Distortion stage with Nonlinear element between inverting pin and ground

[Vivek]

In my whole life, I only saw one distortion circuit with a nonlinear element (diode) between inverting pin of Opamp and ground.

Please show me more such circuits.

Please teach me tricks, benefits, oddities.....

[iainpunk]

if you put a clipper or other non linearity between the inverting pin and ground, you'll get an 'expander', where the gain goes higher when the input voltage goes over a certain threshold. basically a ''soft crossover distortion gate'', i have done this in an overdrive pedal i designed for a friend. its not the most practical circuit, about as practical as anti-parallel diodes in the signal path, and it NEEDS gain up front to cross over the diode threshold. i used 3x gain and hand selected germanium transistors. but i had a lot more going on in the signal path, which also soft clipped the signal and hard clipped at yet another threshold.

just try some stuff out on a breadboard, its fun.

cheers, Iain

[teemuk]

Well.. in an inverting circuit such diode(s) naturally do nothing because the input is a virtual ground and there exists no signal voltage to clamp. (Although I know there are designs that thoughtlessly clone OD channel of a Fender preamp in which such diodes actually do work as overvoltage protection BUT in combination with channel switching and associated switching FET).

In non-inverting amp the diode can create the variable resistor, as which diodes are used as in clipping circuits, but - as is - the diode will be reverse biased at small signals and introduce high resistance causing the amp to have very low gain. For peak clipping the diode must be forward biased at small signal levels, which can be done easily (just establish proper DC voltage across it but capacitively couple the AC signal) but this scheme is patented by First Act, Inc.

[iainpunk]

but this scheme is patented by First Act, Inc.

we're so lucky in the rest of the world where electronic schematics patented in the US have no legal footing. most country's (except for the US) don't allow electronic schematics to be patented, only the specific drawing can be copyrighted, but you aren't prevented from re-drawing it yourself to circumvent this.

cheers, Iain

[garcho]

^ that's the same here in the US, patent is for intellectual property, not schematics. Copyright is for schematics.

[iainpunk]

^ that's the same here in the US, patent is for intellectual property, not schematics. Copyright is for schematics.

what i tried to say is that electrical intellectual properties aren't acknowledged outside of the US.