Transformer instead of battery

[jeer]

Hello. I'm sorry about my bad english, but i will try my best.

I'm interested in making an Ruby-amplifier from runoffgroove.com. There is a 9v battery for power supply in the guide, but I wondered if i can use an transformer instead.
I think i can't use an ordinary unregulated ac --> dc transformer. Am i right? So would a regulated 9v dc work? How about SMPS? Would 9w be enought power for that amp? This is what i thought.

Second question is that what speaker should i buy for that amp. I thought an Celestion super 8 -speaker. Is that ok?

[Mark Hammer]

1) A larger speaker will move more air and have more bass.  But remember that the chip does not produce a lot of power, and may not be enough to produce proper sound from THAT speaker.  Make sure the speaker is aimed at lower power amplifiers (e.g., something rated at 10W or so).

2) A battery-powered amplifier is no different than a battery-powered effect pedal: they both benefit from having a good supply of clean current.  Since the amplifier is the LAST thing before the speaker, however, the power that feeds it needs to be free of any ripple.  Remember, there will be no bass control to reduce unwanted hum between the chip output and the speaker.  So, you should use a well-regulated supply to power the amp, and should probably stick a 220-1000uf cap between V+ and ground, just for "audio insurance" purposes.

3) The LM386 can deliver a little more power, using 12vdc.  I generally use 12vdc (an 8-pack of AA batteries) and they sound great.  But you need to be careful about pulling too much current rhough the chip, or else it will go POOF! like a fuse.  So, if using 12v do NOT use a low-impedance (2-4ohm) speaker.  If the supply can provide lots of current, you might even consider a heat sink on the chip, just to be safe.

[petemoore]

I'm interested in making an Ruby-amplifier from runoffgroove.com. There is a 9v battery for power supply in the guide, but I wondered if i can use an transformer instead.
 LM386 ? 15v max, transformers put out more than rated voltage so measure and don't exceed 15v [10% or better margin].
I think i can't use an ordinary unregulated ac --> dc transformer.
Am i right?
 The amplifier requires a DC supply.
 So would a regulated 9v dc work?
 The ones I tried worked fine.
 How about SMPS?
 If it puts out DC..sometimes they 'whine'.
 Would 9w be enought power for that amp?
 What is 'enough power'? This is what i thought.
 Second question is that what speaker should i buy for that amp.
 No way to tell ye, I'd buy the speaker for the other amp, and use a speaker from some amp for the Ruby.
 I thought an Celestion super 8 -speaker. Is that ok?
 Never tried one, 'super' sounds neat-o, 8 is cool, Celestion..quality speaker.
 The spec sheet on the chip and the speaker make really good reads for these kinds of questions. For the chip it'd be mostly about ratings, for the speaker the frequency response doesn't matter [probably out Freq's the chip anyway] but the effeciency / Db rating does tell 'how loud' at X input level the speaker gets.
 Crotique ? The 386 makes a fun and handy amp, but the 15v supply limit is...limiting. Any of the other chipamp chips offer greater performance and won't be the weak link in the chain. The super 8 should offer excellent 'link strength' OTOH.
 Suggestion ? Use a Chipamp with a good supply voltage, at say 30v operation it'd make a good wide frequency transfer of suitable power for speaker-test.
 For the small increase in expense and a little more trouble...an amplifier that can feed some usable bass content to the speaker.
 

[jeer]

Thanks much for the replys.
This amp will be a 100% training amp, I'm not planning to do any perfomance with larger volumes with it. I'm building this amplifier for a school project, so I'm not trying to make some high-end amp.
So it's okay for me that i can't get very high volumes out of this thing, and that it will cut out some deepest basses.

I'm not sure did i understand right, but this is what I understood about the power supply: I can use a regulated 12volts power supply, and it would be good if I add a 16v 220uF-1000uF capacitor between the output wires from the power supply (I'm not an expert with electronics's basics. I'm not sure what v+ and ground means in this situation).

The celestion super 8 speaker is rated for 15w and it's impedance is 8 ohms. So 12volts power supply should be fine with the speakers impedance? The Chip won't melt?

The power supply i linked is explained like this: Regulated AC/DC Adaptor ... Output voltages: 3-4.5-6-7.5-9-12V DC 1000mA. It says max 12 volts (you can choose it) and 1amp current. I'm not sure what it means, but i think it means that it will give 12 volts with maximum of 1 amp current. So is the current enought for this amp? (These questions may sound stupid for you, but I really am not an expert with electronics. Not very many 14 years old are.)

[Mark Hammer]

The power supply i linked is explained like this: Regulated AC/DC Adaptor ... Output voltages: 3-4.5-6-7.5-9-12V DC 1000mA. It says max 12 volts (you can choose it) and 1amp current. I'm not sure what it means, but i think it means that it will give 12 volts with maximum of 1 amp current. So is the current enought for this amp? (These questions may sound stupid for you, but I really am not an expert with electronics. Not very many 14 years old are.)

1) Good on you for trying this, AND for being humble and wise enough to consult first.  My 14 year-old son prefers SIM-ing architecture and knitting (he's making me a hat just like Billy Gibbons'), so it's nice to get to use what I know for someone his age.

2) The suggested speaker is fine.  You won't push it very hard, but the important thing is that it not push back very hard by being stiff.

3) I snagged about a half dozen of those very supplies at Radio Shack for $0.99@ a few summers back.  They are not very well regulated at all.  Indeed, the suggested add-on capcitor may not do enough to help provide "clean" DC.  You may be better off using one of them to make a regulated supply at a lower voltage.

Huh?  You can feed a 3-pin regulator, like an LM78x09, with a higher DC voltage, and stabilize the supply more in the process.  So what comes from the wall-wart is "DC" but with a lot of ripple (i.e., meeting the barest minimum requirements for being DC).  What comes out of the regulator that you feed it to will be DC at a lower voltage, but with MUCH less ripple.  Now THAT's the sort of thing where the extra capacitor will help out nicely.   Go for a 25-volt rated cap.  They aren't much bigger or pricier, so give yourself the extra measure of confidence.

3-pin regulators want to see a DC voltage at their input which is at least 2 volts more than they provide at their outputs.  This is why I suggest a 9v regulator.  The maximum output voltage of the adaptor is 12vdc, so the next usable standard value regulator below that is 9v.  While you would get a little more power using a 12v supply voltage, the real improvements come by using something that can provide more current than a 9v battery does, so you've got that one under control.

Does this all make sense?

[jeer]

I drew a fast sketch of the locations of cap and regulator in the circuit:

So is the capacitor and the regulator at right places and right connections? Name of the regulator in the shop is "REGULATOR TO220 1,5A +9V 7809". Should it be the right one?(link)
The price of the power supply is 20 dollars (14euros).(There are cheaper SMPS versions, but I'm ready to pay few coins for non-whining power supply) So i guess it should be higher quality than a 99cents one, but I think the regulator is not pointless for any situation.

Edit: In shop it says like this on LM386 chip: "1x0.33W 6V 0.2% Audio power amplifier" Ehh... 6volts? I hope this does not mean the max supply voltage. This datasheet says that the max supply voltage is 15volts.

[merlinb]

You want your big capacitor on the input side of the regulator. You can add a small (10uF say) capacitor on the output side too, but most pedals have them built in already. Adding a really big capacitor to the output of a regulator usually makes the regulation worse rather than better, since it slows down the feedback loop inside the regulator chip.

[Hides-His-Eyes]

(Other than that small point, though, you've got it, and it's very impressive to pick things like that up so quickly that you can draw your own circuit diagrams, so well done )

[Mark Hammer]

+1   

[jeer]

You want your big capacitor on the input side of the regulator. You can add a small (10uF say) capacitor on the output side too, but most pedals have them built in already. Adding a really big capacitor to the output of a regulator usually makes the regulation worse rather than better, since it slows down the feedback loop inside the regulator chip.

Okay, thanks for notice for the cap's side. There is a 100uF capacitor in the ruby schematic input (link), but I don't think I should change it, or should I?

(Other than that small point, though, you've got it, and it's very impressive to pick things like that up so quickly that you can draw your own circuit diagrams, so well done   )

thanks!

+1 

I guess you mean that the regulator is correct?

[Mark Hammer]

yes, the regulator is correct.

The 3-pin regulators come in two sizes/ratings.  The smaller size is in the same TO-92 package as a small-signal transistor.  They are able to regulate up to 100ma withut difficulty.  I suppose you could manage more with additional heatsinking, ut not enough to justify the extra money and space.  The larger size is the same package as a power transistor, and can handle up to 1A safely.  There isn't really anything in between that I know of, at least that is commonly available.

If you were powering multiple devices, it would not be unreasonable to have multiple 100ma regulators connected to the same transformer.  That provides a form of isolation between the various outputs.  But that also assumes that every device being powered will draw less than 100ma, and none of those regulators will be in a position to be stressed.

In the absence of being able to meet those requirements, you are better off using a single 1A-rated regulator.