Re-design stage monitor after a big failure.

gianmarco

Member
2013-02-20 1:33 pm
Hello everybody, as someone read before, I tried to repair my broken stage monitor, but with no success.

So, the thing I want to do is to re-design a new active stage monitor, from scratch (or copying some projects here and there LOL).

Now I have a blank wood edge monitor, even with no holes. I have the transformer, and I have to buy the rest.

Can you please help me in construct something good to use in live?

second, I have two wood case, I could even create a passive monitor to use with an amplifier, but I don't know what component to use or if is cheaper to create one by myself than buying one.

Waiting for your answers.
Gianmarco
 

picbuck

Member
2008-05-31 12:50 pm
You're speaking of a gainclone or chipamp, same difference. Both Google and YouTube are interesting--although YouTube tends toward uninformative videos of speakers playing music.

The good news is that yes, you can solder up some very good equipment at large--huge--savings over retail. And as a matter of fact it's not difficult. Or that is...it's not difficult if you have some idea of what you're doing. Not that you have to be an electrical engineer (you don't), only that some familiarity with the subject helps a lot.

The bad news is that things can get very frustrating until you reach that "some familiarity" point. The first one is the hardest, of course, but no kidding, this stuff can become all-consuming. A musician might be better off spending the time and effort practicing. Nobody ever got to Carnegie Hall by soldering wires together...well...except the techs, of course.

In any case, the electronic parts for a gainclone/chipamp might run some $10. But that's a lowball price.

Potentiometers (volume and tone controls) with knobs run around $3 each. Switches around $2 each. These don't much matter with just an amplifier, but once you get into mixers and effects boxes those dollar bills add up.

Usually the main cost item is the transformer for the power supply, which is in the $20-30 range, or can be much more. The one you have might or might not work. Transformers are rated in voltage, and amps/wattage/VA (same difference), and whether they're CT (center tapped). "Center tapped" is pretty much the standard. CT means it's actually two transformers in a single housing. This is how you get the "plus or minus" power supply, and the center tap is ground (zero volts).

Generally what's used is in the 15-30 volt range, CT. A transformer must (not should) be something like 30% oversize at the very least. That is, a 50watt amp would require something like a 70watt power supply. More is better.

The physical size or shape of a power supply transformer doesn't matter. Many will use only toroids (expensive), but I personally see no point in that.

The tiny black chip that does the amplifying requires a relatively huge heat sink (that heat is why you need an oversize power supply). For a largish amp (50ish watts) these can be hard to find and expensive, which is why Google Images shows some bizarre setups.

However, a 50mm fan/heat-sink combination made for a computer CPU (Central Processing Unit--the chip) is used by many. These run $15ish. Of course, you have to be willing to run the fan. But for an onstage environment fans would probably be a very good idea anyway. By the way, buying just a heat sink is more expensive than buying the combination.

The housing/chassis is, for many, the greatest expense by far. Then again, you can put the whole shebang into a soup can if you want to. Literally. Drill some holes for ventilation.

There's also the matter of the circuit board. Usually a printed circuit board (PCB) that simply supports the components. This can be a noticeable expense. Or you can use perfboard (that's its name) from Radio Shack.

None of these gloomy predictions tell you anything about how to build one, of course. Possibly this page might be of interest.

DIY TDA2050 Hi-Fi Chip Amplifier (chipamp)
 
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gianmarco

Member
2013-02-20 1:33 pm
thanks both for your answers!

@JMFahey - the transformer is 107x90x52mm (LxHxD)

@picbuck - I am actually studying Electronical Engineering at university, I know about circuits, physics laws, few digital and few microelectronics... but I am still studying.
I think I have the basics for make my own amp.

I have a big heatsink (about 250x80x50mm) where there was the stk4048V now burned.
I can solder with a pre-drilled PCB (the ones with many holes) if necessary.
The chassy (as said) is this:
[IMGDEAD]http://img4.mercatinomusicale.com/pics/2020040_1300751009.jpg[/IMGDEAD]

now I am reading the link you gave me.
 
Ok, you have a core of 18.7 square centimeters, which is good for 350VA.
It can easily power a 200/250W RMS amplifier.
+/-60V rails will give you about 150/160W into 8 ohms, or 250W into 4 ohms.
I very much doubt you can fit such a big amp into that tiny cabinet.

I would consider 2 options:

1) forget that big power transformer for now, and build a 50/60W chipamp (with the proper transformer), mounting it inside that cabinet without much trouble.
Anyway remember thar Eminence guitar speaker can't handle more than that.
You'll have a very good active monitor for your keyboards or acoustic guitar.
I would do that and be happy. :)

2) later, when you are more experienced, build a "big" power amp, such as apexaudio QUASI amplifier
http://www.diyaudio.com/forums/solid-state/167394-quasi-amplifier-beginners.html

Don't be misled by the "beginners" label ;) , it's a big mean loud amplifier and perfect for your transformer.
He even gives you the PSU, how's that?

And it's not for beginners, but for people who has at least 3 or 4 amps previously, following something like the classic ladder: TDA20xx (Pickbuck's suggestion) > LM3886/TDA7294 > discrete around 100W amp > Big amp.

Do not skip steps in that ladder, each one prepares you for the next step.

Good luck.
 

gianmarco

Member
2013-02-20 1:33 pm
the eminence cone is gone, i have to buy a new one by ciare, is about 300W why do you think the amplifier can't be fit in the cabinet? There was a 4048V with that transformer and the big heatsink before. Maybe I can build it external with a speakon connector, if the cabinet is too small... there aren't 12" speakers under 300W power, a 60W amp is too small...
 
the eminence cone is gone, i have to buy a new one by ciare, is about 300W why do you think the amplifier can't be fit in the cabinet?
Mounting there limits heat dissipation big way.
No problem with, say, a 60W RMS amplifier, maybe 100W might be the realistic limit.
Yes, JBL/RCF/(insert "big" name here) can fit 300W RMS or higher amps in (much larger than yours) powered speakers, but "they" use Class D or at least class H amplifiers, place heatsink fins in the tuning port so bass notes cool them, have sophisticated thermal protection systems, etc.
Please be realistic.

There was a 4048V with that transformer and the big heatsink before.
True enough ..... and it kept burning :rolleyes:
Big heatsinks mean nothing (or very little) if fresh air can't freely flow around them.

Maybe I can build it external with a speakon connector, if the cabinet is too small...
Excellent idea

there aren't 12" speakers under 300W power,
:confused: :confused:

a 60W amp is too small...
Maybe, but that's what the original Laney used ;)
For a powered monitor, it's enough.

What you have there is the unpowered version of Laney CP12
$T2eC16F,!zEE9s3!(IV6BRO-BDJ7Gw~~60_35.JPG

Which, by the way, is already larger than yours and has an 80W power amp.:eek:
 
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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?
 

picbuck

Member
2008-05-31 12:50 pm
<< 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.
 
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gianmarco

Member
2013-02-20 1:33 pm
@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 :D


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/nferrarese/elettronica/tda7294/tda7294.htm
 
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picbuck

Member
2008-05-31 12:50 pm
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.
 
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

k8060_1.jpg


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/illustrated/illustrated_assembly_manual_k8060_rev1.pdf

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

Member
2008-05-31 12:50 pm
<< 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.
 
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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

k8060_1.jpg


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/illustrated/illustrated_assembly_manual_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)
 

picbuck

Member
2008-05-31 12:50 pm
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.
 
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 pòpular 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.