Pedal saver thing - good idea?

[phector2004]

Hi everyone,

I tuned out of an excessively boring lecture today, dozed into Pedal Land, and thought up a pedal mod/addition... wanted to see if anybody thinks it'll work:

Basically, you have a max1044 or other charge pump set to double, triple, or quadruple the voltage. This then feeds DC through a 9V regulator into the circuit. This whole power section is wired in series with the battery (why should it see DC adaptor power?).

My thought is that you can use batteries down to ~4V, 3V, 2V (or lower, depending on how many cap stages you add in), possibly useful for highly used effects, negative ground circuits, 18V pedals, pseudoenvironmentalism, etc.

Problem is, would the benefits of using "more battery" be greater than what the charge pump will need to do its job?
Sounds like one of those stupid calculus cost:profit problems.... Any thoughts?

[maarten]

Hello Phector,
if the current draw of your pedal remains the same, a doubler that provides this current will itself draw a current twice as much from your battery, I would suppose. So you would be draining your batteries faster....

Maarten

[phector2004]

hmmm but a normal battery is useless at 8ish volts, right?
Lets say a pedal uses 50mA. If the current draw is doubled, would the battery + pump reach 4V (5V from 'fresh') before a battery on its own reaches 8 (1V from 'fresh')?

In other words, is ΔV_{20 hours @ 50mA} = ΔV_{20 hours @ 100mA}?

[PRR]

> feeds DC through a 9V regulator into the circuit.

A lossy regulator??

Then when fresh you are turning 36V into 9V of pedal and 27V of pure waste. 

> but a normal battery is useless at 8ish volts, right?

Depends on the circuit. I used to run 9V radios on discarded 6V lantern batteries. At 5V or 4V the radio would not play loud, but was fine for the bedroom. The peak output of guitar (the guitar-cord chain generally) is not over 1V. Lots of modern chips run great on 3V or less.

[phector2004]

> feeds DC through a 9V regulator into the circuit.

A lossy regulator??

gotcha... its being turned into heat, then?

is there any way to vary the output based on input voltage?

[merlinb]

Perhaps you could arrange it so the battery powers the effect normally, unless the voltage drops blow say 7.5V, at which point a DC converter kicks in?

(For some reason the Joule Thief comes to mind, but it may be irrelevant...)

[zambo]

I seem to recall Beavis Audio having a voltage sag device. I think it caused the sag and didnt kill a battery extra fast or something like that....dont know if that helps...hmm.

[phector2004]

I remember seeing a youtube vid about the joule thief a while back... Didn't pay much attention, cause it was some stupid AAA + LED circuit

after wikipediaing Joule Thief, it looks very similar to what I described above, but an SMPS instead of a charge pump

I guess I could look into that, but I should read up more on SMPSs and blocking oscillators... the example on the wiki article is 50kHz. I know this is way above the <20kHz we can hear, but could this still cause a whine in the audible range?

Might also look into zeners to set a "battery is dead" voltage that the power saver can kick in at (if needed??)

Time to do some reading!  

EDIT:

Sag thing was to simulate a dying battery for 'grittyness'

[zambo]

smps are tricky. Cliff Schect and Rick Holt and another member Ice-9 are all on a thread with the title max1771 something or other. I was just looking at it. A max1771, tlo742 ( ithink ) and a 100uf inductor are the main parts if I remember. They built it with good and quiet results if you are looking for that kind of smps. Might be a little huge for your idea though...it puts out like 240 volts and something crazy like 100ma or so. I think...

[zambo]

http://www.diystompboxes.com/smfforum/index.php?topic=79736.0   here is the smps development thread.

[Processaurus]

Yes, rather than a charge pump and linear regulator, a modern DC to DC converter would be more efficient, and maybe be able to suck a 9v battery dryer.  Or maybe even run off of a couple AA batteries.  I have a little cheap LED flashlight that runs off a single AA, it must have a switching converter inside to be able to get the 3v to turn the white LED on.  Pretty cool.

I wonder if any of the off the shelf integrated DC to DC converters are quiet enough for low level audio?  I wonder what the little handheld digital recorders that make 48v phantom power for mics use for the conversion?

[phector2004]

smaller battery sizes is a great idea! I could look into making a 1590A battery box

1.5V alkaline AAAs have a capacity of 1200mAh
1.5V alkaline AAs have a capacity of 2700mAh
9V alkalines have a capacity of 565mAh

I'm guessing, based on P = VI to relate current draw to voltage, that a single AAA bumped up to 9V (assuming no losses) will get you 1200mAh/6 = 200mAh... AA would give 2700mAh/6 = 450mAh. Maybe putting 3AA's in series could churn out 1350mAh? Then again, if the losses stepping the DC up aren't too high, 4AAs in parallel would give (2700mAh x 4)/6 = 1800mAh. 3 times the battery life

Then again, everything looks better on paper 
I have a gut feeling the losses will be too high to make it anything more than a minor victory. Can't quite get something for nothing in this world... unless you're irresistible to women 


Oh and zambo, I've got some 555s and power inductors I could whip up Rick Holt's nixie SMPS with, but I'm 99% sure the lowest voltage you can get from it is 40V... Gonna see if I can modify a 'lower-duty' SMPS.