Cathode follower for compression

[martin manning]

But JFETs lack an equivalent to a triode’s grid current, which IIRC is supposed to play a significant role in the DCCF’s compression effect.

[cdemike]

Does anybody know if this ’Direct DC coupled cathode follower’ setup for compression can be done with transistors instead, with the same compression result? That is, ’direct DC coupled emitter follower’.
Was thinking of trying this for a pedal..

If I understand RG Keen's Mosfet Follies article (http://www.geofex.com/Article_Folders/m ... tfolly.htm) correctly, you'd want to likely avoid higher powered MOSFETs if you're looking for compression since they'll stay linear for a much wider range. I wonder if a transistor more commonly used in dedicated dirt boxes would work better in a lower-voltage setting where overdrive/compression is the design goal. Maybe something like a BS170? Martin alluded to this, but it seems to me the main goal would be gradually clipping one side of the wave form (as opposed to something like a diode which introduces sudden-onset clipping), so the goal seems like it would be to set the operating point exactly where it'd need to be in order to clip in a way similar to the way a DCCF's grid current impacts its bias point.

[pdf64]

Does anybody know if this ’Direct DC coupled cathode follower’ setup for compression can be done with transistors instead, with the same compression result? That is, ’direct DC coupled emitter follower’.
Was thinking of trying this for a pedal..

I can't envisage how, the effect requires a device with the same characteristics as a valve. Including those characteristics that aren't generally noted on valve info, eg g-k current and voltage plot.

[Tobyk]

Here’s someone who thought of it back in 2016.
A lot of broken links, but one embedded schematic survived in the post.

https://www.diystompboxes.com/smfforum/ ... c=115071.0

[pdf64]

Ok, in retrospect it should have been obvious, but the gate of an n channel jfet is a pn junction, normally reverse biased for linear operation.
So yes, it may be feasible to operate a source follower around zero / slight forward bias, to achieve similar effect to a DCCF.