Landgraff Clean Boost - Unity Gain Only

[Ofek Deitch]

Hi,

I've built a SHO with the Landgraff input resistor mod, and I'm having the same issue as the guy over here:
http://www.diystompboxes.com/smfforum/index.php?topic=94244.0

Bypass signal is fine, but effect on, its just the bypassed signal, but i can hear afaint crackle when turning the knob.

I'm using a J201 and this is the scheme used:



Voltages: (9v)
D: 2.2v
S: 1.1v
G: 0.3v

Thanks for any help!
- Ofek -

[Davelectro]

I'm afraid this is another case of "Crackle OK".

[anchovie]

I'm afraid this is another case of "Crackle OK".

That's not his problem - he wants a booster and he's getting unity.

I'm using a J201

That's a JFET - this circuit calls for a MOSFET.

[Ofek Deitch]

Will replacing the J201 with a BS170 help?

[R.G.]

Yes.

[Gus]

Hi,

I've built a SHO with the Landgraff input resistor mod,

- Ofek -

The series input resistor is something you can read about in textbooks.

[Ofek Deitch]

I replaced it and it works now!
Thanks for the help guys!

[R.G.]

Background:
The gain you get out of a device can be computed as the transconductance (current change on the output per unit change of voltage on the input) times the load resistance, which is then modified by any feedback.

The transconductance of most MOSFETs is many, many times larger than the transconductance of a JFET.

[PRR]

> transconductance of most MOSFETs is many, many times larger than the transconductance of a JFET.

That, *and*... the way that MOSFET was biased, a JFET in the same place has the Gate *forward biased*. Enough to suck-down signal.