Can you sub an OTA w/ a single opamp and two transistors?

[lightningfingers]

:?:  :?:  :?:

I was thinking in particular about the small stone....

[R.G.]

No.

The OTA is fundamentally different from an opamp. The output of an OTA is a current source, not a voltage source like most opamps.

[Arn C.]

While on the topic.....
What can CA3094's and 3080's be used for building?

Thanks!
Arn C.

[Mark Hammer]

While on the topic.....
What can CA3094's and 3080's be used for building?

Thanks!
Arn C.

You name it.  Just about any filter, any type of gain/amplitude modulation, distortion, panning, dynamic processing, VCO's, etc., and stuff you'd normally never think of.  For instance, Aphex uses the 13700 (a dual OTA) for "aural exciters".

Always helpful to have a handful on hand.

[Ge_Whiz]

Question: anybody got a circuit diagram or even a building block diagram for an aural exciter? I know what they do, but how do they do it?

[Mark Hammer]

There are different ways to do it, but the core approach is pretty much the same:  make harmonics of your harmonics and blend those harmonics back in with your original signal to make it sound like it had all those harmonics in the first place.  Because only the mid to upper harmonics are "harmonicized", it sounds crisp rather than fuzzy.

One way to do this is to highpass filter the input signal and clip the bejeezus out of it.  This is what is used in Jules Rykebusch's "Harmonic Sweetener" that first appeared in Electronic Musician and is posted around with some mods I suggested.

Another way that Aphex uses for one of their models is to produce frequency doubling for the high end by means of a balanced modulator.  Normally, if you feed the same signal into the X and Y inputs of a ring-modulator/VCA/balanced-modulator/4-quadrant-multiplier, you get frequency doubling.  Frequency doubling of everything over a certain cutoff is perfectly acceptable as a means of providing more energy at higher frequencies.  Aphex in their grey Model B unit use an LM13700 to accomplish that frequency doubling.

Exciters do NOT sound the same as equalizers of any sort.

[Arn C.]

Thank you Mark!!!

Peace!
Arn C.

[Ge_Whiz]

Thanks, Mark. What sort of frequencies are we talking about for the highpass filtering?