Super clean 1W amp please!

[alparent]

I have a 1W 8 ohms speacker (about 4 inches) in a nice little cabinet.
I want to build a super clean amp with it to use a workbench test amp.

Any suggestions? I've looked at the Ruby or Gem ('cause I have 'lots of 386) but if there are cleaner one you sugest, I don't mind getting other parts.

Thanks for you suggestions..........remember.........clean!

[petey twofinger]

http://www.crazybutable.com/store/stella

[R.G.]

Almost any solid state amplifier, especially chip based, is (to the guitar world at least) "super clean" *given* that it is not ever driven into clipping.

The smaller the power rating on an amplifier, the easier it is to make it clip. So for a 1W or few-watts amplifier, you need to ensure that you have an input volume control to turn the input signal down to the point where it does not get overdriven.

Most solid state amplifiers are designed to have their full rated output with an input of somewhere near 0dbm, which is about 1V peak, regardless of their output power. Many pedals can put out 4V peaks or even more. So the pedals can in many cases overdrive solid state amplifiers just by giving them too big an input.

[Mark Hammer]

Cleanliness is also a function of the power supplied to the amplifier.  For years, I've been recommending to folks that they power their LM386 mini-amps with an 8-pack of penlights, for 12vdc.  That provides not only a higher voltage, but also more current.  Under those conditions, you can ask the chip to do more for you, and it will be able to do a respectable job at it.  A higher supply voltage for any preamp stage will also provide greater headroom.

I think there is also something to be said for matching the speaker and amp to the intended outcome.  Partly because they are mechanical devices, most speakers will behave non-linearly with both too much power AND too little power.  What we call "clean" usually involves a reasonably wide frequency response (at least as wide as we need it to be).  If a cone and magnet structure has enough mass (I guess, enough "inertia" is the more correct way of putting it), then it will take a certain minimum of power from the amp to make that coil and cone respond equally at all frequencies.  Just as you don't expect quick acceleration on a truck unless the engine is powerful enough, you shouldn't expect much top end in a speaker unless either the speaker is light enough or the amp powerful enough.  And, just as applying too much power to a vehicle can make it difficult to control, too much power to a coil and cone may get it moving in ways other than perfectly straight forward and backward.

If a person wants to use a low-power amp chip almost exclusively for distorted sounds, then using it with larger speakers will very likely introduce nonlinearities that complement distortion.  Indeed, one of the reasons why many 4 x 12 stacks are preferred for distorted sound in general is because they trim a lot of the top end off.  Where the goal is to have a cleaner sound, more modest-sized speakers, with more modest power ratings, may be appropriate.  So, a 4-6" speaker rated at 5W power-handling, with a nice light cone, may be a good choice for a clean 1W amp.  If a person wants bass from something like that, then the next step is to design a cabinet that helps with that.  You don't see all that many cabs for 5" speakers with tuned ports (because bass-hounds will often opt for bigger speakers), but that doesn't mean it can't be done.

[earthtonesaudio]

(A 100W amp that you never turn up more than 25%) = (Clean 1W amp at 100%)

[alparent]

So with something like the Little Gem wth the pot after the 386. Nothing is cutting down on the input. So my only option is the guitar volume.
But with the Ruby, the pot is on the input of the 386. So this gives me a chance to control the input.

I always was under the impression that the distortion was caused by the speaker being to small?

So if I controle the input to get a clean sound. Should cranking up the gain keep my sound clear?
I want to controle the input to get a clear sound.......but I stile need this to be an amp! Get a loud enought sound to be usefull! Know what I mean?

[Mark Hammer]

Well, if you feed ANY speaker with more bass than it can handle, the speaker will usually misbehave.  So, a 3" speaker (or smaller) will usually not want to see content arriving that is much below 100-200hz, unless it is a very special kind of speaker.  I have a bunch of 2" speakers pulled from old Mac Classics, with very big magnets and foam surrounds (somethng you rarely see on a speaker that small).  A speaker like that could handle low frequencies, but not the sort like you see in the little Danelectro amp I brought in,

The punch line is that if a person is going to use a low power chip to push a 2-3" speaker, you probably want to use a smaller-value cap to limit bass content going to the 386.  If there was supposed to be an electrolytic between the power amp and speaker, you'd make that a smaller value.  Those changes would not only reduce speaker distortion, but would also reduce the demand on the chip itself, since bass frequencies usually demand more current/power to be reproduced.  It will sound thin, but it won't be distorted.

[alparent]

So I guess I'll try the Ruby and tweek it to my tast (with the speaker I have).

[Gurner]

Assuming you're using a 9V supply, you won't get 1W out of an LM386 into 8 ohms ...best you can probably manage with a fresh battery is about 800mW (& even then I doubt it would be as clean as you seek)

Better to go with a BTL chip (TDA7052 etc), because then you don't have to run your output signal so close to the rails to get your required 1W

[Mark Hammer]

Incidentally, I would happily give you one of those little Mac Classic speakers, but they are 32-ohms.  By the time yu stick 4 of them in parallel to achieve an 8-ohm load, yuo'll need more than 1W to push them.

[alparent]

For the time it's going to take me I'll try the Ruby.......if I'm not happy I'll bug you guys again! 

[tca]

Go for a TDA7052 with a buffer and power it with 6*1.5V AA batteries or, even better, 9V transformer. I've build several with 3'' speakers (TV speakers 5W, big magnet, 89 dB - 1W/1m). Works great.

Cheers.

P.S.
The Ruby will not give 1W clean on any circumstance... even the TDA7052 with a 9V battery will start to distort the input signal without enough current, use 6*1.5V AA batteries.