Why do we bother making our pedals battery powered?

[R.G.]

Hey RG
+1 for the balanced bucking hum being Audio 101.  Even us Audio pre-schoolers know/see/hear it.

With this in mind, I reckon that more balanced (probably XLR) outs will appear on electric guitars (I have a fairly new acoustic with a balanced XLR out from the preamp).  The way forward might be for amp manufacturers to offer a balanced XLR socket as well as the mono 1/4".
cheers

XLRs are great, but we could work around it. It would even be great if we'd change over to two-signal phone jacks, using tip, ring and sleeve. In fact, if you wire up the connectors right, shielded twisted pair with stereo phone plugs makes a compatible cable, as one side of the signal could be connected to ground at the amplifier input and still go into a single ended input. Plug a single-coax cord into a similarly wired guitar and it grounds one side there as well, so it would be backwards compatible with the cords. You'd still need to do quality cable to keep the cable capacitance down, but that's always with us.

But we have too many decades of history; too many amps and guitars with single mono phone plugs.

I think what really drove that original decision to go single ended was economy - you need a whole double-triode to do a diffamp front end, but only half to do a single ended. Using an extra triode section was outrageous luxury back in the day.

From one of the pickup forums, I noticed what I call a current-mode pickup. It's a magnetic pickup with a *single* turn of conductor. The voltage is down in the microvolts, but the impedance is not only low at DC, but the inductance is microscopic, so the cable capacitance almost does not matter within reason. You have to use either a current-input amplifier or use a step-up transformer to get the voltage up to what a single ended amp needs, but it's an interesting step sideways from the design issues of standard pickups.

The design I saw had an integrated step-up transformer; that throws away the cable impedance immunity though.

[cysquatch]

I don't use Power Supply on most of my pedals, because my other guitarist doesn't use
any and therefore doesn't take more than a minute to set his gear up (Guitar -> Amp with Footswitch -> Cab)
and I hate the roaring Noise you get, when you use an Adaptor in our Practice space...
I also think, that there are Pedals, that don't really need a DC Jack, like the Low Drain Zvex Effects or Loopers/Switchers
and other stuff without active Components except for a LED...

[DougH]

I don't really understand the "less hassle finding power outlets" argument. You're going to have to at least find one, for your amp. Usually if you find one, you will find two. And even if not, it's easy enough to carry a power strip to plug multiple stuff into.

Back when I just used one pedal I used a battery. That was a no-brainer. But with 3 or more pedals I find batteries to be a high-maintenance hassle. Then when I take a break I'm always wondering should I unplug the input jacks, is there enough juice, etc, etc. Maybe it's different because I play in church and there's a lot of breaks, 3 services with sermons, etc...

My noise problems are usually due to bad cables or weird interactions between poorly-filtered pedals on a daisy chain. That stuff can be sorted out at home. It's just easier for me to plug all my stuff into a power strip and go.

[AceLuby]

I use only batteries for two personal reasons:

1) Don't have to worry about that part of wiring when building (I know its small, but it's one less thing to screw up  )

2) When I connect via a wallwart in my house I get a terribly loud hum.  This also happens at some places playing out, so my batteries are more reliable.

W/ rechargable batteries you can still have a cost effective power solution.

[frequencycentral]

Who the heck uses pedals for gigs?
I have a rack unit that will do more tha 200 pedals will, and the ditzy girls dancing onstage won't trip over them or notice any difference in tone.

In my band, we never let the dancing girls out of their cages................................

[Eb7+9]

So let me get this straight - you're advocating that we ignore making our inputs hum immune and put the much-hated opamps on every instrument? It's not me you have to convince on that - go try to sell that to the majority of the music community, including some rabid opamp haters.

I'm not advocating anything except clear thinking ... where it makes sense or producing a pleasing effect - coil based interfacing has its sound - no problem, besides how is the amplifier interface to vary to accommodate a differential input circuit ? and the sound ? don't mean to get into that but it's certainly in important aspect ... to be clear, what I'm saying is that the prior way of doing things, before op-amps showed - was the best we could do with the means available ... and not that differential line transmission is a general principle applicable everywhere without looking at the underlying assumptions ... people routinely quote equations or conclusions without looking where exactly they apply - so I'm saying this to make clear really what's at play in terms of producing strong noise immunity in the transfer ...

here's a classic example ... when you build a differential line driver using two op-amps (the so-called poor man's DI circuit) you end up having more noise at the output of the second op-amp simply by additivity of noise ... then, you send those two signals down the lines, and possibly pick up more noise on the way (assumed to be the same En noise voltage which the differential will cancel ...) but the original op-amp noises - not being equal and ALSO being Gaussian un-correlated, will now produce a greater noise figure in the differencing product ... the ONLY way why audio designers include balanced op-amp drivers on their gear is to accommodate balanced input circuits - not because it provides greater noise immunity than a mono op-amp circuit ... like I said, the low-Z of one op-amp is better from a total noise figure than a balanced op-amp circuit ... and much better than a balanced passive driver ...

there are many reasons why differential cabling is not used on guitar systems - I'm not saying that wouldn't work, of course it would ... I wasn't also saying why it's not used - but I may as well here since you think things are the way they are just because ... one of the things that was known at the time when audio designers started playing with balanced circuitry was that the noise floor of a differential gain stage rises to the square root of the number of device tied together at the common node (cathodes) relative to a single deviced biased to the same level of current ... so for a differential stage the noise floor rises by a factor of 1.41, that's almost a 50% increase - and that was enough to scrap the idea altogether (in tube preamp circuits, etc ...) ... there are other things that preclude using stereo cabling ... but that's not the reason why it's done in my opinion ... going single ended produces a slightly richer sound because the transfer curvature of class-A stages produce harmonics - a differential input hookup would produce a cleaner/blander sound - less interesting to a musician try to produce TONE (ie., added harmonics) ... this is not about hating op-amps at all, just about knowing their limitations and working (best) within these ... and understanding why our ears seem to prefer one approach over another ...

please, I don't need to receive personal threats in PM's because you disagree with my derivations ...

best ...

[brett]

Hi
I don't know much.  But this -

you end up having more noise at the output of the second op-amp simply by additivity of noise

seems to imply that op-amps circuits (even a poor one with a S/N ratios of at least 50 dB) are noisey when compared with the noise injected into unbalanced lines by flouro lights (resulting in S/N ratios more like 30 or 40 dB - probably worse on the peaks).  Given that the difference is one or two orders of magnitude, I figure that we could add at least 10 to 100 op-amps into a line before it adds as much noise as a balanced line takes out in a typical situation. 

A noise increase of 1.41 x isn't audible, if we take 3dB as a reasonable lower limit to detection.
cheers 

[R.G.]

I'm not advocating anything except clear thinking ...

Oh, my. The implication being, of course, that only you think clearly, eh? Did you take lessons in this style of address, or do you just have a talent for it?

where it makes sense or producing a pleasing effect - coil based interfacing has its sound - no problem, besides how is the amplifier interface to vary to accommodate a differential input circuit ?

Hmmm... (note grammatically correct use of elipses) I guess that would be the way I last described. Pretty simple when you think about it, eh?

and the sound ? don't mean to get into that but it's certainly in important aspect ...

That set of sentence fragments has no semantic value beyond implying that YOU know all about sound but are too busy or think it's too simple to get into. Did you take lessons in this style of address, or do you just have a talent for it?

to be clear, what I'm saying is that the prior way of doing things, before op-amps showed - was the best we could do with the means available

Really? No one could ever do better than a single ended triode before opamps showed up? Could you cite a source on that? Maybe some scholarly journal stating that the single ended triode input is the best input that's possible with the current technology? That kind of statement is fairly common in today's engineering rags, with people thinking about the stat of the art. So can you find and cite something to support yourself? Let's see - what year was the triode diffamp invented? Was it known AT ANY TIME BETWEEN THE FIRST SINGLE ENDED TRIODE  INPUT STAGE AND THE INVENTION OF THE OPAMP? Or are you a history student? I assume you are, as you're trying to convince me that at no time in the early history of guitar amps before opamps was there any input better than a single ended triode, as "that was the best we could do with the means available".

to be clear, what I'm saying is that the prior way of doing things, before op-amps showed - was the best we could do with the means available ... and not that differential line transmission is a general principle applicable everywhere without looking at the underlying assumptions ...

OK, I'll assume you're working on showing the truth of that little "best we could do" thing. Meanwhile, as I read through the ellipses, you're saying that you are NOT saying:

that differential line transmission is a general principle applicable everywhere without looking at the underlying assumptions ...

OK. I've parsed that carefully for a while. I agree. Differential line techniques are not useful everywhere without knowing what you're doing. Kewl. Although I THINK  you were trying to hint that I was trying to say that all the world should be on differential transmission lines. Nope, that ain't what I said.

people routinely quote equations or conclusions without looking where exactly they apply -

Zing! There's another one. Do you notice when you type this stuff in, or is it second nature to kind of third-person-imply that I "quote equations and conclusions without looking where exactly they apply." Or did you think that by doing in a drive-by, third person passive kind of way that it would only get subliminal notice? As I said, you may have a hitherto unsuspected talent for politicalspeak.

so I'm saying this to make clear really what's at play in terms of producing strong noise immunity in the transfer ...

That is, you know *everything* that is possible about noise, and you want to make it blindingly clear to us peasants? Did I get that right?

here's a classic example ... when you build a differential line driver using two op-amps (the so-called poor man's DI circuit) you end up having more noise at the output of the second op-amp simply by additivity of noise ...

Actually, you end up with square-root-of-two times the noise of the equivalent single ended driver, because noise combines by RMS, not additively. Always good to get those equations where they really apply, but OK. That's a verifiable generality.

then, you send those two signals down the lines, and possibly pick up more noise on the way (assumed to be the same En noise voltage which the differential will cancel ...) but the original op-amp noises - not being equal and ALSO being Gaussian un-correlated, will now produce a greater noise figure in the differencing product ...

Well, WHO SAID ANYTHING ABOUT DIFFERENTIAL LINE DRIVERS? A guitar coil is inherently not single or double ended. Why not use the ends of the (even single) coil differentially, and drive the cable with the same coil? Wouldn't that have the SAME noise as the same coil single ended?

I think I talked about a differential cable to the amp, and a differential jack on both guitar and amp. Where did you get line drivers?

the ONLY way why audio designers include balanced op-amp drivers on their gear is to accommodate balanced input circuits - not because it provides greater noise immunity than a mono op-amp circuit ... like I said, the low-Z of one op-amp is better from a total noise figure than a balanced op-amp circuit ... and much better than a balanced passive driver ...

I have a number of textbooks I pull out when I try to puzzle through noise issues with my poor, slow, dim understanding. One of the things that comes out of that is that, sure, differential techniques have a 41.4% higher inherent noise, assuming you're doing things right. BUT THE THERMAL NOISE OF THE COMPONENTS AND SENSOR IS NOT THE ONLY NOISE PROBLEM. EXTERNAL NOISE, ESPECIALLY HUM, MAY BE ORDERS OF MAGNITUDE BIGGER. You win big time if you trade 40% higher thermal noise for many db of hum rejection, especially if the thermal noise is negligible to begin with.

"but... it's not negligible!" I can hear you think. HOW DO YOU KNOW? It's almost like you have to take the details of the specific case into account, isn't it?

there are many reasons why differential cabling is not used on guitar systems -

How true, how true. My point is that a big one is conservative inertia. Almost no one would buy an amp with such a setup because it would not be plug compatible with their '59 Strat that they don't have but intend to one day. Historical inertia is a big player in the market. In my opinion. Your opinion may vary.

I'm not saying that wouldn't work, of course it would ...

Hey! That's three things we agree on. Um, did I count right?

I wasn't also saying why it's not used - but I may as well here since you think things are the way they are just because ...

Zing!
JC, JC; floats like a butterfly, stings like a bee.
OK, so you didn't disagree that it would work. You just think that my opinion that historical inertia is not the reason it's not here. But you didn't say that, right? You could not contain yourself and started off with a slur. When a simple "Actually, I think it's not used for reasons of excess noise.", after which we could have discussed noise. Wouldn't a noise discussion have been more fruitful? I think it would.

one of the things that was known at the time when audio designers started playing with balanced circuitry was that the noise floor of a differential gain stage rises to the square root of the number of device tied together at the common node (cathodes) relative to a single deviced biased to the same level of current ... so for a differential stage the noise floor rises by a factor of 1.41, that's almost a 50% increase - and that was enough to scrap the idea altogether (in tube preamp circuits, etc ...)

That's curious. So how come those guys over at the oscilloscope design houses grabbed the differential amplifier input stage and ran away with it, never looking back?
'Splain dat to me, OK?

And since I just went through the whys of why one might trade thermal noise for interference immunity, I won't reproduce it here. But for the sake of CLEAR THINKING, it might be good for you to re-read that section.

... there are other things that preclude using stereo cabling ...

KEWL. Can you list those for us? I'm very curious, and I'd like to see if it matches my list. I'm sure you have that at hand since you mention it and I know how much you hate people to toss in conclusions without having a full grasp of them.

but that's not the reason why it's done in my opinion ... going single ended produces a slightly richer sound because the transfer curvature of class-A stages produce harmonics - a differential input hookup would produce a cleaner/blander sound - less interesting to a musician try to produce TONE (ie., added harmonics)

And we have a winner. Why could you not simply say that? In those words? Why do you feel compelled to take pot shots first? Wouldn't it have been simpler to just say that?

'Course, I would have said OK, I'll do class A single ended in the second stage where I don't have to deal with noise rejection issues so much, so I can optimize for 'dat ole Class A magic there, since amps are much more than a single input stage, and that people really seem to enjoy the output stage distortion, and after all that's a differential process. But that's neither here nor there. It would have been a more fruitful and educational exchange.

... this is not about hating op-amps at all, just about knowing their limitations and working (best) within these ... and understanding why our ears seem to prefer one approach over another ...

Kewl. I don't hate opamps, and I'm all for learning their limitations and working issues, as I am for learning the internals of each part, so you can KNOW what matters, and also what does not. And I keep putting in these links and references to interesting stuff about how and why our ears hear what they do. So I guess we're up to - what, four? agreements.

please, I don't need to receive personal threats in PM's because you disagree with my derivations ...

EXCUSE ME?
YOU disagreed with me; YOU flung the "complete nonsense" dart.

I asked you to modify your message before the time to modify it elapsed, you are now playing politics in public, hoping to play the audience for a "poor me" award. Having decided not to remove the "complete nonsense" dart, you're now trying to play a hand of "Blame the Victim" in public. Any threat in my PM was in your mind only. It certainly was not in the message.

Would you PLEASE stop taking personal pot shots at me? Please confine yourself to technical matters or your opinions, noting them as such.

[soulsonic]

Here's the inside of an EMG pickup:
http://www.picvalley.net/u/464/115788_577.JPG
What's this? One coil goes to the "+", and the other goes to the "-". Looks like a differential circuit to me!
The trick to EMG's low-noise spec is that it uses the opamp to actively cancel the hum in a humbucker. It's got nothing to do with whether it is a balanced or unbalanced output. Of course the low impedance drive of the output helps with the issue of noise in the cable, but if this were a differential signal it would likely be even quieter (especially if matched to a differential input, which could be a quality transformer and give you all the good tone mojo you'd ever want). I'm sure I've stepped in it now.

Speaking of batteries: anyone ever use those tiny "A23" 12v batteries? It would be super-easy to stick two in even a small pedal for a nice higher-voltage bipolar supply.

[joegagan]

i like batteries. they cut down on the unpredictability factor at the expense of a little bit of hassle.

i use ni Mh rechargeables from harbor frieght, they seem to hold charge as long as any alkaline.

[ClinchFX]

i like batteries. they cut down on the unpredictability factor at the expense of a little bit of hassle.

i use ni Mh rechargeables from harbor frieght, they seem to hold charge as long as any alkaline.

It's interesting how experience affects one's point of view.  I'd infer from your post that you've had unpleasant experience with power supplies and not with batteries.  In my little corner of the world, I've had the opposite experience, but I'm not disagreeing with you.  While the laws of Physics are set in stone, opinion based on experience counts for so much in cases such as this.  In the end, the right thing is for you to remain in your comfort zone, and for me to remain in mine.

Speaking of the laws of Physics, it's one thing to have learned them, but an entirely separate concept to understand them.

Again, thanks R.G. for your input.

Peter.

[Paul Perry (Frostwave)]

Well it's an issue worth arguing about, but not one worth fighting about.
On the 'predictability' question, I predict half my batteries are more or less flat.
And I predict my wallwart has a broken lead. 

[DougH]

It's interesting how experience affects one's point of view.

Exactly. I think that's what a lot of it comes down to. Whatever method has given you less hassle is the method you won't use.

I fully realize my feelings are based on my personal experience- every gig I do is basically at the same venue. There are no power problems there so it's easier just to plug in and not have to worry about batteries going dead. If I was on the road or playing a different club every week though, I would probably have more issues with noise, bad grounding, and etc. It might be simpler just to use batteries for the pedalboard in that case too.

However something just occured to me... A good way of producing good clean predictable power would be a "battery pack" for the whole pedal board. That way you don't have the hassle of individual batteries for ea pedal, needing to unplug input jacks to conserve power, the whole silly input jack ground wiring, etc, etc. Just put a switch on the battery pack, and use the DC power jacks/wiring from your pedals to plug into it. You could put an indicator on it so you know when it needs to be recharged (yes, it should be rechargeable). Bring a charged up spare to a gig and when one starts dying throw it in the charger and pop in the fresh one. Then you have all the hassle-free convenience and predictability of both methods.

[drewl]

I have a bunch of those little 12v batteries I got from a place I used to work.
I thought about building pedals with them, but you know the whole 9v standard thing.

I used to use a nice fairly small 12v regulated supply to run my wireless and I had a real long cord to power my pedalboard with it too.
I had no hum from that supply at all....I even built a couple backup supplies that were dead quiet.

[R.G.]

On the 'predictability' question, I predict half my batteries are more or less flat.
And I predict my wallwart has a broken lead.

Been studying at Mother Nature's feet again, right?   

However something just occured to me... A good way of producing good clean predictable power would be a "battery pack" for the whole pedal board. That way you don't have the hassle of individual batteries for ea pedal, needing to unplug input jacks to conserve power, the whole silly input jack ground wiring, etc, etc. Just put a switch on the battery pack, and use the DC power jacks/wiring from your pedals to plug into it. You could put an indicator on it so you know when it needs to be recharged (yes, it should be rechargeable). Bring a charged up spare to a gig and when one starts dying throw it in the charger and pop in the fresh one. Then you have all the hassle-free convenience and predictability of both methods.

I first saw that when Mark Hammer suggested it. I can't remember exactly when; it may have been in the old usenet pre-web era. It's a really fine idea!

Hey - with today's emphasis on cordless power tools, how about:
- buy a cheap cordless drill
- cut the handle off to make a battery holder
- wire the handle/holder to a 9V 1A regulator just to keep things steady
- keep the interchangeable second battery pack and charger hot behind your amp

There would always be a ready back up. My cordless drill pack recharges in about 20 minutes.

[Gus]

To add to R.G.'s post.  One can buy a solar cell charger for drill batteries.  I believe I saw one in a HF ad I will look for it.

[drewl]

HA!
I've seen whacky dudes bring CAR BATTERIES to power their board!
kinda' goes against the whole portable aspect.

[Gus]

solar charger that has a drill in the picture I do not see an adapter

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95000

[Wheeman]

HA!
I've seen whacky dudes bring CAR BATTERIES to power their board!
kinda' goes against the whole portable aspect.

I've thought about using one of them. My high school participates in the First Robotics competition. Every time we purchase the kit of parts they send us at least two 12V [small] car batteries and a charger. There is a small stock pile - maybe enough to power a small electric car - of them sitting in the cupboard. They charge up relatively fast and last for a good while in the robot. The only problem is that they are frickin' heavy, at least 15 lbs, compared to their size.

At least the battery can be used as a giant pedal board paperweight. 

[DougH]

The only place where the 'battery pack' concept may have some challenges is with DSP pedals. I have a couple tonecores that would suck the life out of a normal battery in a short period of time. But then I'm thinking the cordless drill batteries must have boatloads of current capacity (I'll have to check some specs)- considering the amt of power those motors need and how long the batteries usually last.

Come to think of it- I've got an old cordless drill that I stripped the gears on a few years ago when installing some hurricane plywood. I've still got the drill, batteries, and charger. Hmmmm... Now you guys have got me thinking...

Good to know Hammer thought of this too. Great minds think alike.. haha!!!