp"

The Hafler 915 preamp uses something like this too and got good reviews. Yes, it sounds good too 🙂

Michael