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Old 24th March 2013, 05:28 PM   #11
JMFahey is offline JMFahey  Argentina
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In USA I'd tell you to buy some (usually Eminence made) 12" speaker pulled from an amp (Peavey/Fender/Crate/etc.) because the owner upgraded to an expensive Celestion or something.
You can get such speakers on EBay or Craigslist for $20/30 , but I don't know what you can get in Italy.

Maybe you can have your old cone reconed for a good price, don't know.
By the way, that was a perfect example of the type of speaker I mention above.

What about a SICA or Italian Jensen 12" "guitar" speaker?
You'll have to search around.

You said you were in contact with a service shop, can't you get something there for low cost?

Italian speakers are *very* high Tech and high Quality (RCF/Faital Pro/Ciare/SICA) but expensive, I'm sure there must be others more affordable, what Eminence or Jensen is in USA.
What does a "normal" guitar amp maker use?
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Old 24th March 2013, 05:30 PM   #12
picbuck is offline picbuck  United States
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<< I am actually studying Electronical Engineering at university >>

Aha? It seems you're pretty much home free. Many, many people building successful amps don't know that E = IR. As a matter of fact, the only real danger you face is making it complicated. It ain't, so don't.

The main thing to know is that flux core solder is useless as such. Ignore the flux core. Buy a tin of general-purpose solder at Radio Shack or from eBay. Always, always apply flux before you apply your 25 (maybe 30) watt soldering iron. How much flux? "There is no such thing as too much flux."

I'm not saying argue with your instructors about this, but a word to the wise...

Amps inside the speaker cabinet are often frowned upon because of vibration. Some ceramic capacitors, in fact, are known to be microphonic. But which way to go is a judgment call.

Speaking of capacitors, use electrolytics in the power supply, of course, but otherwise the hot ticket these days is film capacitors. Polypropylene if possible, but you'll probably wind up using polyester (mylar).

The tiny capacitors (.01uF, .001uF, like that) are RF (radio frequency) bypass caps. When called for by the schematic these are to be placed as close to the chip as possible. Some, including me, say ceramics are OK here, some say no, the bypass caps have to be film also. Many just leave them off--but in a stage environment who knows what you'll run into.

If you build a "60 watt" gainclone it will be a monster. These are RMS watts, not the "music power" watts in advertisements.

BUT don't use a supposedly 60watt (for instance) chip to get 60watts. Derate by 20% or so. Chip manufacturers advertise too.

Just as a ponder, if you're in a group I can see a mixer/preamp feeding line-level (1 volt) signals to multiple speakers with built-in amps. Each instrument playing though its own speaker-amp box. Of course then you have to run power to each speaker-amp box, which I can see being a hassle. You also spend about a million dollars on speakers, also a hassle.

Remember that amplifiers don't produce sound, speakers produce sound. This even more simplified setup might be of interest.

RJM Audio - LM3875 Non-inverting Gainclone

And you might or might not be interested in these people. They do ship internationally, but I dunno.

http://www.parts-express.com/

PS just to mention it, these days a speaker all by itself is called a "driver," strictly speaking. "Speaker" means a speaker inside an enclosure. But this can depend on who's talking and who's listening, so be clear.

Last edited by picbuck; 24th March 2013 at 05:41 PM. Reason: added link
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Old 24th March 2013, 05:52 PM   #13
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@JMFahey The fact is that I don't know if the original eminence is still working, connected to a hi-fi stereo the driver play, but really I can't know if all it's ok, maybe not, because of its resistance (about 4 ohms, instead of 8)...
I told the vendor if they had a cheaper cone and they told me not. Via ebay I can pay it about 70/80€ but nothing cheaper, eminence and co have too high shipping costs...

@picbuck, thanks for the advice, I don't even know that that word was referred to that


Can I start with ESP 60W amplifier? maybe it's too difficult to find the ICs?
60-80W Power Amplifier

any other 60W serious project to build?
can a TDA7294 be the solution?
http://spazioinwind.libero.it/nferra...94/tda7294.htm

Last edited by gianmarco; 24th March 2013 at 06:03 PM.
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Old 24th March 2013, 06:27 PM   #14
picbuck is offline picbuck  United States
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Remember that amplifiers are subject to the log law. Double the volume of, say, a 50watt amp is not 100watts, it's 200watts. Then to double volume again you must go to 400watts, and so on.

(Anyway I think that's the log law. Some law.)

All of which is to say that the volume difference between a 50watt amp and a 60watt amp is not much. At that point speaker [driver] efficiency becomes more significant than amplifier output.

All of which is a lead-in to mentioning the LM3886. Rated at 50watts continuous into 8 ohms, the amp itself is the LM3886 chip, 2 resistors, and a capacitor. Capacitor optional.

Not trying to sell anything, just mentioning.
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Old 24th March 2013, 06:31 PM   #15
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Yeah, if you think that the LM3886, for my purpose is better than the TDA7294, why not try it?

I wrote the TDA because I read it in this forum, I really am a newbie in making amps, but if I buy a ciare driver (rated 300W) even the TDA can be ok? am I wrong?
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Old 24th March 2013, 08:42 PM   #16
JMFahey is offline JMFahey  Argentina
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Download and read the LM3886 datasheet.
http://www.ti.com/lit/gpn/lm3886
It suggests a 68W into 4 ohms amplifier, *perfect* for your 12" speaker.

It needs +/-28V rails , so you need a 20+20VAC transformer, 100 to 120 VA , which you can buy in Italy for a goos price.

So you can use most of what you have, and import nothing from USA.
Unless you want to buy, say, an LM3886 PCB, but that's cheap Mail .

Check Velleman kits , they are very good.
This amplifier looks perfect for your heatsink:

http://www.velleman.eu/products/view/?id=360242

Click the image to open in full size.

and this transformer powers it:

http://www.velleman.eu/products/view/?id=345550

or any other transformer you find at better price.

Download the instructions and schematic:
http://www.velleman.eu/downloads/0/i...k8060_rev1.pdf

EDIT: it speaks of 200W, but it's real 100W/4ohms or around 70W/8 ohms.
And assembly manual is *excellent*.

Last edited by JMFahey; 24th March 2013 at 08:44 PM.
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Old 24th March 2013, 10:47 PM   #17
picbuck is offline picbuck  United States
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<< if you think that the LM3886, for my purpose is better than the TDA7294, why not try it? >>

Hold up, ol' hoss! Never mind what I think you need, since I don't know. But I can say I have no argument whatsoever with the TDA7294. I notice it starts to distort pretty badly after 60 watts, but 60 watts might be about what you're looking for. Also, it achieves 60 watts with a plus/minus 18 volt transformer (25 volts peak, minus a couple of volts for the rectifier bridge), so it's possible to buy the parts.

I mentioned the LM3886 because: 1. It's a very simple circuit, and: 2. I'm familiar with it. I muddied the waters, but I make no apology. We humans always want other people to dance with the devil we like, instead of the devil they like.

However, I do question this 300 watt speaker I keep hearing about. Here's a 10" speaker, 8 ohms, rated at 75 watts. I found it in a couple of minutes of poking around at Parts Express.

Kustom Turbo 10 10" Guitar Speaker 8 Ohm 299-406

Again, I'm not advertising for Parts Express, and they're overseas to you. But if you can't find anything else it might be worthwhile to pay their $10 shipping premium for overseas shipments. But...opera comes from Italy, Caruso came from Italy...you must have speakers?!

There's really no way to know how a 50-60 watt amp would drive a particular 300 watt speaker, but I doubt it would do very well. Just too much speaker for the amp to get moving, is my thinking--though I'm ready to be corrected.

On the other hand, I guess it's obvious by now that my thinking on speakers is summed up by those three magic words: I don't know. I wish somebody who's done it would come along.

Last edited by picbuck; 24th March 2013 at 10:49 PM. Reason: clarity
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Old 25th March 2013, 01:32 AM   #18
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Quote:
Originally Posted by JMFahey View Post
Download and read the LM3886 datasheet.
http://www.ti.com/lit/gpn/lm3886
It suggests a 68W into 4 ohms amplifier, *perfect* for your 12" speaker.

It needs +/-28V rails , so you need a 20+20VAC transformer, 100 to 120 VA , which you can buy in Italy for a goos price.

So you can use most of what you have, and import nothing from USA.
Unless you want to buy, say, an LM3886 PCB, but that's cheap Mail .

Check Velleman kits , they are very good.
This amplifier looks perfect for your heatsink:

http://www.velleman.eu/products/view/?id=360242

Click the image to open in full size.

and this transformer powers it:

http://www.velleman.eu/products/view/?id=345550

or any other transformer you find at better price.

Download the instructions and schematic:
http://www.velleman.eu/downloads/0/i...k8060_rev1.pdf

EDIT: it speaks of 200W, but it's real 100W/4ohms or around 70W/8 ohms.
And assembly manual is *excellent*.
68 into 4 ohms, but the eminence is rated 8ohms (although I can measure 4, but maybe it's burned)
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Old 25th March 2013, 03:19 AM   #19
picbuck is offline picbuck  United States
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The ohms rating of a speaker refers to its impedance (AC version of resistance) when working. Hence "nominal."

Hooking an ohmmeter across speaker terminals is meaningless. It's necessary to find the speaker specifications by looking up the model number.

At moderate volume levels no harm is likely to result from driving an 8-ohm speaker with an amp rated for 4-ohms, or vice versa. But when you crank things up that can change. It's best to find out the manufacturer's specifications.
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Old 25th March 2013, 04:24 AM   #20
JMFahey is offline JMFahey  Argentina
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Quote:
the eminence is rated 8ohms (although I can measure 4, but maybe it's burned)
1) Please measure the voice coil DC resistance.
Since the multimeter leads,switch, etc, have "their own" internal resistance, first touch them (short them) and notice what the multimeter shows.
Use the 200 ohms scale, unless you have a lower one (not very common but not imposible)
Say tour shorted probes measure 0.6 ohms and the VC measures 4.2 ohms, actual VC resistance is 4.2-0.6=3.6 ohms.
Please do it and post results.

2) I suggested LM3886 because it's powerful enough and reasonably matched to your speaker, *and* because it's widely known, very pÚpular and a lot of people can answer your doubts.
It's also available in kit form, or at least the proper PCB.

3) as an option, I checked Velleman for an LM3886 kit.
Found nothing but they carry the amp I suggested, which to boot is somewhat more powerful than LM886, *and* looks like it was made for your heatsink, although you'll have to drill a couple extra holes.

The final choice is yours, of course.
Bit please measure that speaker.

By the way, if it works fine with Music, with no undue buzz, scratchiness or heavy plopping, it seems to be fine.
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