Quicky - input JFET buffer with good drive capabilities and adjustable DC level

[slideman82]

Right, I'm gonna recalculate all with 24V DC, then. In theory, it seems I have to lower the upper resistor...

Thanks!

[Gus]

A few things

First the gate does not have to be at ground you can use a mix of voltage divider and the other bias if you want

If you raise the supply voltage pay attention to IDSS at Vds and Id, Vgs voltage rating.  If you change the Drain resistor work out what else happens.

Note the part numbers in the NS app look up the specs for the fet numbers(s)

Look at the all the curves of the fet and try to understand what they mean and how they can be of help with this type circuit.

[tommymariotti]

I really like this buffer!
How can I make an inverting Buffer based on this schematics?
Thanks to all!

[iainpunk]

if it inverts, it won't be a buffer now, will it?

it needs quite the overhaul to make an inverting buffer out of this, basically a full inverting gain stage tacked on the end, which probably involves removing the DC offset which RG deliberately designed in to this.

i'd simplify the buffer to a single JFET, and use a 2 (or 3) transistor feedback amplifier to produce the inversion.

ill be back to add a schematic soon

cheers

edit: schematic has a gain of -1.1-ish

[merlinb]

How can I make an inverting Buffer based on this schematics?

Change Q2 to NPN

[Rob Strand]

Change Q2 to NPN

Need to loose the emitter feedback as well.

For feedback you have the inverting scheme.  It follows this pattern although this example
isn't for audio:


The inverting scheme has a gain of -1 but the input impedance isn't high.
(Also more effort to stabilize.)

[antonis]

Maintaining 1M input impedance and CFP almost 100% NFB benefits..
(Q3 could be used as phase splitter, as well..)