simple amp circuit for bass/keyboards/etc.

[choklitlove]

i built a ruby and got to thinking.  i've been in need of something to amplify speakers.  i would like to use standard stereo speakers (pretty big ones w/ woofers and tweeters).  i want the output of my mixer to plug into two separate amp circuits, then to two separate speakers.  i run keyboards,   drum machines, an ipod, and various other things in the mixer.

i figured that it was mostly keyboards, the impedence of a bass type amp would be best.  what do you think?  i saw the "bassman" ruby mod, but that's not really a bass amp, is it?  also, would something like this be loud enough to compete with drums?

stupid idea?

[Dragonfly]

how much wattage do you need ?

[choklitlove]

i'm not sure.  in amps, watts are directly linked to volume, correct?  as much as possible.  100 or so?

kind of inexperienced in amps.  that's why i started this thread.  would it just be a better idea to invest in some sort of pa system or something?

[Dragonfly]

you might take a look at this PDF...this chip can be run "bridged" in mono to 120 watts, has decent specs, and costs less than $6....the PDF has circuit diagrams....

might be worth trying....

AC

http://cache.national.com/ds/LM/LM4780.pdf

[choklitlove]

that chip really looks nice.  has it been around for a while?  i'm just curious if anyone has experience with it.  seems really safe and mostly self-explanatory.  they've already got a layout in the pdf, too.

thanks dragonfly.  any experience out there?

[Dragonfly]

that chip really looks nice.  has it been around for a while?  i'm just curious if anyone has experience with it.  seems really safe and mostly self-explanatory.  they've already got a layout in the pdf, too.

thanks dragonfly.  any experience out there?

no experience with it, but in "looking around", it seemed to show quite a bit of promise....\

AC

[choklitlove]

if i try that, i'll end up paying around $10 for it.  i only found 2 places that have it.
digikey was the cheapest: http://sales.digikey.com/scripts/sales.dll?action=lineitem;itemseq=41126478

that's not bad considering what it would do for me.  however, it's sort of a gamble.  i'm not positive if it would do exactly what i need it to.  i'm also not sure if my skills are up to a project that has almost no support and in a field that i'm not comfortable with.

i'm not sure... i'll have to think about it.  any other suggestions?

[Dragonfly]

if i try that, i'll end up paying around $10 for it.  i only found 2 places that have it.
digikey was the cheapest: http://sales.digikey.com/scripts/sales.dll?action=lineitem;itemseq=41126478

that's not bad considering what it would do for me.  however, it's sort of a gamble.  i'm not positive if it would do exactly what i need it to.  i'm also not sure if my skills are up to a project that has almost no support and in a field that i'm not comfortable with.

i'm not sure... i'll have to think about it.  any other suggestions?

should be easy to build the "bridged amplifier" circuit, tack on a fet preamp (maybe with a 3 band eq), and get a nice, clean sounding amp....low parts count for a high powered circuit...

other suggestions ?  well..none really...not for that much power...this would certainly be a ton cheaper than a tube based amp, and less than a comparable PA that you could buy....

AC

[Dragonfly]

BTW...you might PM R.G. and get his thoughts on this...he may have some insight or experience with this chip...

AC

[trevize]

on http://www.ssguitar.com/ you'll find help on
solid state amps and chipamps.

[Dragonfly]

heres another option for you...less wattage, but easy build...

http://www.web-ee.com/Schematics/45WattAmp/45W%20amp.htm

AC

[puretube]

I like the TDA2030, for smaller volumes...

[Dragonfly]

and another possibility...

just a power amp though....

http://europa.spaceports.com/~fishbake/amp/ca100.htm

[Dragonfly]

BTW...theres a zillion more possibilities at http://www.discovercircuits.com/A/a-audioamp.htm


but personally, i think the first one i posted looks very good....

AC

[choklitlove]

BTW...theres a zillion more possibilities at http://www.discovercircuits.com/A/a-audioamp.htm


but personally, i think the first one i posted looks very good....

AC

yeah the first one looks the best so far.  the only thing is, i'll have to make my own layout or perf it or something.  the one in the pdf is a double sided pcb, and i'm not up for that crap.

thanks for all of your help!

[mdh]

I'd recommend that you search for threads on chip amps, particularly RDV's LM3886 threads, paying attention to R.G.'s observations on what a power amp is (to paraphrase: it's a power supply... plus some other stuff), and Mark Hammer's observations regarding the logarithmic relationship between volume and power. Point is, you might end up spending a lot more on the power supply than you're anticipating up front, making the cost of the chip amp itself less of a consideration.

[R.G.]

You will almost certainly blow out the stereo speaker tweeters, if not the main speakers.

Stereo speakers and musical instrument speakers are optimized in different directions. MI speakers are optimize for TOUGH. Stereo is optimized for linear.

This info is in the tube amp FAQ, which no one reads anymore: Loudness is sensed logarithmically. That is, you have to have exponentially more power to get equal increases in apparent loudness. To get twice the apparent volume, you need ten times the amplifier power. A 100W amp is about twice as loud as a 10W amp, not a 50W amp. The 100W is detectably louder than the 50, but much less than double.

Speaker loudness is rated in sound pressure level with (usually) one watt of power in them. A musical instrument speaker will usually be rated for 90 to 96 db SPL with one watt of power. To get apparently twice as loud, you need to pump in another 10x the power, another 20db of SPL. That's 116 db, and the threshold of pain is somewhere between 115db and 120db depending on frequency. The bigger amp may not distort as much, though.

Stereo speakers are usually 82 to 88db, or something a bit more than half as loud as MI speakers at the rated 1W. So they put out much less sound per watt. If you try to get out MI speaker sound levels by driving stereo speakers, you will have to  - literally - drive the guts out of them. They have lower power ratings usually, too.

If you're doing PA kinds of things, look at PA speakers. Using home stereo speakers is like taking a riding your bicycle to compete in a motorcycle race. It can be done, but the results may not be good.

[choklitlove]

You will almost certainly blow out the stereo speaker tweeters, if not the main speakers.

Stereo speakers and musical instrument speakers are optimized in different directions. MI speakers are optimize for TOUGH. Stereo is optimized for linear.

This info is in the tube amp FAQ, which no one reads anymore: Loudness is sensed logarithmically. That is, you have to have exponentially more power to get equal increases in apparent loudness. To get twice the apparent volume, you need ten times the amplifier power. A 100W amp is about twice as loud as a 10W amp, not a 50W amp. The 100W is detectably louder than the 50, but much less than double.

Speaker loudness is rated in sound pressure level with (usually) one watt of power in them. A musical instrument speaker will usually be rated for 90 to 96 db SPL with one watt of power. To get apparently twice as loud, you need to pump in another 10x the power, another 20db of SPL. That's 116 db, and the threshold of pain is somewhere between 115db and 120db depending on frequency. The bigger amp may not distort as much, though.

Stereo speakers are usually 82 to 88db, or something a bit more than half as loud as MI speakers at the rated 1W. So they put out much less sound per watt. If you try to get out MI speaker sound levels by driving stereo speakers, you will have to  - literally - drive the guts out of them. They have lower power ratings usually, too.

If you're doing PA kinds of things, look at PA speakers. Using home stereo speakers is like taking a riding your bicycle to compete in a motorcycle race. It can be done, but the results may not be good.

good info.  i just need to bite the bullet and spend a load for pa speakers or something similar.

if i went that route, would i still need something to drive them?  i wouldn't if the speakers are powered, correct?  if i buy passive, what would be the cheapest route to power them?

also, any suggestions as far as brand or style?  preferrably cheap...  i've been looking at some carvins: http://www.carvin.com/products/single.php?ItemNumber=P410-805&CID=SYS1
looks really nice to me.  how do you think this system would serve my purpose?

thanks!

[Ronsonic]

You have a mixer, and you need to drive speakers, that's the bottom line?

There is no way on earth you can build anything faster or better or cheaper than you can just buy it. Power amps are getting cheaper by the week. Besides, they're no damn fun to build. The good ones all sound alike, where's the fun in that. Just buy an amp.

Or, and this will save those stereo speakers from being blown out if you ever play outside your livingroom or studio, get some powered speakers. Everybody makes them and you can get whatever quality and price point you can afford. If you buy new, pick a company that stands behind their stuff. That's what you're paying for. I hate to say it, but Behringer sells crap, but they really, really stand behind their crap for the full year of the warranty. Which is a lot better than the companies that treat their "Kustomers" and service centers like crap.

Ron