2x9volts = some other battery?

[wafflesomd]

So my current portable amp is running off two 9 volt betteries.

Is there anyway, or any battery out there that can take the place of two 9 volts. Or anyway I can power the amp with some else, I'm trying to fit it into a smaller case.

 

[Joshatdot]

I been looking for something similar, but I couldn't find anything.

 

[kanamin]

li-po or li-ion? get a bunch of kan160AAAs here and solder them into a pack?

 

[balou]

hi wafflesomd,
you could use a step-up switching regulator. and then just use one or two AA or AAA batteries, and increase the voltage from 1.5 or 3v to 9..18V.

I also looked into this some time ago... but I'm quite overwhelmed by the many different step-up regulators available. and it also seems they need some external components, but I have no idea what exactly is needed. well, that doesn't exactly help you, but maybe somebody else may shed some light on how to use a step-up regulator in a portable amp. I also wonder how the switching influences the sound quality.


edit: http://www.linear.com/pc/productDeta...03,C1042,P1627 this seems to be a candidate... and the switching frequency of 600khz is also well above the audio band. only drawback is the price. ok, "expensive" is a relative word... in a simple cmoy, 9$ for a single part will be alot, in another amp it will be just a small sum

 

[threepointone]

yeah, I've been toying with the idea of a switching regulator. I was thinking maybe if some head-fiers could maybe start a new design project on a mini low-noise switching regulator board specifically for ultra-portable amps. There's really no other good way to get that high voltages with batteries; with a switching regulator, you could probably get the same thing with a lot less space:

9.6V*230mAh*2= 4416mWh in 2 9.6V NiMH batteries
2AAs will easily give you more energy than that (1.2V*2700mAh*2 = 6480mWh), and 4AAAs will give you about the same amount of energy (1.2V*1000mAh*4 = 4800mWh).


Lots of opportunity there to get rid of those two huge 9Vs. There's always the problem of noise and complexity in switching regulators, but a lot of the newer regulators these days seem to have much better noise performance, and complexity wouldn't be as much of a problem if we had a preset DIY design for these regulators.

But for now, I'd think you could easily take out one of those 9V batteries; there's been quite a bit of discussion on the topic, and I think 2 9Vs are pretty much overkill for most (if not all) headphones.

 

[beerguy0]

Quote:

Originally Posted by balou /img/forum/go_quote.gif hi wafflesomd, you could use a step-up switching regulator. and then just use one or two AA or AAA batteries, and increase the voltage from 1.5 or 3v to 9..18V. I also looked into this some time ago... but I'm quite overwhelmed by the many different step-up regulators available. and it also seems they need some external components, but I have no idea what exactly is needed. well, that doesn't exactly help you, but maybe somebody else may shed some light on how to use a step-up regulator in a portable amp. I also wonder how the switching influences the sound quality. edit: http://www.linear.com/pc/productDeta...03,C1042,P1627 this seems to be a candidate... and the switching frequency of 600khz is also well above the audio band. only drawback is the price. ok, "expensive" is a relative word... in a simple cmoy, 9$ for a single part will be alot, in another amp it will be just a small sum

Switchers are a pain to work with. As you mention, there are many flavors of switching regulators out there, and they all work a little differently. Besides the external components, layout is crucial, as is grounding. You also need to use low ESR capacitors, which can get pricey as well. Plus, you'll need either a second regulator (inverting) for a negative rail, or use a rail splitter. The part count can get out of hand, even for a small switcher.

Here is part of a prototype -5V converter (+12 to -5V). This doesn't show the output caps. I built this as part of the design phase of my last project. (Large, high-power, multiple output switcher. This section happened to be low power, only 1 amp)

As far as noise, the switching frequency is almost irrelevant. You'll hear it. Between radiated and conducted emissions, switchers are EMI roman candles. (The dI/dT across the inductor is responsible for much of the noise) You'll need plenty of filtering, and you may even need to shield it. There is also the issue of stability under varying load - a switcher that is designed for, say, 5 amps, may not be stable under a very light load.

It's an interesting design challenge, but not for the average DIYer.

 

[mono]

I see a picture. It is either a switching supply or you are the only person who has ever gotten that close to the side of a Borg Cube and escaped without being assimilated.

 

[mono]

Quote:

Originally Posted by wafflesomd /img/forum/go_quote.gif So my current portable amp is running off two 9 volt betteries.

Does it need ~ 18V? If not, what does it need? If you haven't determined the minimum voltage threshold yet, it might be a good start.

Quote:

Is there anyway, or any battery out there that can take the place of two 9 volts. Or anyway I can power the amp with some else, I'm trying to fit it into a smaller case.

Sure, how about 1 x 9V? I think everyone would like to just make everything smaller if there were no negatives involved. Any way you look at it, if you keep the same battery technology and reduce battery size, you approach a result of having to give up voltage or runtime or both. It is not always true but switchers are not always as efficient as we'd like.

While going with fewer cells means less redundant waste on the container aspects of a cell construction, if you have to step up the voltage with a switcher, that alone entails space for the addt'l board, development time and cost, potentially addt'l noise enough to need further filtration.

As noise frequency goes up, a typical opamp PSRR goes down, a lot. Think of it as the frequency of the opamp operation, not the audio frequency, that if it has enough bandwidth to make corrections within the cycle of the switching noise, the % error is lower. You might try a switcher with an LC filter and linear stage after it, though this is getting larger, more expensive, and more lossy. It quickly gets to the point where you have taken as much space with the regulator board but runtime is same or possibly worse.

You've not defined the requirements. Min and max input and output voltage, required runtime vs amp current consumption, actual size limit, cost, etc. As oversimplifed as it might seem, I'll say that there is a reason why many people use 2 x 9V cells, it's not like they just forgot to think about what battery to use, unless they didn't bother to test their chosen amp /can combination to see how low the supply voltage could go before they could hear a difference, then picking the battery combination having that information. Certainly in some cases this seems true, but not applicable to all cases.

 

[kipman725]

you could try constructing an oscilator with a sine wave output and then transform and rectify and regulate the output but that rather defetes the portability aim. DC-DC converters are available but I'm unsure of there viability in audio circuits, you may also consider a redesigned amplifier that can operate from lower supply voltages.

 

[threepointone]

I'm sure a switching supply is still viable for audio; after all, virtually all portable DAPs, including the iPod, definitely use switching regulators (if not for the audio circuitry, definitely for the adjacent digital circuitry), and plenty of people still use amps for portable configurations. It's a matter of selecting the right regulators, circuit design, and board design, which, admittedly, can be pretty difficult.

As for the sine wave idea--iirc, there's a new type of switching regulator toplogy that is designed to use sine waves instead of square waves (zvs/zcs, something like that?). The noise is considerably easier to handle, from what I've heard.

 

[balou]

totally different idea:
first, use a low voltage opamp like the ad823.
then, instead of 1 9v battery, use 3 AAAA batteries. Most 9v alkaline batteries have 6 AAAAs internally, you just have to open the metal case of the 9v to get them.

or use 2 CR2032 3v lithium coin cells - incredibly small, but also incredibly expensive in the long run