More power from an LM380...?

[earthtonesaudio]

I recently got a bunch (about a dozen) of NTE/ECG740A chips, which seem to be pin-for-pin compatible with the LM380 2 watt power amp chip.
I'm hoping I can upgrade my Noisy Cricket to something a little more powerful to hear myself over a drummer.
I'm thinking bridged operation is what I want, for more power, and to eliminate the large output caps.

Does anyone know if paralleling chips would have any benefit, such as increased power or cooler operation?  Or any other tricks to get more volume from this chip?

[Mark Hammer]

Trust me, you won't really notice any difference between 2W and some other slightly higher single-digit power rating.  It is plenty loud when married to an efficient speaker in a decent cab.  There is a layout for what I'm using in this zipfile: http://hammer.ampage.org/files/Miniamp.zip  Be sure to size it appropriately because I don't think it is a 1:1 reproduction.

[earthtonesaudio]

Thanks for the suggestion, Mark.  I know I'm not gonna be able to shake the foundations with a miniamp, but I do want to get more bass than the 386-based amp.

[Minion]

If you want to Bridge 2 chips you will double your output current (Depending on speaker load) but you might have to change your speaker impedance, if your present speaker is 8ohm then each Chip will be Driveing a 4ohm load which is OK for this chip as long as you make sure you are properly heatsinked...But if your Present speaker is a 4 ohm then each Chip will have to drive 2 ohms which is not possible with this chip so in this case Bridgeing is not a good solution....

Paralelling 2 chips will double your output current but only if your speaker load is Halved (you can drive a 2 ohm load when paralelled which will be twice the output current as a 4 ohm load).....

You can also Bridge and Paralell 4+ chips (2 x 2 chips bridged and then Paralelled) to get much more current into a Higher impedance load....

If you want to do this there are a few things to take into consideration....

1) you will most likely have to build another power amp PCB to accomidate the new Topology....
2) you will have to make sure your PSU can supply the extra current and have enough PSU Capacitance....
3) extra heatsinking and air flow to keep the chips cool.....

If you are willing to try this you might then want to consider useing a Higher power chip and drop the LM380 Idea as you can implement a chip like the TDA2030 14w Power amp IC a Lot easier than Bridgeing/Paralelling LM380 chips....

Good luck...

Cheers

[R.G.]

Get a bigger horse.

[earthtonesaudio]

Haha, I know it would be easier to "get a bigger horse," but I'm just curious as to how fast I can go with a herd of goats.

[Mark Hammer]

If you want to hear yourself over a drummer, simply doubling or quadrupling the wattage isn't going to do it.  I can say from experience that what assists in being able to tell your own strumming apart from the din created by the drummer is simply more bass.  Apart from the kick drum, which actually isn't all THAT loud if not mic'd, drumkits generate tons of midrange and top end.  Even a 15W amp gets lost amongst that if there is insufficient bass oomph. It would not be unreasonable to make yourself a cab with a pair of 380-based amps (heatsinked and powered by +18V), each driving a different speaker, and one of them larger and maybe even ported in a sealed compartment.  You COULD also do the bridged mode thing, but the need will still be there to have more bottom so that when you hit a chord with authority it will be discernible against the cymbals and snare.

[Ben N]

Not to hijack, but Mark, out of curiosity, I notice that you use a pair of single opamps for the preamp, and at least one of them is a 5534 (can't read the other from the pic). Any reason for (a) not using a double, and (b) not using a jfet-input opamp, per the schem? Also, would that preamp work with a 386 (the basic Rat Shack version) as is?

[Mark Hammer]

Fair question.  Somebody gave me a couple of fistfuls of 5534s for nothing.  Gotta use them somewhere.

If you want to make a 386-based version of essentially the same thing, make this one: http://hammer.ampage.org/files/PocketRockit.PDF
Runs great on an 8-pack of AA cells (12Vdc).