Dying battery simulator

[yeeshkul]

Just got a pair of 6.8mF caps. What i am gonna do is to feed my Fuzz Face by an old 9V battery - 7V that is. I am gonna hook it up to my scope, play chords and observe the DC changes. When i have a rough perception of what should be going on, i am gonna try your design, again hook it up to the scope and tune it up to what i want to see. If possible.

[Brisance]

Cool, I hope you will post results here too, eager to see them

[yeeshkul]

For the first time i've had a reason to use the battery clips in my Boss DD-3, aka the battery killer.  

[yeeshkul]

Interesting, nothing is really happening to my depleted battery when i play guitar to a Fuzz Face circuit.

I used a 9V Green Cell carbon zinc 1604G 6F22 battery (it really gives 10V open circuit).
I depleted the power down to 6.5V open circuit, and connected it to my silicon Fuzz Face circuit. The voltage went down to 6.2V.
I connected the battery to my oscilloscope, and played guitar (humbuckers) into the FF. Nothing happened. Then i used the Transient recorder
and did the same thing. Again, nothing happened, it drew a straight line 6.2V.

[Brisance]

Last night I played with my mates KORG monotron delay, the batteries were dying, got some REALLY interesting sounds out of it, the delay chip couldn't quite get the power to work properly and the LFO LED kept pulling all the current messing with other parts. When I get the time, I will hook an ammeter and an oscilloscope to it and collect data. I guess analog meter would be better too for this task.

[yeeshkul]

I keep draining the battery. Let's see when it breaks and starts listening

[yeeshkul]

Battery down to 6V open circuit. It gives 5.6V connected to the FF. No change in the voltage when i play guitar into the FF.
I either:
1. do something wrong
2. this carbon zinc battery is not what i am supposed to test this way
3. the battery dynamic response is a highly exaggerated phenomena

[Brisance]

interesting... How's the sound behaving? And what does the voltage do when you switch it on and off?

[yeeshkul]

When on 5.6V, the sound was quieter and more farty, but not ugly. Nothing magical soudwise though.

[yeeshkul]

Oh mine, i've just realized there is a 220u cap (DC-Ground) inside to filter the power source riddles. If anything, this was it.
Now i have to do it again without the cap, just a pure FF circuit.

[lars-musik]

Trying to revive this old thread instead of opening a new one (I never know what is better/gets more attention). However, I have been asked if I could reproduce the sound of this pedal:
https://www.youtube.com/watch?v=yoQVR-hN0PU
To my ears it sounds quite similar to the Peach Fuzz but with the added starving battery bonus. So I'd like to try it. As I found out, there is a simple but according to RG overly simple dying battery simulator (DBS) that Beavis had up on his side (one potentiometer one resistor finito). RG has a better circuit on his site (here) that has the drawback of utilising 12 V AC as power source.

Now finally my question:
Would something like this with a LT1054 as charge pump in front of tthe circuit be suited to replace the transformer/rectifier part?



Thanks all in advance!

Lars

[amz-fx]

The internal resistance of a dying battery changes very little as the chemicals in it are depleted. Certainly the resistance increase is much much less than most dead-battery simulators use.

The change in tone is due to the lowered voltage.

I measured some depleted batteries here: http://www.muzique.com/lab/batteryz.htm

Best regards, Jack

[lars-musik]

Thanks very much Jack. So, if I want to adjust the sag it looks like I could do this with your setup by switches to add diodes for higher forward voltages

.

Beavis audio presented to different approaches: First with raising series resistance (which you say shouldn't be the focus)



Or with a voltage divider (which seems logical to me).



Could you shortly explain pros and cons of beavis's voltage divider and your voltage drop method?

Thanks a lot!

[Mark Hammer]

The internal resistance of a dying battery changes very little as the chemicals in it are depleted. Certainly the resistance increase is much much less than most dead-battery simulators use.

The change in tone is due to the lowered voltage.

I measured some depleted batteries here: http://www.muzique.com/lab/batteryz.htm

Best regards, Jack

I agree with this, partly.

What most "dying battery" simulators really attempt to do is provide a stable reduced supply voltage and/or current.  In my own experience, what most dying carbon-zinc batteries do is provide a dynamically-shifting current (and possibly voltage), that changes in response to transient peaks.  The battery is able to effectively catch its breath a little between notes, or groups of notes, and is only able to provide suitable current for the first transient, after which it limps along, because it hasn't enough juice to carry it the rest of the way.

That dynamic, moment-to-moment variation in current/voltage is what's so hard to mimic via a simple circuit.  As always, whatever provides interesting sounds remains musically valid, whether it is an accurate simulation of something or not.  But for folks who want to mimic exactly what a dying carbon-zinc 9V battery does, it's gonna take more than a few resistors.

And once again, I encourage folks to explore the use of current limiters, as exemplified by the late Charles R. Fischer's EM Fuzz that was published post-humously in Electronic Musician.  You can find all the relevant files in this directory: http://www.generalguitargadgets.com/wp-content/uploads/  Scroll down to files beginning with EM.

[mac]

What about a small, poorly designed home-made 220v to 9v transformer that begins to sag at 1ma?

mac

[Rob Strand]

I measured some depleted batteries here: http://www.muzique.com/lab/batteryz.htm

Nice collection of results Jack!

For the hell of it my DMM battery came-up with low battery the other day I took some measurements from it:

Energizer 9V
Size: 522, 6LR61 -6AM6-9V
Made in USA
Date 2010 (manufacture date)
Code:  0105J
Test Date:  Nov 2016

Measurement take not long after removing from DMM with low battery:
Voc:   7.511V
RL:   980 ohm
VL:   7.355V
I=    7.51 mA
R0 = 20.79 ohm

A short time later again: parenthesized values use original Voc
Voc:   7.602V  (7.511V)
RL:     275 ohm
VL:   7.1V, after 1min and decreasing
I=    25.82mA
R0 =    19.44 ohm  (15.9ohm)

1 day rest time.
Voc:   7.744V

Retest:
Voc:   7.744V
RL:   980 ohm
VL:   7.531V (after 30sec, still decreasing but slowly)
I=    7.685 mA
R0 =    27.72 ohm

Voc:   7.744V
RL:   275 ohm
VL:   7.2V (after 30sec, still decreasing)
I=    26.18mA
R0 =  20.77 ohm

It's pretty normal for battery voltages rise and fall with long time constants after applying and removing loads.

One Energizer 522 datasheet (there are many kicking around) shows impedance vs discharge and terminal voltage vs time.  Based on 7V end-point voltage I estimated my battery is at 70% depth of discharge (as manufactures rate 100% discharge at 5.4V end-point).  The impedance graph for 70% depth of discharge shows 5ohms.  However manufactures show AC impedance at 1kHz and the DC impedance tends to be about double this value so RoDC would be more like 10ohm.
Doesn't match up with my results but my test conditions of an old battery aren't the same as their one-session discharge.  Also my DMM current is lower than the 620ohm energizer test which makes my discharge deeper.
At full discharge the datasheet shows approx RoAC=13ohm so RoDC = 26ohm which is in the ballpark of my results.

Anyway just another data point.

[amz-fx]

In my own experience, what most dying carbon-zinc batteries do is provide a dynamically-shifting current (and possibly voltage), that changes in response to transient peaks.  The battery is able to effectively catch its breath a little between notes, or groups of notes, and is only able to provide suitable current for the first transient, after which it limps along, because it hasn't enough juice to carry it the rest of the way.

I used to believe this too, and it is does happen with some power amplifiers, but there are several reasons that it is not having an impact on effects circuits.

Most effects that depend on the dying battery phenomenon are class A circuits, and the current draw is consistent throughout the wave cycle. There is no dynamic shifting from idling to passing an audio signal. Also, the current draw in effects circuits is so small, that even non-class-A opamp circuits have little difference between idling and working. If you look back at the article that I posted, I measured several effects circuits and there was no difference in the current draw with or without a signal present. Even if there were a small difference in the current draw, the small size of the current and the low value of the battery resistance means that there would be very little voltage-change-dynamics. Also, if there is a filter capacitor on the power rail in the effect pedal, it would tend to smooth out the impact of any small shift from the battery draw - basic Fuzzface circuits that have no filtering would be the most likey impacted, especially since they are usually asymmetrically biased. However, most other effects have a sound change that is only due to the lowered voltage.

Even so, if a modest value resistor inserted in series with the power rail creates a sound that a player likes, then it is valid and there is no reason not to use and enjoy it! 

Best regards, Jack

[Mark Hammer]

In my own experience, what most dying carbon-zinc batteries do is provide a dynamically-shifting current (and possibly voltage), that changes in response to transient peaks.  The battery is able to effectively catch its breath a little between notes, or groups of notes, and is only able to provide suitable current for the first transient, after which it limps along, because it hasn't enough juice to carry it the rest of the way.

I used to believe this too, and it is does happen with some power amplifiers, but there are several reasons that it is not having an impact on effects circuits.

Most effects that depend on the dying battery phenomenon are class A circuits, and the current draw is consistent throughout the wave cycle. There is no dynamic shifting from idling to passing an audio signal. Also, the current draw in effects circuits is so small, that even non-class-A opamp circuits have little difference between idling and working. If you look back at the article that I posted, I measured several effects circuits and there was no difference in the current draw with or without a signal present. Even if there were a small difference in the current draw, the small size of the current and the low value of the battery resistance means that there would be very little voltage-change-dynamics. Also, if there is a filter capacitor on the power rail in the effect pedal, it would tend to smooth out the impact of any small shift from the battery draw - basic Fuzzface circuits that have no filtering would be the most likey impacted, especially since they are usually asymmetrically biased. However, most other effects have a sound change that is only due to the lowered voltage.

Even so, if a modest value resistor inserted in series with the power rail creates a sound that a player likes, then it is valid and there is no reason not to use and enjoy it! 

Best regards, Jack

Bingo.  And it was nearly exclusively Fuzz Face type circuits that prompted the entire notion of "sag" with respect to effects pedals.  Especially when guys like Eric Johnson, et al., started talking about Fuzz Faces and carbon-zinc Eveready batteries.  Eventually, the notion of sag got divorced from its original context, and of course the emergence of robust stable pedalboard supplies pretty much wiped battery concerns off the map, particularly for those with a very recent history in the world of FX.  But I concur with you that, even if one is not talking about the prototypic dying red battery in a round-chassis fuzz, the exploration of "other" supply voltages is not unjustified. 

Someone asked here recently "Why 9V?", and I think the question is legit.  The corollary is "Why not something other than 9V?".  If it sounds good, it sounds good.

I'd offer my warmest regards, Jack, but we have a few inches of snow here, so I'll leave it at "best regards".
Cheers, Mark

[amz-fx]

Isn't it interesting that as we "modernize" some circuits by fixing the bias and adding power supply filtering, that we have engineered much of the character out of it. Many times the "mistakes" make the magic. 

Best regards, Jack

ps: If you need some exercise, we are still mowing the lawns down South since the night temperatures are only about 40F. Come on down! 

[PRR]

> class A circuits, and the current draw is consistent throughout the wave cycle. There is no dynamic shifting from idling to passing an audio signal.

When a "class A" amplifier is driven to OVER-DRIVE, class thinking may go out the window.

The ideal chalk-board "class A" never quite touches cut-off. Some observation of Over-Driven circuits can show full cut-off over large parts of the wave. Many of the simple classic pedals show what we useta call "grid blocking", a cap charges-up/down until the device is biased-off most of the time.

A side-note: the rise of LEDs may mask all this. FuzzFace may be 1mA, and say 0.1mA when beat into blocking; an older LED may be 10mA steady. 11mA to 10.1mA is no real difference to an external battery faker.

200 Ohms is not insignificant. In the FuzzFace we often take a Loud signal off a 680 Ohm tap. With no B+ cap, almost 1/3rd of that appears on B+, sneaks back to the input stage, which is high-gain. (20 Ohms of the fancy cell seems insignificant.)

I agree that Voltage may be the real issue. It is a shame there is no simple way to controllably drop Voltage....... or is there? (Hm.)

It is noteworthy that the FuzzFace's bias is stable many ways, but the drop across Rc2 is nearly fixed (Rc*Vce/Re) so supply voltages have a large effect on Vc2 and on clipping (a)symmetry.