Such a demonstration shows how the analog circuitry controls the flow of electricity organically in the same way that a woodwind or a horn controls the flow of air.
I don't think it can be done with the digital modules though.
I still haven't gotten around to making this a reality for myself; too busy building modules and enjoying the learning curve of patching.
I asked about modding a Blacet power supply a while back on the Blacet list with the same thing in mind, or building a variable power supply. Maybe people here have other ideas.
Some of the things mentioned about the topic on the Blacet list:
Is it just a simple dimmer switch as used for household lighting?
Seems pretty simple - a potentiometer placed between the supply and
module (or power distrubutor) chokes off the voltage.
I'm no engineer or qualified expert, but I wouldn't
crack into my PS500 --you could definitely do
Try instead buying a pair of adjustable voltage
regulators (LM317)--one positive, one negative -- for
a couple bucks from Radio Shack and build a mini
adjustable supply for yourself. Follow the schematic
on the package, add 15v +/_ from your PS500 and you
will have an variable +/_ supply that adjusts from 1v
to 37v via 10k trim or panel pot(s). Or maybe two
trim pots (+/_)running into one master panel pot that
drops both poles at the same time. You can experiment
with dropping the power on individual modules and note
the results, and I don't think you'll hurt anything
--just don't let it get above 15v!
The plus and minus rails must drop equally. I usually experiment with
this on mic pre-amps that use single ended, adjustable (+24v) power
supplies that are easy to adjust.
I thought you can damage op-amps in a bi-polar circuit if the plus and
minus rails do not raise and lower evenly. Correct me if wrong. Perhaps
there's protection for that in newer op-amps used.
It might be real cool to make an adjustable supply module that uses
mechanical and CV controllable potentiometers to carefully scale the
output voltage with proper protection (as a fail safe) if some component
My advice is leave your supply alone and do this circuit on a module
with it's own regulator and op-amp buffer circuit. Maybe build it with
several 'channels' just in/out and mabe dual (inverting, non-inverting)
input as previously mentioned. Then you can patch through it for the effect.
Here is a link to a project for guitar pedal voltage starvation:don't think you would hurt anything by trying out a dimmer switch. You could also use a variac.
Either of those things should let you get a lower voltage, but I'm not sure if they will give you a stable low voltage, because the voltage regulators are still going to try their best to give you +/-15v DC, even if the AC input they are getting drops too low. When the input voltage goes too low they may present a sudden drop in their voltage output, followed by (I think) a sort of linear drop in output voltage as you lower the input voltage.
If you look up the spec sheets for a common voltage regulator, like the LM117 / LM317, there is probably a graph that shows possible output voltages for a given input voltage. The transformer in the power supply probably puts out around 18-20 volts AC when presented with 120V AC input, and it's output is going to drop as you lower it's input. In turn the voltage regulator will try to respond to the input voltage drop. After a certain point (depending on the regulator IC), probably around 16-17VAC input voltage, the 15vDC output voltage will start to drop or become unstable.
If you want to be able to adjust the voltage at will, and keep it stable at a voltage of your choice, you might want to get a power supply that has a 'remote sense' voltage feature. Remote sense means that the power supply has an input that you feed it's voltage output back into. This way, if the output of the power supply travels over a long cable, you can wire it back in a loop to the power supply to try and get it to compensate for the voltage drop caused by the cabling.
If you had an alternate voltage present at the voltage sense input, you should be able to use this to adjust the supply voltage from the front panel. This is just an idea and I have not tried it myself.
Power one makes power supplies with remote sense abilities. You would want to feed back a higher voltage than the input voltage if you wanted it's voltage to drop, and a lower voltage if you wanted it's voltage to rise.