Rebuilt Little Rebel Amp...not satisfied,still searching for better!

[momo]

I write this post to show others how futile this amp build is!...well at least thats my view on it.
I saw a post on another website mentioning to add caps on the chip power section to minimise DC offset...
Any ideas?

My original build was oscillating and bugging, so I decided to build another PCB and restart from scratch. I also put shielded wires everywhere. Now for a few days everything was great, I finally had more power than before and no oscillation.
I thought this was great but I only played 1 minute or so at a time.
So anyway, I now realize that the 2 bridged LM386 get super hot and loose power after a short while playing.
I noticed that with too much current, they get hotter faster too.
I was using 3, 3v batteries together, which has more current than a 9v and it did not help.
I then tried the heatsink you see and it works great but I guess its not big enough as the chips still loose the power fast.

So now I am still looking for some great 9-12v solid state amp to carry around...
Or even a 12v tube amp?

Here are before and after pics, kind of frustrating to put that time in there and still have a dud!

[pappasmurfsharem]

Hard to see from the bottom PIC but is the heatsink touching both ICs?

If so Maybe a little bit of Thermal Paste, like you would use on a CPU would work to make better contact.

However I'd stay away from Arctic Silver (or any brand with metal bits in it) so you don't short anything.

Have you tried putting a fan in it with that heatsink on to see if it keeps it cooler. if that works then you know the heat isn't being "wicked" away fast enough.

[MaxPower]

You might want to try a NJM2073 instead of the LM386. In bridged configuration you should get up to 2Watts depending on the speaker load and power supply. I built one and power it with 6 D size batteries. I didn't use a heatsink but I also don't play it at full volume because it is too loud for my bedroom.

Another option would be to get an audio chip intended for use in automobiles. Some are designed to run on 12V and should give you more power than the 386, 2073s, etc. I remember finding one relatively cheap at Mouser but I can't recall how much power they could output. I want to say 4 watts into a 4 Ohm speaker load but that may be fantasy. I can't remember as I shelved the idea quite a while back.

[sajy_ho]

You can try TDA2040, it can deliver around 2W in 12 volts into 8 ohm load almost whithout getting hot. Here's my practice amp; fetzer valve as clean preamp into TDA2040 poweramp and ROG's Thunderchief as dirty channel:http://i587.photobucket.com/albums/ss312/sajy_ho/15122011460.jpghttp://i587.photobucket.com/albums/ss312/sajy_ho/14122011447.jpg
Also if you're interested in tubes you can built this one:http://www.diystompboxes.com/smfforum/index.php?topic=105966.0, I've built it and it's AWSOME!

[teemuk]

12 volt supply will be seriously limiting with ordinary class-B topologies. 0.5 W - 5 W will always sound "small" no matter what. Basically it comes down to whether you want to build yet another "practice amp" or something more versatile...

If you must use 12 volts then you do have options like TDA1562, which achieves about 50 watts by combining bridged setup and a bootstrapped class H topology. Ordinary batteries will be drained pretty fast though and an external power supply likely is going be as big and heavy as rest of the circuit. Might as well build it all together... Heatsinking at power levels above 2W is pretty much mandatory for anything relying on a single chip.

If portability without need for mains power isn't an issue I would probably kick it up a notch by using a rectified mains supply and some suitable chip amp with higher power rating. (e.g. LM3886 or similar).

LM386 is pretty nice as what it is but it is also a one-trick pony. You either like low headroom or you don't. If you don't then you probably need to abandon the idea of using low power chips with wall warts or batteries.

12 volts and tubes? Doable but you probably need to forget the ordinary "tubeyness" and tube circuit architectures. You likely need to find a good sounding starved plate design gain stage circuit and forget the idea of tube -based power amplification. Another alternative is somekind of an inverter circuit to increase the supply voltages, but they do have their inherent limitation that current supplying capacity usually decreases in same ratio at which power supply voltages increase. Not really ideal for power amplification.

[momo]

Thanks everyone, lots of great options here.
This current setup has reached its max development as far as I am concerned, thats the project that made me realize I went a bit too far with a 386 chip.
I really want to have something battery powered, I show up with a smalll portable cab, flip the switch and I am ready to go, anywhere..

I could buy a Realistic MPA20 for 25 dollars, I could use that enclosure as it has more space, knobs all layed out, just have to put in a new circuit....hehe
https://www.circuitlab.com/circuit/func75/mpa-20-realistic-audio-amp/
http://www.radiomuseum.org/r/radio_shac_realistic_mpa_20.html
There are mods out there for this circuit to use it for guitar, but it uses mains power.
The transfos in there could be used somewhere else, I think this could be a good buy and a step closer to what I want.

I also would enjoy a bit of headroom and so out goes the 386..
I took the leds out of the circuit and it sounded better even without much headroom.

Those are nice builds sajy_ho ! thats the stuff I'm looking for with as much power possible on batteries.
I'm thinking 2 9v together for 18v?

[bool]

old "car audio" dogs tda2002, tda2003 and tda2005 (bridged) are loud, cheap, sturdy, nearly indestructible and very easy to mount on a heatsink.

[PRR]

> as much power possible on batteries

Six motorcycle batteries and an LM3886 will give 60+ Watts into 8 Ohms.

The 300V battery from a Prius can be made into 1,200 Watts in 8 Ohms.

Even my tractor battery could be used with common car-sound chips to give 16 Watts each in four 4-ohm speakers (total 64 Watts) for a very long time.

Bigger battery systems can be imagined.

That bridged-LM386 scheme is very mismatched. The '386 is only good for 0.4 Amperes peak output. So with 9V supply the optimum load is like 20 Ohms, not 4 Ohms! (Try wiring two 8 Ohm speakers in series.) But any way you cut it, two '386 isn't going to deliver more than a Watt or so.

*ANY* of the car-sound chips will deliver clean 16W into 4 Ohms, per channel, with a hefty 12V battery. 9 Watts in 4 Ohms at 9 Volts, but not with pocket-radio batteries. The load on the battery is over 1 Ampere. Six D-cells will barely cut it. Rechargables become more practical.

> buy a Realistic MPA20 for 25 dollars

Buy it. It will run on a motocycle/car battery (you may have to re-create the adapter plug). You can plug guitar right in at "MIC" and it will work fine.

[momo]

thanks Paul, thanks for all your info....
You post alot of stuff and help alot, thanks a bunch..