Weslie whats happening?

[Kipper4]

So looking at the GGG weslie (new to me) schematic i see a twin t network being wobbled by the fet.
But it sounds like more than that.

What am I missing? how does it work? just like a inductorless wah?

link to scheme

http://www.generalguitargadgets.com/pdf/ggg_weslie_sc.pdf

[Mark Hammer]

Nope, it's just a modulated bandpass filter, with some finer control.  It's Dean's adaptation of the old PAiA Synthespin, which was their flagship modulation effect before they introduced the Phlanger.  There was a more recent version, using an LM3900 quad Norton amp, instead of all discrete.  Couldn't tell you if it sounded different or better, but it did have external voltage-control of speed and modulation range.  https://www.paia.com/talk/viewtopic.php?f=6&t=211

[Kipper4]

Thanks mate.
Excellent nothing enigmatic then.
Sweet. I think I might have some lm3900. Norton op amps.
Essentially a differential op amp.

[Mark Hammer]

My Chanukah present to you, Rich. 

[Kipper4]

Merry chanukah  to you. 

[Kipper4]

Does it have to be a differencial op amp or can I use keens law and do it with a 4558 or TL072?

[duck_arse]

Norton amp, an amp with differential inputs but different internal biasing. usually the circuit is designed around the Norton weirdness, current mode and such.

how did you come by LM3900's in yer stash, being as you are only a young'n in the vintage parts-ing caper?

[Kipper4]

Na youse is rite. They're not lm3900's
I'll order some just in case i decide to try it.
And thanks mate for advice.

[Kipper4]

Tayda has stock. Must be reissues

[PRR]

... lm3900. Norton op amps.
Essentially a differential op amp.

Well, no. The Norton is a nearly unique(*) amplifier. Needs very different designs than all the other "op amps". Some say the LM324 (a nearly conventional opamp) was the reaction to NObody liking the LM3900.

Simonton liked the '3900, but he was all into clever use of lowest-cost parts.

(*)There's also a dual Norton and a high-speed Norton.

[bool]

The "LM324" even got an upgrade (well the "358" and "2904" variant)

http://www.ti.com/product/LM358B

...still I must have a small bag of 3900's somewhere