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.
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.
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.
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.
Get a bigger horse.
Try an LM1875 or TDA2030.
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.
....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.
Quote from: Headshot on December 04, 2007, 03:04:28 PM
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.
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?
Quote from: Headshot on December 04, 2007, 03:16:39 PM
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 (http://en.wikipedia.org/wiki/Bridged_amplifier).
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).
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.
Quote from: Mark Hammer on December 04, 2007, 03:10:26 PM
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:D
2073 would be real horrorshow for a mp3 player thingy
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 :icon_cry: Don't go there...
Quote from: ambulancevoice on December 04, 2007, 06:50:40 PM
Quote from: Mark Hammer on December 04, 2007, 03:10:26 PM
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: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).
Quote from: Mark Hammer on December 05, 2007, 09:55:22 AM
Quote from: ambulancevoice on December 04, 2007, 06:50:40 PM
Quote from: Mark Hammer on December 04, 2007, 03:10:26 PM
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: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
IIRC
LM380 = 2W
check out National Semiconductor's LM12CLK
http://www.national.com/mpf/LM/LM12CL.html
its $45 each! cool! :icon_cool:
Quote from: km-r on December 06, 2007, 01:58:11 AM
IIRC
LM380 = 2W
The 14-pin version is 2 watts, but it needs heatsinking and a minimum 10v supply (20v for full power).
Quote from: anchovie on December 06, 2007, 04:37:20 AM
Quote from: km-r on December 06, 2007, 01:58:11 AM
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
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.
(http://img.photobucket.com/albums/v474/mhammer/Chipsink.jpg)
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 (http://rebel.massberg.org/schematic.php)
Thanks for the great info Dano! Looking forward to that Tube Cricket.
Great thread. I've been stewing over 386 amp projects for a while now. The hard part is trying to settle on just one project! Very helpful information here. Thanks.
+1 for the LM380
and an efficient speaker will always be required if real punch is required.
Doesn't the 386 will push out about 0.6 W into 8 ohms (and around 0.4W into 4 ohms.)? So paralleling two 386s into an 8 ohm load will still yield only 1 W (@9V).
So bridging or paralleling 386s doesn't work.... does it?
I actually made a mini amp with 2 LM386-4's in B.T.L. , with a NJM4558 Pre-amp section going into it, adding a Volume control, Tone control, and a Gain control that goes from Clean to Overdrive and finally to Hi-Gain distortion, running it with 6-AA cells for 9V or adapter...I have Clip-on Heat sinks on all the chips and an 18V Zener Diode in the Power section, so that I can use 18V safely without going over, to avoid damage to the IC's with an 18V max limit...I'm using a 5W- 3", $30, 8ohm speaker, but it in a small solid wood enclosure, and at 9V I get at least 1W - 1.5W of power out of it, it sounds louder than an Orange Micro Crush and Mini Fender Twin that I compared it with, but then when I ran it with 18V supply it gave me so much more headroom, it got louder and cleaner, with 18V supply I got 2W power easily, but you need to use the 386-4 that can handle 18V, it also says that this chip will give you 1W power with 18V, so with 2 Bridged I'm getting 2W...The only problem is you need bigger heat sinks with 18V's, I'm getting more out of it with the 18V, you will get the same amount of volume as a Micro Cube, but when the Volume gets too high it starts making a resonating noise while I play, the only thing I can think of is that I need bigger heat sinks for my chips....If I can perfect this design on 18V, I will have a little 6" cube amp that sounds as loud and as good as a Micro Cube, but much smaller, with good loud enough clean, overdrive, and distortion...Does anyone here now a good heat sink part # that I could get bigger than the little clip-on wings for 8-DIP chips, maybe something I can put on with some compound?
And here's my reply to that from the posting by itself:
QuoteThe Dual Inline Package has some sincere power dissipation problems. Most of the heat is *conducted* out the leads, not convected out the plastic.
I say this as background for what I'm about to say.
You're probably right that it's going into thermal overload and shutting down. You may get some relief from heatsinking, but what you are doing is trying to get a small device working right out at the very edge of its capability. This is not a recipe for long term reliability.
It is better to use a bigger device well inside its capabilities. If you used ONE TDA2030 or LM1875, you'd get 4-5W on 18V, and you can do the same bridged trick to get even more from the same 18V. And both of these chips are in the TO-220 package which not only dissipated about 2W in free air, but is made for attaching to an external heat sink, which are also easily available and cheap.
So my advice is to either (1) back down the power supply voltage until the thermal cutouts quit or (2) get a bigger horse; use a TO-220 power amp chip.
To this thread: don't get stuck on the LM386. It happens to be an easy solution to the specific problem of a small, DIP power amp with no need for lots of power. It is NOT all that extensible once you hit its limits. The LM1875 and TDA2030 are GREAT solutions for the next step up in power and thermal issues. They'll go to a decent 20W, more if bridged. They are designed and packaged for heatsinking.
First of all, I recently made a 2W amp (Which I posted about a few days ago) with a 4558 Pre-amp section going into (2) LM386N-4 IC's running on 18V...What is the current drawn normally and about how long would (2) 9V Alkaline batteries last as opposed to (2) 9V Lithium batteries with 1200mAh in series for 18V?....I know that I can use a bunch of AA cells, but I don't have room in the enclosure for so many AA's, so I'm trying to use (2) 9Volts in series instead, but I figured that I would have to use Lithium batteries if I want them to last very long...I know that most 9V Alkaline give you about 500mAh and Lithium gives about 1200mAh, but would (2) regular 9V batteries be enough to run the 4558 with (2) LM386's at 18V for at least an hour or 2, and how long would the Lithium's last???
I also wanted to know the same if I used the 4558 Pre-amp going into an LM380 (2.5W IC) instead...What would the current drawn normally be with 18V in this situation, and would (2) 9V Alkaline batteries even be enough to power this for a little while, or how long would (2) 9V Lithium batteries last running on 18V with the LM380 power section?.....I'm not very good with math, and I'm not sure how many mA these chips draw at 18V???
If anyone can give me these answers or at least a pretty close estimate as to how long the batteries will last or if they even have enough Amp hours to power these chips at 18V, I would really appreciate it...Thanks again for any help.
> how many mA these chips draw at 18V???
Very little when idle and silent.
When roaring, depends on the load.
For the classic (non-Bridge) connection, figure the load on the power supply is similar to a resistor six times the total impedance, useful load plus chip losses.
Take LM386 loss as 3 ohms, LM380 maybe 2 ohms.
IF the load is 8 ohms, add 2 or 3 and round to 10 (makes math easier).
10 ohms times 6 is 60 ohms.
18 volts applied to 60 ohms is 18V/60= 0.3 Amps or 300mA.
That's at full roar. Power consumption goes down as you play softer, but efficiency drops fast also. If you don't play mostly at FULL ROAR, your battery cost will be much less with lower voltage.
> 9V Alkaline give you about 500mAh
It may be able to carry 50mA for 10 hours. It will sag and go flat a lot quicker at 300mA. Maybe less than an hour to 5V/batt, 10V total. At that point you might as well have used a single 9V batt, total 150mA drain, play for 2 hours, or four hours if you brought two batts. If you are busking, 4 hours is a LOT more loose change than under-one-hour.
The real goal is not voltage or power, but LOUDness per battery dollar, right?
9V radio batteries are about the worst buy.
Watts-to-LOUD is largely about CONE AREA. Paddling a yacht with a teaspoon is inefficient. A light Ten inch cone will blow-away a three-inch cone on the same power, or do the same job with LESS power, less battery cost.
Voltage, power, and impedance are related. Since AA is cheaper per watt-hour than 9V, C is cheaper yet, and D is the economy size, you would like to run on four C or D cells. That's 6V DC, which is at best 2.1V RMS. With a good (large) speaker One Watt is pretty loud. 2V in 4 ohms is one watt.
One of the biggest "aaaaahaaa" moments I've had in my hobby electronics pastime, is when the penny dropped that an audio amplifier IC, didn't in itself muster up the power (by that I mean, I'd previously been scouring the datasheets to see which ones could pump out 1w, or 2W etc), but the maximum power achievable actually comes from the supply voltage and the load. That is, the power specification you see for an audio amplifier IC relate to it's maximum supply voltage handling ability ....& more significantly, how well the IC package can dissapate the heat generated - if you could find someway of sumping the heat, there'd be nothing to stop you pumping out 10W from your LM386! In other words, the IC doesn't generate any power.....this gets a little clouded in that just about all audio amplifier IC apply a voltage gain to the signal (& @200x the lm386 can potentially apply the most voltage gain of any audio amplifier IC out there!) , but nevertheless, the important thing to remember is that the IC itself is just a conduit to convert signal voltage to 'current delivery' into the load.
Wrt current draw, here's my take (this is for single ended amplifiers like an LM386 etc).....
when running an LM386 at 9V supply - and assuming a supply that doesn't droop - the best signal level you can expect to achieve across the load is something like 8V ...any more & you'll get clipping. But that's a peak to peak figure, we need RMS - & being of a lazy ilk, I use this calculator ...
http://www.daycounter.com/Calculators/RMS-Calculator.phtml
that calculator wants 'Vpk' as an input, which is half the peak to peak level, so that'll be 4V.....which works out at 2.828V RMS.
so with a 9V supply, the maximum unclipped signal you can put across a load is 2.828V RMS...the rest is easy. If your load is 8 Ohms, the currents draw will be 2.828V/8 ....or 353mA.
applying the same numbers to an 18V supply, well the maximum signal achievable will be somthing in the order of 17V pk-pk, or 8.5Vpk, or 6.01V RMS. therefore into the same 8 Ohm load the current draw will be 751mA.
Bearing in mind your average PP3 is only good for 550maH, then you really need to look at sourcing power from mains once your requirements get above a few hundred milliwatts.
The continuing fascination with LM386 is curious....if you wish to double your output power & keep your circuit supply at 9V & your speaker at 8 ohms, then simply use a BTL IC....a TDA7052 will do nicely. BTL ICs have differential outputs which essentially doubles your achievable signal levels across the same load....to cut a long story short....that translate to 4x the power delivery for the same given situation vs a single ended IC like the LM386. Better still, there's no mandatory requirement to grow a droopy 'tache & wear flares/platform shoes (as you do when using an LM386)
Quoteif you could find someway of sumping the heat, there'd be nothing to stop you pumping out 10W from your LM386!
Peltier?
> just a conduit to convert signal voltage to 'current delivery' into the load.
Yes.
And the LM386 is a skinny pipe.
> if you could find someway of sumping the heat, there'd be nothing to stop you pumping out 10W from your LM386!
No, there's often another limit. CURRENT. If too high, either the transistor melts (for any amount of cooling) or its gain drops to uselessly-low. In many chips, the current is monitored, and cut-back if excessive. The LM386 apparently is too lame to pass much current: push harder and nothing happens.
Fer example, TDA2003 is safe for about 4 Amps. In the ST 1998 datasheet schematic, Q14 watches R10 and shuts-down the amp if R10 current is too high.
The LM386's power in low impedance does NOT increase as you raise supply voltage past some point.
(http://i53.tinypic.com/10qw4k6.jpg)
In 4 ohms, 6V to 12V is all just 0.36 Watts. In 8 ohms, yes it rises from 6V to 12V, but does not rise from 12V to 18V. If you work the numbers, it won't go past 0.42A to 0.44A of peak load current. AND the higher supply voltage translates DIRECTLY into more heat. And this heat is totally a waste on the battery.
The "optimum" for a 18V rating (say 8V peak) and 0.4A peak comes with a 20 ohm load and is 1.6 Watts.
If you want to fool with higher voltages, TDA2003 and kin are MUCH better "conduits", fatter pipes.
They also cool better.
> lm386 can potentially apply the most voltage gain of any audio amplifier IC out there!
It's a lot of gain for 50 cents. More than we can usually use. However TDA2003 datasheet shows gains of 500, and I think there's more in there. At Gv=500 the response may roll-off by 3KHz, but at that level of gain (and hiss and distortion) maybe you want a low-pass.
> use a BTL IC
FWIW: transistor losses are bad, a simple stage has two transistor losses, a bridge has four transistor losses. BTL makes sense when you "can't" change supply voltage. Car battery IS 12V-14V. Good for 2W in 8 ohms or 4W in 4 ohms. 4W in a car is not much. You could always convert it, but that complication is usually reserved for 60W-200W trunk-thumper amps. Instead, a BTL is "almost like" a 24V supply, 16 honest Watts (22 watts boasting). That's enough to overcome road-noise.
Quote from: defaced on December 09, 2010, 11:28:38 AM
Quoteif you could find someway of sumping the heat, there'd be nothing to stop you pumping out 10W from your LM386!
Peltier?
Thank heavens this was picked up upon .... someone might have took me literally (vs me overzealously emphasising a point) ......because, even after implementing some scifi supercooling arrangement, they could have ended up very disappointed with the final performance of their LM386.
So please everyone, don't try to squeeze 10W out of your LM386 ....simply put your ear closer to the speaker.
Quote from: PRR on December 09, 2010, 01:46:16 AM
> how many mA these chips draw at 18V???
Very little when idle and silent.
When roaring, depends on the load.
For the classic (non-Bridge) connection, figure the load on the power supply is similar to a resistor six times the total impedance, useful load plus chip losses.
Take LM386 loss as 3 ohms, LM380 maybe 2 ohms.
IF the load is 8 ohms, add 2 or 3 and round to 10 (makes math easier).
<quote>
If you have 2 - 9V batteries in series for 18V will that bring up the available 500mAh to 1Ah?...Or is that only the case if you parallel the batteries?
10 ohms times 6 is 60 ohms.
18 volts applied to 60 ohms is 18V/60= 0.3 Amps or 300mA.
That's at full roar. Power consumption goes down as you play softer, but efficiency drops fast also. If you don't play mostly at FULL ROAR, your battery cost will be much less with lower voltage.
> 9V Alkaline give you about 500mAh
It may be able to carry 50mA for 10 hours. It will sag and go flat a lot quicker at 300mA. Maybe less than an hour to 5V/batt, 10V total. At that point you might as well have used a single 9V batt, total 150mA drain, play for 2 hours, or four hours if you brought two batts. If you are busking, 4 hours is a LOT more loose change than under-one-hour.
The real goal is not voltage or power, but LOUDness per battery dollar, right?
9V radio batteries are about the worst buy.
Watts-to-LOUD is largely about CONE AREA. Paddling a yacht with a teaspoon is inefficient. A light Ten inch cone will blow-away a three-inch cone on the same power, or do the same job with LESS power, less battery cost.
Voltage, power, and impedance are related. Since AA is cheaper per watt-hour than 9V, C is cheaper yet, and D is the economy size, you would like to run on four C or D cells. That's 6V DC, which is at best 2.1V RMS. With a good (large) speaker One Watt is pretty loud. 2V in 4 ohms is one watt.
Quote from: PRR on December 10, 2010, 02:19:53 AM
> just a conduit to convert signal voltage to 'current delivery' into the load.
Yes.
And the LM386 is a skinny pipe.
> if you could find someway of sumping the heat, there'd be nothing to stop you pumping out 10W from your LM386!
No, there's often another limit. CURRENT. If too high, either the transistor melts (for any amount of cooling) or its gain drops to uselessly-low. In many chips, the current is monitored, and cut-back if excessive. The LM386 apparently is too lame to pass much current: push harder and nothing happens.
Fer example, TDA2003 is safe for about 4 Amps. In the ST 1998 datasheet schematic, Q14 watches R10 and shuts-down the amp if R10 current is too high.
The LM386's power in low impedance does NOT increase as you raise supply voltage past some point.
(http://i53.tinypic.com/10qw4k6.jpg)
In 4 ohms, 6V to 12V is all just 0.36 Watts. In 8 ohms, yes it rises from 6V to 12V, but does not rise from 12V to 18V. If you work the numbers, it won't go past 0.42A to 0.44A of peak load current. AND the higher supply voltage translates DIRECTLY into more heat. And this heat is totally a waste on the battery.
The "optimum" for a 18V rating (say 8V peak) and 0.4A peak comes with a 20 ohm load and is 1.6 Watts.
If you want to fool with higher voltages, TDA2003 and kin are MUCH better "conduits", fatter pipes.
They also cool better.
> lm386 can potentially apply the most voltage gain of any audio amplifier IC out there!
It's a lot of gain for 50 cents. More than we can usually use. However TDA2003 datasheet shows gains of 500, and I think there's more in there. At Gv=500 the response may roll-off by 3KHz, but at that level of gain (and hiss and distortion) maybe you want a low-pass.
> use a BTL IC
FWIW: transistor losses are bad, a simple stage has two transistor losses, a bridge has four transistor losses. BTL makes sense when you "can't" change supply voltage. Car battery IS 12V-14V. Good for 2W in 8 ohms or 4W in 4 ohms. 4W in a car is not much. You could always convert it, but that complication is usually reserved for 60W-200W trunk-thumper amps. Instead, a BTL is "almost like" a 24V supply, 16 honest Watts (22 watts boasting). That's enough to overcome road-noise.
If you have 2 - 9V Batteries in series for 18V, will it bring up the available 500mAh to 1Ah?...Or does this only apply for parallel batteries?
Only applies to parallel. So if you parallel two 9V 500mAh batteries you get a 9V 1000mAh supply. If you put two 9V 500mAh batteries in series you get a 18V 500mAh supply.
I was reading through an old Guitar mag the other day and came across an ad for Pignose amps.
They were touting their new 40 watt combo that ran on 2 sealed lead acid batteries.
Now those must have been some serious batteries to get 40 watts output to the 10" spkr for any amount of time.
I reckon those car batteries will be in series, and the amp will be using a bridged output.
Even then the only way you can get 40W is by taking the impedance of the speaker down to 6 ohms ....that translates to 2.6A ...the average car battery supplies 120AH, so you're gonna get about 46 hours playing AC/DC riffs at full whack (less in reality) before you need to reach for your jump leads &/or call roadside services.
Personally, I wouldn't buy one unless it had a cigarette lighter socket on the fascia.
> the average car battery
They are often 50 Amp-hours. At 12V this is like 600 Watt-hours. Taking 50% efficiency, this is 30 Watts for 10 hours.
Any recent car radio makes 16W-22W into 4 ohms with just the 12V supply. Most have four such channels, like 70 Watts total honest output. They can play LOUD for several hours (but when they get weak, the battery is too flat to re-start the car).
You don't carry two car batteries.
There are smaller lead batts for emergency lights, security alarms, etc. All the way down to a D-cell good for 2V 2.5AH. (I have seen even smaller lead cells.) LA1270 12V/7.0AH is readily available around $20.
I was assuming in this day & age, if someone is gonna design an amp of that power to run off batteries, then Class D would be the only game in town....and at full whack, you can get 90% efficiency.
Some techie background is in order.
Power delivered by DC is easy: it's P = voltage * current; this is the same as power being the square of the voltage divided by the load resistance, or the square of the current times the load resistance; these are all equivalent statements.
Power delivered by AC waveforms is more complicated. The voltage changes all the time. It was found long ago that if you took the square of the instantaneous voltage at all points of the waveform, added those, divided by the waveform period, and then took the square root, you came up with a number which was the practical equivalent to a DC voltage in terms of heating a resistor (that is, delivered real power).
This is, of course, what is meant by "RMS", being Root of the Mean Square. It's different for every waveform. For a sine wave, the RMS value of a wave with a peak voltage of Vpk is Vrms = Vpk/1.414. 1.414 is approximate; the real number is the square root of two.
The reason this is important is because if you know the peak value of a sine wave across a resistor, you know how much heating it's doing (that is, how much heating is delivered).
For any non-bridged amplifier working from a power supply of Vpower, if the amplifier was theoretically perfect, it could only swing its output between 0V and Vpower. So at the output, Vpk would be Vpower/2. In real amplifiers, you never get here, because the output devices cannot make the output voltage go to fully Vpower or 0V. Notice that if the amplifier is powered from a bipolar power supply, you get the same result, but the power supply voltage Vpower is equal to the sum of the + and - power supply voltages.
So once you know the power supply voltage for your amplifier and also its load resistance, you know how much power it can even possibly put out if everything is perfect (as it never is.)
For a standard class B output amplifier working from 9V into 8 ohms, the peak AC voltage out can't be more than 4.5V; the RMS can't be more than 3.18Vrms. Then the power into 8 ohms can't be more than (3.18)*(3.18)/8 = 1.26W. For a 4 ohm load, it can't be more than 2.53W.
If you bridge such an amplifier, you get 5.06W into 8 ohms and 10W into 4 ohms. The problem is that this is not a real amplifier. It can't swing that big a power supply voltage, and the output transistors can't swing fully to the power supplies, and they also start to burn up. You can't get the heat out.
The worst case condition for a class B amplifier heating is NOT at full power out. It's more like half power. At the max dissipation point, the amplifier has to get rid of about 40% of the maximum possible power output.
When you pick a speaker load, you pick what power outputs are possible for any given power supply to the amplifier. If you have a defined speaker load and a defined power supply, you have defined how much power you can get out. If you use the amplifier in bridge, this is exactly the same as two other situations: one is having each amplifier running a load of half the speaker load, the other is the real speaker load driven from twice the power supply. Real output transistors and drive conditions will give you less than the theoretical maximums.
> in this day & age
Define "this".
See my last post. I'm Firmly in the 1960s, when not in the 1880s.
> Class D .... 90% efficiency
Yeah, well, if we really wanted efficiency we'd run wires from the guitar into every listener's brain. That only takes micro-Watts, not many-Watts.
And 50% to 90%, battery life is only 1.8 times better.
And some plans here appear to do 25% efficiency at best. Raising pressure (voltage) is not always the answer; sometimes you need a fatter pipe.
R.G. has the math, of course. That's been well-known since the 1870s when power systems developed, since the 1920s when audio engineers gained some control of their power. You can even simplify by saying Sine RMS voltage is 1/3rd of total DC voltage (within half-dB error). But even that math may not be popular here.
None of this is new. Part-Watt, several-Watt, and dozens-Watt markets have existed in radios, TVs, and cars for decades. There's chips engineered FOR these uses.