I'm toying with a portable (i.e. battery powered) amp design and would like folks opinions on low power ICs for this type of application. Think Micro Cube only better.
I dont know about better than a Micro-Cube. Too many bells and whistles. But if you are talking about a simple low power battery operated amp, there are lots of chips available for use on battery power that will give you decent power.
The LM386-4 will give you about 1Watt RMS using only 8 cells (12V). Can operate down to 4.5 volts but at reduced power, maybe a little less than 1/2 watt. Just 1 tiny 9V battery should give you a few hours of run time at a little less than 1 watt. 8 c cells should last quite long.
TDA2003 should give you about 2 1/2 Watts on 6 cells, and about 4 watts on 8 cells. need 15volts (10 cells) to get max power around 6Watts.
There are several chips that can be used for battery powering a small amp.
Do you want to scratch build or do you want kits????
I suggest the LM386 as well. I run one of my own on 3 AA batteries (4.5v DC) and it sounds great.
I'm working on a 12volt portable using the HA13118. It's available as a kit from q-kits or other online retailers. Max voltage is 18 volts @ 1 A to put out 18w through a 4 ohm speaker. If you run it of a 12V sealed lead-acid battery you should be able to pul 10-12w depending on the amp-hour rating of the particular bat you choose. You can get smallish sized rechargeable sealed LA bats from many outdoor suppliers for $10-12 or in the ~$20ish range if you also opt for a charger wall-wart (not a bad idea). I've salvaged mine from one of those "million candle power" flashlights that hada busted bulb...
I got the amp module built, and have tested it directly with a 12v source. It has good output, and doesn't really need a preamp to get volume, but I think it could use a pre for some tone shaping/distortion character so I'm gonna add one...
I've been a bit pressed for free "amp buildin' time" lately, so I haven;t really worked on this in a couple of months... I'm not sure when I'll get a chance to finish it, but I'll definately post it here when I finally get around to it.
Thanks for the info - what's the largest portable amp design out there? I'm looking to scratch build a biamp design and would like to get 20W for the low end.
A killer combination that I use for loud and clean battery powered amps , great for vocals and acoustic stuff, is an TDA2005 (20 W RMS/4ohms) for low/mids, driving a 10" 4 ohm speaker, and a TDA2003/LM383 (10 W RMS into 2 ohms) driving a couple of cone tweeters (much sweeter than piezos), powered from a 12.6 V 7AH gelled lead battery, the kind used in alarms and such.
Loud and clean.
J M Fahey
I haven't yet used a TDA chip, but I hear good things about them. Actually, you could probably use most any chip meant for car audio applications with good/acceptable results.
I would think the main concerns for such an amp would be 1) Preamp construction and 2) battery type and charging method.
Simplest build is like the little gem/noisy cricket that many of us have built (including me). In this case preamp section is a single FET gain stage/buffer stage, and power amp is half watt LM386. Battery power needed is only 9v, so we use rechargeable/throwaway 9volts. The power output is low, so the current draw is also low, and there is no complicated type of charging circuitry needed.
More power requires more amperage. In this case you are left looking at these 12v rechargeables that are some kind of lead acid or gel lead acid varieties. In this case you want to look at the AmpHour rating of the battery. A 12v 8AH battery will produce 12volts (more or less) at 1 Amp for 8 hours. This means yo can run a 12 watt amplifier for a total of 8 hours from that battery. If your circuit has a higher wattage (say 24 watts) that means it draws more current (2 amps instead of 1), you'll get a run time of 4 hours off the same battery. I'm pretty sure that as long as the AH rating of the battery is as big as the current draw of your amp, your amplifier will yield maximum power. As the AH rating gets bigger than your current draw, you just get longer life at that max power, not more power.
Charging the battery is another matter. For lead acid batteries, you need some kind of "smart" charger that varies the voltage supply according to how fully charged the battery is. If you don't do this, the battery will quikly become useless. The most simple is to just buy a cheap outboard wall wart type charger, and extract the battery and charge it externally when it is low. You could also build in some kind of power jack with switching to enable the wall wart to plug into the back of the amp. You should make it so that when the plug is in, the thing won't turn on. Most difficult is to build the charging circuitry into the chassis itself, and just plug mains power directly into it. You will need and mains to 18v transformer, DC rectification bridge, and a battery charging circuit (these can be purchased as modules). This setup has the advantage of the fact that you can make the amp switchable from mains power when plugged in to battery power when unplugged.
The preamp can be any kind of circuitry you like. You can run it at 12volts, but I would definately use some sort of regulator IC to control the amount of power it will have to disperse, especially if used with high AH batteries. Another possibility is to use some sort of current isolating transformer. Otherwise you will have to use bigger more expensive resistors and have caps rated for higher power. Make sure you use a regulator IC that is rated for higher power too, and it will probably need a heatsink or to be mounted to the chassis.
Cheers,
DDC