Want to design a Battery powered Portable Amplifier; where to start?

[Astronaurt]

A friend of mine recently asked me to build him a Battery powered Amp that he can go out busking with, so I'm trying to do some research and design one for him! I've played around on little 9v Supro Cigarette Box amps and other things before, but I'm always really disappointed with the head room that they just don't have. I know that I want it to be based on an IC Power Amplifier and have a higher supply voltage, 2 9v Batteries seem convenient to design around. I'm vaguely looking to design something that will amplify cleanly and get up to a break-up or crunchy overdrive type of tone, but definitely not something that only gives you crazy Fuzzy Rail-bumping noise like other Battery amps I've played with. The important thing though is if it can get enough volume to be heard reasonably enough over passers-by and cars on the street.

Because I'm not at all familiar with IC Amps though, I was wondering if any body had any favorites or suggestions of Power Amp chips to design around?

[Seljer]

Get a chip like the TDA2003, it does 10watts into 4ohms with relatively low supply voltages. You can more or less follow the example in the datasheet to build it. A heatsink is also a neccessity.

Rather than 9volt batteries try using 8 to 12 AA batteries or larger for better battery life, you're going to be eating up power like mad if you want reasonable volume so extra capacity is always welcome. Another option is to get a small sealed lead acid battery (in the 6Ah size range) and build a charger circuit for it.

Then build yourself a preamp for it. Aside from bells and whistles like tone/drive controls, you mainly want to make the preamp clips before the power chip is allowed to (because as you've experienced, the sound of the amp clipping on the power rails is usually pretty awful). An easy option is probably to just take any overdrive pedal your chosing, let the "gain" control be the combined volume/gain control, and set the volume control which is usually at the end of the circuit to some fixed value where you're sure it doesn't clip the power amp.

[petey twofinger]

i messed around with some battery amps , look thru all the videos here , maybe you could get some ideas of what not to do  .

http://www.youtube.com/watch?v=d_OsZsA32m4

scroll down a bit , i have a few amps up there , including a stella amp kit (the guy gave it to me to beta test the kit .... )

http://www.youtube.com/user/peteytwofinger

i use 12 volt sla batteries now , the latest one has a korg pamdora front end and a tda chip amp ,stereo  30 watt , two 6.5 auto speakers (tried jensen mods , sounded like crap compared to the sony explodes i got free on this set up ! ) .... it has 9 out , filtered for pedals / sustainiac , 4.5 for the korg , and 12 for the amp , bult in ac transofrmers (filtered) dc too .

going simpler , there is a kit called a stella amp that is great . i built one , its nice , and loud enough for busking .

http://www.crazybutable.com/store/stella

really cheap  , go to salvation army , get a preshool , kiddie tape deck , one of the loud ones , older , cut into the mic jack .

build in a tillman jfet buffer , that really helps if the signal is low , cant stress that enough . add a bazz fuss if u like too .

for echo get a hanna montana guitar with mic echo , mod that out for delay time / feedback  , use a tillman pre infront or whatever , then feed the hanna out to a powered speaker , like a sh*t sub / pc speaker from a garage sale . go with a lower ohm speaker if u can (4) it will be louder (this is bad , mini amps have to be QUIET !!)  ... i dont go smaller than 6 inches on speakers , but ... i have a full rig of battery poered stuff , including a pa , we use that outdoors and its LOUD ...

mind you i am doing it wrong .

the right thing to do is make a noisey cricket , lil gem , or ruby amp . look into a fetzer valve one maybe .

i do not care for lm386 chip amps though .

good luck , and remember , the more power in the battery  , the louder , the longer . add a pramp / booster or three of some sort .

typically the rules with these thing is , they can not plug into a wall ,  whatso ever .

they have to have a tiny speaker .

spker out jack is a must ( so u plug it into a 4 x 12 it will ALMOST keep up with a drummer .... )

they can only run on 9 volts

you may attempt to get a good clean tone from them but will fail  .

if you attempt to break these rules , duck and cover .



http://lmgtfy.com/?q=lil+gem+amp

http://lmgtfy.com/?q=noisey+cricket+amp

http://lmgtfy.com/?q=ruby+amp

actually the best way to go is to buy a kit , that is much safer . make sure you pay at least 50 bucks for everything as well .  

https://www.cbgitty.com/cubecart/amplifier-parts/amp-kits.html

at that point the main concern is drilling holes in the dice or should i say die , for the one knob . if u buy a gross of 9 volters they throw in your choice of  skull / skeleton / snake / dagger / devil / pitchfork lady sticker for free , i believe . they are 1.5 inches , ( just a bit larger than the speaker )

* hides *

[R.G.]

I'd start some non-standard places.

How big and how heavy can it be? This determines what speaker and what batteries you can use. These two items are the fundamental determiners of how loud it can be (and therefore how much clean headroom) and how un-convenient it is to haul around.

Once you determine the tolerance of the owner for big and heavy, you can design an amplifier and speaker cab around that. The actual amplifier is not a big issue, only the speaker and power supply. It is possible to get multi-hundred watt class D amplifiers which you can comfortably hold in one hand. But the multi-hundred watt power supply is not going to be so easy. Neither is the multi-hundred watt speaker system. Amps can be tiny and light weight. Not so much speakers and batteries.

Once you have a Size Budget and a Weight Budget, you can go to work. The lightest currently practical speakers are neodymium magnet types. Go find the smallest Neodymium guitar speakers you can get. Then look at their efficiency, in terms of SPL db with 1W drive. You want something over 95 or 96 db with 1W drive. Once you've found the speaker(s), go design a cabinet for them which fits the size budget.

Then compute how many pounds/kg you have left for everything else, which will be mostly batteries. Fill up the rest of the weight budget with batteries, minus maybe 1 pound/0.5kg for the amplifier and everything else.

NOW you can pick battery voltages, etc. You can coincidentally compute playing time. A battery is rated in amp-hours. If you have 24V of battery voltage in two 12 6a-h batteries, then you can play a 1A (that is, 24W total draw) output for six hours. If you have two 12V 1ah batteries, you can play at 1A for one hour.

Using a linear class AB amplifier will result in efficiencies of about 60%, so if you have 24 watt-hours (volts times amp-hours) available, you can put out 10W for two and a fraction hours.

Notice that all this can be done before you know anything at all about the actual amplifier. And in fact, with the exception of the choice about Class AB linear amplifiers and Class D switching, the choice of the amplifier chip/circuit itself is almost immaterial. The results are pretty much predetermined after the choice of how much weight/size can be tolerated. After that, it's just how close you can come to the edges with available components.

This whole approach to design is kind of a economics approach to electronic design, and it gives newcomers a new insight into why economics is called "the dismal science".

[ludashoeless]

I built one with a lm386 chip and put it in a nike shoebox. sounds pretty good but I wish I had put it in a better box

[markeebee]

Taylor's 'Tiny Giant'.

20W, plenty of clean headroom, nice easy build:
http://www.diystompboxes.com/smfforum/index.php?topic=89233.0

[Mark Hammer]

1) Don't underestimate how loud 2W can be; especially when you consider that there are often limits to how much noise you're allowed to make in a public space, and how loud you can be and still talk/sing over it, unamplified.  There are plenty of two-channel power amp chips that can be easily repurposed in those plastic computer speakers yo often see in the trash.  Many will produce 1.5W and up when run in bridged mode.

2) At amplifier power levels in the under-5W range, speaker choice and cab design can matter a LOT.  You will want an efficient speaker, and you will want the cab to squeeze every last audible decibel out of that speaker.  That likely means a closed-back cab, and probably a front-port.  The cab should point slightly upwards; partly because that's where other people's ears are and where your own are.  You'll be able to make do with less power/volume if everyone can easily hear the entire speaker output.  Playing outdoors, you won't really care about bandwidth lower than maybe 150hz or so, or above 10khz or so.  RG is spot on by recommending to keep your eyes peeled for something spec'd for at least 96db with 1W.  You may be able to find something with 98db ratings, but those will likely be larger speakers (12") with bigger/heavier magnets, and big-n-heavy is not what you want.  

3) An 8" speaker can provide suitable loudness and smooth tone, and the cab doesn't have to be huge.  Choice of materials here can make for a light and sturdy box.  MDF may be sturdy and cheap, but makes for a heavy box.  And at low power levels, without the need for big bottom, slightly thinner plywood with a bit of bracing won't be punitive.

4) An octet of 8 C-cells makes a nice compromise.  Twelve volts, with that much current capacity, will get you respectable lifespan at usable levels.  I don't know about where you live, but I find C-cells are often available at low prices from dollar stores.  On my battery-powered amp, I lucked into a place that had rechargeables for a buck apiece, so I'm using 8 rechargeables.   It gets me about 11V when fully charged up, but I don't have to buy any more.  D-cells will obviously last a little longer, but weigh more, require a bigger box, and tend to be less readily available.  If you go with batteries you have to get at, then you'll want to make the cab interior readily accessible.

5) To compete with ambient noise, some sort of suitable EQing will be helpful to "cut through".  In fact that may well be more useful to you than more wattage.  Besides, the difference between 2W and 8-10W is not all that great.  Two watts with the "right" peaks may do a better job.

I made myself an LM380-based amp some time back.  I imagine my construction skills would produce a better effort nowadays, and some of the advice I offer above is a result of what I think I did wrong, but you can see what I did here: http://hammer.ampage.org/files/Miniamp.zip  It is pretty dang loud.

[asatbluesboy]

How many D-cells did the EHX Freedom Amp use again?  I remember it was like... I dunno... billions.

Can't add anything useful except you should try and get some info on those SS power amps in pedal form from EHX.

[Mark Hammer]

I believe the Freedom amp used just over 40 batteries...which is handier than this car, actually.  The tricky part is finding the bad one. 

[rackstab]

I've got a Vox DA10 that runs off of sealed lead acid batteries used for home alarm systems.  There's plenty of room for 2 12W 7.2Ah batteries, and you can use one of the batteries to power some pedals.  The batteries will last you a good while, too.  That's 10 watts on battery power.  Pretty cool!  Here's where I first read about it:

http://www.voxamps.com/forum/topic.php?id=1262

[azrael]

If you're in the US, you can often find used Roland Micro Cubes for around 50 bucks.

Because you want a battery powered amp, headroom is always going to be an issue.