How should I implement a voltage regulator to switch my pedal to 6V on the fly?

[mzy12]

Hello!

I am building a Devi Ever Ruby on stripboard and I want to be able to change from standard 9V input to 6V via a 78L06 with the flick of switch. It should be pretty simple, just have the power strip attached to a switch and flick between the 9V coming from the filter caps and 6V from the regulator. Are there any steps I should take to make sure the transition is as seamless as possible? I will be supplying the 78L06 with 9V constantly and just take the output from an SPDT when I need it. Should I do something like make sure it is provided with a load at all times?

Thanks in advance!

 

[jwin615]

Bicolor led might be a good touch.
Common cathode so you can use different CLR for each color and use the voltage as the switch(still work with a single pole switch).

A large resistor to ground, after the filtering caps of the 6v side may be needed to keep the caps in a charged state and avoid popping.
I think I'm correct in this, anyway.
Not sure if that reg requires a load to operate but that resistor would do that, if sized appropriately.

 

[mzy12]

Bicolor led might be a good touch.
Common cathode so you can use different CLR for each color and use the voltage as the switch(still work with a single pole switch).

A large resistor to ground, after the filtering caps of the 6v side may be needed to keep the caps in a charged state and avoid popping.
I think I'm correct in this, anyway.
Not sure if that reg requires a load to operate but that resistor would do that, if sized appropriately.

Thank you. I was thinking I would have to load it alright. The LED is a clever idea alright, though I don't reaaaally feel like fiddling with resistors to get brightness to match. Although it is just a simple equation and that barely even matters with bicolour ones so I might just do that.

A 1K load would be plenty, consuming about 5mA of power. I know the correct thing to do here is use something like an LM317 so that I can just switch between resistor values off the one regulator powering everything, but that would require effort and I don't have any spare ones lying around so

 

[jwin615]

Thank you. I was thinking I would have to load it alright. The LED is a clever idea alright, though I don't reaaaally feel like fiddling with resistors to get brightness to match.

That's what trimmers are for
Speaking of, why not just load down the 9v using a lot as a voltage divider and switch the pot in and out?

 

[mzy12]

That's what trimmers are for
Speaking of, why not just load down the 9v using a lot as a voltage divider and switch the pot in and out?

Voltage dividers create a 'virtual ground' which are generally fine for say providing bias voltage to an opamp/transistor but are not ideal for power rails. They aren't as stable as a regulator. How much would this effect a guitar pedal? I don't know enough to say. But I never have seen a voltage divider used in any pedal circuit to supply power for something, like supplying the 5V needed for a PT2399.

 

[jwin615]

Voltage dividers create a 'virtual ground' which are generally fine for say providing bias voltage to an opamp/transistor but are not ideal for power rails. They aren't as stable as a regulator. How much would this effect a guitar pedal? I don't know enough to say. But I never have seen a voltage divider used in any pedal circuit to supply power for something, like supplying the 5V needed for a PT2399.

Not sure how it would be different than any other "sag" control ala DAM Methead, KMA Fuzzly Bear

 

[Feral Feline]

Interesting idea.

Had I not seen this thread and someone asked me to get 9v down to 6v, I would employ a "sag" control via a 2knobjob or similar.

sub'd.

 

[mzy12]

Not sure how it would be different than any other "sag" control ala DAM Methead, KMA Fuzzly Bear

Those use resisitors to adjust the bias. Definitely different to supplying 6V á la a dead battery. Again, how different is it? I don't have the knowledge to make a definitive statement on this.

Interesting idea.

Had I not seen this thread and someone asked me to get 9v down to 6v, I would employ a "sag" control via a 2knobjob or similar.

sub'd.

A "sag" control actually is fairly different to supplying a constant voltage! Traditional "sag" controls on pedals basically act as a current limiting resisitor in series with supply. This does drop the voltage supplied, but it's not anything like definively stating, "Hey this is going to be 6V at the end of of this knob." It does change the voltage for sure; in the real world, voltage is dropped at different amounts across different resistors. That's why "dead battery" simulators that are just a simple 1/5k pot aren't really battery simulators (even though battery do start acting as if they have a currenting limiting resistor in them as they start dying).

 

[Feral Feline]

Cool. That's why I'm finding this thread so interesting — as mentioned it would've never occurred to me to use a voltage-regulator.

I like learning from (what is to me) out-of-box thinking. You seem to always have interesting ideas/threads, such as the Intelligent Relay switching in a guitar.

I'm curious if there would be audible pops when switching from 9v to 6v.

 

[mzy12]

Cool. That's why I'm finding this thread so interesting — as mentioned it would've never occurred to me to use a voltage-regulator.

I like learning from (what is to me) out-of-box thinking. You seem to always have interesting ideas/threads, such as the Intelligent Relay switching in a guitar.

I'm curious if there would be audible pops when switching from 9v to 6v.

Thank you! I'm currently doing an electronic engineering course in college and I'm trying to combine all the stuff I'm learning theory wise with the practical knowledge I have from messing with pedals and other electronics. Of course, a modern bachelor of electronics engineering isn't that concerned with small signal amplification in regards to instrument signals, so I'm going back and forwards between college stuff and the applied wisdom of the people on this forum.

I will keep people posted on how this ends up working/not working haha.

 

[swyse]

I've never done anything quite like this for regulating the power supply down like that, but I do have some insight on the pt2399 using a voltage regulator instead of a divider. The PT2399 is pretty sensitive to voltage changes, it causes the repeats to warble or change pitch. Some designs use this to their advantage to make the pt2399 into a chorus by putting a LFO on the internal reference pin. I personally would use resistors in your case for simplicity, I'd probably run a trimmer and a very small resistor on a switch to jumper it to switch between 6ish and 9ish. I'm also interested to hear your results, the idea is making me curious about using a regulator on a fuzz face type circuit for more consistency.

 

[mzy12]

I've never done anything quite like this for regulating the power supply down like that, but I do have some insight on the pt2399 using a voltage regulator instead of a divider. The PT2399 is pretty sensitive to voltage changes, it causes the repeats to warble or change pitch. Some designs use this to their advantage to make the pt2399 into a chorus by putting a LFO on the internal reference pin. I personally would use resistors in your case for simplicity, I'd probably run a trimmer and a very small resistor on a switch to jumper it to switch between 6ish and 9ish. I'm also interested to hear your results, the idea is making me curious about using a regulator on a fuzz face type circuit for more consistency.

Hmmm, a voltage regulator for fuzz face bias? Now that's an interesting idea! I wonder if it's been done before?

 

[swyse]

Hmmm, a voltage regulator for fuzz face bias? Now that's an interesting idea! I wonder if it's been done before?

Servo Fuzz Face

Just in case anyone missed it (and so I can find it more easily), here is a pointer to that thread over in Fig's Test Kitchen.

forum.pedalpcb.com

New mini-breadboard

Jubal81 & I have been messing with a servo-biased Germanium Fuzz-Face. Here's my rendition. Controls are FUZZ, BIAS, TONE & LEVEL. The trimmer sets the servo's operating point. The collector currents don't drift; the servo keeps the DC component of Q2's emitter current constant. Thanks for...

forum.pedalpcb.com

@Chuck D. Bones has a couple very interesting threads of a similar concept for a germanium fuzz face that's definitely worth a read

 

[mzy12]

Servo Fuzz Face

Just in case anyone missed it (and so I can find it more easily), here is a pointer to that thread over in Fig's Test Kitchen.

forum.pedalpcb.com

New mini-breadboard

Jubal81 & I have been messing with a servo-biased Germanium Fuzz-Face. Here's my rendition. Controls are FUZZ, BIAS, TONE & LEVEL. The trimmer sets the servo's operating point. The collector currents don't drift; the servo keeps the DC component of Q2's emitter current constant. Thanks for...

forum.pedalpcb.com

@Chuck D. Bones has a couple very interesting threads of a similar concept for a germanium fuzz face that's definitely worth a read

Haha Chuck strikes again! It feels like the xkcd rule: there's a relevant xkcd post for everything, just as there is a Chuck D. Bones thread for everything pedal related =P