Transistors as clippers (MOSFET's and BJT's)

[gjcamann]

I'm screwing around with some clipping ideas for a pedal like an SHO (ala Electra drive).

I'm investigating MOSFET's and BJT's as the primary clippers. The 2N7000 as a clipper is well known and I plan to try a few more usual suspects.

Are there any specific tranny's make good clippers?

I'd be open to any type (MOSFET, BJT, FET, others?) but I think a 100% MOSFET pedal sounds cool.

[midwayfair]

Germanium transistors as clippers are kind of cool: They have some of the softness of a germanium diode but the Fv of a silicon diode.

Personally, I think there's nothing about a silicon transistor as a diode that's anything specially. It's just a silicon diode, and the diodes are cheaper.

MOSFETs can be used as clipping diodes in two ways: As a generic silicon diode (G+S > D), and ... another far more special way (D+G > S). Here's a thread with tons of info about it:
http://www.diystompboxes.com/smfforum/index.php?topic=90474.0

One of Jack Orman's articles (DO NOT use the first example, it's actually wrong!):
http://www.muzique.com/lab/zenmos.htm

Some additional recent experimentation/discussion over on Madbean:
http://www.madbeanpedals.com/forum/index.php?topic=11044.0

And for fun, here's one of my projects that uses four MOSFETs as clipping devices all by themselves in three different ways:
http://www.diystompboxes.com/smfforum/index.php?topic=103335.0

[gjcamann]

Thanks for the great resources midway - all those links have a bunch of other great links = i'll be busy all day!!
Just the info I was looking for.

[kurtlives]

Germanium transistors as clippers are kind of cool: They have some of the softness of a germanium diode but the Fv of a silicon diode.

Personally, I think there's nothing about a silicon transistor as a diode that's anything specially. It's just a silicon diode, and the diodes are cheaper.

MOSFETs can be used as clipping diodes in two ways: As a generic silicon diode (G+S > D), and ... another far more special way (D+G > S). Here's a thread with tons of info about it:
http://www.diystompboxes.com/smfforum/index.php?topic=90474.0

One of Jack Orman's articles (DO NOT use the first example, it's actually wrong!):
http://www.muzique.com/lab/zenmos.htm

Some additional recent experimentation/discussion over on Madbean:
http://www.madbeanpedals.com/forum/index.php?topic=11044.0

And for fun, here's one of my projects that uses four MOSFETs as clipping devices all by themselves in three different ways:
http://www.diystompboxes.com/smfforum/index.php?topic=103335.0

Are you sure Ge transistors have the same Fv as silicon diodes (0.6V). Pretty sure that's a no

Measure base to emitter on a Ge transistor when in active non-saturation mode and you'll get 0.3V.

[midwayfair]

Woops, you're right.

Seems to be prtly gain dependent too. 20hfe was .2 just now. 100hfe was .25.

[edvard]

Read from page 7 here, under the title "Alternative uses for transistors":
http://www.epemag3.com/lib/free_projects/home/1202-%20Door%20Defender.pdf

Apparently, shorting Base to Collector creates a "superdiode" with a lower forward voltage that varies (slightly) according to input current.
I have used that in place of clipping diodes in the feedback path of an op-amp.  The difference was very subtle, but pleasant.
Shorting Base to Emitter creates something similar to a Zener diode.
Haven't tried that one yet.