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Voltage regulator to "simulate" a battery

schlick vicious

schlick vicious

Sep 1, 2014
33
21
Berlin
#1
a lot of people claim that a fuzz does only sound the way it should when using it with battery.

i recently build wooly mammoth clone and it was noisy as hell when using it a wall wart and also did not sound right. with a battery it worked just perfectly.

i used a 78L09 to get rid of the noise and give the circuit a constant voltage. it worked great but seemed overkill to me, but simply filtering the supply voltage did not do the job.

does anyone else of you use voltage regulators to give your pedal a solid voltage supply?
 
#6
This is a cool little gadget I use with great results on some of my guitar pedals. It's adjustable from 3 to 9 volts and can cause some pedals to react really neat to the voltage drop. Kinda mimics a dying battery.
Link Removed
 
#9
A battery makes DC, Direct Current, only one polarity and a constant voltage (well until they start to die).

Your wall/mains plug provides AC, Alternating Current, which reverses polarity every cycle (50 or 60 times per second), passing through zero volts on the way.

All "DC" adapters/wall warts/whatever "simulate" a battery's DC. They do this by forcing the AC wave to flow in only one direction with an arrangement of "diodes" (yeah, even switching converters have diodes - more on those in a minute). What comes out is a very nasty, ripply DC-like voltage.

<WARNING!!! Techno-Nerd content to follow!!!>

Now, with enough "filtering" that nasty DC-like voltage can be made virtually indistinguishable (within certain operating parameters) from the nice smooth battery DC. Some supplies are much better at this than others. Some do almost no filtering, assuming that whatever you hook them to will do all of that.

Now, the voltage regulator helps a lot because it tries really hard to provide that constant DC voltage by continuously turning it's output up and down. If you put big capacitors (filters) on each side of the regulator, it can do an even better job since the caps will hold the voltage up during the low points (they work like miniature short term batteries).

I mentioned switching converters. A lot of modern (light weight, wide input voltage range) wall warts are switchers. These take the 50/60Hz wall current, turn it into a nasty high voltage DC, then switch the output on and off to charge filter caps and maintain a constant output voltage. They can do a better job with smaller filter caps because they switch at high frequency, so the "dips" don't last as long. Often, they operate far above audio frequency, so any "noise" they make can't even be heard.

So, if you want quieter "wall warts" look for the switching types. Usually the ones that advertise running from 100-264VAC 50/60Hz input will be this type...
 
#10
schlick vicious said:
that is exactly my thought! but it does something.
Click to expand...

If it is blocking the AC noise, then mission accomplished!

I also use voltage regulation in my pedals. I use it as a clamp at 10V for over-voltage protection on the charge pump. I use a discrete LDO circuit that basically follows the input voltage for anything under 10V... example 9.35V in 9.25V out. For audio power filtering, I use a standard Miller capacitor multiplier circuit... for the price of a 1.2V drop I can get A LOT of filter.

-Frank
 
#11
I will use a regulator for pedals I make that don't use 9V, say in a circuit that uses a valve and needs 12V or ones that has 5V TTL components.

I would not say they are overkill, especially in high gain circuits that don't have good noise rejection as they keep the supply voltage predictable and fairly clean. As has been mentioned before (cjj), used with capacitors improves the power clean up process immensely. I would never use a regulator without a larger smoothing capacitor and a smaller filtering capacitor.

I would like to point out that as a battery gets older (as the charge depletes) its characteristics change. To some, this will change how the circuit sounds. If you are interested in this have a read of http://www.beavisaudio.com/Projects/DBS/ and maybe make yourself a dying batter simulator!
 
#12
mrmills said:
I would like to point out that as a battery gets older (as the charge depletes) its characteristics change. To some, this will change how the circuit sounds. If you are interested in this have a read of (...) and maybe make yourself a dying batter simulator!
Click to expand...

The idea of an old battery was not what I intended. It is more the idea of having the same operating conditions for your pedal, no matter how ripply or bad the power supply is.
However I tried the simple "sag circuit" on stuff like a BazzFuss and is fun to see where it can take the sound of other pedals too. When building a proper dying battery simulator I would go one step further and use an adjustable voltage regulator e.g. LM317. That way you get the beauty of a clean supply voltage with the feature of playing with different voltages.

But here is another question, since I do not have an oscilloscope: What does the the output voltage look like when the input voltage is under the recommended minimum? Is there just a voltage drop and the output looks like the input?

boomertech said:
For audio power filtering, I use a standard Miller capacitor multiplier circuit... for the price of a 1.2V drop I can get A LOT of filter.
Click to expand...

That's interesting! What capacitance are you realizing with the multiplier?
 
#13
schlick vicious said:
But here is another question, since I do not have an oscilloscope: What does the output voltage look like when the input voltage is under the recommended minimum? Is there just a voltage drop and the output looks like the input?
Click to expand...

Below the drop out voltage, the voltage out of the regulator will be what is coming in to it. This voltage is around 2V for a LM78xx series regulator so you need at least 11V minimum for a 9V regulator to work and any dips below will then pass through the regulator unfiltered.
 
#14
schlick vicious said:
But here is another question, since I do not have an oscilloscope: What does the the output voltage look like when the input voltage is under the recommended minimum? Is there just a voltage drop and the output looks like the input?
Click to expand...

Exactly! There is always a voltage drop for any input voltage under the minimum input voltage. If the 7809 has a 2V drop and then if you feed it an input of 9V, the output will be 7V. Since it is not regulating at that input voltage, any AC noise on the input will be also seen on the 7V output. The best way to reduce input power noise with a voltage regulator is to have the regulator regulating properly.

schlick vicious said:
That's interesting! What capacitance are you realizing with the multiplier?
Click to expand...

With the Miller cap multiplier I can get an equivalent filter capacitor of at least 10,000uF with a general purpose NPN transistor with a DC gain of 100 or more and using a 100uF capacitor. If you want to do the same for the negative rail of a dual-rail power supply, you would just use a general purpose PNP transistor with the same DC gain.

Here is a simple explanation of the cap multiplier:

http://www.seekic.com/circuit_diagram/Basic_Circuit/SIMPLE_RIPPLE_SUPPRESSOR.html

High gain circuits can be very sensitive to noise on the input power. Whenever I have had to remedy a sensitive circuit, these cap multipliers have always worked wonderfully. The only downside is that you reduce the available voltage headroom by approx 1.2V. But there are usually other ways to get that headroom back with other circuit tricks.

Also, the 78xx and 79xx three terminal regulators use an internal Zener diode reference. That Zener reference can be quite hissy and that hiss can propagate thru high gain circuits. So always use plenty of RC filtering and good circuit layouts after one of these regulators.

-Frank
 

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