another boost

[Gus]

The following is another JFET boost.
There is one thing a little different.
It has been built
The gate, one side of the diodes, input cap and one side of the input resistor have the connection in the "air" not touching the board

[vortex]

Interesting.

How does it sound?

[Gus]

It sounds like a boost with a higher input resistance as shown.
R2 is a 10K trim.
A SMD 2N5457 was used.
I left notes in the screenshot for experimentation.
Shift the collector voltage and test.

Some of the differences in simple boosts
input resistance changes how the guitar interacts.
The output resistance sets what it can drive
Coupling and bypass caps the EQ
Biasing can change the harmonics

This post was more about D1 to D4
This is not something new.
The thing different in this JFET boost the only gate to ground path is with the diodes(perf, PCB leakage and flux/dirt can act as a high value resistor) with out resistors in parallel gate to ground

[samhay]

Cool idea. As your flying layout suggests, layout is probably quite important here, much like when bootstrapping the input impedance. Did you try on the breadboard?

To play devil's advocate, could you tell the difference between biasing with diodes vs. with e.g. a 10M resistor though?

[Rob Strand]

The following is another JFET boost.
There is one thing a little different.
It has been built
The gate, one side of the diodes, input cap and one side of the input resistor have the connection in the "air" not touching the board

Interesting idea. 

Was that inspired by the thread on JFETs a few weeks back?

[Gus]

Diode idea is from AT microphone circuits

[Rob Strand]

Diode idea is from AT microphone circuits

Ah.  I guess the idea comes from not loading the mic.

[PRR]

> I guess the idea comes from not loading the mic.

914 diodes are tons cheaper than 1Gig resistors.

At this scale, the impedance is not that different. For good-batch diodes. (The published specs probably allow far more leakage than a mike wants, but 99.44% of modern diodes will be on extra-clean Silicon and not leak near that much.)

[Gus]

If anyone builds this you might want to add a series input resistor

A volume control could be installed at the input with a 100k pulldown to replace the output volume control