is this amp any good?

[justin66]

hey guys im about to buy parts for this amp. i have eagle schematics and stuff i need to know if this amp is good for 2 8ohm speakers connected to make 4 ohm the IC is LM3886T
also i have a transformer that looks like daughnut it says it is 100va 230v to 17v 5.88A i want to convet it into a 50v 4A DC (200w) transformer. the secondary winding has 100 turns so my calculations are that i need 218 turns to get 37v AC(50v DC) i know its overkill but i will connect two of thiese amps so my setup would be like this two LM3886t amps to power 4 subs than i will  use something like tda1554q to power mids and highs.

my question is this lm 3886t amp with eagle schematics provided any good i have downloaded thiese and idk if its gonna work   . and can anybody recommend me a good active low pass filter? possibly with a schematics coz idk how to use pcb designing programs
http://www.failai.lt/neytmo3ea55b/SP0001.zip

[Richard Crowley]

The data sheet says that LM3886T is rated for 68W into 4 ohms @ +/- 28Vf
I do not see any reason to doubt that information.
Certainly, it requires a sufficient heat sink to prevent damage to the amplifier chip.

You say that the transformer is rated for 100W, but you want to take 200W out of it.
You cannot safely get 200W out of a 100W transformer.
You probably do not even have enough space to replace (or add) windings to get 50V anyway.
Recommend using a proper transformer.

There are many high-pass and low-pass and crossover circuits available on the internet.

[wraper]

You say that the transformer is rated for 100W, but you want to take 200W out of it.
You cannot safely get 200W out of a 100W transformer.

Moreover it is not 100W but 100VA transformer. As this is not a restrictive load, considering power factor of about 0.6, this is more like 60W.

[justin66]

but it also says 5.88 amps so 6a times 17v is 250w . yes i want to add an other coil on top its fairly thin wire out of induction motor i need about 150 watts is it possible to get it out if it or should i just go and spend a lot of money witch i dont want to but i will if i will be in a must what you guys think?

[Kleinstein]

There is not mauch you can do to get more than the 100 VA out of the transformer - long term. For short pulse (e.g. 1 min) one can get something like 200 W (e.g. 300 VA). So it may be OK to power two of the LM3886 amps - preferrable with a protection circuit based on transformer temperature.

If the amplifier want +-28 V for maximum power one would need somthing like two windings of about 20-22 V each. With a weak transformer better go for little less, or a class D amplifier for the subs. 

[justin66]

thanks for the info but i wanna shake the floor lol so i guess if i wanted to hook up something more on it i would have to buy an other transformer. data sheet says 28v but i wanna put a little bit more to get more power so i will go with ~50 volts dc as data sheet says above 60 distortion occurs. or maybe i will buy a 32v transformer witch will give 42volts dc what do you think?

[Kleinstein]

As far as I see the data, you won't get more power for timeframe of about 100 ms if you raise the voltage much above 30 volts. The higher the voltage, the higher the peak power, but heat dissipation also increses. So the time over which such a high power is available will get shorter. So I would stay in the 28-35 V range, thus something like 22-27 V AC. Peak power of the time of a few 100 ms will go down if the voltage is higher - especially if the heat sink is not exceptionally large.

If you really need more power consider one more amp/ speaker or a discrete transistor amplifier instead of a chip.

You may not need such a large transformer, as normal speaker can't stand high power for an extended time too.  A 100 W speaker may have trouble dissipating more than constantly 20 W for am hour.  It's better to have the amplifier to signal a power limit because of a hot transformer that to burn the speaks.

[wraper]

but it also says 5.88 amps so 6a times 17v is 250w .

It seems you have a serious problem with math. 6 * 17 = 102
And those are not W but VA, they are two different things.

[justin66]

volt amps i know. i have no idea how can i calculate up to such ridiculous number yea its 102. so should i keep 23v dc transformer for two of thiese amps or should i stay with it also now im using one (not assembled yet) so should i raise voltage or not?

[dom0]

If all you want is to "shake the floor" (to annoy your parents, neighbors, and basically anyone around you) buy some class D car sub amp and a car battery.

[fcb]

The LM3886T is indeed a very good amplifier - but it isn't very powerful, and in real terms doesn't have the headroom to cope with much above 'normal' levels (very subjective I know, but I built a stereo LM3886T amplifier 10 years ago, and it's still in daily use).

For higher power you'll have to build an amp out of discrete semi's or as someone else mentioned, look at class-D etc...

[justin66]

im 17 years old and i live alone but lets move that aside i want quality as well as shaking floor i mean i can already feel vibrations with tda2050 23v supply and two 6.5inch 8ohm woofers with unknown power rating but its over 20 watts each and is not even in a box its just hanging on a table for now. also i have a question to clarify things coz i bouht wrong cap. whats the difference between electrolythic and film capacitor on the input of the ic. coz tda2050 has the one with plus and minus and lm3886 needs film cap. it would be best to represent it with a scope or something. idk how do you guys learn stuff like the way it works ? i wanna learn but  how

[Kleinstein]

You can learn a lot from reading application notes an similar texts from the IC companis. It also helps to buid one or the other circuit an get a real feeling on how they work and smell (if it gets to hot).  There is also a lot to learn from good circuit plans - just from understanding how they work.

[justin66]

thanks people who replied to me