Morning glory mod

[SprinkleSpraycan]

I've been tinkering with a morning glory schematic for awhile. What I'm calling the character control is...well....what is it? What did I do? It boosts volume and gain by.....miss biasing the transistor? Sounds cool, totally useful but I want to understand what I stumbled into. Hope someone can help.

[antonis]

As it is, it shouldn't do anything..

TL071 is unbiased (no DC on pin3) so it should permanently be topped or bottomed..

Character pot is set in parallel with Q1 Source resistance (R16//R17) with its wiper AC grounded (almost) via TL071 pin 6 so it contributes to Q1 Gain setting..
(Drain resistance / Source resistance)

P.S.1
In case of TL071 properly biased, you have a "weird"  NFB configuration..
(it should be better to be connected on Q1 Gate..)

P.S.2
Never seen before a resistor of 470pF value..

[SprinkleSpraycan]

P.S.1
In case of TL071 properly biased, you have a "weird"  NFB configuration..
(it should be better to be connected on Q1 Gate..)
:

When I connect it to gate it goes dead. I'll try biasing leg 3 and see how it goes. That must be why it doesn't do much until about 2 or 3 o'clock.

[ElectricDruid]

Nfb?

NFB = Negative FeedBack

on the op-amp in this case.

[GGBB]

Never seen before a resistor of 470pF value..

There's no "F" written Antonis - clearly it's 470pOhms. 

[antonis]

There's no "F" written Antonis - clearly it's 470pOhms. 

Eagle eye, Gord..!! 
No tolerance stated so I presume we could round it up to half a milliohm..

[antonis]

When I connect it to gate it goes dead.

Could you imagine the reason for this..??


hint: Either Gate is -almost- AC grounded or equal amplitude signals of 180^o phase shift are met there..