Has anyone run dual LM386 for more power

[Headshot]

I built myself a Noisy Cricket last night.  Very cool circuit, and thanks to Beavis to sharing!  It's just a shade too quiet for me.  Has anyone tried running parallel or push pull 386 op amps?  Any advice on how I would go about it?  Thanks.

[mdh]

Look at the Little Gem MkII on runoffgroove.com.  It's a bridged design.  IIRC, a gain control a la Ruby will require a dual-gang pot.

[Mark Hammer]

MDH beat me to it be mere seconds!!!

Probably a good idea to use the LM386-4 for that however.  The higher-suffix parts are comfortable passing more current in the absence of heat-sinking.

[DryRoasted]

I've just built a Mk2 gem and use two 1k pots for the gain (haven't got a dual ) and they work very well, except on mine if you max both pots it goes a bit buzzy, prob a dodgy pot cos only does it on one pot.

[R.G.]

Get a bigger horse.

Try an LM1875 or TDA2030.

[Headshot]

Thanks everyone.   What would happen if I just stacked two 386 op omps?  That way the all the controls would already be connected.  Wouldn't that "double" my output, or would I just blow things up?

Might have to try one of those bigger options in another design RG.

[Mark Hammer]

....but, but, but, they go through a 9v battery in, like, 20 seconds, and sticking a 2lb gel cell into a belt-strap chassis is a bit of a non-starter!!

Cogent advice, brother Keen, but sometimes less is more when it comes to battery-operated stuff.  Once you start talking LM1875 or TDA20x0, you're immediately into the realm of heat sinks, mounting heat-sinks, calculating suitable supply transformers, etc. etc., which is, I suspect, not what the typical 386-user thinks they're getting themselves into when they want just a wee bit more power and loudness.

Other things people can consider looking at for a little more oomph than a single 386 are the TBA820, which is an 8-pin chip that can, under friendly circumstances, pump out 2W on its own, or the NJM2073 (for which I think there is a "special version" L'il Gem schematic posted).  The 2073 is frequently found in those $8 plastic desktop computer speakers (rated at 180W PMP!!!).  It, and many other 8-pin and 14-pin chips like it (e.g., the TEA2025, found on many older 8 and 16-bit ISA and PCI sound cards) are able to provide under 1W to a 4 or 8R load in stereo, but are easily configured for BTL (bridged) mode, with each channel providing half of the push-pull circuit that effectively quadruples the potential power.  Most datasheets for chips capable of that configuration will show you how its done, and what you can expect with various loads and supply voltages.

Thanks everyone.   What would happen if I just stacked two 386 op omps?  That way the all the controls would already be connected.  Wouldn't that "double" my output, or would I just blow things up?

Might have to try one of those bigger options in another design RG.

You CAN parallel output stages, but using the same two stages in push-pull bridged mode gives you twice as much power.  Note that a mere 2W can provide surprisingly loud listening levels if you have a decent speaker and cab, and a decent power supply.

[Headshot]

Thanks Mark.  Yes I'm looking to be close to that 2 watt range.  Right now the 1 386 is just a little too light for me at 1/2 watt, so 2 watts would be plenty.  So stacking the op amps is not the same thing as push pull bridged mode? 

[mdh]

So stacking the op amps is not the same thing as push pull bridged mode? 

Nope. Take a look at this for clarification: http://en.wikipedia.org/wiki/Bridged_amplifier.

[kvb]

Also, another solution to controlling the gain of two chips is to use a 2 pole switch. This could be on/off = all or none, or one could use a 2 pole center off switch to get 3 levels of gain: none (middle), med= cap with resistor (one side), full = cap with no resistor (the other side).

[Mark Hammer]

The sonic implications of wattage is one of the most regularly misunderstood things in the musician's lexicon.  Music store sales staff and misleading ad copy on audio components certainly doesn't help any, and as more and more people do the burnt of their listening on personal devices going straight to the ear the level of audio-specs literacy declines day by day.

That lament aside, consider that:

a) When the input signal and output driver are held constant, it takes roughly 10x the wattage to be translated into double the perceived loudness.  In other words, 10W sounds twice as loud as 1W, and 5W sounds twice as loud as 1/2W.  The implication is that sometimes you need a whole helluva lot more wattage than you might think to make a difference, but also that sometimes wattage differences between devices that might appear to be meaningful (e.g., the difference between a 10W and 20W amp) simply aren't.

b) Power amp chips vary in output power as a function of output load (4, 8, 16R, etc) and supply voltage (6, 9, 12Vdc etc).  Since those little suckers can't pass THAT much current in the absence of heatsinks, you need to be careful about how you exploit those properties.  I'd feel comfortable feeding a 386 to a 3.2R speaker at 6V supply, and an 8R speaker at 12V supply, but not a 3.2R speaker at 12V, even though the theoretical wattage seems attractive.

c) Speakers vary considerably in efficiency and there the specs are often VERY meaningful.  If speaker A provides a sound pressure level of 93.2db at one meter distance with 1W fed into it, then it is MUCH louder than speaker B that measures 87.4db SPL under the same conditions.  Keep in mind that a 3db difference in measured SPL is tantamount to a big increase in wattage, more or less.  I won't say 3db = 10x the wattage because perceived increase in loudness depends on what the current loudness IS.  That being said, often simply changing the speaker can produce a change in loudness well beyond what diddling with supply voltage or even power-amp chip can provide.  Additionally, the efficiency of the speaker is a function of the enclosure that lets it move air efficiently...or not.  A better enclosure and a more efficient speaker can make a huge difference in loudness.  I have a dinky little 2W LM380-powered amp into a decent Marsland 6.5" speaker in a sealed cab and that baby rocks much harder than you'd think 2W has a right to.

d) All a power amp does is add more gain to an existing amplified signal, using devices that can withstand passing all the current required to do that.  If you feed it a hotter signal, then you get more out of it.  So providing a hot input signal within headroom limits can also increase the apparent loudness of the amp.

[ambulancevoice]

or the NJM2073 (for which I think there is a "special version" L'il Gem schematic posted).  The 2073 is frequently found in those $8 plastic desktop computer speakers (rated at 180W PMP!!!). 

its a stereo amp!!! :D:D:D:D
2073 would be real horrorshow for a mp3 player thingy

[Paul Perry (Frostwave)]

If you have an amp with 386, and wish it was louder, by far the most effective route is to replace the speaker with a more efficient one.
And as for stacking 396s - well, it isn't all that stable just by itself, so i doubt it would be happy paralleled Don't go there...

[Mark Hammer]

or the NJM2073 (for which I think there is a "special version" L'il Gem schematic posted).  The 2073 is frequently found in those $8 plastic desktop computer speakers (rated at 180W PMP!!!). 

its a stereo amp!!! :D:D:D:D
2073 would be real horrorshow for a mp3 player thingy

Given that it is available in a flat surface-mount package, and can be powered by as little as 1.8vdc, I have little doubt that it HAS been exploited for those uses, though I imagine that for MP3-player purposes it has been eclipsed by more recent chips.

I mention the NJM2073 and TEA2025 because they are both examples of the sort of thing you'll find in the sort of cheap crappy computer speakers that people throw out or give away.  Quite frankly, if you find a pair at the end of someone's driveway, snag them.  As computer speakers they may do precious little for playing Bioshock or Orange Box (or even Doom 1 for that matter!), but if you take the two speakers out and wire them up like a 4-ohm parallel load in a decent cabinet (bit of wood, bit of space, smarter form factor), and reconfigure the desoldered power-amp chip for BTL mode, you can have a sweet little battery-powerable practice amp that can sound surprisingly good.  Certainly every bit as good or better than any of those battery-powered amps you see near the cash register at music stores (the teeny Marshall and Fender amps or the Danelectro ones).

[ambulancevoice]

or the NJM2073 (for which I think there is a "special version" L'il Gem schematic posted).  The 2073 is frequently found in those $8 plastic desktop computer speakers (rated at 180W PMP!!!). 

its a stereo amp!!! :D:D:D:D
2073 would be real horrorshow for a mp3 player thingy

Given that it is available in a flat surface-mount package, and can be powered by as little as 1.8vdc, I have little doubt that it HAS been exploited for those uses, though I imagine that for MP3-player purposes it has been eclipsed by more recent chips.

hey! some guys on here have been making mp3 players out of 386 chips!
hehe

[km-r]

IIRC

LM380 = 2W

check out National Semiconductor's LM12CLK
http://www.national.com/mpf/LM/LM12CL.html
its $45 each! cool! 

[anchovie]

IIRC

LM380 = 2W

The 14-pin version is 2 watts, but it needs heatsinking and a minimum 10v supply (20v for full power).

[ambulancevoice]

IIRC

LM380 = 2W

The 14-pin version is 2 watts, but it needs heatsinking and a minimum 10v supply (20v for full power).

yeah, and heat sinking that thing can be a bitch

[Mark Hammer]

Here's what I use for my 380-based amp.  The 380 is obviously underneath the black thing on the lower right.  I have a bit of thermal compound between the top of the chip and the heatsink.

[dano12]

Just another couple of tidbits to add to the discussion. First, I have found after building *lots* of 386-based projects, that the NJM/JRC part is a lot more stable, and a tad better sounding than the National Semi/LM ones. This is especially true when you start pushing north of 9 volts. The NJM386D solved some head-scratching  instability/oscillation issues I encountered when finalizing the next Cricket amp (the one with the 12A*7 preamp stage). FWIW.

Also, there is another bridged 386 design that has been mentioned here, haven't built it personally, but if you peel off all the preamp/distortion stuff from this configuration, you may end up with something interesting: http://rebel.massberg.org/schematic.php