Making supply for power amplifier

[Enzy]

I find it very difficult to get transfromers in my country to build amplifiers but a thought came to me just now what if I use the mains supply to my house and send it straight to diodes to convert it to dc then send it to capacitors, wouldnt that be just the same as getting a powerful 120v transformer to make a power amplifier?
Would it be possible for me to try that method can anyone give me an example of anything I need t add t the circuit to protect it or I would just need some fuse.

 

[KlausST]

Hi,

don´t do this!

It´s dangerous. Dangerous for you and for others.
You need a transformer to maintain galvanic isolation.

Klaus

 

[Audioguru]

If your electricity is 120V then its peak is 170V and the full wave bridge rectifier drops it to about 168VDC. You need a transformer to isolate it so that if its ground is at 120V instead of 0V and you touch it and touch something that is grounded then the isolation prevents you from dying with a severe shock.

If you make an audio amplifier with 168VDC power supply then its output will probably be 163V p-p which is 81.5V peak which produces 20.4A peak in a 4 ohm speaker and the power at clipping is 830W.

Most amplifiers have a center-tapped transformer making it easy to make a plus and minus power supply then the amplifier does not need a huge and expensive high capacitance and high voltage output capacitor.

Oh, since you have 120V then you also have 240V for the oven, clothes dryer and air conditioner so you have 240V with a center tap. The power from your amplifier into a 4 ohm speaker will be 3451W.
It will break all your windows and also break your neighbour's windows.

 

[BradtheRad]

It is fine to do what you describe, although the output will be 170 V peak, not 120V.

You lose certain advantages:

* A transformer provides isolation from mains.
* A transformer allows you to draw only a limited amount of current from it, then its voltage automatically drops. (Thus reducing inrush current surge on powerup).

 

[BradtheRad]

By saying 'fine' I only mean fine in electrical concept. I agree with warnings given in the other replies.

 

[Enzy]

ok then so I guess for powerful amplifiers I need to be able to build switch mode power supplies. I have never built one before plus ferrite core sint sold in m country I would have to import it and most transformer rewind persons here only seems to wrap iron core and toroid core but ill try to learn how to do it myself because I want to build some powerful amplifiers.

 

[c_mitra]

Try to salvage ferrite cores and bobbins from computer SMPS - they are usually good but removing the glue may be the real hard work.

 

[marce]

This concept is dangerous beyond belief, only a fool would use mains direct without a transformer, it is so dangerous that it should not be really be discussed on an open forum.
If you are going to build a high wattage SMPS then I would suggest some reading firstly... You may also need litz wired transformers and chokes to minimise switching losses, plus the EMC implications.
I would also familiarise yourself with any rules and regulations regarding mains in your country and also look a SELV regulations....
Why so much power, look at the relationship between speaker efficiency and SPL levels and amp power output, lots of watts does not always equate to loud...

 

[Enzy]

the idea about the mains supply was an idea in my head and I have always wanted to ask someone about the idea.

the amount of power now is all on me because a friend of mine is building up a music system where he has 18,18" 1000 watt speaker wanting to play bass and its for outdoor use only so I decided I would try to build an amplifier for it.

 

[KlausST]

Hi,

the amount of power now is all on me because a friend of mine is building up a music system where he has 18,18" 1000 watt speaker wanting to play bass and its for outdoor use only so I decided I would try to build an amplifier for it.

This will be a challenge for an experienced audio/power electronics developer.

Klaus

 

[Enzy]

Well in my case I do want it to sound good but it doesnt have to be anything perfect. On a normal basis guys doing music systems in country mostly buy Qsc amplifiers, for a set up like that they would normally use 4000 watt amplifers and it would normally give good base even though they would use things like Eq and Dbx but for now my friend would only use 12 of those 18" speakers.

 

[chuckey]

Look around for scrap microwave cookers, they have a big transformer in them, 800-1KW. The secondary would need rewinding, Loads of amateurs have done this for a low voltage output for welding. You will need to rewind the secondary for a higher voltage. Look on youtube for some videos.
Frank

 

[c_mitra]

I guess if you are planning to get 4kW out from the amplifier, you should seriously consider using three phase power supply for the input.

 

[Enzy]

I dont have 3 phase supply, whats wrong with using single phase like how the manufacturers do it.

Ok whats the highest wattage amplifer I could get a pcb design for, does anyone have a class D amp I could try.

 

[chuckey]

Single phase supplies in the UK are 230V @13A, on the continent I think 220V@ 16A, about 3kW in both cases.
I think your 4kW is actually MUSIC POWER (not RMS), which is 1kW RMS or true power.
Frank

 

[Enzy]

I am not sure about that info I am in jamaica, but if in the Uk you only receive roughly 3kw Im sure we get alot more were I am. why I say that its because each and everyone is able to pull much more than 16amps directly from their house, I can run heavy load like a couple welding plants normally for wat the guys do around me they would have them at about 80 or 120 amps for some heavy welding.

But regaurdless are you saying those sound system amplifiers arent rated by RMS for example those powerful QSC and Crown amps at say 5000 and 10,000 watts arent actually rms ratings?

 

[c_mitra]

the guys do around me they would have them at about 80 or 120 amps for some heavy welding.

Taking 80-120A from a single phase should cause lots of problems down the line. But perhaps you can tolerate lots of overvoltage /undervoltage problems as well as phase faults.

...amps at say 5000 and 10,000 watts arent actually rms ratings...

You can often guess their actual power rating by looking at the plug and the cable... 5kW device cannot use standard plugs and sockets.

 

[KlausST]

Hi,

they would have them at about 80 or 120 amps for some heavy welding.

Welding machines have transformers inside. The transformers amplify current but lower the voltage.

Klaus

 

[Enzy]

Ok now that starts to make sence to me I always wondered how is it those powerful amplifiers use such a small wire but then because I am not an electronics pro I normally just assumed that its some form of boost converter/buck converter process stepping up frequency and voltage and then increasing current in some way. SO if I see a power amp how do I actually calculate the power consumption.

 

[chuckey]

Jamaica uses "Type A" or "Type B" mains connectors same as the USA. Both 110V 15 A, A is two pin, B is three pin. I looked at the Crown Harman 3000 amps, a pair will deliver 1600W in bridge mode consuming 19.6A from 110V. Just as well as they use IEC 16A mains input connectors.
Frank