Mosfet clipping by Jack Orman

[GuyB]

I'm been experimenting with this interesting but unusual Mosfet clipping design by Jack Orman, using the following info:
http://www.muzique.com/lab/zenmos.htm

Quote "In this configuration, a positive signal will pass through the gate-source junction of the upper mosfet (Q1), then through the body diode of the lower one. For negative signals it will take the opposite path through the upper body diode and then through the gate-source of Q2."
I'm unsure what pins go where:

If Q1 has pins S1, G1, D1
and Q2 has pins S2, G2, D2

D1 is to out

D2 is to Ground

What about pins S1, G1 and S2, G2?

Thanks
Guy

[R.G.]

Quote "In this configuration, a positive signal will pass through the gate-source junction of the upper mosfet (Q1), then through the body diode of the lower one. For negative signals it will take the opposite path through the upper body diode and then through the gate-source of Q2."
I'm unsure what pins go where:
What about pins S1, G1 and S2, G2?

G1 connects to D1, G2 to D2. S1 connects to S2.

The description as stated is confused and confusing. MOSFETs don't have gate-source junctions in the normal sense like bipolars and JFETs do. But they do have gates and sources, and the voltage between these two does affect how the MOSFET conducts.

In this  circuit, connecting the gate of each MOSFET to its drain makes the voltage on the gate with respect to the source follow the input voltage. However, the gate of a MOSFET cannot let any current - or signal - through in the sense the explanation uses. When the gate-to-source voltage on the MOSFET reaches the threshold voltage for conduction, the MOSFET drains begin to conduct, and this lets signal current through the drain-to-source. The characteristic curve of drain current versus drain-and-gate voltage to source voltage looks and acts much like the forward conduction current versus voltage of a single diode, but with a bigger forward voltage and different curvature. That is, it acts like an unusual diode, but it does this through the interaction of the gate-source voltage and drain current. The gate-to-drain connection of a MOSFET is sometimes called and "amplified diode" connection in the techie jargon.

Each MOSFET has an inherent diode built into it, which conducts the reverse direction to the drain-to-source channel. If you do nothing about this, a single MOSFET conducts int the drain-to-source direction according to the amplified diode curve, but will conduct in the source-to-drain direction by the body diode. The body diode is a simple silicon junction, and not like the few-volts forward voltage of the amplified MOSFET diode in the other direction, so the results are very, very asymmetrical.

That's why there is a second MOSFET. The second MOSFET is hooked up the opposite direction, with both its amplified diode connection and body diode opposite to the other.

With + and - signals, the + signal conducts through one amplified diode connection and the opposite MOSFET's body diode. The - signal does the same thing, but in the opposite direction. In essence, the series connection as shown lets you use the body diode of each MOSFET to steer the signal to the correctly-pointed MOSFET amplified diode.

[duck_arse]

both Q1 and Q2 are some ordinary mosfet part. each is a three pin packages, with source (s), drain (d) and gate (gate) pins. if you short each gate to it's respective drain, you're down to 4 connections. now connect the source of each to the other, and you have the two terminal device in the orman. the "body diodes" are sometimes included on the diagrams, but usually only on the datasheet. they point "the other way".

search for 2n7000 or bs170, for examples, at somewhere like www.datasheetcatalog.com, for another example.

[edit :] and now I'll read rg's response .....

[GuyB]

Many thanks for the excellent responses, it's an interesting clipping design and on my bread board, G1 connected to D1, G2 to D2. S1 connected to S2, D1 connected to out, D2 to ground. Just testing how it effects the sound compared the typical parallel Mosfet clipper design.

Thanks again
Guy

[GuyB]

It has a nice soft clipping sound using 2N7000, I added a 100pf cap in parallel.  Soft clipping is what I'm trying to achieve. I like it.

Thanks great advice.
Guy

[noisette]

These are my favourit clipping devices, very pleasant sound, you just need 2-3V level, also try them in the fb loop!