Could somebody explain this circuit to me?

[leadbelly]

From: http://homepage.ntlworld.com/henry01...ic_decoder.htm

In a non-inverting op-amp feedback circuit it is easy to use a variable resistor to GND to create increasing gain with a reducing resistance. And in a slightly different op-amp circuit it is easy to have a resistor to GND create reducing gain with reducing resistance. The cunning part is to use each end of one single gang potentiometer connected in both of these circuits, with the wiper grounded. So, as the wiper is grounded there is no crosstalk between the circuits and as you move the wiper from one end of the track to the other, the gain increases or decreases in both circuits. It's clever, and as far as my very sketchy thought about this circuit goes, should still be fine with log pots, so it will be fine for audio weighted controls. Using this system, a cheap double gang pot from Farnell becomes a quad gang pot; Ideal for B format volume control.

I get the first part, the increasing gain with reducing resistance. But what about the second part? If the feedback resistor is grounded, doesn't that change the relationship of gain to resistance from the first circuit?

[paulb]

What circuit?
I don't see how it can work properly either.

[richie00boy]

I think he means that each half of the pot is providing the lower resistor in each op-amps feedback network. i.e. wiper grounded, left side of pot goes to chip a, right side of pot goes to chip b. Then when pot is turned chip a increases gain while chip b decreases gain, and vice versa.

[leadbelly]

Originally posted by richie00boy
I think he means that each half of the pot is providing the lower resistor in each op-amps feedback network. i.e. wiper grounded, left side of pot goes to chip a, right side of pot goes to chip b. Then when pot is turned chip a increases gain while chip b decreases gain, and vice versa.

Thanks, but no, I'm pretty sure that's not what he means.

Anybody?

[paulb]

Originally posted by richie00boy
I think he means that each half of the pot is providing the lower resistor in each op-amps feedback network. i.e. wiper grounded, left side of pot goes to chip a, right side of pot goes to chip b. Then when pot is turned chip a increases gain while chip b decreases gain, and vice versa.

Well, I think that is almost what he means; I just don't see how it could work while matching the gains at all volume settings.

[soongsc]

I you search Ambisonics, you will probably get some sites with simpler circuits for explanation. Al the information I can find really don't show a solid ground for acurrate sound reproduction. It might give you a sensation of having a large room though.

[janneman]

I think he meant this:


Jan Didden

[richie00boy]

Thanks Jan. I like how you have TM a name and (C) a schematic from somebody elses description

[janneman]

Originally posted by richie00boy
Thanks Jan. I like how you have TM a name and (C) a schematic from somebody elses description

Well, since I'm the first to come up with it, I thought I'd try. But rest assured, you all can freely use it, no license fees, make lots of money from it, nothin' .

Jan Didden

[poobah]

Jan,

Is this a volume or balance control?