Dying battery simulator (variable voltage pedal) aka JHS Volture

marksescon

marksescon

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Video demonstration:

Dying battery simulator - aka variable voltage regulator - aka (modded) JHS Volture. Overall circuit design by RG Keen. I also used Volos Projects' insight on the LM317 for additional assistance. PCB by me in Eagle.

When the Volture first came out, I immediately knew it wasn't simply a potentiometer in series with a power supply. As soon as gut shots for the Volture became available, it was pretty clear the circuit was based on RG Keen's original concept, which in turn is probably from the actual datasheet for the LM317.

For my version, I added in a LED voltmeter from Amazon and internal Age control: New batteries differ from old batteries in that, “while new batteries can put out a lot of current, old ones can't - they develop a high internal resistance.” The Age knobs acts a rheostat. Putting “a resistor on the output of our regulator…will fake the internal resistance of the battery" (source). Voltmeter addition was inspired by MAS Effects’ UV Meter Drive and Silktone Fuzz. I did attempt to have a rotary switch for a Battery Simulator (carbon zinc, alkaline, “wall wort”) to play off the JHS April Fool’s joke, but the idea was too ambitious and overly complicated to implement. I also would've loved the Age control to be an actual potentiometer, but I could not find a reasonably priced and appropriately sized 100 ohm potentiometer.

This is one of my first builds using SMD, so please be forgiving towards my soldering skills. Also if you compare the JHS Volture gut shot to my build, you can see that I did in fact purposely copy the layout of the JHS Volture because it simply made the most sense.

This circuit allows you to go from ~7.5VDC to 1.25VDC which is similar to the Voluture specs on the JHS website ("...adjustable voltage from 7.5VDC down to 1.25VDC..."). The basic circuit is 5-6 different components and takes a matter of minutes to piece together.

Two changes I would've liked to implement were:
  • Reverse polarity protection.
  • 100uF to 1000uF electrolytic output capacitor for stability.
(I did make a smaller PCB to "drop-in" to different pedals that does implement the above.)

This isn’t for sale, and I have included a demo video and the schematic on final slide. I also have free Gerber files for PCB fabrication. I haven’t found a reliable place to upload the actual files. I have included the schematic. If anyone knows a good place to upload Gerber files for download, let me know, please.
 
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Big Monk said:
I would use this without the dying battery mumbo jumbo as a benchtop power tap.

Very cool.
Click to expand...

If I were to applying this variable voltage control onto a bench top (or into a test box), I’d probably tack it on to the Mad Bean Pedals RoadRage’s 15V output. The LM317 does have a voltage drop of 2-3V, so the 15V will be now be a max 12ishV output, but that’s fine because I don’t know many pedals that require 15V to power…but I do know many that require 12V.
 
marksescon said:
If I were to applying this variable voltage control onto a bench top (or into a test box), I’d probably tack it on to the Mad Bean Pedals RoadRage’s 15V output. The LM317 does have a voltage drop of 2-3V, so the 15V will be now be a max 12ishV output, but that’s fine because I don’t know many pedals that require 15V to power…but I do know many that require 12V.
Click to expand...

I'll probably feed it from a 24vDC wall-wart. That'll give me enough range to test the Univibe all the way down to fuzz and drive effects with exact voltage.
 
I noticed that in the video the pot change the voltage just in the first half. Is that an issue or is it normal?
 
Elijah-Baley said:
I noticed that in the video the pot change the voltage just in the first half. Is that an issue or is it normal?
Click to expand...
In Video 1, it’s the quality of LED voltmeter I am using. It can only read a minimum of 3V and requires calibration. It costs $2-3, so my expectations on quality are very low to begin with. I am sure if you use a better voltmeter with better range, you’ll get better read outs.

If you refer to Video 2, which is the same circuit but on a breadboard, the voltage is read via Multimeter, which is far more accurate and attenuated for volt readings, which is why the reading is much smoother. Note that I used a 200 ohm resistor, which is why the max voltage starts at 8V when fed a 9V input. If you go with a different value (240 ohms or even those suggest by RG Keen), you can get the 7.5V.

Also, note there is a voltage drop of 1-2V when the circuit is active. If I were to drop this circuit into a pedal for a Sag function, I’d make plans to supply 12V - either power supply or charge pump or even allow users to bypass it all together.
 
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BuddytheReow said:
You could use a Dropbox link for the Gerber files. Those are allowed here I think.
Click to expand...
I will try this.

I’ve also tried GitHub but the Gerber files (zips) downloaded from GitHub never worked when sent to JLCPCB, OshPark, etc.

If I emailed those same zip files directly to people, the files always worked.
 
Hello, I was thinking to build a variable voltage pedal like your. But I don't like the voltage range: ~7.5VDC to 1.25VDC.
The minimum 1.25v seems to me very small. Maybe a smaller pot, 2k, will drop less voltage.
But what I want to solve is that starting drop voltage of 1.5v. My ideal range should start from 9v.
 
Elijah-Baley said:
Hello, I was thinking to build a variable voltage pedal like your. But I don't like the voltage range: ~7.5VDC to 1.25VDC.
The minimum 1.25v seems to me very small. Maybe a smaller pot, 2k, will drop less voltage.
But what I want to solve is that starting drop voltage of 1.5v. My ideal range should start from 9v.
Click to expand...
Admittedly, anything less than 4.5V is unusable. You can play around with the values to approximate a better range.

For example, the Truetone power supply has a sag feature that’s 4V-9V.

Cool fact: RG, who wrote about the battery sag circuit with a voltage regulator, actually works for Truetone.
 
josephka06 said:
I saw my fuzz works really well at 8.5 V sir.
Click to expand...

Just thinking in a practical sense: With the source voltage at 8.5vDC, what were the collector voltages on the transistors?

The easier way would be to just use a voltage box like this but it means an extra piece of gear.

You could simply tweak the collector voltages to the values you get with a 8.5vDC source and not have to worry about an additional box.
 
im here after looking for info on the PedalGear Vbat, which is an older 2 knob DBS.

it's got "voltage" and "ratio". I think ratio is the same as age on your device.

whats weird is the vbat label asks for 12-18v input. I havent tested yet what it outputs with 12v, but I would like to know what your power reqs are. I think im gonna be able to run the VBat with 9v instead of 12v
 
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