XOR gates (4030/4070) as amplifiers?

[earthtonesaudio]

I've seen them used in noisemakers (Escobedo's Digital Octave Fuzz, Jmusser's XOR Ultra Sick) but never as simple gain stages.

Could you (ab)use them in the same way that is often done with 4049/4069 inverters, in their linear(ish) region?

[John Lyons]

The XOR ultra sick is used as an amplifier but it's square wave city...I built a couple
and tried to work out some bugs with biasing the input. It gates pretty hard.
Cool but needs some work.

[earthtonesaudio]

Did you try tying one pin high and using feedback from output-input?


From the truth table it seems like that should do it, but then you have something like this:
http://srstansfield.com/Electrical-Engineering/Hyperlinks/Logic-CMOS-Chips/4070.htm
which, if these indeed oscillate, clearly indicate something else is going on (either phase shift or Schmitt trigger action).

The TI datasheet shows a maximum of 3 CMOS inverters in series, which should not (in my experience) oscillate when configured as an inverting amplifier.  The only thing I can think of the propagation delay through the gate is 180 degrees of phase shift at a certain frequency.

[John Lyons]

I tied the input to ground and v+ with a voltage divider (pot).
Feeding some of the output into the input would do it probably though.
I have used that before with sucess.

[Lurco]

some other 4000 : http://www.diystompboxes.com/smfforum/index.php?topic=11853.0

[anchovie]

Jmusser's XOR Ultra Sick

Is there a schematic available for this?

If I Google it, the top hit is this thread!

[John Lyons]

Here you go.

http://www.diystompboxes.com/smfforum/index.php?topic=42693.0

[earthtonesaudio]

I tied the input to ground and v+ with a voltage divider (pot).
Feeding some of the output into the input would do it probably though.
I have used that before with sucess.

So tying one input high and treating the rest as an inverting op-amp... that did work?


P.S. All the stages of the XORUS are non-inverting, which could be part of your gating problem (feedback from out to in is positive, causing hysteresis).

[John Lyons]

Feeding the output into the input forces the gate open.
The only tweak I did to the XORUS was to "bias" the input.
I have not tried the feedback things yet, that was another circuit.
With that I fed the out to the in through a 2M7 resistoance and
that opened up the gate yet didn't oscillate.
And all this was a least a couple years ago so...

Fool around and see what you get.

John