Battery dynamic sag supply

[Steben]

I guess this will work? Putting two resistors (stereo pot) the positive swing of an opamp as well as the negative swing will draw the voltage down. If you put only one resistor in single supply both the swings will cancel each other out and you'll ahve only the quiescent current draw.
The caps will hold the voltage change on each side a bit before stabilizing again.



The only thing I am concerned about is the connection of the "ground" in opamp circuits, previously connected to single supply. The "ground" connection in some circuits are connected to 0V = -4.5V in the dual.

[Steben]

I made a spice sim: 

http://www.diystompboxes.com/smfforum/index.php?topic=91601.msg781919#msg781919

[petemoore]

   Not sure what the intended result is.
  This would be introducing a 0-1k R on the ground line ?
  ...perhaps dropping the V+ before the divider will satisfy having a Gnd. wire, keeping the Vbias centered, and voltage 'sag'...
  If I understand what you're asking/intending about calling it ''voltage drop'' would be more appropriate, ''sag'' is associated in tube amp/talk..when a note draws X amount of current through the speaker, the PS voltage drops a little.
     

[Steben]

The sag we're talking about is what happens because of a dynamic voltage drop. So first you need a voltage drop that is controlled by strength of signal. In a tube amp it's all simple and for free, but also ... set for a given amp. Set as in: max drop, attack and decay time...

No, not a resistor in ground line but in the virtual + and -. The caps hold the temporary drop (the bigger the cap, the slower the attack and decay). Without symmetric trick, positive swing and negative swing would fill and suck the caps, resulting in inaudible drops. With symmetry, each cap gets sucked without the fill as long as the current draw is high enough, so you get build up of power supply drop.

[petemoore]

  The 1k's drawn like dual gang pot makes me thing 'knob'.
   Perhaps make these resistors LDR's driven by dynamically driven LEDs ?

[Steben]

  The 1k's drawn like dual gang pot makes me thing 'knob'.
   Perhaps make these resistors LDR's driven by dynamically driven LEDs ?

'tis a knob of course it is a "sag" pot.

that's possible as well but a bit more complicated?

[petemoore]

...perhaps dropping the V+ before the divider will satisfy having a Gnd. wire, keeping the Vbias centered, and voltage 'sag'...?
   Ie LM317 voltage regulator before the resitive divider as suggested alternative option. That way the divider would always provide the same proportions as the +/- supply is reduced, also it eliminates 2 pots and any anomolies they might add.
  But since I'm not sure what the application or intention is for the supply these comments may seem off target.
  'tis a knob of course it is a "sag" pot.
that's possible as well but a bit more complicated?
I thought about why it wouldn't work, LDR's don't go to no ohms for one thing.
 

[The Tone God]

Punisher ?

Andrew

[Taylor]

Punisher ?

Andrew

Here's the link for those who don't know TTG's site:

http://tech.thetonegod.com/punisher/punisher.html

[Steben]

Punisher works fine, but it is relatively very complicated compared to adding 3 components to a stomp, no?
anything that has a class AB opamp (TS-x, DS-1, ...) can be modded.

[Steben]

...perhaps dropping the V+ before the divider will satisfy having a Gnd. wire, keeping the Vbias centered, and voltage 'sag'...?
   

yes, ... single pot in series with battery works fine!
But you need that extra cap from gnd to + side that is missing in most pedals. Again: only in class AB opamps

summary: not the symmetry of the resistor is capital, but the stabilizing with the caps.