Any benefit to having a power filter cap on a battery operated fuzz face??

[mordechai]

I've got a germanium fuzz face project that will be running only off of a battery.  I've built these circuits before but always for use with an external power supply, so I've included a 100uF power filter cap on the power rail.  Is there any benefit to having a cap like that -- 100uF or even 47uF -- remain on the power rail if I'm using a battery to power the circuit?  Or...to put it differently...is there any DOWN SIDE to having a filter cap on the power rail when using a battery?

[SISKO]

From a technical point of view, its better with no caps. A battery is already a f***ing giant capacitor alone,
a cap in parallel will only consume current when its energized and do nothing else.
Thats because, when a cap is discharged, it look like a short circuit. Then, when its fully charged, it looks like a open circuit.

So, it will make you waste a minimalistic point of current from your battery .

A fuzz face can be very minimalistic with its current consumption, so  whats written above may be of your interest.

From a practical point, i would leave it (and place a ceramic cap in parallel too). It doesn't hurt..

[TejfolvonDanone]

is there any DOWN SIDE to having a filter cap on the power rail when using a battery?

The charge cunsumption is neglectable of the caps. A Lithium battery has about 1200mAh charge. The charge stored in the filter caps is Q = C*V = 100uF*9V = 0.0009 C = 250 nAh. (or less than half of it when using the 47uF)

As SISKO said the battery is already a giant cap so it doesn't have any ripple as opposed to an external supply. There's NO UP SIDE to use another cap. Electrolytic caps can leak and maybe it cause some trouble in the long run. For me it would be enough reason to leave it out.

[mordechai]

Thanks for the insights.  But that brings me to another three points:

1. If someone wanted to, at some point, modify a fuzz face to run off of external power, wouldn't having a filter cap already on board make that a much easier modification? 

2. We DO see a filter cap (47uF) on the Tonebender Mk II.  It's my understanding that it helps with oscillation.  Why wouldn't having a similar cap help ensure against that with a Fuzz Face...is it because the TB Mk II has so much more gain, whereas the FF is a milder sort of circuit so oscillation isn't as much of a problem?

3. Related to the second question...the Fuzz Central Axis Face, which is a really great sounding circuit, is also pretty mild in terms of gain (the transistors have roughly the same gain range as a Ge FF).  But it is also fitted with a 100uF filter cap -- does a silicon based device demand this?  Or is this because the circuit was **meant** to run off of an external power supply?

[antonis]

The charge cunsumption is neglectable of the caps. A Lithium battery has about 1200mAh charge. The charge stored in the filter caps is Q = C*V = 100uF*9V = 0.0009 C = 250 nAh. (or less than half of it when using the 47uF)

But if you multiply it with 4800 On-Off switchings you get an overall consumption of 1200mAh...

[TejfolvonDanone]

1. If someone wanted to, at some point, modify a fuzz face to run off of external power, wouldn't having a filter cap already on board make that a much easier modification? 

Also you could include the reverse polarity protection diode just in case...
To be honest i wouldn't do that for the modder. If i made the pedal for myself i would put these in just in case. But i wouldn't create anything only for battery operation in the first place.

2. We DO see a filter cap (47uF) on the Tonebender Mk II.  It's my understanding that it helps with oscillation.  Why wouldn't having a similar cap help ensure against that with a Fuzz Face...is it because the TB Mk II has so much more gain, whereas the FF is a milder sort of circuit so oscillation isn't as much of a problem?

There's several schems where they put a 10-220pF cap between the collector and the base of each transistor. Which basicly decreases the gain at higher frequencies. Both work.

3. Related to the second question...the Fuzz Central Axis Face, which is a really great sounding circuit, is also pretty mild in terms of gain (the transistors have roughly the same gain range as a Ge FF).  But it is also fitted with a 100uF filter cap -- does a silicon based device demand this?  Or is this because the circuit was **meant** to run off of a battery?

There's also a section about power filtering in the description of that circiut along with the power jack on the side of the final pedal. http://fuzzcentral.ssguitar.com/axisface.php

[TejfolvonDanone]

But if you multiply it with 4800 On-Off switchings you get an overall consumption of 1200mAh...

I'm playing google:
Did you mean 4800000?

[antonis]

I'm playing google:
Did you mean 4800000?

You haven't to be so sarcastic for a little mistake..
(which after all it deals with 3 zeros lost...)

[TejfolvonDanone]

Sorry i didn't mean to sound sarcastic.

[miech]

When the measurement frequency goes up, the battery becomes more and more noisy. A very small capacitor should take care of that, but no electrolytic is needed.

[mordechai]

So...maybe something like a 4n7 cap?  Or do you mean a cap in the pF range?

[ashcat_lt]

So...maybe something like a 4n7 cap?  Or do you mean a cap in the pF range?

I think the actual value doesn't matter much, but electro caps have the same problem that they are less effective at filtering higher frequencies, so a value small enough to find in a practical non-electrolytic package is the trick.

[PRR]

In the past, a nearly-flat transistor radio battery would increase in resistance and "crackle". In a many-stage radio, the increased resistance encouraged sneak-back from high level stages to low level stages, oscillation. We "always" threw 10-100uFd across the battery so we could use-up the battery right down to the nub.

I don't think it is a big deal in DIY pedals. The cost of a cap is small. You should probably leave space for a cap, in case some day a weak battery makes trouble. However many classic fuzzes will go sour for low voltage before the battery is really weak. And you should always carry a spare battery.

[mordechai]

In the past, a nearly-flat transistor radio battery would increase in resistance and "crackle". In a many-stage radio, the increased resistance encouraged sneak-back from high level stages to low level stages, oscillation. We "always" threw 10-100uFd across the battery so we could use-up the battery right down to the nub.

So, if that's the case...would having an electrolytic after the battery actually "extend" battery life by sort of coagulating as much of a charge as possible coming out of the battery before it goes kaput?

[LightSoundGeometry]

just watched a guy on the tubes, he was recapping a tube amp, talking about too much power filter takes away from the tone ..not so sure about that ..I think it has no effect other than smoothing out the DC signal. I would think pure DC power is already pretty quiet and clean being is does not have to be rectified from AC to DC

I dont own an O scope but I am guessing pure DC does not have ripple nor look like a rectified wave - not too sure how the caps charge and discharge on a DC signal. Cant remember exactly how an IC regulator works ..Are IC regulators the same as voltage regulators ? or do they regulate I and E ? I was under the impression this was mainly for digital devices?


This is my educated guess. I would think a tube amp circuit would function better with a cleaner waveform of power. maybe you could build the bridge rectifier with old school germaniums lol ..doesn't those parts of teh amp already come assembled like a transformer, I dont think people are out there building amps from ground up but rather assembling the parts so to say. I know some people do though, you can watch people hand make tubes, or someone like jeri ellswot handmaking ic's and homemade transistors.

probably cheaper to buy the trutone/one spot wall wart than the transformer needed to build the rectifier.

[thermionix]

Changing the filter cap values does change the tone (and feel) of a tube amp.  Look at a simple 5F1 Champ, the three filter caps are 16, 8, 8 uF.  I prefer 16, 16, 8 in this circuit to thicken the tone up just a bit.  My current amp is based on an AB763 Super Reverb type of circuit, but I omitted the "Normal" channel.  I had to adapt the preamp filter values (among some more obvious things) to get the sound and feel just right with only one channel.

I haven't tried to look for videos of people "hand making" their own tubes, but I think you would need a factory for this.  My last job was at a place that made high end CRTs for military and aviation industries, so I have some familiarity with the various processes.  The guns were pretty much assembled by hand, but the exhaust ovens weren't exactly EZ Bakes.  Then there's tipoff, getter flashing, cathode activation...

[LightSoundGeometry]

Changing the filter cap values does change the tone (and feel) of a tube amp.  Look at a simple 5F1 Champ, the three filter caps are 16, 8, 8 uF.  I prefer 16, 16, 8 in this circuit to thicken the tone up just a bit.  My current amp is based on an AB763 Super Reverb type of circuit, but I omitted the "Normal" channel.  I had to adapt the preamp filter values (among some more obvious things) to get the sound and feel just right with only one channel.

I haven't tried to look for videos of people "hand making" their own tubes, but I think you would need a factory for this.  My last job was at a place that made high end CRTs for military and aviation industries, so I have some familiarity with the various processes.  The guns were pretty much assembled by hand, but the exhaust ovens weren't exactly EZ Bakes.  Then there's tipoff, getter flashing, cathode activation...

sweet..I understand now what he was talking about with the 16, 16 etc ..just a little. I am really digging tubes and amps now  over pedals.


Finding out there are some super smart people out there and hand fabricating everything from scratch is more common than one might think; but you need the proper tools and space which you know how that can add up in the tens of thousands of dollars very rapidly.

https://www.youtube.com/watch?v=EzyXMEpq4qw

the guys and gals who work on old radios seem to be the most gifted with the craftsmanship  type skills ..along with watch makers lol

this guy makes his own turret board which caught my eye ..among other fabrications

Jeri making IC and transistors -

home brew is the best 

[teemuk]

A battery is already a f***ing giant capacitor alone

Within certain conditions I guess you could say that...

Theoretically the battery should be a DC voltage source with low internal resistance. If any AC signals happen to couple into such power source its low impedance effectively shunts them, similarly to what a filter - or "decoupling" - capacitor does when it provides a low impedance for AC signals above very low frequencies.

In nutshell, one wishes to "decouple" AC signals from the power sources because otherwise they effectively become feed forwarded or fed back into other gain stages, and if this feedback / feed forward happens to be positive you're probably in for a serious trouble considering overall stability of the circuit.

A battery with low internal impedance effectively behaves very well as "decoupling element". Problem is that when the battery charge gets drained the internal impedance of the battery starts to increase. Now it not only "sags" the supply voltage down but also becomes a much inferior decoupling element than a fresh battery. The thing could have charge left for hours of operation, but due to increased series resistance the circuit stability is compromised.

A cheap decoupling capacitor will prevent that. Its "filtering" effects for a pure DC supply are, of course, almost entirely negligible but (once charged) it retains constant low impedance characteristics and therefore works as a decoupling element. With a decoupling capacitor in place the power supply retains ideal decoupling characteristics even when the internal impedance of the battery starts to increase.

[thermionix]

I am really digging tubes and amps now  over pedals.

Certainly agree with that.  You should be able to get a great tone just plugging straight in.  Then use pedals just as effects when needed.  That's always been my approach, anyway.

Cool videos, very interesting.

[LightSoundGeometry]

yeop those are just a few off the top of my head, but you know the subset and side scroller videos with the same key words show a lot of great engineers fabricating and repairing all sorts of stuff .