Increasing Output for an audio amplifier?

[Briantrey]

Hi,

I made a post before for repairing my 40 watt amp. I was wondering if it was possible to maybe add an additional power supply to increase the power output of the supply rails, to supplement the 120 watt IC chip I would like to install (to increase total output). I was thinking maybe trying to get it close to 120W RMS. Think this can be done and/or would I would also have to modify the circuitboard as well? Even if I have to rebuild the whole circuitboard, it really doesn't matter. It Would be a great learning experience.

Currently I'm learning a lot about electronics right now. I went and purchased an electronic learning lab from RadioShack, so learning a lot about ohms Law transistors capacitors etc. and the whole nine yards. And previously I have studied electronics at a trade school. But dropped out within a few months unfortunately.

But anyways, not to get off topic. So, would this be Plausible? Anybody has any good advice, for a beginner to lead me In the right direction? It would be greatly appreciated. I plan on solving most of these problems, on my own for good learning experience. But need some idea, direction, and scope of this project.

P.S Would I also have to put in a larger heat sink, to supplement the larger IC chip?

Thanks in advance,
Briantrey

 

[audioguru]

There is so much to be considered to increase the power of an amplifier by 3 or 4 times that you should start from the beginning with a good design for a 120W amplifier.
The heatsinks would need to be 3 or 4 times bigger and most capacitors would need to be replaced with a higher voltage rating. Each resistor will need to be calculated for power dissipation and many will need to be replaced with bigger ones. Even the wiring and pcb traces would carry much higher current and would need to be replaced.

 

[Briantrey]

....

I have been looking at some circuit diagrams of some power amplifiers. Some of them seemed pretty simple and straight forth. But anyways, there was this one design, that says it uses a bridged circuit which means that it both output wires are hot. What does this mean?

As I said before, the power output is directly proportional to the supply rails, 40W into 8 ohms requires an output swing of 52V, which (due to losses) means you're looking at something like a 60V HT rail (probably +/-30V). 40W is the maximum possible power that you can get from this supply voltage, UNLESS you use a bridged circuit.

Nigel Goodwin mentioned something about bridging circuit's.

I know they may be a simple question to many of you. But they're still alot of terminology that I still have to learn.

Thanks,
Briantrey

 

[audioguru]

Bridged amps are used in cars to get a fairly high output power from the low voltage car battery.
A bridged amp is two amps, each one driving one wire of a speaker opposing. When one amp goes up then the other goes down, effectively doubling the voltage across the speaker and also doubling the current through it. Since both the voltage and the current are doubled then the power is quadrupled (almost, the losses are also quadrupled).

 

[Nigel Goodwin]

Bridged amps are used in cars to get a fairly high output power from the low voltage car battery.
A bridged amp is two amps, each one driving one wire of a speaker opposing. When one amp goes up then the other goes down, effectively doubling the voltage across the speaker and also doubling the current through it. Since both the voltage and the current are doubled then the power is quadrupled (almost, the losses are also quadrupled).

Except the amp will then self destruct! - you CAN'T get quadruple power from a bridged amplifer - it merely gives TWICE the power into TWICE the impedance. Each amplifier is simply delivering it's rated power into it's rated load (which is effectively half the actual bridged load).

For the car amplifier example, off the 12V supply you can only get a maximum of 4W into 4 ohms, or 8W into 2 ohms - a bridged amplifier gives 16W into 4 ohms. If you connected a 2 ohm load then the amplifier would attempt to provide 32 watts (16W each into 1 ohm), and the amplifier would die :lol:

BTW, such a 16W amplifer is normally called 25W, 50W, or even 100W in the car amplifier specifications! - they are incredibly exaggerated.

But back to the original question! - the problem is further complicated by the amplifier having an output transformer. You would need to remove (or replace with a larger one) that, replace the mains transformer with a suitable larger one, replace all the power supply components with better ones, completely redesign and build a new power amplifier, and provide a suitable supply for the preamp stages.

It's NOT a trivial task! - far easier (and probably cheaper?) to buy a proper amplifier in the first place?.

What actually are you wanting the amplifier to do?.

 

[audioguru]

you CAN'T get quadruple power from a bridged amplifer.

For the car amplifier example, off the 12V supply you can only get a maximum of 4W into 4 ohms - a bridged amplifier gives 16W into 4 ohms.

Um, hee, hee. My slide rule shows that the power is quadrupled. :lol:
2-ohm speakers are kinda rare, but my new car has some. I haven't measured them yet to see if they are being driven single-ended or bridged.

There's a car stereo amp IC that gives about 10W into a 1.6 ohm load per channel, or 20W into a 3.2 ohm speaker when bridged, TDA2004 and TDA2005. Maybe this year there will be a TDA2006 with even more power into a dead short! :lol: It might be able to drive all the speakers in the world, all connected in parallel.

 

[Nigel Goodwin]

Um, hee, hee. My slide rule shows that the power is quadrupled. :lol:

Slide rules never did make any sense :lol: It's also VERY hard to enter the amplifiers maximum possible current output into your slide rule :lol:

I always preferred log books to slide rules!.

Funnily enough I made a six foot long slide rule at school in woodwork, for the maths department - obviously made of wood, but covered with white Formica, and the maths department did the markings on it.

 

[audioguru]

I showed my slide-rule to a visiting Japanese engineer, and his eyes nearly fell out. He couldn't believe it and how it calculates things so well. :lol: