starve pot?

[larrylegend]

hi everyone - my name is larry - this is my first real post here on EA.  i love this message board!

i've seen para and colin talking about something called a "starve pot".  am i correct in thinking that this is a pot that divides the power voltage to the circuit, giving a similar effect as a dying battery?  

i found a similar reference on the beavis audio site here: http://http://www.beavisaudio.com/techpages/Pots/9voltsag.gif  
dano calls it a "voltage sag circuit" and uses a 2K pot as a voltage divider straight off the 9V battery.  are we all talking about the same thing?

if we're good up to this point, i have the following followup question - what size resistance pot should you use and why?  and will inserting a starve pot use more or less battery juice than if you left the circuit alone?

larry

[expanoncolin]

hi everyone - my name is larry - this is my first real post here on EA.  i love this message board!

i've seen para and colin talking about something called a "starve pot".  am i correct in thinking that this is a pot that divides the power voltage to the circuit, giving a similar effect as a dying battery?  

i found a similar reference on the beavis audio site here: http://http://www.beavisaudio.com/techpages/Pots/9voltsag.gif  
dano calls it a "voltage sag circuit" and uses a 2K pot as a voltage divider straight off the 9V battery.  are we all talking about the same thing?

if we're good up to this point, i have the following followup question - what size resistance pot should you use and why?  and will inserting a starve pot use more or less battery juice than if you left the circuit alone?

larry

Not quite... the starve pot is a series resistance, not a voltage divider.  A voltage divider would have one side conneted to V+ and one side connected to ground with the center to the circuit.  This is just a variable resistance in series between the battery and the circuit.  It limits the amount of power the circuit can get.  1k, 2k, 5k, 10k are all values to try, effects will vary greatly from circuit to circuit.  I've written a few times here about what happens as a battery dies, it's not quite the same as this, but you can still get comparable and often different but still interesting effects from a starve pot.

-Colin

[larrylegend]

oh right... series!  i don't know why i was stuck on the voltage divider thing.  i now realize that even the little schematic i linked to in series now that i look at it again.

is there a way to measure the total resistance of your circuit while it is in operation?  is it as simple as hooking up an ohmeter where you would connect the battery?  or better yet hook up an amp-meter in series with the circuit while the circuit is running?

larry

[expanoncolin]

oh right... series!  i don't know why i was stuck on the voltage divider thing.  i now realize that even the little schematic i linked to in series now that i look at it again.

is there a way to measure the total resistance of your circuit while it is in operation?  is it as simple as hooking up an ohmeter where you would connect the battery?  or better yet hook up an amp-meter in series with the circuit while the circuit is running?

larry

Since the load of the circuit is not necessarily just ohmic, it is ideal to do what you mentioned second and to connect the ammeter in series between the battery and the circuit.

-Colin

[Grogberries]

One thing I've been doing lately that I like is having a couple pots starve the batteries. One's like a course adjustment and the other one is a very low value pot where you can fine tweak it.

[para]

Kerr is that you?


"is there a way to measure the total resistance of your circuit while it is in operation? " just curious, why would you want to?



steven

[larrylegend]

yes sir it's me!

the reason i was thinking i would want to measure the resistance of the circuit is because it might help calculate what value pot you'd need for the starve pot.  my thinking was that to get a full range of starvation (from 9V or whatever all the way down to almost 0V), you'd want it to be several times larger than the total resistance of the circuit?

also in audio we're always talking about the impedance of microphones, guitar pickups, high impedance, low impedance, etc. etc. so i wondered if you could just measure it with the ohmmeter but i seem to remember something about the inductive component of impedance being the other part of it....so i think that's what colin is talking about not being totally ohmmic.

while we're still talking about starve pots --- why does starving circuits sometimes make them create random noise or otherwise freak out?  i would have thought that they would just get lower in pitch, or softer in volume.  but apparently they sometimes just go crazy.  for example:
http://experimentalistsanonymous.com/bo ... =fuzz+4049

larry

[larrylegend]

and grogberries - i love the "coarse starve/fine starve" idea!  

(it's like being stranded in a lifeboat with no food, and then going on a diet on top of that...)

larry

[para]

thats what i thought, for that what i do is just grab a large value pot, usually 1m, and then slowly turn it down until the effect starts happening and  hits it peak result. then i remove it from the circuit and measure it, then if thats like 50k or close i grab a 50k and use it. every circuit will be different so you have to test each one separately, there is no standard. some don't starve at all


"the resistance of the circuit" this is an odd expression – and doesn’t really exist as its stated

measuring input and out impedance is an entirely different procedure and to do it correctly is incredibly complicated. there is a method to get you very close but it still requires a bit of hardware. scope, meter, pot and an oscillator at hopefully 1k and other standards 10k, 100, if possible. each freq will give you a different result. i can find a link to explain it if you want


most of the craziness of starving happens with digital chips and its not voltage thats being taken away its current. so if you think of the battery as the source of a river feeding the chip the water it needs to run, then by starving it you are only giving it a small glass of water at a time so it can only do little sections of its job at a time and those are accomplished randomly by chance in most cases, or at least that’s how i understand it

i’m sure colin can explain it better, or tell me i have it wrong?


steven

[expanoncolin]

thats what i thought, for that what i do is just grab a large value pot, usually 1m, and then slowly turn it down until the effect starts happening and  hits it peak result. then i remove it from the circuit and measure it, then if thats like 50k or close i grab a 50k and use it. every circuit will be different so you have to test each one separately, there is no standard. some don't starve at all


"the resistance of the circuit" this is an odd expression – and doesn’t really exist as its stated

measuring input and out impedance is an entirely different procedure and to do it correctly is incredibly complicated. there is a method to get you very close but it still requires a bit of hardware. scope, meter, pot and an oscillator at hopefully 1k and other standards 10k, 100, if possible. each freq will give you a different result. i can find a link to explain it if you want


most of the craziness of starving happens with digital chips and its not voltage thats being taken away its current. so if you think of the battery as the source of a river feeding the chip the water it needs to run, then by starving it you are only giving it a small glass of water at a time so it can only do little sections of its job at a time and those are accomplished randomly by chance in most cases, or at least that’s how i understand it

i’m sure colin can explain it better, or tell me i have it wrong?


steven

He's talking about overall circuit load, not input/output impedance.  In this situation it's easiest to measure the current, then divide the voltage by it to find the approx. load of the circuit...

Starving circuits is a lot like bending... in fact, I'd say it was a simple bend in the end.  There's always a reason or a way to explain what's going on or the effect effect created, but normally to many things are happening at once.  If you starve a whole circuit you could be doing 10 things at once, starving the input and output buffers, the processing, the vbias setup, and the sum of all of those things is what you hear... it's analyzing chaos and randomness.  Don't question, just do

-Colin

[larrylegend]

hey colin and para - i really appreciate all the help with the starve pots.  

btw i think i was sort of ignorantly co-mingling the concepts of overall circuit load vs. input & output impedance, so thanks for setting me straight.

over the weekend, i was bending a black blob based toy keytar kind of thing called "cool keyz" and of course the first thing i tried (after finding the pitch resistor) was a starve pot.  

however, i noticed right away that it was starving both the blob and the transitor based amplifier for the speaker, so as you starved it, it just went down in pitch a little and quickly went down in volume.  so it became inaudible before any sonic chaos had a chance to manifest itself.

so then, i thought i figured out which traces brought power to the amplifier circuit, which powered the blob, and which went to the keyboard triggers, so i cut the traces with a razor blade and tried to starve just the blob and made jumpers for the other two.  however, i guess i figured it wrong because the trace going to the chip didn't even need to be connected and the circuit worked normally.  so not sure what happened there but i wasn't able to figure out where the blob power trace was in order to starve the chip by itself.

but i was still super psyched because i figured out how to make a 40106 oscillator retrigger the sounds as i had read about people doing here.  with a pot, i have the rate varying from like 1 HZ to 20 Hz.  faster than that, the chip just seems to get confused and won't retrigger any faster.  i was really surprised the 401016 is capable of running off of the 2.5V coming from the two AA batteries that power the toy.

i also found some cool bends in what i think is the transistor amplifier to the speaker using capacitors.  so thanks too for all the general inspiration!

larry

[expanoncolin]

Congrats on getting the triggering working.  Resolder up that trace and try again to find the V+ to the chip.

-Colin