Build my own simple 9v voltage sag control?

[dano12]

I'm building a Fuzz clone and want to add a trim pot that allows me to sag the voltage between 4 and 9v from the wall wart. Is it as simple as adding a pot?

I did some experimenting with my meter and found that a 1 megaohm resistor dropped it by 1 volt. Am I in the ballpark?

Many thanks.

[petemoore]

  I had good luck and LM317 or other voltage regulator is the 'recommended' method.

[dano12]

Hmmm... A voltage regulator chip. Hadn't thought that far ahead.

Basically I want to be able to simulate a dying 9 volt battery as I've read much about this in the lore of effects history.

Cork-sniffing? Maybe, but I'm building a fuzz box where the design goal is to have as many controllable options as possible. It is a fuzz clone, but I have built a simple switch array that allows me to switch between geranium and silicon or a hybrid of the two. Plus it has adjustable bias for the transistors and I'm adding a small panel meter to read the bias level. Finally (and this is the really crazy part), I've built a small board to mount the transistors--on one side is a small cooling fan from and old laptop, on the other side a small light bulb. I can switch either on or off to simulate temperature extremes on the trannys. Yeah, I know its lunacy, but it sure is fun.

Back on topic, I wonder what battery depletion does in terms of voltage drop and amperage drop? Are they equally linear? In other words if I use a voltage regulator will it change voltage and leave amps intact? If so, would that accurately model a dying 9V battery.

(I searched the forums for 'sag' and waded through the first three or so pages before asking

[The Tone God]

Did you read this ?

http://www.geofex.com/Article_Folders/pedalbdpwr/pedalbd.htm

Andrew

[dano12]

Did you read this ?

http://www.geofex.com/Article_Folders/pedalbdpwr/pedalbd.htm

Andrew

I hadn't read that, thanks much for the link.

After reading it, it may be a bit extreme. My "Fuzz Lab" is actually going to have a fuzz clone, a TS808 clone, a Rangemaster circuit, a clean boost and a SolaSound Tonebender clone. Each will be wired in a seperate modules in one monster enclosure, perhaps with a basic mixer. All in/outs will be discrete 1/4" jacks in the back. So I want to add an individual sag control for each stage, plus I want to keep everything inside the box off a 9vdc bus. R.G. Keen's article is a really flexible and well-thought out idea. But I don't have the skills (or enclosure real-estate) to build enough of those to meet the design goals and keep the AC outside of the box.

For simplicity's sake, maybe I'll just try the pot idea for sag and see how that works.

Thanks much.

[The Tone God]

Its almost become a classic trick around here to stick a pot in series with the power supply to simulate a dying battery. It will only work with certain effects. I doubt it will do much with your tube screamer for example so I would skip it for that.

Andrew

[Paul Perry (Frostwave)]

There are two different aspects, 1. reducing voltage (which can change or create distortion characteristics) and 2. power supply series resistance (which can cause feedback between parts of the circuit).

And the second effect, can be influenced by what (if any) value power supply bypass caps are on the effect. So there are a number of variables, if you want toget right into it.

But whateve you do, don't confuse it with the 'tube amp sag', where a loud chord temporarily lowers the voltage by sucking too much current from the power supply.

[newperson]

"'tube amp sag', where a loud chord temporarily lowers the voltage by sucking too much current from the power supply"

what is the value of this?  what does this do to the sound or feel that makes people talk about 'tube sag' so much?

thanks,
paul.

[The Tone God]

what is the value of this?  what does this do to the sound or feel that makes people talk about 'tube sag' so much?

Me thinks someone hasn't played a cranked tube amp just before its gonna blow. 

Andrew

[jxoco]

Hmmm... A voltage regulator chip. Hadn't thought that far ahead.

Basically I want to be able to simulate a dying 9 volt battery as I've read much about this in the lore of effects history.

Yeah, I know its lunacy, but it sure is fun.

A silicon diode in series causes a .7 volt drop. For fun try a couple..

[amz-fx]

I'm building a Fuzz clone and want to add a trim pot that allows me to sag the voltage between 4 and 9v from the wall wart. Is it as simple as adding a pot?

There are some complete designs here:

http://www.muzique.com/lab/patent2.htm

-Jack

[Quackzed]

what does sag sound/feel like? it feels goood! 
    its when you play a chord and really lean into it the amp just cant deliver the power right away and the volume sort of dips a bit or "sag"'s with the loudest part of the signal...then smoothly comes up as the chord starts to fade, the volume really sounds like its trying to lift something really heavy and is ... GRRRR!!! having a hard time... surprisingly, this sag, rather than make the guitar sound lower in volume, makes a guitar sound like its getting a push!!! it sort of slides the volume down   during the attack then pushes it right back up for the meat of the chord!!! kind of like a compressor that is pumping and breathing...high compression /slow attack /fast release oomph!!! it reminds me of action movies where something blows up and theres that slo-mo of the explosion and then up to speed booom!!!
My twin reverb doesnt really sag ...it just looks at me and smiles as if to say "is that all you GOT???!!!"

[zachary vex]

easy.  put a 5k linear pot in series with the positive terminal to the circuit.  that's all you need to simulate a typical dying 9V battery.  the resistance range is almost identical to the chemical build-up over time using a pedal that draws around 5mA.  if you don't believe me. try it, and then substitute a dead/dying battery and listen for a difference with the pot shorted.

[newperson]

i was googling around and found this:
http://www.aikenamps.com/Sag.html
about sag.  i guess i need to turn up my amp more.  i have never felt this to the degree that it is spoken about.
-paul.

[zachary vex]

There are two different aspects, 1. reducing voltage (which can change or create distortion characteristics) and 2. power supply series resistance (which can cause feedback between parts of the circuit).

And the second effect, can be influenced by what (if any) value power supply bypass caps are on the effect. So there are a number of variables, if you want toget right into it.

But whateve you do, don't confuse it with the 'tube amp sag', where a loud chord temporarily lowers the voltage by sucking too much current from the power supply.

hi Paul! 

batteries can't die without building up series resistance.  likewise, the reason for voltage drop is a result of the increased series resistance!

i put it to you... the lowering of battery voltage is a result of exactly the same mechanism as increased series resistance.  a pot in series with a battery will most certainly simulate the dying of a battery.

[dano12]

easy.  put a 5k linear pot in series with the positive terminal to the circuit.  that's all you need to simulate a typical dying 9V battery.  the resistance range is almost identical to the chemical build-up over time using a pedal that draws around 5mA.  if you don't believe me. try it, and then substitute a dead/dying battery and listen for a difference with the pot shorted.

Thanks, I like that answer because it is the easiest to implement My project has four distinct effects and I want to add individual sag controls to each effect, plus a small scale voltmeter lcd panel meter for each so you can see the voltage for each effect as you play around with it. Since I'm also adding bias controls with voltmeters to two of the effects, I'll probably end up spending more in digital panel meters than all the other parts combined. But the end result will be pretty tweakable.

BTW, love my Ooh-Wah II.

-dano

[dano12]

what does sag sound/feel like? it feels goood! 
    its when you play a chord and really lean into it the amp just cant deliver the power right away and the volume sort of dips a bit or "sag"'s with the loudest part of the signal...then smoothly comes up as the chord starts to fade, the volume really sounds like its trying to lift something really heavy and is ... GRRRR!!! having a hard time... surprisingly, this sag, rather than make the guitar sound lower in volume, makes a guitar sound like its getting a push!!! it sort of slides the volume down   during the attack then pushes it right back up for the meat of the chord!!! kind of like a compressor that is pumping and breathing...high compression /slow attack /fast release oomph!!! it reminds me of action movies where something blows up and theres that slo-mo of the explosion and then up to speed booom!!!
My twin reverb doesnt really sag ...it just looks at me and smiles as if to say "is that all you GOT???!!!"

I can't get my Twin Reverb RI to sag either--it's just too powerful and too clean. On the other hand, my '65 Bassman and my little 8w Gilmore Ardmore will sag nicely when you push them hard.

I think we need to come up with a better name for what I was originally talking about. When I said "sag" I was referring to voltage drops on a dying 9V battery for effects tweaking. Completely different I think from tube amp sag.

[Quackzed]

yeah... i was just trying to give a good description of tube amp sag for new person, or other curious souls... a dying battery is a totally different thing... i'm gonna try a series resistance pot in front of a battery tho...thats a great idea and simple... i usually find that the simplest way to achieve a desired effect is the best sounding way too... zen and the art of signal shaping.
i've really got to stop typing "..." everywhere!
    any effects more prone to dying battery effects? fuzzes? tube screamers? i'm sure the tube screamer lot would give it a try:)
   what size pot to use ? 100kb?

[dano12]

yeah... i was just trying to give a good description of tube amp sag for new person, or other curious souls... a dying battery is a totally different thing... i'm gonna try a series resistance pot in front of a battery tho...thats a great idea and simple... i usually find that the simplest way to achieve a desired effect is the best sounding way too... zen and the art of signal shaping.
i've really got to stop typing "..." everywhere!
    any effects more prone to dying battery effects? fuzzes? tube screamers? i'm sure the tube screamer lot would give it a try:)
   what size pot to use ? 100kb?

Zvex suggest a 500k linear. That's what I'll try. I don't know yet which effects lend themselves well to voltage starvation. I first heard about voltage sag a few years ago in the context of a tubescreamer.

[Peter Snowberg]

If you look a few posts up, Zachary is recommending a 5K.

In general, discrete circuits will work better that opamps when starved. At least the sound is more interesting to me.