Amz buffer question

[nsteen]

So amz has a buffer schematic where you can run 3 different outputs on the same source signal. They're all jfet buffers but I got to wondering - could you attach a mosfet boost? In parallel with one of the buffers. I don't know nearly enough about electronics to describe coherently what I'm think Ming of so here's a grossly incomplete and hackneyed "schematic"

Like so (is the photo showing up?):



Man that was a lot harder to accomplish than I expected

[duck_arse]

Man that was a lot harder to accomplish than I expected

the circuit drawing or the image posting?

you may well (probably) have biasing problems as drawn. have a look at the biasing for the amz mosfet boost, it is variable to suit each device. the top jfet cares less, is happy with V/2. looking again, I think you should maybe connect the mosfet gate, via a blocking cap (and with its own biasing arrangment), to the jfet source lead.

if you're lucky, one of the experts will be along to correct me/guide you.

[antonis]

With your arrangement the two signals are out of phase (In phase on JFET's Source  - Out of phase on MosFet's Drain)...

So probably the one will cancel the other..

[GibsonGM]

Yup ^^^  So, the idea is "do-able", but needs some modifications.

Can I ask - what's the purpose?  Could you use the mosfet after a buffer stage?  (looking for a gain stage here?)

JFETs and Mosfets - close, but different enough to matter.

[PBE6]

Both the JFET and MOSFET buffers/boosters have very high input impedances so they will present almost no additional load to the incoming signal. You shouldn't have any problems connecting two or more such stages in parallel.

Do check for phase issues if you plan on mixing the signals back together at some point.

[antonis]

Can I ask - what's the purpose?  Could you use the mosfet after a buffer stage?  (looking for a gain stage here?)

Maybe ansteen wants to boost a separate line and then mix the signals...

If so, it yould be obtained with a JFET (for biasing simplicity and material homogeneity purposes) and invert the boosted (or the buffered) signal before they get mixed...

[GibsonGM]

+1   I was wondering why it has to be MOS, and not just the same FET as being used in the splitter.

The trouble with mixing MOSFET and JFET as he's drawn is that the bias voltage won't be the same for each type of device.   That could be gotten around, it just takes more parts.

[nsteen]

Hey guys, sorry I didn't get back here sooner - I didn't think I'd have any replies let alone this many! Thanks for all the help.

Honestly I hadn't decided yet what I want to do with it. Originally I wanted to mix and blend an EP style boost with a SHO boost (with the jfet in the EP operating at 24v to keep up with the Mosfet in the SHO). I love both of those sounds and the idea just seemed cool. Either that or something like the defunct JHS banana boost.

Another idea was to implement what the klon does as a conceptual matter (clean/OD in parallel) but use a source bias potentiometer (kind of like what the EP boost and the madbean fatpants do) to affect the timbre of the clean boost, rather than the array of capacitors and resistors used in the klon. Also I quite like how Jfets distort so in parallel with that clean boost I was hoping to use something like the ROG peppermill.

It's not a very well fleshed out idea and I'm really thankful for all of your guys input. This weekend I should finally have some free time so I hope to experiment with the idea some.