Envelope Filter without opamps

[Rayman]

Does anyone know of any envelope filter designs that don't use opamps?  Is the Kechiwah an "autowah"?

[Transmogrifox]

I can't think of any envelope filter circuits that don't use op amps, but you can make an envelope filter out of a Bad Horsie quite easily.  Pick your favorite envelope follower circuit and wire the output to the LED that drives the LDR.  Your "Range" control is the wah pedal, and you can easily install a pot for sensitivity on the Bad Horsie.  In addition, there's plenty of space inside for adding circuits. I would recommend the follower section from the Mutron as a good balance between simplicity and performance.  There was also a thread recently about a simple envelope follower,  I think a good simple EF was developed in that thread.  You can usually score a Bad Horsie on eBay for $40.

It does the funky EF thing better than  the DOD FX25 (as if that says much)...but I make the comparison because it's about that simple as far as controls and its operation:  sensitivity, range...so for the simplicity, it's great.

[StephenGiles]

The MXR Envelope Filter does not use op amps. There is a kit for this.
Stephen

[R.G.]

Does anyone know of any envelope filter designs that don't use opamps?  Is the Kechiwah an "autowah"

Why?

[Rayman]

I was just wondering.  I'm relatively new at this and have become interested in using jfet's and bjt's for distortion circuits, and was wondering about using them in other circuits.  I guess there's probably no advantage for an EF.  Op-amps would be much more practical.

[R.G.]

OK - that's a good reason!

What opamps, as a special case of feedback stabilized amps, give you is control. In one small package with no annoying cross-component and biasing mysteries, they let you choose gain and frequency response simply. The time and frequency responses are relatively independent of the underlying device except for those edge cases where you're at high gains and high frequencies.

Envelope followers require some fairly touchy interactions between small signal rectification, level manipulation, and gain modification. These are possible with all discrete designs, but I doubt you could do them reliabily without liberal use of negative feedback to stabilize the operation.

The forward gain filter that has its response modified by the signal level sensing does not particularly need to be an opamp. In fact, a two-transistor twin-T will do that nicely, and that can be bipolar, FET, MOSFET, triode, pentode or combinations as well as opamp.

But doing the sidechain well and reliably without opamps is difficult for anything more complicated than something like the Dr Q and its derivatives.

[StephenGiles]

...........and we also know that doing the sidechain efficiently with opamps is no easy ride......but if I could just urge a little more enthusiasm for the Multi Space Filter option......
Stephen

[Rayman]

Thanks R.G.  That definately answers my question.

[lovekraft0]

.....but if I could just urge a little more enthusiasm for the Multi Space Filter option......

My 13600s are on order! Did you ever have time to get yours working?

[StephenGiles]

After a fashion, I was rather hoping someone else would take up the battle as I'm a little short of time this week.
Stephen

[A.S.P.]

information lost...

[Steben]

completely free of solidstates...

Here we go ... a-geynn (Gump voice...) ...
Not for me. To me tubes will last because of the gain and overdrive.

[A.S.P.]

information lost...