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Flat battery simulator

10/9/1998 9:00 AM
paul perry
Flat battery simulator
Just built a 'flat battery' simulator for a customer... he has an Ebow that gives a very gnarly effect when the battery is near gone... so I made a variable regulated supply (9.3 to 5.2v)from a 317 regulator. Didn't seem quite rough enuff, so added a 1k resistor in series in the output... given time, i would like to put a variable 1k pot there.  
As you wind the voltage up and down, the Ebow excites different harmonics, presumeably as the feedback loop's distortion characteristics change. A unit like this should be even more useful with fuzz and distortion fx.
10/9/1998 10:23 AM
Good idea Paul ;-)  
That's the circuit of my pedalboard power supply's battery simulator circuit. I used a voltage range of 7 to 9.5V and a fixed resistor as well. The PCB containing the circuit and the AC transformer/rectifier as well, are on GEO in the "Schematics" section.
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10/12/1998 6:23 AM
paul perry

well "Doh!" is me.... Perhaps I will invent the wheel next.... one thing though, perhaps there should be a choice of filter caps after the series resistor...this might give a cool 'power sag' effect with tube simulators.  
Still, I needed that high school algebra workout figuring the voltage output range,, and, anybody making adjustable power supplies, have a think about what might happen if the wiper arm of the control pot jumps off the track for a bit.. sometimes this is cool, sometimes kablowie!
10/12/1998 7:25 AM
I was pleased to see the same answers come out - kind of independent design verification. On the sag, that is a reasonable thing to experiment with, but you need a big cap to get much detectable sag. To hear sag, you need a time constant that's a fraction of a second. With even a 1K resistor in there (that would drop one volt per milliamp, a huge drop in a 9V supply for a 3-to-5ma draw) you'd get a 6 ms sag per 1000uF; you'd need a 10kuF to get an appreciably slow 60ms sag. More reasonable values of resistor like 100 to 500 ohms would require even bigger caps to slow the sag down enough.  
You're right, running your $900 VintageBlaster box from a homemade supply, you should consider the consequences of any single component failure.
10/13/1998 7:12 AM
paul perry

Certainly for true amp sag simulation you need big cap values.... but for f*cking up poor unsuspecting d*gital fx units, distortion pedals etc a much shorter time constant might be in order. Cheap thrills for winter nights!
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